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[Help] Engine Misfires

1K views 13 replies 4 participants last post by  POS VETT 
#1 ·
I noticed this yesterday. It happened at higher rpm/throttle inputs randomly (CEL flashed). Then this morning on the way to work, it misfired again at low rpm (starting from stationary and no flashing CEL). Spark plugs (TR55IX) are about 2k miles old (wires are original) and other than K&N and Borla, the car is stock. What could it be ?
 
#4 ·
Sounds like something in the ingnition.

- First culprit would be plug wires: Double check and make sure none are loose.
- Then check the coils to make sure none of them are loose.
- Then I'd pull the wires and inspect them. See if there is any signs or arcing
- Then I'd pull the plugs, and double check them.

I'd be willing to bet you'll find your problem in one of those 4 steps.

-Chris
 
#5 ·
Ok, I replaced plug wires. It persisted. None were loose.

I took off the plugs, they look good and none are cracked. Hate to spend more money to replace those NGK Ir with such a low mileage on them.

The car is now sitting in the garage with its ignition coils and spark plugs disassembled.

What else should I check ?
 
#8 ·
It still should have stored the code. I would lean to one of 2 causes.

1.) Leaned out the mixture caused by a clogged fuel injector or clogged fuel filter
2.) Bad plug (check your gaps to make sure they are the same, factories do make mistakes), and make sure they are infact all the same plug. I used to work for pepboys, and I've seen a cheaper plug stuck into a more expensive box. I had a parts guy who liked to "help" his friends. $8 plugs for the $0.99 copper ones. That sort of stuff. Would cause someone else to unsuspectingly get 5 good plugs and one bad one. (Or 7 and a bad 1). That and the hairline crack would be my two best guesses.

Otherwise put her back together and go get her scanned up. That code should be stored even if the light is off.
 
#10 · (Edited)
There are a ton of flags that will not trigger a Check engine light, but are logged in log tables, some are labeled for MIL for several times, ie. needs to happen and create an error x3 before turning on the CEL.


Plugs and their ends should be checked (loose ends, cracked ,etc is possible)
Your mod list also says K&N... when is the last time you cleaned your MAF sensor? ... oil will coat those little wires and give tip in (variant change) values and calculations incorrectly as well as air flow measurements into the engine. Its a cheap check.
 
#11 ·
Gaps were all equal. Put the car back together and cleaned the MAF sensor. Car fired up and now the misfire/stumbling in high rpm/large throttle inputs are gone. It's still there during the brief period when engaging a gear. That should rule out injector/fuel filter, right ?

Now, in order to see "logs", what kind of device I need ? Is this the stuff like LS Edit or EFI Live ?
 
#14 ·
Well, I think it's fixed.

Reduced the gap to 0.040" (specified gap for NGK TR5IX) and misfire/stumble was gone. 0.050" may have worked, but I'm not going back in there for a long time. TR55IX (gap 0.060") works on the '03 Z06 I had and it also works on the LS7. It baffles me why it didn't work on the V.
 
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