Does Your Engine Hesitate at 7500rpm?
07-21-2010, 03:15 PM
#1
Does Your Engine Hesitate at 7500rpm?
Please help. During acceleration, at exactly 7500rpm my engine would hesitate and bog momentarily before it accelerates normally to the redline. Although the hesitation/bogging is only for a split second during acceleration, it is severe enough to decelerate the car to the point that the occupants jerk forward, and then get slammed backwards when the bogging passes and acceleration resumes "violently". The acceleration feels more "violent" after this point only because of the suddenly lag. It has been upsetting at times when its happened in a bend and almost sent me into a wall once. To my passenger, it feels as if I had accidentally depressed and released the clutch at that rpm to cause that jerk. Anyone has any ideas on what is causing this? It is consistent and happens 100% of the time at exactly 7500rpm and so far I have experienced it in the first 3 gears (have not tried redlining the car in higher gears so far). The car is an EU/UK spec 2005 6MT with about 30,000miles (50,000km) when I got it 3 weeks ago. Its been doing this since I got it and the CEL light has not shown up. Ex-ex owner used to have a Fujitsubo exhaust and that was replaced one year ago to a USED stock exahust (including cat) by the last owner. Does this sound more like an issue with the cat or a sticky valve or fuel starvation?
07-21-2010, 04:25 PM
#6
considering the instrument error of around 300rpm i'd say you could check the vdi 
researching the term "Ssv" (the other valve) should lead to a diy on how to clean those valves.
researching the term "Ssv" (the other valve) should lead to a diy on how to clean those valves.
07-21-2010, 05:20 PM
#7
And as you pointed out, the VDI 'begins' to open at 7250rpm.
The DIY bse50 might have been referring to is this:
https://www.rx8club.com/series-i-do-yourself-forum-73/diy-troubleshoot-intake-valves-174009/
07-22-2010, 09:00 AM
#8
First, I would like to extend my gratitude to all those who tried to help me out. Its so nice when there are knowledgeble people out there who are so helpful to newbies like me.
Jon, that video in the other thread was awesome, thanks so much for sharing your knowledge! Its a lot more difficult to understand how those actuators work when its all attached to the engine. When you can see through the manifold and observe how the pressure moves the actuators, it suddenly makes sense and reinforces what I saw at the workshop today. They say a picture speaks a thousand words. Well, a video says more than a million and it helps when there's a nice song in the background.
Ok guys, now for the update and the bad news... Took the car down to a rotary specialist this afternoon (our time zone is GMT+8hours) and we talked about the possibility of it being the VDI, SSV, APV and cat. He had a look at my VDI and SSV valves and used a long screw driver to push on them. Other than a slight return-spring resistance, the actuators moved smoothly. There was no binding or roughness in the movement. He then pointed out where the APV motor was and no me that for the SSV and VDI, its not difficult to service them but for the APV, anything further than a replacement motor would require "dropping the engine". He then showed me an intake manifold that was carbon-locked and it felt like more force was needed to move that particular SSV actuator. He said there is nothing wrong with mine. He said he didn't think it was the cat because the exhaust did not smell bad and there was no CEL light. Also it was not a high rpm loss of power but just a really bad jerk at 7500rpm. Power resumes after that. He said he thinks it could be the ECU. He opens the ECU cover and we all got a shock. The ECU was sitting "loosely" in the black box without any protection...there was no padding. The wiring loom was a mess with several wires having been cut and connectors wired to them. He told me that for the EU spec cars (mine), there should be a metal cover which should have a lock on it and that was clearly missing. The lock was broken. He said that someone probably connected a "piggyback" system to this or messed around with it. And he says that he is 100% certain that that is the cause of my problem. Is this a probably cause for the hesitation/bog at 7500rpm? There were 4 owners before me and I've had the car for 3 weeks now. Why would someone mess with the ECU like that? Is it possible that it was remapped for a turbo (that was subsequently dekitted before sale) such that at 7500rpm, the ECU was programmed to dump in more fuel to coincide with an increased in turbocharged air coming in? However, the removal of the turbo without restoring the stock mapping is causing a sudden dumping of fuel and richening of the mixture and therefore the bogging. I hope this theory doesn't sound far fetched. Also, in my radio controlled model cars, sometimes when the carburretor's high speed/low speed needle are not set up properly, you get a poor transition between high speed and low speed and it feels like this.
Assuming that its the ECU, what should my next step be? Thanks.
Jon, that video in the other thread was awesome, thanks so much for sharing your knowledge! Its a lot more difficult to understand how those actuators work when its all attached to the engine. When you can see through the manifold and observe how the pressure moves the actuators, it suddenly makes sense and reinforces what I saw at the workshop today. They say a picture speaks a thousand words. Well, a video says more than a million and it helps when there's a nice song in the background.
Ok guys, now for the update and the bad news... Took the car down to a rotary specialist this afternoon (our time zone is GMT+8hours) and we talked about the possibility of it being the VDI, SSV, APV and cat. He had a look at my VDI and SSV valves and used a long screw driver to push on them. Other than a slight return-spring resistance, the actuators moved smoothly. There was no binding or roughness in the movement. He then pointed out where the APV motor was and no me that for the SSV and VDI, its not difficult to service them but for the APV, anything further than a replacement motor would require "dropping the engine". He then showed me an intake manifold that was carbon-locked and it felt like more force was needed to move that particular SSV actuator. He said there is nothing wrong with mine. He said he didn't think it was the cat because the exhaust did not smell bad and there was no CEL light. Also it was not a high rpm loss of power but just a really bad jerk at 7500rpm. Power resumes after that. He said he thinks it could be the ECU. He opens the ECU cover and we all got a shock. The ECU was sitting "loosely" in the black box without any protection...there was no padding. The wiring loom was a mess with several wires having been cut and connectors wired to them. He told me that for the EU spec cars (mine), there should be a metal cover which should have a lock on it and that was clearly missing. The lock was broken. He said that someone probably connected a "piggyback" system to this or messed around with it. And he says that he is 100% certain that that is the cause of my problem. Is this a probably cause for the hesitation/bog at 7500rpm? There were 4 owners before me and I've had the car for 3 weeks now. Why would someone mess with the ECU like that? Is it possible that it was remapped for a turbo (that was subsequently dekitted before sale) such that at 7500rpm, the ECU was programmed to dump in more fuel to coincide with an increased in turbocharged air coming in? However, the removal of the turbo without restoring the stock mapping is causing a sudden dumping of fuel and richening of the mixture and therefore the bogging. I hope this theory doesn't sound far fetched. Also, in my radio controlled model cars, sometimes when the carburretor's high speed/low speed needle are not set up properly, you get a poor transition between high speed and low speed and it feels like this.
Assuming that its the ECU, what should my next step be? Thanks.
07-22-2010, 11:57 AM
#9
Having several wires cut/connected to the PCM is a huge variable that could be a possibility.
This was possibly done for FI purposes, but difficult to tell if the PCM was reflashed or if it was just a piggy-back EMS.
I guess you could always take it to the dealer and have them reflash the PCM, that way you know its an OEM flash.
Did you guys test the APV also?
Even though its a PITA to remove with the manifold still in the car, you can still cycle the valve.
If you look beside the OMP you'll see the electrical connection to the APV motor.
Remove the connector and simply apply 12VDC to it and you'll hear the valve cycle (its really noticeable).
Then swap wires to run the motor in the opposite direction.
Now yes, the APV starts to open at 6250rpm... but the keyword is 'starts to' and it also depends on engine load.
It doesn't take much time to go from 6250 to 7500rpm when you're accelerating, so keep that in mind.
And don't rule out the cat just because there is no smell and CEL.
Many cats that get clogged don't produce a smell.
And many RX8s (especially '04 models) don't even generate a CEL when the cat gets clogged.
This was possibly done for FI purposes, but difficult to tell if the PCM was reflashed or if it was just a piggy-back EMS.
I guess you could always take it to the dealer and have them reflash the PCM, that way you know its an OEM flash.
Did you guys test the APV also?
Even though its a PITA to remove with the manifold still in the car, you can still cycle the valve.
If you look beside the OMP you'll see the electrical connection to the APV motor.
Remove the connector and simply apply 12VDC to it and you'll hear the valve cycle (its really noticeable).
Then swap wires to run the motor in the opposite direction.
Now yes, the APV starts to open at 6250rpm... but the keyword is 'starts to' and it also depends on engine load.
It doesn't take much time to go from 6250 to 7500rpm when you're accelerating, so keep that in mind.
And don't rule out the cat just because there is no smell and CEL.
Many cats that get clogged don't produce a smell.
And many RX8s (especially '04 models) don't even generate a CEL when the cat gets clogged.
07-22-2010, 01:52 PM
#10
Hi again, I would like to make some corrections. My mechanic speaks in another language and I translated poorly into English earlier. I know this after looking up the PCM (ECU) section in the workshop manual. I think I mentioned that the mechanic said that the PCM should have a "metal cover", and a "locking device". Actually he even said something about a "cooler". What he is probably referring to is the heat sink that the PCM sits in. What he said was a lock is probably the bolts. Sorry if I caused any confusion, I really should have referred to the manual for the proper terms.
Now, I am speculating on further possibilities of the 7500rpm jerk. Please tell me if I am hot or cold. To summarize, we found SSV and VDI valves working smoothly. APV not checked but I can easily do what Jon recommended. PCM's wiring harness has been tampered with and many wires were cut and have connectors wired to them. Heat sink (PCM cooler) has been broken off and missing. PCM sits loosely under the PCM cover. Additional Observation: (i) On the exhaust manifold at a 90 degree angle to the front O2 sensor (prop shaft side), there appears to be a plugged hole with some screw thread left behind so there must have been some form of a sensor attached previously. (ii) Between the MAF sensor and the TB, on the "accodion section" of the intake pipe, there is supposed to be a little flat rectangular plastic box as depicted in the manual. I'm not sure what the function of this box is but it looks to me like some sort of a catch tank. Anyway, this was missing on my intake and instead, a shiny aluminum cap/plug was inserted in this hole. I am not sure why the owner before me did this but today, it was replaced with the original black plastic "box". Does this shiny aluminum cap sound like it came from the plumbing parts of a turbo kit?
Given the above evidence and what Jon suggested above, would it be reasonable for me to assume that there probably was some sort of a piggyback system installed previously to alter FI? I am wondering if it could be something like a Greddy eManage Fuel Management System. http://rx7.com/store/rx8/rx8ecu.html My understanding of a piggyback system is that it "tricks" the factory PCM and once removed, the ECU should revert to OEM mapping. Anyway, do you guys think that its possible that the removal of such a device could leave me with the 7500rpm hesitation symptom?
Now, I am speculating on further possibilities of the 7500rpm jerk. Please tell me if I am hot or cold. To summarize, we found SSV and VDI valves working smoothly. APV not checked but I can easily do what Jon recommended. PCM's wiring harness has been tampered with and many wires were cut and have connectors wired to them. Heat sink (PCM cooler) has been broken off and missing. PCM sits loosely under the PCM cover. Additional Observation: (i) On the exhaust manifold at a 90 degree angle to the front O2 sensor (prop shaft side), there appears to be a plugged hole with some screw thread left behind so there must have been some form of a sensor attached previously. (ii) Between the MAF sensor and the TB, on the "accodion section" of the intake pipe, there is supposed to be a little flat rectangular plastic box as depicted in the manual. I'm not sure what the function of this box is but it looks to me like some sort of a catch tank. Anyway, this was missing on my intake and instead, a shiny aluminum cap/plug was inserted in this hole. I am not sure why the owner before me did this but today, it was replaced with the original black plastic "box". Does this shiny aluminum cap sound like it came from the plumbing parts of a turbo kit?
Given the above evidence and what Jon suggested above, would it be reasonable for me to assume that there probably was some sort of a piggyback system installed previously to alter FI? I am wondering if it could be something like a Greddy eManage Fuel Management System. http://rx7.com/store/rx8/rx8ecu.html My understanding of a piggyback system is that it "tricks" the factory PCM and once removed, the ECU should revert to OEM mapping. Anyway, do you guys think that its possible that the removal of such a device could leave me with the 7500rpm hesitation symptom?
07-22-2010, 02:11 PM
#11
Can you take a pic of your PCM box so we can see what you see?
Might have been used for exhaust temps. 
Is the threaded hole plugged with anything to prevent exhaust leaks?
Maybe a pic of this can be helpful too.
That box is called a resonance chamber and is simply used to quiet the sound coming from the engine.
Removing this can make the car slightly louder, which some people like.
As long as its fully plugged and not introducing a leak, you should be fine.
Is the threaded hole plugged with anything to prevent exhaust leaks?
Maybe a pic of this can be helpful too.
Removing this can make the car slightly louder, which some people like.
As long as its fully plugged and not introducing a leak, you should be fine.
07-27-2010, 07:16 AM
#12
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I guess I'll throw two cents two.
Allot of good information posted here, but I wanted to add these thoughts.
My car had a "hesitation" at about 7500 rpm as well. As mentioned earlier, the VDI operates in this range. As far as I can tell it appears to the engine as a hesitation due too a small lean spike, which gets quickly resolved do to the MAF mapping of incoming air. You should also notice these spikes at other rpms as well, like the APV valve at 6100 should be noticeable. Here again, the MAF adjusts the fueling after it sees the increase of air (which is why acceleration comes back), not before. At that point your engine has already seen several cycles that were leaner than the mapping do to the additional port openings and playing catch-up. Some careful tuning can map this out and minimize the effect, but the cause is still there.
My opinion, based on your posts about the consistent rpm and the valves move freely, is that the system is working as intended.
Here is a reference from a reputable tuner to verify the hesitation at the mentioned rpms, although it doesn't say why, they coincide with the S-DAIS system operating points.
Allot of good information posted here, but I wanted to add these thoughts.
My car had a "hesitation" at about 7500 rpm as well. As mentioned earlier, the VDI operates in this range. As far as I can tell it appears to the engine as a hesitation due too a small lean spike, which gets quickly resolved do to the MAF mapping of incoming air. You should also notice these spikes at other rpms as well, like the APV valve at 6100 should be noticeable. Here again, the MAF adjusts the fueling after it sees the increase of air (which is why acceleration comes back), not before. At that point your engine has already seen several cycles that were leaner than the mapping do to the additional port openings and playing catch-up. Some careful tuning can map this out and minimize the effect, but the cause is still there.
My opinion, based on your posts about the consistent rpm and the valves move freely, is that the system is working as intended.
Here is a reference from a reputable tuner to verify the hesitation at the mentioned rpms, although it doesn't say why, they coincide with the S-DAIS system operating points.
07-28-2010, 12:48 PM
#13
Can you take a pic of your PCM box so we can see what you see?
Might have been used for exhaust temps.
Is the threaded hole plugged with anything to prevent exhaust leaks?
Maybe a pic of this can be helpful too.
That box is called a resonance chamber and is simply used to quiet the sound coming from the engine.
Removing this can make the car slightly louder, which some people like.
As long as its fully plugged and not introducing a leak, you should be fine.
Might have been used for exhaust temps.
Is the threaded hole plugged with anything to prevent exhaust leaks?
Maybe a pic of this can be helpful too.
That box is called a resonance chamber and is simply used to quiet the sound coming from the engine.
Removing this can make the car slightly louder, which some people like.
As long as its fully plugged and not introducing a leak, you should be fine.
Yes, the hole in the exhaust manifold (90 degree to the front O2 sensor) has been plugged. No photos I'm afraid. Will cost me more to get the workshop to lift it. Your exhaust gas temp assumption sounds absolutely logical.
Thanks, I learnt something new - I now know that the box is a resonance chamber. Beats me as to how it lessens noise.
UPDATE: (1) I found a tiny crack on the rim of the front half of the airbox, where the VFAD and intake duct insert. There's a layer of sponge surrounding this seal and it has shrunken somewhat. Logically, this should not pose an erroroneous reading by the MAF since this is before the airbox and MAF. (2) I found a stripped thread for ONE of the two MAF mounting screws. In particular, its the one on the opposite side of the resonance chamber. The plastic screw thread in the airbox (where the MAF screws into) is stripped and there is not much tension when screwing this screw on so it is dependent on the other screw. If air leaks in at this point, I should have an erroneous MAF reading and this should lead to poor combustion and erratic throttle response... but it should not lead to a consistent hesitation problem at 7500rpm right? Anyway, what do you recommend I do to fix the stripped plastic thread (other than buying a replacement airbox)?
07-28-2010, 01:04 PM
#14
I guess I'll throw two cents two.
Allot of good information posted here, but I wanted to add these thoughts.
My car had a "hesitation" at about 7500 rpm as well. As mentioned earlier, the VDI operates in this range. As far as I can tell it appears to the engine as a hesitation due too a small lean spike, which gets quickly resolved do to the MAF mapping of incoming air. You should also notice these spikes at other rpms as well, like the APV valve at 6100 should be noticeable. Here again, the MAF adjusts the fueling after it sees the increase of air (which is why acceleration comes back), not before. At that point your engine has already seen several cycles that were leaner than the mapping do to the additional port openings and playing catch-up. Some careful tuning can map this out and minimize the effect, but the cause is still there.
My opinion, based on your posts about the consistent rpm and the valves move freely, is that the system is working as intended.
Here is a reference from a reputable tuner to verify the hesitation at the mentioned rpms, although it doesn't say why, they coincide with the S-DAIS system operating points.
Allot of good information posted here, but I wanted to add these thoughts.
My car had a "hesitation" at about 7500 rpm as well. As mentioned earlier, the VDI operates in this range. As far as I can tell it appears to the engine as a hesitation due too a small lean spike, which gets quickly resolved do to the MAF mapping of incoming air. You should also notice these spikes at other rpms as well, like the APV valve at 6100 should be noticeable. Here again, the MAF adjusts the fueling after it sees the increase of air (which is why acceleration comes back), not before. At that point your engine has already seen several cycles that were leaner than the mapping do to the additional port openings and playing catch-up. Some careful tuning can map this out and minimize the effect, but the cause is still there.
My opinion, based on your posts about the consistent rpm and the valves move freely, is that the system is working as intended.
Here is a reference from a reputable tuner to verify the hesitation at the mentioned rpms, although it doesn't say why, they coincide with the S-DAIS system operating points.
This led us to initially believe it could be a stuck/carbon-locked valve that was slow to open. Since this is not the case, I am wondering if it could be the VDI solenoid or a fault in the fuel injection (or fuel management) at the time that the VDI opens. What do you think?
07-28-2010, 10:31 PM
#15
Registered
It has been my personal experience that events at 7,250 (ish) can reveal the status of your engine. Technically the engine is transitioning it's air flow and and adding MORE air rather abruptly. This is upsetting to the previous air flow and takes a brief moment before the air flow/velocity gets all squared away.
Have you ever seen the dips in the dyno curve which indicate drops in power? Sure you have. This is disrupted air flow.
Now for the ahah moment. If your motors ability to seal is weak, the 7,250 (ish) event which allows for more air can overtax your engine. Consider it a "shocker" event. Sort of like if you were bench pressing 200 and the 210 and then 215 lbs and somebody adding 50 lbs. BIG change. You'd feel this right? Of course you would. Your engine feels the same thing. The slope of the 7,250 and above power curve is more steep than below 7,250. More power (air) is flowing through the engine.
This may not help you diagnose your situation but is helpful to know should your valves work properly.
Keep us posted.
Have you ever seen the dips in the dyno curve which indicate drops in power? Sure you have. This is disrupted air flow.
Now for the ahah moment. If your motors ability to seal is weak, the 7,250 (ish) event which allows for more air can overtax your engine. Consider it a "shocker" event. Sort of like if you were bench pressing 200 and the 210 and then 215 lbs and somebody adding 50 lbs. BIG change. You'd feel this right? Of course you would. Your engine feels the same thing. The slope of the 7,250 and above power curve is more steep than below 7,250. More power (air) is flowing through the engine.
This may not help you diagnose your situation but is helpful to know should your valves work properly.
Keep us posted.
07-29-2010, 06:42 AM
#16
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The Tach in the dash isn't 100% accurate.
Anybody chime in on when the 3 set of injectors (P2) shoot?
Maybe they're dirty...
Another thought, along the same lines as mentioned with airflow. An AFR reading could be beneficial. If you're already on the lean side, like a dirty injector, the disrupted airflow would seem much greater because it shifts you even further lean. For instance, if you're running 12.5 and it spikes to 13.5, should only be a minor blip, but from 13.5 to 14.5 it could get progressively worse and so on. Plus the afr could tell you alot about what the pcm sees and is outputting, like if the maf, or injectors, or an intake leak, and so on, could all be seen in the exhaust gasses.
Even a questionable plug/coil/wire could be misfiring at that heavy load when it's lean, if it's bad enough.
Does it happen at part throttle, full throttle, all the above?
I'm not even sure if you could rule out knock but seems unlikely (a few degrees of retard shouldn't be a huge drop of power like you're experiencing).
If you don't have an AFR meter, how about a scantool, it may indicate an intake leak if your fuel trims are far away from 0%. Plus it may pickup the semi wideband and allow you to log it, not sure.
Just some more thoughts.
Let us know
Anybody chime in on when the 3 set of injectors (P2) shoot?
Maybe they're dirty...
Another thought, along the same lines as mentioned with airflow. An AFR reading could be beneficial. If you're already on the lean side, like a dirty injector, the disrupted airflow would seem much greater because it shifts you even further lean. For instance, if you're running 12.5 and it spikes to 13.5, should only be a minor blip, but from 13.5 to 14.5 it could get progressively worse and so on. Plus the afr could tell you alot about what the pcm sees and is outputting, like if the maf, or injectors, or an intake leak, and so on, could all be seen in the exhaust gasses.
Even a questionable plug/coil/wire could be misfiring at that heavy load when it's lean, if it's bad enough.
Does it happen at part throttle, full throttle, all the above?
I'm not even sure if you could rule out knock but seems unlikely (a few degrees of retard shouldn't be a huge drop of power like you're experiencing).
If you don't have an AFR meter, how about a scantool, it may indicate an intake leak if your fuel trims are far away from 0%. Plus it may pickup the semi wideband and allow you to log it, not sure.
Just some more thoughts.
Let us know
07-29-2010, 09:03 AM
#17
Thanks for the suggestions. Here's some additional information about the car. I did a compression test on the engine about 2 weeks back. It was done on a proper digital rotary compression tester and in accordance to Mazda's guidelines on how to perform the test. The front rotor showed 101.53PSI, 100.08PSI, 101.53PSI while the rear rotor showed 104.43PSI, 105.88PSI, 113.13PSI at 250rpm. Although the engine did not fail the 98.6PSI minimum, I can see that the front rotor is getting close to that figure.
Eric, with such compression figures, will the extra air coming in shock the system into doing that?
Vansickey, fuel system and injectors are the other avenue that we will investigate. Ignition coils are brand new, spark plugs less than a year. It does this exactly at 7500rpm under full throttle and part throttle. Even if I accelerate at a moderate rate from 7000rpm to 8000, it will happen at 7500rpm. Then if I back off and let the revs fall back to just under 7500rpm and then accelerate to 7500rpm, it will do it again at 7500rpm. It is so consistent that my mechanic thinks the ecu has been flashed to do that. He suggests that I go to Mazda and have the PCM flashed back to the factory maps before taking it from there. Is this a reasobable solution? There's a long waiting list for non-emergency repairs/troubleshooting.
Eric, with such compression figures, will the extra air coming in shock the system into doing that?
Vansickey, fuel system and injectors are the other avenue that we will investigate. Ignition coils are brand new, spark plugs less than a year. It does this exactly at 7500rpm under full throttle and part throttle. Even if I accelerate at a moderate rate from 7000rpm to 8000, it will happen at 7500rpm. Then if I back off and let the revs fall back to just under 7500rpm and then accelerate to 7500rpm, it will do it again at 7500rpm. It is so consistent that my mechanic thinks the ecu has been flashed to do that. He suggests that I go to Mazda and have the PCM flashed back to the factory maps before taking it from there. Is this a reasobable solution? There's a long waiting list for non-emergency repairs/troubleshooting.
07-31-2010, 09:29 AM
#18
4AT ECU in 6MT
Well, it seems I'm not the only one with this problem. Take a look at this unresolved old thread I dug up... https://www.rx8club.com/series-i-trouble-shooting-95/rev-limiter-04-mt-rx-8-a-125207/ I wonder how the issue was resolved.
If an ECU from a 4AT car was placed in a 6MT or a 4AT map was flashed onto my ECU, would it lead to a situation like what I am experiencing? I know its far-fetched but the rationale for my question: 4AT has a rev limiter at 7500rpm (the magical rpm number when this happens) which I believe leads to a fuel cut at that point. If one of the previous owners of my car had dekitted his aftermarket ECU hastily before a sale, and replaced with a wrong ECU (the 4AT's ECU), would it lead to hesitation at 7500rpm on a 6MT? There must be a reason why the ECU cables in my car have been cut at some stage.
If an ECU from a 4AT car was placed in a 6MT or a 4AT map was flashed onto my ECU, would it lead to a situation like what I am experiencing? I know its far-fetched but the rationale for my question: 4AT has a rev limiter at 7500rpm (the magical rpm number when this happens) which I believe leads to a fuel cut at that point. If one of the previous owners of my car had dekitted his aftermarket ECU hastily before a sale, and replaced with a wrong ECU (the 4AT's ECU), would it lead to hesitation at 7500rpm on a 6MT? There must be a reason why the ECU cables in my car have been cut at some stage.
07-31-2010, 03:34 PM
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Well, it seems I'm not the only one with this problem. Take a look at this unresolved old thread I dug up... https://www.rx8club.com/showthread.php?t=125207 I wonder how the issue was resolved.
If an ECU from a 4AT car was placed in a 6MT or a 4AT map was flashed onto my ECU, would it lead to a situation like what I am experiencing? I know its far-fetched but the rationale for my question: 4AT has a rev limiter at 7500rpm (the magical rpm number when this happens) which I believe leads to a fuel cut at that point. If one of the previous owners of my car had dekitted his aftermarket ECU hastily before a sale, and replaced with a wrong ECU (the 4AT's ECU), would it lead to hesitation at 7500rpm on a 6MT? There must be a reason why the ECU cables in my car have been cut at some stage.
If an ECU from a 4AT car was placed in a 6MT or a 4AT map was flashed onto my ECU, would it lead to a situation like what I am experiencing? I know its far-fetched but the rationale for my question: 4AT has a rev limiter at 7500rpm (the magical rpm number when this happens) which I believe leads to a fuel cut at that point. If one of the previous owners of my car had dekitted his aftermarket ECU hastily before a sale, and replaced with a wrong ECU (the 4AT's ECU), would it lead to hesitation at 7500rpm on a 6MT? There must be a reason why the ECU cables in my car have been cut at some stage.
If the rev limiter was set for 7500, you wouldn't be able to rev past it.
Plus looking at the ROM would tell you were the rev limiter is.
I agree, it's something the pcm is doing on purpose, but whatever it's doing, why is it killing power?
I wonder how it would act if you drove it with the VDI disconnected. Possibly at the pcm on that center plug...?
Can you get access to a scan tool?
And yes, if your pcm was altered, ( I think is unlikely, few people are tuning these cars ), then the dealer flash could fix it, but what if it doesn't fix? A little tip, I know here, I have gotten the pcm replaced that was defective, as an emmisions control device, under warranty.
Speculation on the cut wires... No real way of knowing, just speculation. Since you are having problems, it would be worth while determining what the functions of the cut wires are, and verifying the correct splices. If they are injector leads, try to determine if installed injectors are stock.
08-02-2010, 12:10 PM
#21
Well first thought is immobilzer issues with wrong ecu, but simple to check for an auto/mt, the auto has a missing plug in the middle of the wiring harness connected to the pcm,( I think 4 total plugs) and the mt has connectors the whole way across it(I think 5 ) it's been awhile. If I recall correctly, that center one is the plug that controls the extra ports and possibly the injectors.
If the rev limiter was set for 7500, you wouldn't be able to rev past it.
Plus looking at the ROM would tell you were the rev limiter is.
I agree, it's something the pcm is doing on purpose, but whatever it's doing, why is it killing power?
I wonder how it would act if you drove it with the VDI disconnected. Possibly at the pcm on that center plug...?
Can you get access to a scan tool?
And yes, if your pcm was altered, ( I think is unlikely, few people are tuning these cars ), then the dealer flash could fix it, but what if it doesn't fix? A little tip, I know here, I have gotten the pcm replaced that was defective, as an emmisions control device, under warranty.
Speculation on the cut wires... No real way of knowing, just speculation. Since you are having problems, it would be worth while determining what the functions of the cut wires are, and verifying the correct splices. If they are injector leads, try to determine if installed injectors are stock.
If the rev limiter was set for 7500, you wouldn't be able to rev past it.
Plus looking at the ROM would tell you were the rev limiter is.
I agree, it's something the pcm is doing on purpose, but whatever it's doing, why is it killing power?
I wonder how it would act if you drove it with the VDI disconnected. Possibly at the pcm on that center plug...?
Can you get access to a scan tool?
And yes, if your pcm was altered, ( I think is unlikely, few people are tuning these cars ), then the dealer flash could fix it, but what if it doesn't fix? A little tip, I know here, I have gotten the pcm replaced that was defective, as an emmisions control device, under warranty.
Speculation on the cut wires... No real way of knowing, just speculation. Since you are having problems, it would be worth while determining what the functions of the cut wires are, and verifying the correct splices. If they are injector leads, try to determine if installed injectors are stock.
The other thing you mentioned about disconnecting the VDI.... I too, am curious as to how it'll behave. You reckon I should just pull off the VDI actuator's vacuum hose and rev it pass 7500rpm to see what happens?
Damn, can't use the old "emissions" excuse on them. Over here, the warranty covers only 60,000km or 36 months, whichever comes first. Its crossed the 4.5 year mark so no more warranty claims. I would have loved to get a Cat out of them too but in our country, we are not protected the way the US consumer is protected up to 80,000miles on the Cat. We also have poor consumer rights here. This is something I hope the government would look at improving.
What's a scan tool?
I will be getting back to you guys (and my car) on 10 August. Thanks for all the input and please keep it coming...
10-21-2012, 12:48 PM
#23
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Please help. During acceleration, at exactly 7500rpm my engine would hesitate and bog momentarily before it accelerates normally to the redline. Although the hesitation/bogging is only for a split second during acceleration, it is severe enough to decelerate the car to the point that the occupants jerk forward, and then get slammed backwards when the bogging passes and acceleration resumes "violently". The acceleration feels more "violent" after this point only because of the suddenly lag. It has been upsetting at times when its happened in a bend and almost sent me into a wall once. To my passenger, it feels as if I had accidentally depressed and released the clutch at that rpm to cause that jerk. Anyone has any ideas on what is causing this? It is consistent and happens 100% of the time at exactly 7500rpm and so far I have experienced it in the first 3 gears (have not tried redlining the car in higher gears so far). The car is an EU/UK spec 2005 6MT with about 30,000miles (50,000km) when I got it 3 weeks ago. Its been doing this since I got it and the CEL light has not shown up. Ex-ex owner used to have a Fujitsubo exhaust and that was replaced one year ago to a USED stock exahust (including cat) by the last owner. Does this sound more like an issue with the cat or a sticky valve or fuel starvation?
Well I would like to share my own experience on my RX8. When I first got it I noticed that exactly at 7500rpm the car will pretty much stop accelerating for just a second and returning with what felt like a "power kick" that sticked you and the passenger to the car seats.
I first thought that maybe it was just a "system like Hondaīs V-tec, nissanīs VVL and so on". Being honest I was a TOTAL newbie on rotary engines.
After watching some youtube videos and driving other rx8īs around my area, I learned that my RX8 wasnt working properly
To make a long story short, One day I decided to remove my CAT and replace it with a custom made 2.5" resonated mid pipe. After doing that I ended up installing my brand new Stage 3 clutch which took me to take the whole air admission/ intake an clean it which apparently cleared some sort of "debris" being guilt closer to the Throttle body.
At the end I finished putting everything back in and started the car. I took it for a little test drive and guess what, now it runs just perfectly fine
It is not kicking at 7500rpm anymore and to be honest I donīt know what may had been the issue.
10-23-2012, 10:12 AM
#24
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Hi crave4speed, i somehow seems to experience the same issue like your 8. Mine was working fine before i took it to the workshop for some fixes. After sitting in the workshop for 3 days, they open up the intake manifold valves and blah blah, ruined my batt, change a new batt. then my car seems to lag at 7250 rpm. makes my acceleration so crappy. Suspecting a faulty vdi solenoid. I wonder if yours is fixed?
