Still Stuck
02-08-2008, 01:16 AM
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Still Stuck Ok I have been dealing with this problem for over a month on and off now to no avail. I have a random missfire at idle which is causing my cats to smell like rotten eggs. I can watch the missfires appear on the scan tool. They occur on all cylinders. In a graph, I can see the MAP spiking in response to a problem. LTFT is around 8% on one bank and 9% on the other which a little on the high side. No MIL. Heres a list of what I have checked:
-Checked several times for vacuum leaks. Used the evap smoke machine, listened with a stethescope, sprayed brake clean around and used acetylene.
-Checked the AIR system by blocking it off
-Checked the EGR by blocking it off with a piece of cardboard
-Did a backpressure test on both cats
-Checked the MAP a couple different ways and replaced it 3 times
-Did a tune with plugs and wires
-Did compression test
-Checked for HCs in the coolant just out of paranioa
-smoke tested the EVAP system
Im running out of ideas. The only mod it had when the problem began (that I can tell. I'm not the original owner) is an SLP air lid. I was thinking of taking it and getting it tuned. The computer thinks the car is running lean and maybe a tune could convince it otherwise. Maybe it has other mods that I dont know about. Any ideas? Its driving me crazy.
-Checked several times for vacuum leaks. Used the evap smoke machine, listened with a stethescope, sprayed brake clean around and used acetylene.
-Checked the AIR system by blocking it off
-Checked the EGR by blocking it off with a piece of cardboard
-Did a backpressure test on both cats
-Checked the MAP a couple different ways and replaced it 3 times
-Did a tune with plugs and wires
-Did compression test
-Checked for HCs in the coolant just out of paranioa
-smoke tested the EVAP system
Im running out of ideas. The only mod it had when the problem began (that I can tell. I'm not the original owner) is an SLP air lid. I was thinking of taking it and getting it tuned. The computer thinks the car is running lean and maybe a tune could convince it otherwise. Maybe it has other mods that I dont know about. Any ideas? Its driving me crazy.
02-08-2008, 09:02 AM
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I do not believe the misfires have anything to do with
the rotten egg smell. That I think is a fuel quality
problem (sulfur). I always saw low levels of misfire
(and the usual LS1 engine shake) at idle, even stock.
Note that misfire is only an engine computation and
comes from crank jitter, which at low RPM may just be
the normal mixture variance and spark dithering getting
a little too busy. Just because the PCM says so,
doesn't mean it actually failed to fire. Just exceeded
the amount of ripple, to raise the flag.
2000 was the "lean year". Don't know whether anyone
has compared the tune and the motor hardware to see
what the difference comes back to. It had the '99 cam,
intake, EGR but the exhaust is more like the '01/'02 so
the real VE may be higher than the '99, a bit. If the
exhaust is better but the tables are the same, that is
the kind of discrepancy you'd like to fix. Though at idle
I'd think it was too little to be a 10% mixture error.
How fresh are your O2 sensors? If they have become
slow, your mixture loop will be prone to overtravel
(sensor does not return feedback until later) and the
mixture will spend proportionally more time off in the
weeds, being stanky, and less time close to center.
Still the same average but not the same chemical
output by a long shot. You could be throwing NOx
one second and CO the next and it all averages out
to some kind of unpleasant smell. The cats can only
do so much. If you can see a graphical scan of the
O2 voltage, a good system will be balanced and
symmetric with a good amount of switching; a slow
unhappy one will be uneven and look like it's just
wandering around (which it basically is).
the rotten egg smell. That I think is a fuel quality
problem (sulfur). I always saw low levels of misfire
(and the usual LS1 engine shake) at idle, even stock.
Note that misfire is only an engine computation and
comes from crank jitter, which at low RPM may just be
the normal mixture variance and spark dithering getting
a little too busy. Just because the PCM says so,
doesn't mean it actually failed to fire. Just exceeded
the amount of ripple, to raise the flag.
2000 was the "lean year". Don't know whether anyone
has compared the tune and the motor hardware to see
what the difference comes back to. It had the '99 cam,
intake, EGR but the exhaust is more like the '01/'02 so
the real VE may be higher than the '99, a bit. If the
exhaust is better but the tables are the same, that is
the kind of discrepancy you'd like to fix. Though at idle
I'd think it was too little to be a 10% mixture error.
How fresh are your O2 sensors? If they have become
slow, your mixture loop will be prone to overtravel
(sensor does not return feedback until later) and the
mixture will spend proportionally more time off in the
weeds, being stanky, and less time close to center.
Still the same average but not the same chemical
output by a long shot. You could be throwing NOx
one second and CO the next and it all averages out
to some kind of unpleasant smell. The cats can only
do so much. If you can see a graphical scan of the
O2 voltage, a good system will be balanced and
symmetric with a good amount of switching; a slow
unhappy one will be uneven and look like it's just
wandering around (which it basically is).
02-10-2008, 01:47 PM
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I do not believe the misfires have anything to do with
the rotten egg smell. That I think is a fuel quality
problem (sulfur). I always saw low levels of misfire
(and the usual LS1 engine shake) at idle, even stock.
Note that misfire is only an engine computation and
comes from crank jitter, which at low RPM may just be
the normal mixture variance and spark dithering getting
a little too busy. Just because the PCM says so,
doesn't mean it actually failed to fire. Just exceeded
the amount of ripple, to raise the flag.
2000 was the "lean year". Don't know whether anyone
has compared the tune and the motor hardware to see
what the difference comes back to. It had the '99 cam,
intake, EGR but the exhaust is more like the '01/'02 so
the real VE may be higher than the '99, a bit. If the
exhaust is better but the tables are the same, that is
the kind of discrepancy you'd like to fix. Though at idle
I'd think it was too little to be a 10% mixture error.
How fresh are your O2 sensors? If they have become
slow, your mixture loop will be prone to overtravel
(sensor does not return feedback until later) and the
mixture will spend proportionally more time off in the
weeds, being stanky, and less time close to center.
Still the same average but not the same chemical
output by a long shot. You could be throwing NOx
one second and CO the next and it all averages out
to some kind of unpleasant smell. The cats can only
do so much. If you can see a graphical scan of the
O2 voltage, a good system will be balanced and
symmetric with a good amount of switching; a slow
unhappy one will be uneven and look like it's just
wandering around (which it basically is).
the rotten egg smell. That I think is a fuel quality
problem (sulfur). I always saw low levels of misfire
(and the usual LS1 engine shake) at idle, even stock.
Note that misfire is only an engine computation and
comes from crank jitter, which at low RPM may just be
the normal mixture variance and spark dithering getting
a little too busy. Just because the PCM says so,
doesn't mean it actually failed to fire. Just exceeded
the amount of ripple, to raise the flag.
2000 was the "lean year". Don't know whether anyone
has compared the tune and the motor hardware to see
what the difference comes back to. It had the '99 cam,
intake, EGR but the exhaust is more like the '01/'02 so
the real VE may be higher than the '99, a bit. If the
exhaust is better but the tables are the same, that is
the kind of discrepancy you'd like to fix. Though at idle
I'd think it was too little to be a 10% mixture error.
How fresh are your O2 sensors? If they have become
slow, your mixture loop will be prone to overtravel
(sensor does not return feedback until later) and the
mixture will spend proportionally more time off in the
weeds, being stanky, and less time close to center.
Still the same average but not the same chemical
output by a long shot. You could be throwing NOx
one second and CO the next and it all averages out
to some kind of unpleasant smell. The cats can only
do so much. If you can see a graphical scan of the
O2 voltage, a good system will be balanced and
symmetric with a good amount of switching; a slow
unhappy one will be uneven and look like it's just
wandering around (which it basically is).
02-10-2008, 02:20 PM
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I agree with jimmy. Misfire will pull timing, but not add or subtract fuel. What is ur complant? Have you mointored a/f with a wide band? What is ur smell? unburned fuel? If so there is something else there. Rotten egg smell is sulfur. They did a recall on cats. I got the letter. But I think it is Sulfur.
02-14-2008, 02:53 PM
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I agree with jimmy. Misfire will pull timing, but not add or subtract fuel. What is ur complant? Have you mointored a/f with a wide band? What is ur smell? unburned fuel? If so there is something else there. Rotten egg smell is sulfur. They did a recall on cats. I got the letter. But I think it is Sulfur.
02-14-2008, 02:56 PM
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02-14-2008, 05:38 PM
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If you see that the misfire "prefers" certain cylinders
you might try an injector balance test. Can you see
"misfire current cylinder 1" through misfire current
cylinder 8"?
If it is truly random then I'd be back to looking at the
O2 sensor waveforms to see if they are swinging fast
and tight, or wandering around looking dazed. See if
the misfires get "quiet" and then "busy", see if that
follows short trim value or a particular O2 sensor
behavior etc.
I still think a small amount of declared misfires at
idle seems to be "normal" on these cars. Or at
least, common.
Other things to try - force it to open loop and
14.7:1, does it stop misfiring? If so suspect the
fuel trim loop spending too much time off in the
weeds. Force it to a fixed timing; if misfires get
better look at the idle adaptive spark maybe
"trying too hard" to stabilize some idle issue, if
it stumbles at highest or lowest delivered spark
then push the idle advance tables or cut the
adaptive idle value (the adaptive spark tables
are also kind of whack on certain models).
you might try an injector balance test. Can you see
"misfire current cylinder 1" through misfire current
cylinder 8"?
If it is truly random then I'd be back to looking at the
O2 sensor waveforms to see if they are swinging fast
and tight, or wandering around looking dazed. See if
the misfires get "quiet" and then "busy", see if that
follows short trim value or a particular O2 sensor
behavior etc.
I still think a small amount of declared misfires at
idle seems to be "normal" on these cars. Or at
least, common.
Other things to try - force it to open loop and
14.7:1, does it stop misfiring? If so suspect the
fuel trim loop spending too much time off in the
weeds. Force it to a fixed timing; if misfires get
better look at the idle adaptive spark maybe
"trying too hard" to stabilize some idle issue, if
it stumbles at highest or lowest delivered spark
then push the idle advance tables or cut the
adaptive idle value (the adaptive spark tables
are also kind of whack on certain models).
02-21-2008, 09:34 AM
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Ok, check this. I had the same issue late last summer. Misfire codes being thrown, all sorts of crazy stuff happening, I don't recall exhaust issues, but I didn't drive it much at all when this started happening because I didn't want to hurt anything and I didn't know what the hell was really happening.
My problem ended up being that I got some water in the blue PCM connector. It got into the connections between the PCM and the bulk harness and started allowing slight-shorts to happen giving the PCM all sorts of weird data to deal with...
I eventually found the problem after many many posts... took it all apart, pulled the PCM too. Cleaned the harness side with a MIG welder cleaning tool (has various gauges of round files for cleaning the tips) and a wire brush. Cleaned the PCM with alcohol and q-tips. Put it all back together and BINGO, everything started working like normal again...
Just a thought, might not hurt to look at when everything else seems fine!
Pic of the blue harness that was affected:
You can see the discoloring primarily on the top left pins:
Fun times... Whodathunkit a good think to put the PCM right under where water drains off the windshield???
-Eagle
My problem ended up being that I got some water in the blue PCM connector. It got into the connections between the PCM and the bulk harness and started allowing slight-shorts to happen giving the PCM all sorts of weird data to deal with...
I eventually found the problem after many many posts... took it all apart, pulled the PCM too. Cleaned the harness side with a MIG welder cleaning tool (has various gauges of round files for cleaning the tips) and a wire brush. Cleaned the PCM with alcohol and q-tips. Put it all back together and BINGO, everything started working like normal again...
Just a thought, might not hurt to look at when everything else seems fine!
Pic of the blue harness that was affected:
You can see the discoloring primarily on the top left pins:
Fun times... Whodathunkit a good think to put the PCM right under where water drains off the windshield???
-Eagle
02-21-2008, 09:53 AM
#11
LS1BirdGirl , I agree that the sulphur smell is a sign of a cat failure. The random miss certainly indicates ignition issues, rather than fuel (especially in CA, where fuel is very closely monitored). You seem to have troubleshot the "normal" issues very thoroughly. I would lean toward the PCM being the cause, and investigate that. Best of luck.
