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Old 03-14-2014, 05:52 PM   #1
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Default Troublingshoot ECU/Car after VVT swap

The MSM engine ate it's bearings, so I grabbed a junkyard VVT engine and dropped it in it's place. The car won't rev past 2.5-3K due to a horrible mis-fire.

2004 MSM chassis/wiring harness
Adaptronic e420c
VVT is not currently hooked up.
Plugs are gapped at 25 I think. NGK 6's.

The car fires and idles like a champ. I found a base 2001 timing map that someone from FM uploaded to and loaded it into the car. Also pulled fuel (~20%) from the previous turbo map. I am getting reasonable AFRs during the increasing revs and including the mis-fire event (11-13). The plugs look fine. The interesting deal is during the mis-fire the RPM reading gets kicked around (typically down). During the increase of revs, the RPM is correct, but during the mis-fire event, it will briefly show 900 or 1500 or similar . This does not obviously match the tach or the actual engine. I also tried various timing values (11-25) and this did not seem to affect the problem.

I suspect it might be a ground issue. The IAT (DIY gm element) seems to be pretty far off all of a sudden. I checked the ground by the exhaust, and looked at the grounds on the Adaptronic adapter board. Both of those seem to be in order.

Did I forgot to hook up one of the grounds?
Are the trigger settings the same for VVT and non-VVT?
Could this be a base timing problem where the Engine and the ECU are not in sync?
If the timing belt is off a tooth (or 2) would these symptoms match?

EDIT: Log uploaded. The VVT columns are default and I never used them with the BP4W. I honestly have no idea what value they are reported.

Thanks for your help!
Attached Files
File Type: csv misfire.csv (39.1 KB, 29 views)

Last edited by ILoveOffRamps; 03-14-2014 at 06:50 PM.
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Old 03-15-2014, 05:14 PM   #2
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I resigned myself to start swapping sensors. It was the cam sensor. I'm not sure if the cam sensor is different on the BP4W compared to the BP6D, but the swap fixed it. Maybe it was a bad sensor. Who knows. It runs now.
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