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91 GTP misfire.


9lumina6

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Since I got the car 2 saturdays ago It's been running awesome. Drove it all last week (didn't even touch the other 2 Grand Prixs) Drove it to Canada this passed weekend and back with absolutely no issues what so ever. I decided to take the 03 to work the last 2 days....and the 91 has been sitting now for 2 days untouched.

 

I go to start it and it had absolutely no trouble starting. I take it down the street and it didnt seem to have alot of power. When I drove by a parked car on the street I noticed a very loud "putting" noise coming from the exhaust......Immediately turned around and put it back in the driveway.

 

Camron did say that the plugs and wires were recently replaced, and he put a set of injectors onn a 95 LQ1 on when he got the car.....

 

I don't know where to start......suggestions??

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Try pulling plug wires one at a time while running to isolate which cylinder is misfiring.

 

Then swap out coils on that cylinder with a spare.

 

If that fails look at the injector.....

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Pulled each of he 3 front wires and each one of those effected how the motor ran.............each of the 3 back plugs made absolutely no difference. (even popped all three up at the same time) and didnt seem to make the car run any worse............????

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If you listen to it....it doesnt sound like a random miss........when yu're driving it... you can hear a loud put put. And standing behind the car it smells like straight gasoline. If I pull the front 3 plugs...it makes it run worse....pull any of the back 3 wires...and it doesnt change how it runs at all.

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Yeah wen I start it up.....it doesnt sound TOO abnormal......Enough that when I first fired it up to take it for a ride I honestly didnt notice it til I backed out of my driveway and took off then noticed less power than usual. Also....when I parked the car it was running perfict...then the very next time driving it it was doing this.

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Huh, id try and pull the back three plugs, clean them up and put some dielectric grease on the wires and see what that does first, plus its free to try. If that doesn't help I dunno, its never had any kind of problem like that. My euro would do weird shit like that every now and then but that car was the spawn on satan im pretty sure.

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Yeah I'm clueless at this point....like Nunzi said earlier...I wasleaning towards the ICM being bad. That would make sense seeing as the car does have 183K miles and most likely the original one. I was going to go buy one tomorrow after work.....and also use the stock coils that were off the 03 that have less miles on them (same part #, already checked)

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when timing jumps it sounds ungodly.

 

That depends really. One tooth isn't going to sound that awful and jumping a cam sprocket isn't nearly as bad as the crank sprocket. I've seen an LQ1 jump time on a cam sprocket and it didn't sound bad, would only miss below 1500 RPM, and above 2000 RPM it ran perfectly fine.

 

Put a vacuum gauge on the engine if you have one. Should be just below 20 inches at idle. If its not I'd be looking at cam timing.

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I'm not sure if you remember this, but back in 2006 I was having an issue with the 90 missing at idle but not under a load and even WOT it was fine. I tried everything, pulled wires, plugs, each wire I pulled made no difference.

 

I put in an ICM and it didn't make a difference, put in 2 new coil packs, and it was almost better. Then Jeff found a bad injector. Now it runs good.

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Have you verified spark on those cylinders? Just because pulling the wires did not change the way the car runs does not mean that there was no spark. I agree with Chris that it is likely the ICM, though I'm also thinking it might be an injector.

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SPARK TEST:

tools: spare plug wire, screw driver... otherwise you must unplug each wire one at a time...

procedure: You should not be changing the wires with the engine running (unless you like licking bug zappers?) You must insert the screwdriver into the end of each wire being tested(why a spare wire is so much easier) and lay it on solid metal so that a spark gap exists and can be observed. You can remove the fuel pump relay to prevent the engine from actually starting, and then crank engine separately for each of the six coil points to observe for solid spark. spark should be consistent and even across all the coils.

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