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Stock ECU/Electrical guru's needed

Old 03-28-2016, 12:43 PM
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Stock ECU/Electrical guru's needed

Have an interesting project and set of problems here and hoping someone can shed some light on this for me.

1985 RX7, FC subframe swap and full renni transplant.
Used the stock ECU and called one of the patch harness makers and bought the plastic connectors and pins and built a harness from scratch. As far as I can tell after checking, double and triple checking all the wiring is correct. There are no other sensors or inputs except what's on the engine. Front 02 sensor, not a rear one.

No chassis inputs, PS, speed, nothing.

I was told by the folks @ RB that with their flash, removing the immobilizer and wiring it the way described and the way I did, it would work. The OBDII would work for troubleshooting

Rebuilt engine.

Now, she'll start, and start right up but goes into limp mode almost instantly. She'll rev a few times and sounds sexy as **** but then drops down to 2250 (as seen on my 2stroke timing light) with the pedal to the floor, and if you're gentle enough with your foot and bring the idle all the way down, she will actually idle @ 460rpms for a few minutes.

The OBDII I wired the CAN hi and CAN lo, 12vdc, CGrnound and chassis ground. I was also told doing this would allow the the OBDII scanners to read what's going on but that can't either. It just rolls around and finally after waiting a while will say, cannot establish communication with vehicle

I called Racing Beat this morning and they're totally backtracking on me. Saying they would never tell me that simply removing the immobilizer would allow the ECU to run on it's own without ALL the factory inputs. OK, than what's the point of the immobilizer delete if not to transplant the renni? I highly doubt RB is so desperate for cash that they would tell me wrong info to get $400 worth of flashing out of me.

My questions
-Has anyone successfully transplanted a renni using the stock ECU without the use of the dash or anything else on the CAN bus network?
-I seem to remember something about the CAN needing some sort or resistors in order for it to work without all the added crap on the network. Can someone shed some light onto that for me.
-Without having the OBD working, and hearing the symptoms (oh yeah, the TB whines when the key is on) anyone want to take a stab at what's throwing this little bitch into limp mode?
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Old 03-28-2016, 02:25 PM
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brian my heeeerro! what ya been! sorry on your luck i plan to traverse this same Endeavor.

i think can in the clutster is the end point , if this system is anything like this CCD in a chrysler...
can you get the cluster to try it? i can pull moduals until my scanner doesnt read obdII for you...

Last edited by lastphaseofthis; 03-28-2016 at 02:30 PM.
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Old 03-28-2016, 03:30 PM
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Originally Posted by Titaniumtt View Post
Now, she'll start, and start right up but goes into limp mode almost instantly. She'll rev a few times and sounds sexy as **** but then drops down to 2250 (as seen on my 2stroke timing light) with the pedal to the floor, and if you're gentle enough with your foot and bring the idle all the way down, she will actually idle @ 460rpms for a few minutes.
You sure you're getting fuel? When I first got my V8 running in my RX-8, it died on me after about 10 seconds. I was concerned it was VATS, but what it actually turned out to be was a bad ground. The fuel pump would prime fine when I was getting ready to crank, but as soon as it was under any actual load, the pump was under powered. The symptoms were good start, then as fuel pressure dropped, it died. I was actually missing a grounding clip from my harness, so I soldered one in, grounded it up by the firewall, and viola.

Good Luck
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Old 03-28-2016, 04:11 PM
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to make sure is a can/ ecu problem have you tried cycling the key with the engine running, like so fast it doesnt die, but slow enough it resets the pcm routine... "

i used to do this on my s5 FC with the omp failure. for about 3 seconds the ecu would not be in limp mode, and i could redline and pass people... yeah i cycled the key right before passing people knowing i had a 3 second window.. call me nuts.
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Old 03-28-2016, 04:41 PM
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Originally Posted by lastphaseofthis View Post
brian my heeeerro! what ya been! sorry on your luck i plan to traverse this same Endeavor.

i think can in the clutster is the end point , if this system is anything like this CCD in a chrysler...
can you get the cluster to try it? i can pull moduals until my scanner doesnt read obdII for you...
Whats up man!

This is interesting because I do know of one renni transplant that didn't have these problems and he was using the stock dash. We may be onto something. I don't have the greatest understanding of CAN comms.

Really don't need to either, just need to be able to get my scanner hooked to it or working through the OBDII and maybe even use my unmarried Cobb to turn **** off if I need to.

Originally Posted by zendrums View Post
You sure you're getting fuel? When I first got my V8 running in my RX-8, it died on me after about 10 seconds. I was concerned it was VATS, but what it actually turned out to be was a bad ground. The fuel pump would prime fine when I was getting ready to crank, but as soon as it was under any actual load, the pump was under powered. The symptoms were good start, then as fuel pressure dropped, it died. I was actually missing a grounding clip from my harness, so I soldered one in, grounded it up by the firewall, and viola.

Good Luck
110% absolutely positive it is not fuel pressure related. Hooked up a mechanical gauge to it to verify. The engine will run long enough to get hot and kick the fan on.

Originally Posted by lastphaseofthis View Post
to make sure is a can/ ecu problem have you tried cycling the key with the engine running, like so fast it doesnt die, but slow enough it resets the pcm routine... "

i used to do this on my s5 FC with the omp failure. for about 3 seconds the ecu would not be in limp mode, and i could redline and pass people... yeah i cycled the key right before passing people knowing i had a 3 second window.. call me nuts.
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Old 03-28-2016, 07:14 PM
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I can't give Mazda specific info, but I can tell you that on CAN communications systems on other manufacturers vehicles require a specific impedance of 60 ohms between high and low. If this condition is not satisfied, certain nodes may not communicate at all. This condition can easily be ascertained by measuring impedance between high and low with a multi meter set to resistance. Reading should be 60 ohms. Typical CAN architecture achieves this with 120 ohm resistors on either end of a line set. If there are no resistors there will be no resistance, if there is one resistor the reading will be 120, if there are two resistors the reading will be 60. Not sure how many CAN nodes there are on the 8. And polarity must be observed for correct CAN network functionality. Sometimes the resistors may be built into nodes such as ECU. I hope this helps if only marginally........Good luck!
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Old 03-28-2016, 07:53 PM
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Originally Posted by StarSpinner View Post
I can't give Mazda specific info, but I can tell you that on CAN communications systems on other manufacturers vehicles require a specific impedance of 60 ohms between high and low. If this condition is not satisfied, certain nodes may not communicate at all. This condition can easily be ascertained by measuring impedance between high and low with a multi meter set to resistance. Reading should be 60 ohms. Typical CAN architecture achieves this with 120 ohm resistors on either end of a line set. If there are no resistors there will be no resistance, if there is one resistor the reading will be 120, if there are two resistors the reading will be 60. Not sure how many CAN nodes there are on the 8. And polarity must be observed for correct CAN network functionality. Sometimes the resistors may be built into nodes such as ECU. I hope this helps if only marginally........Good luck!
THIS!!! thank you! i for the love of god i could not remember nore find the information in alldata.. but yeah your pcm is the 60 pcm is the 60ohm start and you need to add a 60 ohm between hi and lo and it should be set!! and this is easy to test!

i also have a vq35de with stock ecu/immob/immob annt/original key/. and cluster. same for a vk45de

i did more digging in ondemand5... there are error msg codes for failing moduals for the whole system every one, but the cluster. even the pcm can be out of the loop..

also i ran thru the troubleshooter and it says basically if trouble with **M... check wiring between **M and cluster. pcm, tcm, abs, eps, keyless(i think immob ), steering angle sensor, dsc, tpms... those 9 but any of the 9 can be missing but the cluster...a resistor may or may not work. ;{ luck 2 you!

Last edited by lastphaseofthis; 03-28-2016 at 08:15 PM.
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Old 03-28-2016, 10:30 PM
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Originally Posted by StarSpinner View Post
I can't give Mazda specific info, but I can tell you that on CAN communications systems on other manufacturers vehicles require a specific impedance of 60 ohms between high and low. If this condition is not satisfied, certain nodes may not communicate at all. This condition can easily be ascertained by measuring impedance between high and low with a multi meter set to resistance. Reading should be 60 ohms. Typical CAN architecture achieves this with 120 ohm resistors on either end of a line set. If there are no resistors there will be no resistance, if there is one resistor the reading will be 120, if there are two resistors the reading will be 60. Not sure how many CAN nodes there are on the 8. And polarity must be observed for correct CAN network functionality. Sometimes the resistors may be built into nodes such as ECU. I hope this helps if only marginally........Good luck!
It helps tremendously actually, thank you very much. Ok, so step one is going to be getting the scanner to talk to the ECU. And if I'm understanding this correctly I can crimp two 120ohm resistors, one on each CAN hi & lo and it should then talk to the scanner?

Reading the post below it seems that the resistors are in the dash somewhere and having them and a return, or the dash hooked up will take the damn thing out of limp mode? Is that pretty much what I'm hearing?

I do have a buddy who helped with a rally FB that had a renni transplant. They used way more factory wiring than I did, as well as a dash and his **** ran. Every single warning light was on but it ran.

I really want to get this car to DGRR, so time is of the essence, sadly, as it usually is.
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Old 03-28-2016, 10:34 PM
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Originally Posted by lastphaseofthis View Post
THIS!!! thank you! i for the love of god i could not remember nore find the information in alldata.. but yeah your pcm is the 60 pcm is the 60ohm start and you need to add a 60 ohm between hi and lo and it should be set!! and this is easy to test!

i also have a vq35de with stock ecu/immob/immob annt/original key/. and cluster. same for a vk45de

i did more digging in ondemand5... there are error msg codes for failing moduals for the whole system every one, but the cluster. even the pcm can be out of the loop..

also i ran thru the troubleshooter and it says basically if trouble with **M... check wiring between **M and cluster. pcm, tcm, abs, eps, keyless(i think immob ), steering angle sensor, dsc, tpms... those 9 but any of the 9 can be missing but the cluster...a resistor may or may not work. ;{ luck 2 you!
Ok, so I've been drinking for the last 5 hours so this will probably make more sense to me in the morning but lets go through this step by step, after thinking about it it doesn't make sense, putting a resistor in line with the can hi/lo. Like cutting the line and adding a resistor. What it sounds like what you're saying is possibly bridging the hi/lo together with a single 60ohm MAY fool the ECU enough into thinking that the dash is there, take it out of limp mode and allow the OBDII to communicate with my scanner? Could it possibly be that damn simple? What am I missing? Cause I'll drive my *** to the last open radio shack in CT to get a bundle of resistors and drive my *** the 45 minutes to my shop to try this **** out tomorrow if we're thinking we're on to something which I'm thinking we are
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Old 03-28-2016, 10:35 PM
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And thanks for the help guys. I'm a pro with ECU's, but none of them are stock :D
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Old 03-28-2016, 10:42 PM
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we are there bro.
What it sounds like what you're saying is possibly bridging the hi/lo together with a single 60ohm MAY fool the ECU enough into thinking that the dash is there,
whats your location? im in lousiville now..
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Old 03-28-2016, 10:55 PM
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Resistors do need to be at each end, but NOT IN-LINE. They do ......"bridge the gap" as it were.
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Old 03-29-2016, 09:06 AM
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Originally Posted by lastphaseofthis View Post
we are there bro.
whats your location? im in lousiville now..
:awesome: Still up in CT

Originally Posted by StarSpinner View Post
Resistors do need to be at each end, but NOT IN-LINE. They do ......"bridge the gap" as it were.
Ok, so, I've got a few feet of wire going from the ECU directly to the OBDII plug. If I'm hearing this correctly I can add a foot or so to each wire, hi/lo and connect the ends together with a 60ohm resistor. Tap into the same lines about where I added the extra foot and connect my OBDII lines and I should be good to go, at least talk to the damn thing?

If still nothing it sounds like I'll need to pull my dash from my 8 and wire it in and see what happens. This.... will be fun. I doubt I'll have the time to get to the dash thing tongith, but will definitely be finding a radio shack and procuring some resistors today.
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Old 03-29-2016, 10:09 AM
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Originally Posted by Titaniumtt View Post
:awesome: Still up in CT



Ok, so, I've got a few feet of wire going from the ECU directly to the OBDII plug. If I'm hearing this correctly I can add a foot or so to each wire, hi/lo and connect the ends together with a 60ohm resistor. Tap into the same lines about where I added the extra foot and connect my OBDII lines and I should be good to go, at least talk to the damn thing?

If still nothing it sounds like I'll need to pull my dash from my 8 and wire it in and see what happens. This.... will be fun. I doubt I'll have the time to get to the dash thing tongith, but will definitely be finding a radio shack and procuring some resistors today.
not the whole dash just the cluster power ground and 2 can lines should be good for testing.
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Old 03-29-2016, 11:56 AM
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Yeah, that's what I meant, just the cluster
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Old 03-29-2016, 09:02 PM
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Well alrighty than.... here's where we're at. She's out of limp dick mode. I wired it as close to factory as possible which means the W/R wire from the EGI relay touches alot of things, SSV, APV, 5th6th aaaaaannnnnnnndddddddd Front 02 and dun dun dun, OMP. So the OMP wasn't working and that's what threw it into limp mode. Sooooooo that's solved Onto the next two problems...

1) Still can't hook up the OBDII scanner.... this is causing me great annoyance. Went to radio shack and picked up 6 10ohm 1watt resistors and wired them in, bridging the gap if you will and I ended up with 59 ohms (radio shack) across pins 6 & 14 of the OBDII connector, as it should be. Still won't talk to the damn thing.... son of a bitch. I'll pull my dash on Thursday and wire that up and see what happens. But I'm not holding my breath on that working either

2) The idle. It'll hold around 1350 on my timing light (oh btw, got the tach working while she was warming up so there's that) and now the tach as well however, when she get's up to temp, she drops, like alot. as in down to 460 AGAIN. SHe'll hold there but not for long. Car can't be driven like this so this is basically the last thing that needs to happen. Any thoughts on this idle issue? Or should I post this up in the generally tech section?
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Old 03-29-2016, 10:30 PM
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i found later on the 120 ohm thing was for the first standard of CAN. cluster is a good shot tho.
add some air around the throttle body. like by pass it, there is hoses on the rx8 that bypass the throttle i bet you have them capped? you have rx8 lower intake with air ports?
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Old 03-30-2016, 12:18 AM
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Old 03-30-2016, 09:11 AM
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Originally Posted by lastphaseofthis View Post
i found later on the 120 ohm thing was for the first standard of CAN. cluster is a good shot tho.
add some air around the throttle body. like by pass it, there is hoses on the rx8 that bypass the throttle i bet you have them capped? you have rx8 lower intake with air ports?
Intake was put back together as stock. Well, almost. There are three fav lines that attach to the compression elbow. On this car they were all run together, adapted to a -6 and run to the intake tube as well. So that shouldn't be the issue.
I also don't think it's the MAF as it idles @ 460 rpm's which amazes me. So I think the trims and MAF are fine.
Is there a re-learn procedure that needs to be dealt with?

Interesting you should say that about the ports on the primaries. I did uncap them and expected the thing to start screaming, that did not happen. Still died out which leads me to believe one of the valves may be acting...... wrong.

Originally Posted by dannobre View Post
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Oh, believe me, I pushed that HARD, he didn't want to. There are two options around the $1300 range that would solve all these problems, but after putting close to $15k into an FB, another 10% is a hard sell.

Throttle Body coolant lines.... do they have any function whatsoever?

Last edited by Titaniumtt; 03-30-2016 at 09:14 AM.
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Old 03-31-2016, 08:12 AM
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Originally Posted by Titaniumtt View Post
Throttle Body coolant lines.... do they have any function whatsoever?
They heat the TB so that it doesn't stick when it's cold.
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Old 03-31-2016, 08:57 AM
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I don't think this is the problem as the car gets warm plus I'm doing this is a heated shop, so I don't believe that to be the problem.

I'm thinking more the TB is FUBAR as it whines like a stuck pig key on, engine off. Going to put this TB on my car and see what happens, then my TB on his car and see what happens.
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Old 03-31-2016, 08:59 AM
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lmk if you need a tb
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Old 03-31-2016, 02:30 PM
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no... let me know if you neeed a tb...

never mind im keeping my spare.
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Old 04-04-2016, 10:35 AM
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As it turns out, it was the throttle body. The thing was ******* disgusting. So much carbon buildup that you could see virtually no light when looking through it. Cleaned it out, fired her up, went through the entire temp range just idling and it held. Stone cold, or scalding hot, blip the throttle or let it snap shut from 4k she just idles down.

She does idle a little rough but because RB flash and turn in the intake tube right before the MAF, but she's done and basically ready for DGRR
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Old 08-02-2017, 02:50 AM
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Sorry to revive an old thread 'Titaniumtt' but you seem to be the only one here that has successfully done a engine and ECU transplant. (after about 10 hrs of searching RX8 forum) lol and about 20hrs online

I'd love a writeup on this process - and I'm sure it would be an instant sticky!
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