can't figure out misfire problem

[easytoremember]

I don't want to start throwing parts at this to figure it out. I want to diagnose this right and fix the problem, not throw parts at it to guess...

On a cold startup you can hear it puttering once it catches idle.

When you first drive it you can feel the misfires, car is weak. Then after about 10 minutes they're better but crusing on the highway you can hear the occasional putter...

Hit the gas and the car is strong but very very faintly you can still hear a put here and there...

HP (http://www.clubgp.com/newforum/tm.asp?m=5398125&p=1&tmode=1&smode=1#) Tuner scanner does not register any misfires. Tech II scanner does not register any either.

The only misfire code turned off is the P0300 the 301, 302, 303, 304, 305 and 306 are all on, but no misfires are reported.

Someone gave me the tip of pulling a fuel injector plug and the cylander you pull the plug on that doesn't make the engine run for shit is the one. Funny thing though, pull a fuel injector plug... car still runs the same, and still no misfires detected...

All spark plugs look fine, none are burnt, or fouled out with oil or fuel or anything.

Thoughts on next diagnostic procedure before I start throwing parts at it?

[u_say_go]

I don't want to start throwing parts at this to figure it out. I want to diagnose this right and fix the problem, not throw parts at it to guess...

On a cold startup you can hear it puttering once it catches idle.

When you first drive it you can feel the misfires, car is weak. Then after about 10 minutes they're better but crusing on the highway you can hear the occasional putter...

Hit the gas and the car is strong but very very faintly you can still hear a put here and there...

HP (http://www.clubgp.com/newforum/tm.asp?m=5398125&p=1&tmode=1&smode=1#) Tuner scanner does not register any misfires. Tech II scanner does not register any either.

The only misfire code turned off is the P0300 the 301, 302, 303, 304, 305 and 306 are all on, but no misfires are reported.

Someone gave me the tip of pulling a fuel injector plug and the cylander you pull the plug on that doesn't make the engine run for shit is the one. Funny thing though, pull a fuel injector plug... car still runs the same, and still no misfires detected...

All spark plugs look fine, none are burnt, or fouled out with oil or fuel or anything.

Thoughts on next diagnostic procedure before I start throwing parts at it?
change the plug wires. had this same problem, overthought it for weeks...finally changes the wires and no more spit and sputter

[Slow Joe]

What kind of car?

Turbo? Not turbo?

I know with our 9-3 we were having a misfire issue, and it ended up being the plugs... I had iridium plugs in, and they burn too hot, which was causing our misfire... (It was only misfiring during aceleration with full boost). Swapped them for double platinum as Saab says, and voila. like new. Also, even though the plugs look good, are they gapped right?

[Reverend Cooper]

way to many things to go after here,if its not registering a misfire that tells me if its obII that wires,coils plugs and fuel inj. are good,as they will all set a single cylinder or multiple misfire code. what year make and model along with any mods please
this could be as simple as a plugged fuel filter,ecm temp sensor,maf,map or other.
unless im missunderstanding,and you have al the po300 series shut down,if you do there is no way it would register a misfire?

[lordairgtar]

Vacuum leak? They tend to improve as the engine warms if it's a gasket somewhere.

[Al]

Seeing that you posted this on a GP board, I am assuming you have a Gran Prix with the 3800. In dealing with similar symptoms in my Olds 88, I found that the cam magnets can become loose in their fitting on the cam sprocket.

-Remove wheel
-Losen water pump pulley bolts
-Pull serpentine belt
-Remove water pump pulley
-Remove cam sensor
-Crank engine with socket wrench untill magnet comes into view.

Run your finger over the magnet when you find it. If it is loose, buy a new one for $10 and follow the JB weld installation method as described on many web forums. If the magnet is loose, it can throw the timing off a few degrees and that is enough for a misfire.

[brotherbenn83]

If the original post was in ENGLISH, that might help too.

[Daytonapacecar959]

If you already changed plugs,wires and the injs. are good maybe it's something like Travis's truck broken Lifter,push rod,spring?

[easytoremember]

Fred figured it out. Thanks for looking at the plugs, sure enough new plugs did the trick.

ps its a 96 GTP w L67swap and modded. Last ran 12.3, havent ran it in a couple years now though...

[hrsp]

Fred figured it out. Thanks for looking at the plugs, sure enough new plugs did the trick.

ps its a 96 GTP w L67swap and modded. Last ran 12.3, havent ran it in a couple years now though...


any pics? sounds like a fun car...and a sleeper

[easytoremember]

thanks, I'll find some pics tonight

[BadAzzGTA89]

You can get those small even smaller than hairline cracks and will cause all kinds of misfire hell i seen it alot on no 6