reasons for misfire
reasons for misfire wondering what could be some reasons for an engine misfire? I was going to check plugs and wires to be sure that all is gapped right and wires on snug. What else could it be?
TECH Senior Member
Joined: Apr 2002
Posts: 6,080
Likes: 17
From: So.Cal.
Poor spark.
Insufficient fuel.
Over-fueling.
Insufficient air (e.g. restricted cats).
Excess air (air leaks).
Poor compression.
Coolant in combustion chamber.
Each one of those can be caused by a number of things, e.g. insufficient fuel can be caused by bad O2's, bad MAF, bad fuel pump, etc.
Insufficient fuel.
Over-fueling.
Insufficient air (e.g. restricted cats).
Excess air (air leaks).
Poor compression.
Coolant in combustion chamber.
Each one of those can be caused by a number of things, e.g. insufficient fuel can be caused by bad O2's, bad MAF, bad fuel pump, etc.
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Yes, but how recent was the last modification?
What was the last modification?
Are you assuming it’s a misfire or is it throwing the misfire code?
Does it seem to be an Isolated and controlled miss that tends to stay in rhythm with the Idle (this is usually a single cylinder miss)?
Or does it just seem to randomly miss on any # of cylinders (with this type, the motor usually shimmies very rough and idles very rough).
Does the miss ever seem to go away throughout different RPM ranges?
Answer these questions. It will help narrow down what is going on.
What was the last modification?
Are you assuming it’s a misfire or is it throwing the misfire code?
Does it seem to be an Isolated and controlled miss that tends to stay in rhythm with the Idle (this is usually a single cylinder miss)?
Or does it just seem to randomly miss on any # of cylinders (with this type, the motor usually shimmies very rough and idles very rough).
Does the miss ever seem to go away throughout different RPM ranges?
Answer these questions. It will help narrow down what is going on.
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if the egr is still installed, the egr valve could sticking open from carbon build up. if it has a miss at heavy load then the egr valve is stuck open. but again this is assuming you still have egr installed.
do compression check
do vacuum test
do cylinder leak down test
do fuel pressure test
do compression check
do vacuum test
do cylinder leak down test
do fuel pressure test
if the egr is still installed, the egr valve could sticking open from carbon build up. if it has a miss at heavy load then the egr valve is stuck open. but again this is assuming you still have egr installed.
do compression check
do vacuum test
do cylinder leak down test
do fuel pressure test
do compression check
do vacuum test
do cylinder leak down test
do fuel pressure test
I assume he drives a 2002 Z28. So EGR should'nt be the issue.
