Odd misfiring problem...

Yontrop · Feb 20th, 2005, 02:13 PM

On occasion, after deceleration, the truck will start misfiring at idle. It's only firing three out of four times, like one cylinder isn't getting a combustion. I'm thinking it's an injector issue, because in most cases, when you decelerate, the injectors basically shut off until idle. Well, I think one of the injectors isn't coming back on. I have to spike it and rev it up to about 4, and it'll come back in.

I think today I'm gonna pull the injectors and see if there's clogging or some sort of build-up. I haven't ran cleaner through it in a while; I suppose I should. I checked the harnesses... each one had a little bit of dust build-up, and I simply took my airgun and sprayed them out and cleaned them, but that didn't help.

Has anyone else had this problem?

**88pathoffroad** · Feb 21st, 2005, 02:23 AM

I would think that if one of the injectors were misfiring, it'd cause the ECU to go into fail-safe mode and only rev up to 2800 RPM's. You could go by an auto parts store and see if they'd retrieve your trouble codes for you to see what's not working right. Call around and ask if they do freebie OBDII scans. Another thing to check is your plug wires, a vibrating wire with a crack or a cracked spark plug could occasionally cause misfiring like that.

Yontrop · Feb 22nd, 2005, 06:46 PM

Quote:

Originally Posted by 88pathoffroad

I would think that if one of the injectors were misfiring, it'd cause the ECU to go into fail-safe mode and only rev up to 2800 RPM's. You could go by an auto parts store and see if they'd retrieve your trouble codes for you to see what's not working right. Call around and ask if they do freebie OBDII scans. Another thing to check is your plug wires, a vibrating wire with a crack or a cracked spark plug could occasionally cause misfiring like that.

Well, it's not setting off a code. The light isn't coming on.

I also looked at the wires and plugs, and both of them are fine.

**88pathoffroad** · Feb 23rd, 2005, 12:51 AM

The ECU can store error codes without turning on the check engine light. The CEL comes on only if there's a significant emissions-related problem, basically. Run the error codes anyway and see if anything comes up...

jerryp58 · Feb 23rd, 2005, 06:12 AM

Quote:

Originally Posted by Yontrop

On occasion, after deceleration, the truck will start misfiring at idle. It's only firing three out of four times, like one cylinder isn't getting a combustion. I'm thinking it's an injector issue, because in most cases, when you decelerate, the injectors basically shut off until idle. Well, I think one of the injectors isn't coming back on. I have to spike it and rev it up to about 4, and it'll come back in.

I think today I'm gonna pull the injectors and see if there's clogging or some sort of build-up. I haven't ran cleaner through it in a while; I suppose I should. I checked the harnesses... each one had a little bit of dust build-up, and I simply took my airgun and sprayed them out and cleaned them, but that didn't help.

Has anyone else had this problem?

My '00 Grand Am had a stumble/miss at idle and it turned out to be a dirty fuel filter. Just a thought.

Yontrop · Feb 23rd, 2005, 10:12 AM

Hmm, alright... I'll probably have someone at work scan it for me (I'm an entry-level mechanic at a shop). I learn something new every day.

As far as the fuel filter - I changed it about 8-10k ago. The truck isn't acting like its starving for fuel; it's just this simple idle misfire.

Thanks guys.

EDIT: Oh yea, it does rev just fine... it doesn't stop at 2800rpms. During this misfire, it bumbles up until about 1200, then it smooths out and drives normally.

**88pathoffroad** · Feb 23rd, 2005, 10:34 PM

Check your O2 sensor.