Hello all,

Just recently, my car has developed what feels like a bad misfire......it started out a couple of weeks ago as a little sputter if i got on the throttle quickly, it would spit and shake a little and then start to wind up in less than a second.....it has since developed into something i cant seem to put my finger on....when i start it in the morning, its fine and seems to be smooth and firing properly.....but when it starts to get to full operating temp. it starts to shake like hell and im not sure if it is a miss but it sure feels like a bad 1.....maybe more than 1-2 cylinders......im hesitant to think its ignition .....my opti,plugs,wires,ICM,& coil are all relatively new (less than 20-30,000 miles)...this past weekend for the hell of it i cleaned my air filter and disconnected the battery to reset the computer, and it seemed to improve for a time.....that is untill it got fully warmed up again. i also checked the PCV for the hell of it, and it is good....id like to not take it anywhere and take care of it myself...but im running out of ideas and may need to hook it up to a comp.....and no , no it hasnt been throwing a code ....not yet at least.....here's a little info on the car.

93' firebird formula - K&N filter, MSD coil, Hypertech chip, 160 deg. stat, SLP 1&3/4" uncoated headers (i know,i know), throttle body air foil,24 lb. injectors, high flow CAT, spintech muffler & exhaust,.....everything else at least engine wise is stock parts......and she's got alot of miles....a little over 140,000 and up until now, running quite well for an older car.....

any suggestions/insight would be appreciated.....

 

ttt

 

Check the plug wires. Typically it's a routing issue, especially if they were installed fairly recently. Never assume they're good, just because they're new. You can try the "park in the dark and look under the hood" method to see if you see any arcing around any of the wires.

 

i have the exact same damn problem...started yesterday on the way to work! i wouldnt think a plug wire would cause it to miss when only warm would it?

 

I can always tell if it's a bad spark plug wire if you drive at low speeds and put it into 4th , 5th , low RPM. The car will shake and stumble.

 

My thoughts exactly.

very puzzling.....

 

Just to make you feel better.......

I've been battling this same issue now for over a year. And I've done everything, including a new shortblock.

You say you're not throwing any codes. What does your exhaust smell like?? Have you pulled a plug?? If not, just pull one from each side and take a look, see if they're all fouled out.

This thread is a essential summary of everything I've gone through in trying to track down this problem. It may or may not be of use to you.

Also, seeing as how you have a 93, swing on by the speed density link in my sig. You're more than welcome there!!!

 

but why would it not do it when the motor is cold? who knows!

 

That's what I've been trying to figure out for a very long time. I'm going to chase my fuel injectors next.

 

You may want to check the mass air sensor wire...If you use a oiled type air filter chances are that the wire and assembly is caked with oily dirt. Take it off and spray it with a electrical parts cleaner. Mine was FILTHY after 10 years of a K&N. This helped my off idle stumble when warm. If thats not it, I would go with a plug wire or plug...
--Alan

 

He's a 93 and thus has no Mass Air Sensor.

 

oops...didn't see that...nevermind I could swear he had a 95...time for laser surgery on the ol eyes...

 

I was just thinking......could this possibly be a malfunctioning sensor thats telling the computer to retard my timing? off the top of my head, the only sensors that i know of that can do that would be the knock sensor, and possibly the TPS.....has anybody already thought of this or checked on it with any results?

 

1 thing i also forgot to mention.....i notice that when im driving, as the engine is missing/shaking and the revs are increasing, the tach starts to jump up and down like 1-200 rpm's.....

 

speaking of the timing thing, after mine warms up and starts to miss/stumble under load, if i get on it real hard up in the rpm range it will start backfiring . does sorta sound like a timing issue to me!