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Revs jumping after WOT in 1st gear
So the story goes, The other day I noticed when I started my car, a bunch of dash lights would come on (ABS, TCS, Brake, Battery, Power Steering, etc.) as well as the power steering not working. A free diagnosis proved that the alternator was dead so I just replaced my alternator, and when I started the car, everything was running fine, the battery was charging, and all seemed well. I let the car warm up and charge the battery a little bit, and decided to take it for a drive. I was easy on it for a good 15 minutes, but then decided to open it up in first gear. I revved up to around 8k or so, and pushed in the clutch so I could coast to a stop. As soon as I pushed in the clutch and let go of the gas, the engine revved itself all the way to redline, but fell down to about 3k RPM where it sat and jumped up and down by itself (was not idling). When I tried to push the gas, nothing happened. It did not respond to the gas pedal. I eventually coasted to the side of the road and cut the ignition. After I cut the gas off, I tried to start the car again, but it wouldn't turn over (edit: the starter would spin, but the engine would not ignite). The battery had plenty of charge to start it, so that is not the issue. As soon as it started revving itself, I got a CEL. Haven't had a chance to get the code read yet. I posted a video here (note that the TCS light is only on because this was the first driving cycle after reinstalling the battery):
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A failed alternator is not good news. It is rare, but when it happens it can fry a lot of expensive electronics.
Can you confirm that when you attempted to restart it would not turn over? As in the did nothing, or the starter spun but the engine did not? Or do you mean "turned over but would not fire" Many people use "turn over" incorrectly, despite it meaning exactly as it says, so I want to be sure I understand you right. |
Unplug the MAF and the battery for 10 minutes then plug them back in.
That too^ |
Originally Posted by RIWWP
(Post 4664384)
A failed alternator is not good news. It is rare, but when it happens it can fry a lot of expensive electronics.
Can you confirm that when you attempted to restart it would not turn over? As in the did nothing, or the starter spun but the engine did not? Or do you mean "turned over but would not fire" Many people use "turn over" incorrectly, despite it meaning exactly as it says, so I want to be sure I understand you right. |
Ok, there are a bunch of possibilities, and this probably isn't going to end up being cheap. However, some free stuff to start with, a couple that J already mentioned.
- Unplug the battery for several minutes - unplug the maf at the same time for several minutes - clean the ESS while you are waiting (you are about to clear it's profile, might as well make sure it's a good one) - after reconnecting, reset the ESS profile I'm suggesting this because the ESS drives both the tach and the fuel/ignition. If there is an ESS problem, then it would cause the tach to have problems easily, and could also cause the engine to not fire when cranking. IF the problem is just in a profile problem, then this will clear it, along with any residual configurations that the ECU has stored. Rebooting it all so to speak. If no change, then either replace the ESS or swap yours with someone else's known good one, to see if you get a change. If still no luck, you will probably need a dealer to test the ECU for problems/errors, and almost certainly deeper than just 'checking codes'. The ECU can and will fry rather quickly with an alternator over-voltage. It rarely just goes dead, resistors inside the ECU will burn out and allow far too much current through whatever circuit was involved with it, causing all sorts of problems. Which circuit it happens with is virtually random. |
Originally Posted by RIWWP
(Post 4664388)
Ok, there are a bunch of possibilities, and this probably isn't going to end up being cheap. However, some free stuff to start with, a couple that J already mentioned.
- Unplug the battery for several minutes - unplug the maf at the same time for several minutes - clean the ESS while you are waiting (you are about to clear it's profile, might as well make sure it's a good one) - after reconnecting, reset the ESS profile I'm suggesting this because the ESS drives both the tach and the fuel/ignition. If there is an ESS problem, then it would cause the tach to have problems easily, and could also cause the engine to not fire when cranking. IF the problem is just in a profile problem, then this will clear it, along with any residual configurations that the ECU has stored. Rebooting it all so to speak. If no change, then either replace the ESS or swap yours with someone else's known good one, to see if you get a change. If still no luck, you will probably need a dealer to test the ECU for problems/errors, and almost certainly deeper than just 'checking codes'. The ECU can and will fry rather quickly with an alternator over-voltage. It rarely just goes dead, resistors inside the ECU will burn out and allow far too much current through whatever circuit was involved with it, causing all sorts of problems. Which circuit it happens with is virtually random. |
Yup, could be.
Generic code readers will show "crank sensor" codes for the ESS, only Mazda specific code readers will show "eccentric shaft sensor" or "ess" or "e-shaft sensor". Same function, same sensor design, same trigger method. |
Originally Posted by RIWWP
(Post 4664391)
Yup, could be.
Generic code readers will show "crank sensor" codes for the ESS, only Mazda specific code readers will show "eccentric shaft sensor" or "ess" or "e-shaft sensor". Same function, same sensor design, same trigger method. |
You replace it and then everything works. Lol. I'm sure there is a real answer that riwwp is typing into a short story
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There are 2 images missing that don't copy paste into text. See the Mazda service manual (foxed.ca) for the full article and the images showing the pinnout.
2005 - RX8 - Workshop Manual - Engine ECCENTRIC SHAFT POSITION SENSOR INSPECTION NOTE: Before performing the following inspection, make sure to follow the troubleshooting flowchart. (See FOREWORD.) Visual Inspection 1. Remove the eccentric shaft position sensor. 2. Verify that there are no metal shavings on the sensor. If the monitor item condition (reference) is not within the specification even though there is no malfunction, perform the “Circuit Open/Short Inspection”. Resistance Inspection 1. Disconnect the eccentric shaft position sensor connector. 2. Measure the coil resistance between eccentric shaft position sensor terminals A and B. If not within the specification, replace the eccentric shaft position sensor. If the monitor item condition/specification (reference) is not within the specification, even though the eccentric shaft position sensor resistance is within the specification, perform the “Circuit Open/Short Inspection” and repair or replace the malfunctioning part. Eccentric shaft position sensor resistance 950—1,250 ohms (at room temperature) Circuit Open/Short Inspection 1. Disconnect the PCM connector. 2. Disconnect the eccentric shaft position sensor connector. 3. Inspect the following wiring harnesses for open or short circuit. (Continuity inspection) Open circuit If there is no continuity in the following wiring harnesses, there is an open circuit. Repair or replace the wiring harness. Eccentric shaft position sensor terminal A and PCM terminal 2U Eccentric shaft position sensor terminal B and PCM terminal 2X Short circuit If there is continuity in the following wiring harnesses, there is a short circuit. Repair or replace the wiring harness. Eccentric shaft position sensor terminal A and body ground Eccentric shaft position sensor terminal A and power supply Eccentric shaft position sensor terminal B and body ground Eccentric shaft position sensor terminal B and power supply |
Originally Posted by J8635621
(Post 4664394)
You replace it and then everything works. Lol. I'm sure there is a real answer that riwwp is typing into a short story
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Originally Posted by RIWWP
(Post 4664395)
There are 2 images missing that don't copy paste into text. See the Mazda service manual (foxed.ca) for the full article and the images showing the pinnout.
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Are you familiar with the "20 brake pedal stomp"? That clears the ESS. It's Key to ON position from off, and then 20 brake pedal presses (just enough to trigger the brake lights is fine) within 8 seconds. If you have a 2005 or later, or a 2004 with the later flashes, the oil pressure gauge will sweep full right to indicate that it was successful.
If you aren't able to test the ESS, then swapping it with someone else's known good one, or ordering a new one, would be how you would 'test' it. Removal would happen in either case if the reset doesn't fix anything. |
Originally Posted by RIWWP
(Post 4664399)
Are you familiar with the "20 brake pedal stomp"? That clears the ESS. It's Key to ON position from off, and then 20 brake pedal presses (just enough to trigger the brake lights is fine) within 8 seconds. If you have a 2005 or later, or a 2004 with the later flashes, the oil pressure gauge will sweep full right to indicate that it was successful.
If you aren't able to test the ESS, then swapping it with someone else's known good one, or ordering a new one, would be how you would 'test' it. Removal would happen in either case if the reset doesn't fix anything. |
At first it sounded like it went into limp mode like an OMP issue, but you still have some limited throttle then. The other limp mode feature though is e-throttle safety related. The fact that the engine revs shot up when you lifted and then it had no throttle at all seems to suggest an e-throttle issue. I'm not familiar enough it to know if engine starting/idling might be affected.
I have some spare ESS if you would like me to mail one to you to check against. There typically would be ESS related codes though so unless you have those that's probably not it. Did you check all your fuses in both the engine bay and driver foot panel? A blown fuel/ignition/room fuse will prevent start up. There may be more ... Also don't understand why people are suggesting to unplug the MAF along with the battery? . |
Originally Posted by TeamRX8
(Post 4664474)
At first it sounded like it went into limp mode like an OMP issue, but you still have some limited throttle then. The other limp mode feature though is e-throttle safety related. The fact that the engine revs shot up when you lifted and then it had no throttle at all seems to suggest an e-throttle issue. I'm not familiar enough it to know if engine starting/idling might be affected.
I have some spare ESS if you would like me to mail one to you to check against. There typically would be ESS related codes though so unless you have those that's probably not it. Did you check all your fuses in both the engine bay and driver foot panel? A blown fuel/ignition/room fuse will prevent start up. There may be more ... Also don't understand why people are suggesting to unplug the MAF along with the battery? . Also, it did throw a code, I just haven't been able to get it checked yet. That's another thing I will be looking at today while I'm over there. I'll keep you guys posted, and appreciate the responses. |
Aem: 1, rx-8: 0
Checked codes and got P0638 and P2109, both throttle body related. I took apart my AEM intake near the throttle body and found this little guy hanging out.
https://cimg8.ibsrv.net/gimg/www.rx8...12047fc3c6.jpg https://cimg9.ibsrv.net/gimg/www.rx8...d9ec92bd44.jpg Now that's not supposed to be there, is it? :lol: Nope. Removed it, cleared codes; she started right up. When I hit around 8k RPM at WOT, the intake sucked up the screen that was inside the intake tubing, and caused the throttle body to be stuck open. That's why the RPM's were jumping, and the car wouldn't start because the codes it threw disabled ignition. As soon as the codes were cleared, it started fine. *Thanks Obama/AEM* |
You put the screen back?
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Originally Posted by J8635621
(Post 4664545)
You put the screen back?
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:lol:
That will do it. Glad it was a cheap fix. |
Emphasizes the point that we're all e-guessing prior to the codes being pulled and pointing you in a possible direction to go. Had this happen locally to WTBRotary, though his screen didn't get that far into the TB, so it wasn't as extreme as yours. You should be able to straighten and re-use the screen. It's fairly common on the AEM intake, which I don't really care for much. It's important to push the coupling and pipe togegher and get the screen squeezed in tight between them while tightening the coupling hose clamp to get it all held tight in place.
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That screen does have a job. It is not a debris catcher. It helps even out the air flow for the MAF. I suggest following through and getting it, or a replacement, back in there. The fact that it was sucked out, confirms it was doing something to the air flow.
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Yes, restricting airflow. The AEM screen with the thick rubber donut perimeter is not as good of a
design as OE in this regard. The screen has larger ooenings, but the donut design results in a less-than-OE inside diameter flow path. There is another section that is also smaller ID than the factory MAF tube. |
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