Help! Engine misfiring. Running out of things to change
Thread Starter
Staging Lane
Joined: Jan 2002
Posts: 75
Likes: 0
Help! Engine misfiring. Running out of things to change My car is idling rough and has a smell of unburnt fuel from the exhaust at idle. At 2000 - 3500rpm car misses and pops out of the exhaust with the slightest load applied.
So far have changed:
Injectors
PCM
all coils
iginition leads
crank angle sensor
spark plugs
Have also done a crankshaft position relearn with EFILive, to no avail. From what I can gather cylinder 1, 5, 2, 6 and 8 are not firing correctly. There's bugger all heat in the header pipes.
EFILive doesn't show any misfire codes or crank angle sensor problems. PCM is not setting MIL/SES light.
Engine was recently built with JE pistons, Crower rods and GM Grand Am cam kit.
Engine has 210psi cylinder pressure in all cylinders. Have removed manifold and saw that one of the injectors didn't seem to be firing (inlet port showed no signs of fuel spray).
What are the chances of the reluctor wheel having moved? Engine does get turned to around 7K RPM with stock crank.
Any suggestions?????
So far have changed:
Injectors
PCM
all coils
iginition leads
crank angle sensor
spark plugs
Have also done a crankshaft position relearn with EFILive, to no avail. From what I can gather cylinder 1, 5, 2, 6 and 8 are not firing correctly. There's bugger all heat in the header pipes.
EFILive doesn't show any misfire codes or crank angle sensor problems. PCM is not setting MIL/SES light.
Engine was recently built with JE pistons, Crower rods and GM Grand Am cam kit.
Engine has 210psi cylinder pressure in all cylinders. Have removed manifold and saw that one of the injectors didn't seem to be firing (inlet port showed no signs of fuel spray).
What are the chances of the reluctor wheel having moved? Engine does get turned to around 7K RPM with stock crank.
Any suggestions?????
I would start by logging the timing and fueling
related params, and O2s; does "bugger all heat"
mean a lot, or none? Super hot pipes at low /
mid RPM may mean a late burn. A cheap "noid
light" should show you whether you are getting
injector drive pulses on all 8. Logger misfire data
would reveal cylinder spark dropout or fuel
imbalance problems.
related params, and O2s; does "bugger all heat"
mean a lot, or none? Super hot pipes at low /
mid RPM may mean a late burn. A cheap "noid
light" should show you whether you are getting
injector drive pulses on all 8. Logger misfire data
would reveal cylinder spark dropout or fuel
imbalance problems.
Thread Starter
Staging Lane
Joined: Jan 2002
Posts: 75
Likes: 0
The engine is running in speed density mode, and in open loop. Unfortunately, the PCM is not detecting any misfire codes making misfire detection difficult. "Bugger all heat" mean you can touch the pipes with your fingers - it's as if the cylinder isn't firing.
I've logged ignition timing and O2 readings - nothing out of the ordinary showing.
I'm kinda leaning towards the engine having to come out
I've logged ignition timing and O2 readings - nothing out of the ordinary showing.
I'm kinda leaning towards the engine having to come out
There's misfire codes, and there's live misfire counts.
You can suppress codes (and maybe somebody did,
like helped you a little too much?) but the counters
should still be looking? Are the "active misfire" by-
cylinder values all zero too? That would be odd, to
have cylinders that don't fire but no misfire count.
You can suppress codes (and maybe somebody did,
like helped you a little too much?) but the counters
should still be looking? Are the "active misfire" by-
cylinder values all zero too? That would be odd, to
have cylinders that don't fire but no misfire count.
Thread Starter
Staging Lane
Joined: Jan 2002
Posts: 75
Likes: 0
P0300 code in the PCM is turned off, but the misfire by cylinder DTC codes are enabled. EFILive is showing no misfire counts. Checked the PCM wiring harness today, continuity is ok. Will check the crank angle sensor wiring tomorrow ( it touch the headers and melted the convoluted tubing but didn't melt through the casing exposing wiring). If that checks ok then the engine's coming out.
what about plug wires, i didnt see them in the parts changed list. i had that same problem, under load i would have a miss fire, however, no codes and no live counter missfires. All (8) were 0's in the counter. Other than that it could be in the computer.
Thread Starter
Staging Lane
Joined: Jan 2002
Posts: 75
Likes: 0
Problem fixed. Ends up being the removed cats and straight through pipes installed in their place causing the problem. Noticed the problem occured only after the cats were removed. Reinstalled the cats today and car runs like a dream again.
Who would of ever thought that a too big/free flowing exhaust could cause problems like that!
Who would of ever thought that a too big/free flowing exhaust could cause problems like that!
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Originally Posted by 01350ss
what about plug wires, i didnt see them in the parts changed list. i had that same problem, under load i would have a miss fire, however, no codes and no live counter missfires. All (8) were 0's in the counter. Other than that it could be in the computer.
It doesn't Did you ever turn off the rear o2's? You mentioned it was in was in open loop. It probably switched back to closed loop with the cats back on. If you didn't have the o2 sensors in then you would of needed sims or the rear o2's turned off 