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Misfire under load?


PCGUY112887

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It's kind of odd, every once in a great while if I'm going to pass someone, or pull out real quick, all of a sudden my engine starts missing. Sometimes it trips a flashing SES code, sometimes it doesn't. The SES is just for "random cyl misfire" and doesn't tell me much.

 

I just installed my new sway bar and I was messing around in a parking lot giving it plenty of load and it did it a bit, enough to look down and see the SES. Stopped flashing right away and didn't do it anymore that evening. Just had the code cleared.

 

It runs great at any other time. It almost feels as if the transmission is having issues or something but I get no codes for the tranny or anything.

 

I put new plugs and wires in last summer and it's all been fine till a few months ago when it started doing this one evening when passing an SUV. I had the injectors cleaned and I use fuel injector cleaner all of the time. Fuel pump was replaced this summer. Coil packs tested OK but that's about all I've done with them.

 

Any ideas? I don't want to just go replacing stuff trying to find the problem, I'd like to find a good place to start.

 

Thanks.

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mine does the same thing except i don't get a ses light. It has done if for probably 6 years now.

 

I have all new gaskets, new plugs and wires countless times, new coils, new fuel filter, new fuel pump, new knock sensor, new o2 sensor.

 

Only thing i can think of is fuel injectors, and maybe a puter..... It pisses me off though.

 

Im going to try and get a video.

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If you know all your ignition parts are good, you could look at the injectors. Even if they spec out ok, doesnt mean that they are clean. try running some injector cleaner through it.

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My dads '01 Silhoutte was doing the exact same thing, a few months after he bought it (used from a dealer) and they said they just replaced the spark plugs and wires, and some other stuff. For him the problem was the spark wires... Good luck, it was hard to see if it's fixed or not, since it didn't happen often.

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My Cutlass has been doing the same lately.. it's just getting worse and worse. I'm thinking wires as well.. but I forgot I had a second spare set until this minute, so maybe I'll try swapping them tomorrow. Maybe I'll grow some balls and change the bottom motor mount too, this weekend, before the damn thing dislodges itself from the subframe.

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If you know all your ignition parts are good, you could look at the injectors. Even if they spec out ok, doesnt mean that they are clean. try running some injector cleaner through it.

 

Read my first post, I have already had the injectors cleaned.

 

The wires were some white box house brand wires... but it seems that if they were bad I would have more issues. Same with coil packs.

 

The guy at advanced suggested the module thingy under the coil packs.

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i'd say plugs/wires or injectors. plugs/wires are cheap enough to replace as a guess. if this doesnt do it, then have the injectors ohm tested. its good that they have been cleaned but they still may be out of spec ohm wise.

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I got a new ignition control module and that still didn't stop it from happening. I have also been through 2 new sets of wires still no luck. Im not trying to hijack or anything but im just comparaing what ive done with what you have done to maybe find a culprit....?

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What year is the car in question?

 

If its a 1996 (OBD-II), you can look at the misfire history with the right scan tool.....to help pinpoint whats wrong. If there are two cylinders acting up, swap the coil packs.....if the misfire(s) follow, replace that coil pack.

 

If its just a cylinder, pull that spark plug....although I doubt thats it. Misfires unload typically mean injectors....measuring their resistance is one way of checking them, but doesn't give the full story. The proper way is to do an injector balance test....the pump is primed and the injector is fired by the PCM with a scan tool. The pressure drop is noted...one that is off (be it more or less) is bad.....this test both the mechanical and eletrical side. Just because you had an injector flush, doesn't mean their isn't a fault.

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The injectors tested out OK as far as ohms go.

 

Can a vac leak only happen under load? I know my upper intake gasket is part of an old one that was half way scraped off combined with a new one...

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Yes.... although as the poster before it's more likely with injectors/plugs/wires... btw running injector cleaner in the tank will not clean injectors that are gummed up a ultrasonic clean will.

 

Gimper

 

Can a vac leak only happen under load? I know my upper intake gasket is part of an old one that was half way scraped off combined with a new one...

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OK did some testing today, and I am ordering a OBD2 to USB interface via ebay so I can run my laptop out there and monitor everything.

 

Pulled the front 3 spark plugs. #2cyl plug was kinda wet and kinda white, #4 was kinda white and so was #6.

 

Tested coil packs. Put the multimeter on 20k and I got right around a reading of 6.20 on each pack.

 

Wires, tried to test em but couldn't get an ohm reading at all for some reason (on any setting I put it on, I think since the wires on my multimeter is short I'm going to have to totally pull the wire to get em close so I can hold them tight and get a good reading).

 

Checked the PCV system, seems to OK.

 

Started the car, within around 30 seconds I can smell exhaust. Really strong exhaust. Under the hood mainly, I can only get a smell like that if I put my head by my muffler.

 

I can also hear a light tapping in the valve train, kinda sounds like it's from the front valve cover. Gets faster with RPM. I don't believe it's piston slap.

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the second videos shows what it does 70% of the time. It if it misfires, it will always do it at about 4300 rpm. always. not before or not after. It used to get to 4300 and just sit there with constant misfires and i would have to release the throttle. Almost like it was in nuetral bouncing off the rev limiter.

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