High RPM misfire only at WOT?
06-26-2008, 09:34 PM
#31
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Thread Starter
My understanding is that at WOT the ECU runs with fixed maps and ignores AFM, O2. This means if problem with fueling or air flow you may get misfire. When not WOT ECU monitors AFM O2 and can correct small fueling or air flow issues.
Its easy to tell a valve spring is broken as when compared to a good one the resistance will be very small. Hope this helps.
Its easy to tell a valve spring is broken as when compared to a good one the resistance will be very small. Hope this helps.
ok steve they should check out at about 1.030k ohms or abouts that but not below 1k and the fact that ur car is runnin means there are both ok but the in the area of adj they need to b 8mm for the keyways on the flywheel they way it soundin is that u have too much of a gap so u need to bring it in ..but if u dont have the tool to alin the reference sensors housin u need to have sumone turn the motor over till u c the allen keyway in there(needed even with tool) threw the sensor hole(the closes one to the block) and then put about 8mm of tape on the end of the closes to block sensor and c if it tags the keyway (u put it in all the way in place and remove again) and c if it has marked the tape if not u have to loosen the housin and adj down to where it circles the tape ......(sorry bout the typin im not a fan of it ...lol)
No, not yet. I wasn't really planning on it (planning on keeping the car pretty stock, at least for now), but it would certainly help to t/s this problem. Can you recommend a good one and where to get it?
Thanks.
06-26-2008, 11:20 PM
#32
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well to check the adj of the reference sensors is fairly easy u just need alil time and check the distance from the sensor to the allen keyway i my have made it earlier sound like a serious thing but its not ....ok on the gauge i prefur the uego 2000 for the a/r gauge and if u had one of thses in there and the a/r started to bounc around on u at that point u would know that it is the sensors cuz the ecu can get a good readin off the magentics in it cuz of the incorrect distance(adjment) at that fast of a full pedal effort so when u let off it has time to "catch up " then u are ok but im a 100% sure that is ur area of problem keep me posted goodluck!!!
06-27-2008, 06:51 AM
#33
The fact that the problem is RPM related and you seem to have good power suggest to me that the problem is not valve spring. I suspect in this case the problem to be reference sensor or ECU. In the ECU case is possible that the fuel/ignition maps that are stored in internal ROM have been corrupted. As there are 2 maps one for WOT and one for normal operation is possible that the map for WOT has been corrupted. Replacing the ROM should fix this. Try swapping your ECU with one that is known to work OK.
06-27-2008, 09:09 AM
#34
Rennlist Member
The fact that the problem is RPM related and you seem to have good power suggest to me that the problem is not valve spring. I suspect in this case the problem to be reference sensor or ECU. In the ECU case is possible that the fuel/ignition maps that are stored in internal ROM have been corrupted. As there are 2 maps one for WOT and one for normal operation is possible that the map for WOT has been corrupted. Replacing the ROM should fix this. Try swapping your ECU with one that is known to work OK.
06-27-2008, 11:15 AM
#35
Race Director
Yeah it does sound more electrical related. It could be a bad DME maybe. Seems strange that only WOT at 5400 rpm is there an problem. At WOT you run only on the map in the chip. Maybe there is a problem with the map near 5400? I don't understand how that could, but when you are not WOT and just on it the DME uses a different map. Swap the entire DME or chip if you have an aftermarket one.
06-27-2008, 09:20 PM
#36
Rennlist Member
Please do enlighten me on how one would do that without pulling the head. Yeah, I've done it on 351s and 350s. But you can use an overhead valve spring compressor to get valves out of those.
06-28-2008, 02:30 PM
#37
Rennlist Member
Thread Starter
The fact that the problem is RPM related and you seem to have good power suggest to me that the problem is not valve spring. I suspect in this case the problem to be reference sensor or ECU. In the ECU case is possible that the fuel/ignition maps that are stored in internal ROM have been corrupted. As there are 2 maps one for WOT and one for normal operation is possible that the map for WOT has been corrupted. Replacing the ROM should fix this. Try swapping your ECU with one that is known to work OK.
Yeah it does sound more electrical related. It could be a bad DME maybe. Seems strange that only WOT at 5400 rpm is there an problem. At WOT you run only on the map in the chip. Maybe there is a problem with the map near 5400? I don't understand how that could, but when you are not WOT and just on it the DME uses a different map. Swap the entire DME or chip if you have an aftermarket one.
Thanks a ton for all of the feedback - you guys rock. Here is what I think I am going to try (in order):
1. Swap out DME (need to find someone to swap with...)
2. Check Reference sensors (doesn't look as hard as I thought initially, though not convinced I would be able to tell if they are really the problem without swapping them out)
3. Check for broken valve spring (for peace of mind, mostly... may get this done this weekend)
4. FPR / Fuel Pump / Fuel Filter (need to buy a fuel pressure gauge first)
5. Look for problem with CAT/Exhaust
6. Squeeze motor from my 928 into this car as a last resort
Anything I missed?
06-28-2008, 03:41 PM
#38
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My understanding is that at WOT the ECU runs with fixed maps and ignores AFM, O2. This means if problem with fueling or air flow you may get misfire. When not WOT ECU monitors AFM O2 and can correct small fueling or air flow issues.
Its easy to tell a valve spring is broken as when compared to a good one the resistance will be very small. Hope this helps.
Its easy to tell a valve spring is broken as when compared to a good one the resistance will be very small. Hope this helps.
I had the same symptoms and the cause was the AFM track being worn out. It cut out around 5000-5200 rpm when at WOT, but not at partial throttle. It also didn't do it when free-revving... the engine had to be under load, and the more load there was, the worse it would do it. I re-tracked the AFM and the problem went away.
06-28-2008, 03:52 PM
#39
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Thread Starter
It ignores the O2 sensor, but not the AFM. The AFM is always in use, and is a prime suspect for this problem.
I had the same symptoms and the cause was the AFM track being worn out. It cut out around 5000-5200 rpm when at WOT, but not at partial throttle. It also didn't do it when free-revving... the engine had to be under load, and the more load there was, the worse it would do it. I re-tracked the AFM and the problem went away.
I had the same symptoms and the cause was the AFM track being worn out. It cut out around 5000-5200 rpm when at WOT, but not at partial throttle. It also didn't do it when free-revving... the engine had to be under load, and the more load there was, the worse it would do it. I re-tracked the AFM and the problem went away.
06-28-2008, 04:26 PM
#40
Is possible the AFM is actually not adjusted correctly. The track is spring loaded and the spring action can be adjusted. It may be worth trying to adjust the spring action and see if the hesitation moves to a different rpm. If it does then then you know the AFM needs attention.
06-28-2008, 04:34 PM
#41
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Try simply unplugging your TPS. The only way the DME knows you are at WOT is the WOT switch in the TPS. If it still has the problem you can probably rule out the DME.
jmd_forest
jmd_forest
06-28-2008, 05:01 PM
#42
This is pretty good suggestion. I think the TPS controls the IDLE as well so IDLE may be bad. If the car is still drivable then WOT action should still be testable.
06-28-2008, 07:40 PM
#43
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Thread Starter
It may be my imagination, but after I reconnected the TPS, even though the car was still missing, I don't think it was quite as bad. I am probably over-analyzing it...
I guess I am off to check the AFM next.
Thanks again for all the great suggestions.
06-28-2008, 08:04 PM
#44
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Have you tested your TPS? At the very least, I'd want to verify it was working since it tells the DME that you are at WOT.
Have you tried a compression and/or leakdown test? Backfire says you are getting spark and fuel at the right combination at the wrong time. Have you checked your timing belt; is it possible you slipped/stripped a tooth?
Open up the hood at night and inspect the entire length of the ignition wires looking for little sparks. Gun it a little to try and induce sparking. If you see any, replace the wires.
jmd_forest
jmd_forest
Have you tried a compression and/or leakdown test? Backfire says you are getting spark and fuel at the right combination at the wrong time. Have you checked your timing belt; is it possible you slipped/stripped a tooth?
Open up the hood at night and inspect the entire length of the ignition wires looking for little sparks. Gun it a little to try and induce sparking. If you see any, replace the wires.
jmd_forest
jmd_forest