Random Missfire Problem!!!

[Got_Hemi]

Hey, I'm new to this forum, but i have a 91 cavalier and just started noticing a big problem. It randomly starts missfiring on 1-2 cylinders! I've replaced plugs, wires, coils, and cleaned the carb, but the problem persists. Any help would be much appreciated. I've heard that it could possible be the head gasket, which can be a pricey replacement, but i'm hoping that's not the problem.
Thanks,
DAVE

[Mod'd_Cav]

also could be something as easy as clogged injectors

[deadBird]

Make sure you spark plug gap is perfect.

[KayJay]

I had a random misfire multi-cylinder and it was the Crankshaft position sensor - they are made of plastic and crack in normal use (Thanks GM!). This may not help as you seem to have only cyl. 1&2, but...

[Clarissa]

We had a mis in our '96 and it was an emission control valve , but the car ran like crap too. ( dont let the mechanic tell you its the timeing okay!)

[VWfinatic27]

It could even be a valve not opening, I have seen it happen before or a worn camshaft or camshaft movement

[sideshot72]

My '96 Cavalier is also presenting what seems to be a random misfire problem. But, I also see the Check Engine light doing many entertaining things. Sometimes it stays on steady, sometimes it goes out, and this morning, it was actually flashing. Does your Check Engine light do anything while this is going on?

Also, I sometimes get a pop from the engine when trying to accelerate. It's not quite as explosive as traditional backfire, but sounds like something really didn't fire right in there.

- I tried fuel injector cleaner, which seemed to help some.
- Some are suggesting the EGR valve be replaced.
- Another Cavalier owner has ridden in the car and suggested either fuel injector, fuel filter, or fuel pump.

[Ryan066]

does it hesitate on the highway when u mat it? does it feel like its picking up slowly?

my bet is a clogged catylictic converter. but it should misfire on all cylinders randomly rather then just 1 & 2

[deadBird]

Once again, make sure you spark plug gap is perfect. Faulty (cheap/old) spark plug wires may also cause this.

Does high-octane make a difference?

[4dr92cavi4cyl]

Originally Posted by VWfinatic27

It could even be a valve not opening, I have seen it happen before or a worn camshaft or camshaft movement

^Could be, but wouldn't it miss consistently if that was the problem.


Maybe this is the problem...

My 92 will miss a little when cold, but only at low RPMs when barely moving. It has done this since I got the motor a year ago.

I have since replaced the EGR valve, (the old one was causing the car to not start sometimes) it didn't help the miss, it made it miss worse, so now I have a $50 investment bolted to my motor that's been disconnected. I tried swaping coil packs, bought new wires, replaced injector rings (which were leaking anyway) still, a little miss at low throttle.

I went to check my plugs a month ago and, to my amazement, the #4 plug is in only half way! Someone had cross-threaded a plug, and did it good too! My old motor had the same problem, #3 was not going in all the way, after having a pro tap-and-groove, it never missed like that again.

The problem is that the plug doesn't creat an air tight seal and the cylinder losses a little compression, plus the electrode is up too far in the hole for the air/fuel mixture to reach it, so it doesn't burn all the mixture.


People underestimate spark plug maintenance as being easy. It IS very easy to screw up! You MUST let the motor cool completely. Never FORCE a plug unless you know it's reached the end of the hole. Count the number of turns it takes to reach the end of the threads on a good cylinder. You will feel it "stop", then tighten 1/16 of a turn.

Sorry this was so long, but it pisses me off that someone screwed up my motor before I even bought it because they didn't take their time. Hopefully this will help everyone.

[sideshot72]

Ryan,

I have not checked my computer codes yet. You are the first to mention the catalytic converter in any of these threads, though. This is very interesting seeing as I do get "exhaust noise" from time to time, and have been wondering what is going on back there. It does sometimes sound like the air is not flowing through there right. I haven't noticed these two things happening at the same time, though.

I do see some hesitation at various times at various speeds. If I floor it, no matter what speed I am going when I floor it (0-50), sometimes it picks up and is just fine. Sometimes, the engine acts like there's not power being produced at all. And sometimes I get this hiccup as though it is missing on a cylilnder (or more). It feels like the engine has lost it's rhythm whenever this happens, and finally it comes back. The engine has never died from this.

Originally Posted by Ryan066

does it hesitate on the highway when u mat it? does it feel like its picking up slowly?

my bet is a clogged catylictic converter. but it should misfire on all cylinders randomly rather then just 1 & 2

[Ryan066]

Originally Posted by sideshot72

Ryan,

I have not checked my computer codes yet. You are the first to mention the catalytic converter in any of these threads, though. This is very interesting seeing as I do get "exhaust noise" from time to time, and have been wondering what is going on back there. It does sometimes sound like the air is not flowing through there right. I haven't noticed these two things happening at the same time, though.

I do see some hesitation at various times at various speeds. If I floor it, no matter what speed I am going when I floor it (0-50), sometimes it picks up and is just fine. Sometimes, the engine acts like there's not power being produced at all. And sometimes I get this hiccup as though it is missing on a cylilnder (or more). It feels like the engine has lost it's rhythm whenever this happens, and finally it comes back. The engine has never died from this.

theres an easy ttest to do provided your 02 sensor comes off easy

its called a back pressure test ... all you do is dissconnect your O2 sensor before the cat and connect a pressure tester... kinda like what you use to check compression (it treads in)... the specification is anything less 1 psi... if its anything over 2 psi, its clogged... i've seen 03's with clogged cat at 4-5psi

if you dont wanna do it yourself then just go to a shop (dealership is best) and ask them to do a backpressure test because you supsect a clogged catylitic converter.

or just get it gutted will still pass safety.

have you had any recent fuel problems? because raw fuel into the tailpipe or running rich ( or too much fuel) will clogg a cat up.

[AMDXP]

Originally Posted by sideshot72

My '96 Cavalier is also presenting what seems to be a random misfire problem. But, I also see the Check Engine light doing many entertaining things. Sometimes it stays on steady, sometimes it goes out, and this morning, it was actually flashing. Does your Check Engine light do anything while this is going on?

Also, I sometimes get a pop from the engine when trying to accelerate. It's not quite as explosive as traditional backfire, but sounds like something really didn't fire right in there.

- I tried fuel injector cleaner, which seemed to help some.
- Some are suggesting the EGR valve be replaced.
- Another Cavalier owner has ridden in the car and suggested either fuel injector, fuel filter, or fuel pump.

Hello, new here.

This sounds like what happened to me a few months back. I had a spark pop loose and had to have the hold retapped. Any who, it would still misfire, and hesitate badly. I finally figured out it the spark wire on the plug that popped out was bad (I know I should have changed it in the first place). I only wish GM made it easier to get to the coil packs!

[Ryan066]

oh yeah.. my buddie porcilen part of one of his spark plugs snapped in half... u could feel the wire and misfires... cause it was only making contact every so often