Hey, hope someone can help here. I've had some drivability problems since saturday, and maybe you can shed some light on them. Kind of a long post but I'm putting out all the pertinent info I can right away.
Symptoms: surging/unsteady engine output while holding speed (mild throttle)... not while decelerating or mildly accelerating. Also, it's cutting out under full throttle, but not all the time and not consistently.
Background on the car: 220k+ M20b25, but runs very well (until now). m30 AFM + 19# injectors, with MarkD chip for that application (many miles of smooth running with that setup), new fuel pump and filter last summer, etc. 2.5" single magnaflow setup, no cats.
Saturday I ran at a local autox, and everything seemed fine all day. On the way home i bought a couple of gallons of 93 at a busy gas station i do Not usually go to. Midway home from there I had to get around traffic and hit it - 3000 rpm or so it starts breaking up; alternating power and no power, as if i was misfiring badly. I get out of the throttle and relax the rest of the way. It seems to be surging a bit at steady speed, powering on and off somewhat as I hold speed.
Got home, pulled the plugs to look - they looked decent, worn, but not fouled. Light grey / slightly tan deposits, maybe a bit of oil residue but not much at all. I replaced them with some copper Champions (the store wouldn't have bosches until today) and found I had the same issues.
Considering the fill-up (which was only about 3 gallons) I added a can of Heet in case of water in the gas, and also added 3 gallons of (known good) 100 octane racegas to fight detonation. The car seems to run better now, a bit, and doesn't seem to be breaking up under load like before.. However, the surging at steady speed is still there.
Last night I replaced some vacuum lines (fpr, brake booster) that looked a bit hard, and also checked for intake air leaks. Filter, AFM, elbow boot, IAC, all seem tight and leak-free. Same surging. Tonight I am swapping the champion plugs out for bosch supers, cleaning the AFM and IAC, and doing a compression test.
Is there any place else to look? I've had bad fuel issues before, and the symptom was just like the breaking-up under load. I should run this tank out in the next day or two, and I'm betting that's the main issue.
However, the surging is new to me - seems that an intake tract leak would cause that, but not sure where it's coming from. Is there a way to locate any other vacuum/intake leaks?
Any other thoughts?
PS: I trophied on saturday :) and now with the race gas, everywhere I go I think there's a badboy in a blown LS1 stalking me!
Symptoms: surging/unsteady engine output while holding speed (mild throttle)... not while decelerating or mildly accelerating. Also, it's cutting out under full throttle, but not all the time and not consistently.
Background on the car: 220k+ M20b25, but runs very well (until now). m30 AFM + 19# injectors, with MarkD chip for that application (many miles of smooth running with that setup), new fuel pump and filter last summer, etc. 2.5" single magnaflow setup, no cats.
Saturday I ran at a local autox, and everything seemed fine all day. On the way home i bought a couple of gallons of 93 at a busy gas station i do Not usually go to. Midway home from there I had to get around traffic and hit it - 3000 rpm or so it starts breaking up; alternating power and no power, as if i was misfiring badly. I get out of the throttle and relax the rest of the way. It seems to be surging a bit at steady speed, powering on and off somewhat as I hold speed.
Got home, pulled the plugs to look - they looked decent, worn, but not fouled. Light grey / slightly tan deposits, maybe a bit of oil residue but not much at all. I replaced them with some copper Champions (the store wouldn't have bosches until today) and found I had the same issues.
Considering the fill-up (which was only about 3 gallons) I added a can of Heet in case of water in the gas, and also added 3 gallons of (known good) 100 octane racegas to fight detonation. The car seems to run better now, a bit, and doesn't seem to be breaking up under load like before.. However, the surging at steady speed is still there.
Last night I replaced some vacuum lines (fpr, brake booster) that looked a bit hard, and also checked for intake air leaks. Filter, AFM, elbow boot, IAC, all seem tight and leak-free. Same surging. Tonight I am swapping the champion plugs out for bosch supers, cleaning the AFM and IAC, and doing a compression test.
Is there any place else to look? I've had bad fuel issues before, and the symptom was just like the breaking-up under load. I should run this tank out in the next day or two, and I'm betting that's the main issue.
However, the surging is new to me - seems that an intake tract leak would cause that, but not sure where it's coming from. Is there a way to locate any other vacuum/intake leaks?
Any other thoughts?
PS: I trophied on saturday :) and now with the race gas, everywhere I go I think there's a badboy in a blown LS1 stalking me!
Comment