High RPM stumble, almost like a governor...
02-26-2013, 02:50 PM
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High RPM stumble, almost like a governor... ***FIXED!!! See post #8 for solution.***
I am in need of some help. Aside from averaging about 18 mpg, 3 mpg lower than my last '99 SS M6, my '99 SS M6 with 90k miles runs completely normal during regular driving. When doing some spirited driving, it stumbles like it is hitting a governor, from around 5,200 RPM on up to the 6,000 RPM I shift at, and sometimes bogs down a lot right after the up-shift, but then picks back up until it gets into that RPM range and proceeds to do the same thing. I thought it was a tuning issue, so I had my tuner look into it, and he said that it wasn't a tuning issue. He found that bank 1 was cutting fuel approximately 10% while bank 2 seemed to operate normally. It does this whether I'm in gear with a load or sitting still in neutral without a load.
I've replaced my fuel filter, spark plugs with AC Delco iridium 41-110s, wires with Taylor Thundervolt 50 10.4mm (not touching headers), currently running a tank with Red Line SI-1 added, replaced injectors with a set a buddy had lying around from another '99 LS1, checked for vacuum leaks, verified 58 psi fuel pressure throughout all RPM, swapped ECM with a stock '02 Trans Am (made it misfire), then swapped back to original ECM, and checked to make sure all the grounds were connected and in good condition.
The guy that had it before me only drove it approximately 2k miles in the 5 years he had it. He put a new clutch on it before selling it, which is why I didn't romp on it to find out the car had this problem in the first place, to get a proper break-in for the clutch. It has mac mid-length headers and y-pipe with deleted cats and rear O2 sensors (must me tuned for the deleted sensors, no sims), Flowmaster cat-back, SLP lid, SSRA intake, de-screened MAF, PRO 5.0 shifter, and SFCs. Eveything else is stock, even the LS1 manifold with EGR, but EGR was cut where it is inside the manifold. Any help or suggestions would be greatly appreciated!
I am in need of some help. Aside from averaging about 18 mpg, 3 mpg lower than my last '99 SS M6, my '99 SS M6 with 90k miles runs completely normal during regular driving. When doing some spirited driving, it stumbles like it is hitting a governor, from around 5,200 RPM on up to the 6,000 RPM I shift at, and sometimes bogs down a lot right after the up-shift, but then picks back up until it gets into that RPM range and proceeds to do the same thing. I thought it was a tuning issue, so I had my tuner look into it, and he said that it wasn't a tuning issue. He found that bank 1 was cutting fuel approximately 10% while bank 2 seemed to operate normally. It does this whether I'm in gear with a load or sitting still in neutral without a load.
I've replaced my fuel filter, spark plugs with AC Delco iridium 41-110s, wires with Taylor Thundervolt 50 10.4mm (not touching headers), currently running a tank with Red Line SI-1 added, replaced injectors with a set a buddy had lying around from another '99 LS1, checked for vacuum leaks, verified 58 psi fuel pressure throughout all RPM, swapped ECM with a stock '02 Trans Am (made it misfire), then swapped back to original ECM, and checked to make sure all the grounds were connected and in good condition.
The guy that had it before me only drove it approximately 2k miles in the 5 years he had it. He put a new clutch on it before selling it, which is why I didn't romp on it to find out the car had this problem in the first place, to get a proper break-in for the clutch. It has mac mid-length headers and y-pipe with deleted cats and rear O2 sensors (must me tuned for the deleted sensors, no sims), Flowmaster cat-back, SLP lid, SSRA intake, de-screened MAF, PRO 5.0 shifter, and SFCs. Eveything else is stock, even the LS1 manifold with EGR, but EGR was cut where it is inside the manifold. Any help or suggestions would be greatly appreciated!
Last edited by sk8rax350; 05-06-2013 at 01:42 AM.
03-29-2013, 05:32 PM
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I replaced my front O2 sensors since they had 90k miles on them anyways. Went for a run to see if I had the same problem, and of course it was still there. To shine some light on the situation, I had an ELM 327 bluetooth OBD 2 adapter linked to Torque Pro on my phone, and found that I was running on one bank's O2 sensor alone due to a fault. I checked for faults (No SES light) and found that I had a pending P0138. Bank 1 sensor 2 circuit high voltage. My guess is that the rear O2 sensor wasn't tuned out properly on that bank by the previous owner's tuner. I will be taking it to my tuner to properly tune it out sometime this weekend and will post an update as to whether or not that was the fix. Fingers crossed!
03-29-2013, 11:45 PM
#6
I replaced my front O2 sensors since they had 90k miles on them anyways. Went for a run to see if I had the same problem, and of course it was still there. To shine some light on the situation, I had an ELM 327 bluetooth OBD 2 adapter linked to Torque Pro on my phone, and found that I was running on one bank's O2 sensor alone due to a fault. I checked for faults (No SES light) and found that I had a pending P0138. Bank 1 sensor 2 circuit high voltage. My guess is that the rear O2 sensor wasn't tuned out properly on that bank by the previous owner's tuner. I will be taking it to my tuner to properly tune it out sometime this weekend and will post an update as to whether or not that was the fix. Fingers crossed!
Check the 02 sensor wiring on the suspect side, make sure the wiring is not ripped or melted anywhere.
.
04-10-2013, 02:07 PM
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Bank 1 sensor 2 doesn't look right compared to bank 2 sensor 2. I would think that this fault making it run on bank 2's O2 sensor alone would be the cause of bank 1 running lean.
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05-03-2013, 09:23 PM
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Resolution: The "O2 sensor" was messing up because it had a sim that I'm guessing was on its way out. Removed the sims and had my tuner properly tune out the rears. That was the end of that portion of the problem, but I was still getting the stumble at high RPM. After all of the troubleshooting we went through, he suggested that I was getting valve float. I replaced the stock valve springs with the ones I wanted for my cam swap in the near future, got a few heat cycles on them, hammered the throttle, and no more stumbling! The SS runs at high RPM without a problem now! 
