HELP....ignition woes...i think :(
09-05-11, 10:10 PM
#1
HELP....ignition woes...i think :(
relavent background... rebuilt S4 NA motor using S5 turbo housings, ported and sleevless, TB mod, emission removal, full S4 EFI swap into a FB chassis, MSD6AL on leading, and an inline walbro 255 fuel pump (i know its over kill, but its what i had)
before the typical suggestions of check TPS and Vac leaks, the TPS is set dead on at 1volt KOER, and i have already scoped the resistance sweep on my snap-on Vantage and it has no dead spots or static through the whole range of motion, as well as min/max values are withing spec. and i have re-done all my manifold gaskets with new gaskets and gasket sealer from block to TB, as well as smoke tested the system and have no leaks.
that being said, im having 2 issues, which could be related, but im unsure.
1) minor amount of surging at partial throttle accel. it doesnt do it all the time, and I cant always duplicate it. when it does it i can watch my wideband jump all around from 13:1 up to 16.5:1. once again this is only part throttle. full throttle is a consistant, smooth pull w/o surging.
2)now this is the one concerning me, and its getting worse with out me adjusting anything. i dont know if its a rich or lean misfire, detonation, preignition, severely out of time ignition or what, but it definately changes how the car sounds and when i clear it out with a small stab of the throttle, a small back fire. when it happens it sounds/feels like my car is running on one rotor, with a strange distinctive bassier "put put put" sound . if you put your hand in front of the tail pipe when my engine is running normal, the exhaust pulses are smooth and consitant, but when it starts what may be a mis, the pulses alternate between strong and normal. when this happens my wideband flatlines and just reads "-----"
this started happening last week, and would only happen between 10-20% throttle, just off idle. it would idle solid and smooth at 800RPM, and under a load the engine would pull relatively smooth and consistant. through out the week, the range of where this happens is getting wider and wider. now when i start the car, if i hold the throttle (out of gear) at all, itll start missing. and today, 50% of the time when i got off of the throttle to let it idle, it will idle with the mis. if i snap the throttle quickly or rev the engine, it revs smooth and the mis will stop but as it drops down to idle will start missing again. strangely enough though, WOT accel is fine.
so today after work i was gonna try to find out where the mis was using my timing light, and noticed that during the misfire event my T2 coil wire wasnt making the light flash at all, and T1 was also inactive 90% of the time and would sometimes flash at random (but my tach is still working fine) while both leading wires are firing perfect without any hiccups. from what i recall, the trailing coils shouldnt have that much of an effect on idle or ignition in general, but my symptoms seem to coincide with the mysterious drop in trailing spark
i want to start measuring sensor input voltages at the ecu, and scoping the CAS signals with the engine running, but the mis has become so iffy, i dont want to risk damaging anything inside my motor letting it run like that for any long period of time.
could my ECU be bad? trailing coils? ignitor? CAS?
if anyone has run into this before please help, im open to any suggestions of what it can be, or even what i should start looking at
before the typical suggestions of check TPS and Vac leaks, the TPS is set dead on at 1volt KOER, and i have already scoped the resistance sweep on my snap-on Vantage and it has no dead spots or static through the whole range of motion, as well as min/max values are withing spec. and i have re-done all my manifold gaskets with new gaskets and gasket sealer from block to TB, as well as smoke tested the system and have no leaks.
that being said, im having 2 issues, which could be related, but im unsure.
1) minor amount of surging at partial throttle accel. it doesnt do it all the time, and I cant always duplicate it. when it does it i can watch my wideband jump all around from 13:1 up to 16.5:1. once again this is only part throttle. full throttle is a consistant, smooth pull w/o surging.
2)now this is the one concerning me, and its getting worse with out me adjusting anything. i dont know if its a rich or lean misfire, detonation, preignition, severely out of time ignition or what, but it definately changes how the car sounds and when i clear it out with a small stab of the throttle, a small back fire. when it happens it sounds/feels like my car is running on one rotor, with a strange distinctive bassier "put put put" sound . if you put your hand in front of the tail pipe when my engine is running normal, the exhaust pulses are smooth and consitant, but when it starts what may be a mis, the pulses alternate between strong and normal. when this happens my wideband flatlines and just reads "-----"
this started happening last week, and would only happen between 10-20% throttle, just off idle. it would idle solid and smooth at 800RPM, and under a load the engine would pull relatively smooth and consistant. through out the week, the range of where this happens is getting wider and wider. now when i start the car, if i hold the throttle (out of gear) at all, itll start missing. and today, 50% of the time when i got off of the throttle to let it idle, it will idle with the mis. if i snap the throttle quickly or rev the engine, it revs smooth and the mis will stop but as it drops down to idle will start missing again. strangely enough though, WOT accel is fine.
so today after work i was gonna try to find out where the mis was using my timing light, and noticed that during the misfire event my T2 coil wire wasnt making the light flash at all, and T1 was also inactive 90% of the time and would sometimes flash at random (but my tach is still working fine) while both leading wires are firing perfect without any hiccups. from what i recall, the trailing coils shouldnt have that much of an effect on idle or ignition in general, but my symptoms seem to coincide with the mysterious drop in trailing spark
i want to start measuring sensor input voltages at the ecu, and scoping the CAS signals with the engine running, but the mis has become so iffy, i dont want to risk damaging anything inside my motor letting it run like that for any long period of time.
could my ECU be bad? trailing coils? ignitor? CAS?
if anyone has run into this before please help, im open to any suggestions of what it can be, or even what i should start looking at
