Need Help...Surging and possible misfiring after mods
05-07-2008, 10:29 AM
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Need Help...Surging and possible misfiring after mods I have an '01 Z28 M6 that I just did a H/C swap and headers. I am using a small 222-224 comp cam (XR-275HR-12). The car seems to have an inconsistent idle. Sometimes it idles fine, then it misses idle, and sometimes it idles high (over 1000 RPMs). When driving, it sometimes begins surging and bucking, almost like it is hitting a governor or rev limiter. This has happened in all gears and a high and low speeds/RPMs. I had the car tuned (HP Tuners) and dyno'ed after the mods. The air/fuel ratio is smooth around the 12 mark. Any suggestions???
05-07-2008, 01:21 PM
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It was tuned at SRC (not a sponsor, sorry). I am not sure how they tuned it. I know they used HP tuners and the dynojet. The air/fuel ratio was nice, steady, and smooth. Does the car need time to "adjust" to the new set-up? Thanks for the input...
05-07-2008, 01:24 PM
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what was the afr, you said around 12 in your first post, but 12 what? 12.0 would be too rich on motor, 12.8 would be good, althought that most likely isn't causing the driveability problems, but it could be helpful info.
05-07-2008, 01:29 PM
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I had this problem a few weeks after I put it my new motor, and it turned out that the PCV vaccuum hose deteriorated and had a hole in it. Listen for a sucking sound while it's running, that's how I came across mine.
I'm having some surging again because of a misfire. If you're misfire tables are up and running, you'll get a flashing SES from a miss, but mine were deleted by with my tune, so the PCM thinks everything's hunky doory. I think it's a bad coil pack, but not 100% sure yet.
I'm having some surging again because of a misfire. If you're misfire tables are up and running, you'll get a flashing SES from a miss, but mine were deleted by with my tune, so the PCM thinks everything's hunky doory. I think it's a bad coil pack, but not 100% sure yet.
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05-07-2008, 01:52 PM
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Right now, I am coming up short on fuel. I was told I need a better fuel pump because I am running out of fuel around the 6K+ RPM mark...Injectors are working at 103% currently, should be okay after new fuel pump.
05-07-2008, 01:53 PM
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well your afr looks pretty good up to about 5500, then starts getting a touch lean. Maybe check your plugs for the correct gap and make sure the porcelein isn't cracked on any of them. If its cracked on one of them it will sputter like crazy.
05-07-2008, 03:07 PM
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Does the fuel pump typically need replacing when modding? Most people I see still have their stocker pumping just fine with more horsepower than I am working with. <sigh>
05-08-2008, 08:08 AM
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Okay, update: My temperature sensor wasn't reading at all. This was making me run very rich, resulting in the horrible driving conditions. Fixed the connection, got the sensor to read, fixed 90% of my problems. Still having idle issues here and there. Doesn't seem to want to find idle sometimes. Is this something the car will "learn"?
Regarding the fueling issue: At around 5K+ RPM's, the fuel pump can't hold 55psi. Drops somewhere in the 20psi range. I think I need to drop a buck on a bigger fuel pump.
Regarding the fueling issue: At around 5K+ RPM's, the fuel pump can't hold 55psi. Drops somewhere in the 20psi range. I think I need to drop a buck on a bigger fuel pump.