jgedde
Well-Known Member
- Joined
- May 17, 2016
- Threads
- 38
- Messages
- 297
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- Location
- Middle Island, NY
- First Name
- John
- Vehicle(s)
- 2015 GT Premium PP, M6, Triple Yellow
- Thread starter
- #1
Help! I am having an issue with my car that I simply cannot pin down. The Whipple has been installed for a few months and everything was fine until about 2 weeks ago.
On a WOT run, the engine started to misfire at about 6500 RPM and threw a P0300 random misfire code. I cleared the code and it did not repeat at first. The code is NOT the result of a bad crank relearn. Misfire is actually occurring.
I did, however, notice the car seemed down on power slightly. Over the next week, the problem got progressively worse. Now she won't rev over 4000 RPM at WOT. It coughs, spits, backfires through intake, pings slightly and misfires badly. This is sometimes accompanied by whitish gray smoke from exhaust. Mainly out the left side.
Things seem to have started to get worse after Mantic clutch install, but I do not think this is at all related. I mention it because it's a data point. I did a crank profile relearn after installation.
I also notice the exhaust sound sounds differently at light throttle and idle. It's like one or more cylinders are firing weakly.
I have tried numerous tests to try an pin down what is causing this. Here's what I know:
1) Compression check shows 230-240 psi on all cylinders.
2) Leakdown test shows almost no pressure drop.
3) Injectors removed, cleaned and flow tested. All are good.
4) Spark plus replaced. Gapped at 0.030"
5) Coils tested. All are throwing good spark.
6) KOER and KOEO tests pass.
7) Mode $06 data shows misfire counts on all cylinders after WOT. Highest count on cylinder 8
8) Checked for vacuum leaks including intake manifold. All good.
9) Checked SC bypass valve. Works fine.
10) Removed SC and manifold to check for issues and reinstalled/retorqued. No issues found.
11) Checked fuel pressure at idle and WOT. Reads 58-60 psi at all times.
12) PCM throws no codes except for P0300 at WOT and once threw Bank 2 catalyst efficiency code.
13) Plugs all look fine and are more or less identically colored.
14) No apparent coolant loss.
15) Bank 1 and Bank 2 LTFT are dramatically different. Bank 1 is +10-12%. Bank 1 is about -2%. If I remember correctly they both used to be around +10%.
16) Car seems to run well for about 45 seconds after a cold start before the engine sound changes to the slight misfire sound. Thinking this a closed loop issue I tried disconnecting both front O2 sensors to force open loop. Did not make any difference.
17) Intake tube clamps are secure and nothing is leaking.
18) Intake tube and MAF are visibly clean.
19) Idle vacuum is good. 18 inHg.
20) SC builds boost properly.
21) Thinking bad gas I Ran tank dry twice and refilled twice from different stations. I also took a fuel sample during the FP test. Fuel shows no evidence of staleness or water contamination.
22) No mode $06 misfire counts during light throttle when I can feel a slight miss.
23) Did cylinder balance test by pulling one coil at a time. Bank 1 seems strong: when a coil is unplugged it makes a big difference. bank 2 seems a bit more subtle. Especially cylinder 6. Pulling that coil makes only a slight difference.
I am completely out of ideas... HELP ME! A bottle of the liquor of your choice gets shipped to he who knows what will fix this!!!
John
On a WOT run, the engine started to misfire at about 6500 RPM and threw a P0300 random misfire code. I cleared the code and it did not repeat at first. The code is NOT the result of a bad crank relearn. Misfire is actually occurring.
I did, however, notice the car seemed down on power slightly. Over the next week, the problem got progressively worse. Now she won't rev over 4000 RPM at WOT. It coughs, spits, backfires through intake, pings slightly and misfires badly. This is sometimes accompanied by whitish gray smoke from exhaust. Mainly out the left side.
Things seem to have started to get worse after Mantic clutch install, but I do not think this is at all related. I mention it because it's a data point. I did a crank profile relearn after installation.
I also notice the exhaust sound sounds differently at light throttle and idle. It's like one or more cylinders are firing weakly.
I have tried numerous tests to try an pin down what is causing this. Here's what I know:
1) Compression check shows 230-240 psi on all cylinders.
2) Leakdown test shows almost no pressure drop.
3) Injectors removed, cleaned and flow tested. All are good.
4) Spark plus replaced. Gapped at 0.030"
5) Coils tested. All are throwing good spark.
6) KOER and KOEO tests pass.
7) Mode $06 data shows misfire counts on all cylinders after WOT. Highest count on cylinder 8
8) Checked for vacuum leaks including intake manifold. All good.
9) Checked SC bypass valve. Works fine.
10) Removed SC and manifold to check for issues and reinstalled/retorqued. No issues found.
11) Checked fuel pressure at idle and WOT. Reads 58-60 psi at all times.
12) PCM throws no codes except for P0300 at WOT and once threw Bank 2 catalyst efficiency code.
13) Plugs all look fine and are more or less identically colored.
14) No apparent coolant loss.
15) Bank 1 and Bank 2 LTFT are dramatically different. Bank 1 is +10-12%. Bank 1 is about -2%. If I remember correctly they both used to be around +10%.
16) Car seems to run well for about 45 seconds after a cold start before the engine sound changes to the slight misfire sound. Thinking this a closed loop issue I tried disconnecting both front O2 sensors to force open loop. Did not make any difference.
17) Intake tube clamps are secure and nothing is leaking.
18) Intake tube and MAF are visibly clean.
19) Idle vacuum is good. 18 inHg.
20) SC builds boost properly.
21) Thinking bad gas I Ran tank dry twice and refilled twice from different stations. I also took a fuel sample during the FP test. Fuel shows no evidence of staleness or water contamination.
22) No mode $06 misfire counts during light throttle when I can feel a slight miss.
23) Did cylinder balance test by pulling one coil at a time. Bank 1 seems strong: when a coil is unplugged it makes a big difference. bank 2 seems a bit more subtle. Especially cylinder 6. Pulling that coil makes only a slight difference.
I am completely out of ideas... HELP ME! A bottle of the liquor of your choice gets shipped to he who knows what will fix this!!!
John
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