2002 Blazer misfire at idle.
#11
11-24-2022, 02:27 AM
We cant trust the misfire cylinder assignments until CMPR is within spec but it looks like 1,2 and 3 which is more than bank 1 if these hold up.
our fuel trims are good but the banks are the opposite (lean/rich), might turn out to be a clue later if we get stuck.
Your MAF reading is low at idle. When you get a chance, capture it at the 1-2 full throttle shift
Your 2 pre cat O2 sensors are switching OK but the post cat B1S2 sensor should be close to a flat line between 0.5 and 0.7V and its not. Whats the history on the cat?
Do you still have the ignition code?
Travel with the ability to measure fuel pressure ans spark so you cane see which it is the next time it dies and wont start.
George
our fuel trims are good but the banks are the opposite (lean/rich), might turn out to be a clue later if we get stuck.
Your MAF reading is low at idle. When you get a chance, capture it at the 1-2 full throttle shift
Your 2 pre cat O2 sensors are switching OK but the post cat B1S2 sensor should be close to a flat line between 0.5 and 0.7V and its not. Whats the history on the cat?
Do you still have the ignition code?
Travel with the ability to measure fuel pressure ans spark so you cane see which it is the next time it dies and wont start.
George
#12
11-25-2022, 12:43 PM
We cant trust the misfire cylinder assignments until CMPR is within spec but it looks like 1,2 and 3 which is more than bank 1 if these hold up.
our fuel trims are good but the banks are the opposite (lean/rich), might turn out to be a clue later if we get stuck.
Your MAF reading is low at idle. When you get a chance, capture it at the 1-2 full throttle shift
Your 2 pre cat O2 sensors are switching OK but the post cat B1S2 sensor should be close to a flat line between 0.5 and 0.7V and its not. Whats the history on the cat?
Do you still have the ignition code?
Travel with the ability to measure fuel pressure ans spark so you cane see which it is the next time it dies and wont start.
George
our fuel trims are good but the banks are the opposite (lean/rich), might turn out to be a clue later if we get stuck.
Your MAF reading is low at idle. When you get a chance, capture it at the 1-2 full throttle shift
Your 2 pre cat O2 sensors are switching OK but the post cat B1S2 sensor should be close to a flat line between 0.5 and 0.7V and its not. Whats the history on the cat?
Do you still have the ignition code?
Travel with the ability to measure fuel pressure ans spark so you cane see which it is the next time it dies and wont start.
George
#13
11-25-2022, 01:28 PM
CMPR is good so the misfire data is valid but not sure what it tells us. Interestingly this motor fires in descending sequential order and you have 4,3,2,1. Why not 5/6? Now that the distr is replaced and CMPR is in spec, is there any history with the crank sensor or reluctor wheel or a relearn?
That fuel pressure is no good and needs to be addressed. The brand of fuel pump is a notorious topic here with the universal rule that AC Delco or Delphi is the only way to go for a trouble free replacement. Same used to be true for the spiders but then ACD/Delphi was not available for a while. I see them back on Rock Auto but I don't know what the reliability situation is on these. You might be flirting with low pressure at idle and the voltage bump at speed may be just enough, until it isn't. You can cut your problem in half by testing at the fuel filter. If its in the intake plenum a regulator might be worth a try if your trying to save money and salvage the work already performed. This could be the whole problem.
P300 was only a matter of time with those misfires counts.
P0351 can cast a wide net. The PCM does not like the way the primary circuit is behaving but its the entire circuit that's in play not just the ICM or PCM which is where everyone wants to go first. Can be:
A spent cat does not in itself cause the engine to run crappy, just increase emissions ans flunk inspection. However, a damaged cat from say a rich fuel mixture or coolant contamination can cause the catalyst metal to start flaking off and plug the exhaust. The resultant high back pressure can cause the truck to run crappy. Might be worth a look if the fuel pressure fix does not fix everything.
George
That fuel pressure is no good and needs to be addressed. The brand of fuel pump is a notorious topic here with the universal rule that AC Delco or Delphi is the only way to go for a trouble free replacement. Same used to be true for the spiders but then ACD/Delphi was not available for a while. I see them back on Rock Auto but I don't know what the reliability situation is on these. You might be flirting with low pressure at idle and the voltage bump at speed may be just enough, until it isn't. You can cut your problem in half by testing at the fuel filter. If its in the intake plenum a regulator might be worth a try if your trying to save money and salvage the work already performed. This could be the whole problem.
P300 was only a matter of time with those misfires counts.
P0351 can cast a wide net. The PCM does not like the way the primary circuit is behaving but its the entire circuit that's in play not just the ICM or PCM which is where everyone wants to go first. Can be:
- Power or grounds to the ICM/coil/PCM
- Signal wiring from PCM/ICM/coil
- The secondary circuit can be a mess causing preturbed primary circuit (plugs/wires/distr/high tension coil lead)
- The ICM/coil/PCM
A spent cat does not in itself cause the engine to run crappy, just increase emissions ans flunk inspection. However, a damaged cat from say a rich fuel mixture or coolant contamination can cause the catalyst metal to start flaking off and plug the exhaust. The resultant high back pressure can cause the truck to run crappy. Might be worth a look if the fuel pressure fix does not fix everything.
George
#14
11-26-2022, 04:32 PM
CMPR is good so the misfire data is valid but not sure what it tells us. Interestingly this motor fires in descending sequential order and you have 4,3,2,1. Why not 5/6? Now that the distr is replaced and CMPR is in spec, is there any history with the crank sensor or reluctor wheel or a relearn?
That fuel pressure is no good and needs to be addressed. The brand of fuel pump is a notorious topic here with the universal rule that AC Delco or Delphi is the only way to go for a trouble free replacement. Same used to be true for the spiders but then ACD/Delphi was not available for a while. I see them back on Rock Auto but I don't know what the reliability situation is on these. You might be flirting with low pressure at idle and the voltage bump at speed may be just enough, until it isn't. You can cut your problem in half by testing at the fuel filter. If its in the intake plenum a regulator might be worth a try if your trying to save money and salvage the work already performed. This could be the whole problem.
P300 was only a matter of time with those misfires counts.
P0351 can cast a wide net. The PCM does not like the way the primary circuit is behaving but its the entire circuit that's in play not just the ICM or PCM which is where everyone wants to go first. Can be:
A spent cat does not in itself cause the engine to run crappy, just increase emissions ans flunk inspection. However, a damaged cat from say a rich fuel mixture or coolant contamination can cause the catalyst metal to start flaking off and plug the exhaust. The resultant high back pressure can cause the truck to run crappy. Might be worth a look if the fuel pressure fix does not fix everything.
George
That fuel pressure is no good and needs to be addressed. The brand of fuel pump is a notorious topic here with the universal rule that AC Delco or Delphi is the only way to go for a trouble free replacement. Same used to be true for the spiders but then ACD/Delphi was not available for a while. I see them back on Rock Auto but I don't know what the reliability situation is on these. You might be flirting with low pressure at idle and the voltage bump at speed may be just enough, until it isn't. You can cut your problem in half by testing at the fuel filter. If its in the intake plenum a regulator might be worth a try if your trying to save money and salvage the work already performed. This could be the whole problem.
P300 was only a matter of time with those misfires counts.
P0351 can cast a wide net. The PCM does not like the way the primary circuit is behaving but its the entire circuit that's in play not just the ICM or PCM which is where everyone wants to go first. Can be:
- Power or grounds to the ICM/coil/PCM
- Signal wiring from PCM/ICM/coil
- The secondary circuit can be a mess causing preturbed primary circuit (plugs/wires/distr/high tension coil lead)
- The ICM/coil/PCM
A spent cat does not in itself cause the engine to run crappy, just increase emissions ans flunk inspection. However, a damaged cat from say a rich fuel mixture or coolant contamination can cause the catalyst metal to start flaking off and plug the exhaust. The resultant high back pressure can cause the truck to run crappy. Might be worth a look if the fuel pressure fix does not fix everything.
George
I really appreciate the help with this. I ended up getting the P0351 to go way. The misfire isn’t as bad anymore. I ended up selling it today as is. Tired of throwing money and time at it. Thanks for all the help.
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