Please Help! Misfire [Archive] - Forum


View Full Version : Please Help! Misfire

03-13-2006, 03:35 PM
i have been having a PO305 for a few days now. Which is a cylinder 5 misfire. Spark plugs is ok, wires are ok, coil is ok,Changed the injector & it is still missing..... I really need some advice on what to do next!

It is a 99 Grand Am se wit ha 3.4 v6. It has 82,000 miles on it


03-13-2006, 05:06 PM
did you change plugs, wires, coils??

03-13-2006, 05:40 PM
yes, like i said before i changed the plugs wires coils and the number 5 injector

03-13-2006, 06:14 PM
first I would try a compresion check. If thats ok then plug in a noid light to see if your getting injector pulse. Maybe a broken wire to your injector, bad computer who knows.

03-14-2006, 08:24 AM
vacuum leak into the cylinder , like he said the do the compression check tho

oil leakage froma valve stem seal or piston ring maybe?

03-14-2006, 02:44 PM
how can i get a noid light on the connections??? their under the upper intake manifold.

03-14-2006, 05:04 PM
dont know never really looked at it to see how hard they are to get at.

03-14-2006, 05:07 PM
you should be able to take the upper intake off to get at them. I know its a pain, but its not that bad. Then make sure you unplug the coils and crank it over to see if you have a pulse.

03-16-2006, 04:32 PM
ok well now we have changed coils, wires, plugs, upper gasket,#5 injector, reflashed the PCM,compression tested,node tested. AND I STILL HAVE A CYLINDER 5 MISFIRE!!! is the last thing to do is change the lower intake gasket???????

03-16-2006, 05:02 PM
But how often is it misfiring? I get misfires all the time, but its intermittant.

03-16-2006, 08:52 PM
its a constant misfire

03-17-2006, 07:09 PM
ok now i put in bars leak.... just to see if it would do anything...... i put it in. drove for about 30 minutes. Parked it over night & then i went to drive it in the morning & the miss was gone!

About 5 minutes later it was back.


03-19-2006, 01:00 PM
does this mean i need a new lim gasket??!??! please someone answer!

03-19-2006, 01:01 PM
does this mean i need a new lim gasket??!??! please someone answer!

btw.... every morning the car starts up fine .... then after it gets up to about 150 degrees the miss starts again

03-19-2006, 07:03 PM
Could be the LIM. Antifreeze getting into number 5 maybe. Sadly its not a do at home job for most. And I know we dont do it for less that $750 usually. If you know what your doing then its about $60-$80 bucks in parts.

03-19-2006, 07:06 PM
thanks.... i pretty sure thats all their is left to check. I will bring it over to the garage tomorrow.

thanks again for all your help