QuestionQUESTION: Hi, I've had a "slight engine miss" for over a year which has gotten worse to the point where the engine may stall under steering load. I've replaced the head gasket, narrowed the valve seats (just to make me feel better), they were ok, coils, plugs, wires, filters, changed fuels, injectors, ect... I've ran the car on a tech II and it shows a misfire count on cyl three about 30 percent of the engine running time but it has gotten worse. Ive noticed that if i hold the throttle to the floor for 10 mins on a long road, the exhaust will turn cherry red, I think that means running rich in most cases but the misfire is only happening on one cyl which rules out all sensors except crank and cam, fuel pressure, vacuum leaks. There is the standard faint ticking noise of the lifters which sounds even on all cylinders, no knocking ect. A few things ive noticed are that when the engine is running rough, if I load it up there is a rattle coming out of the exhaust, which i think is a sign of improper fuel/spark/time. And the best part, every so often the car will run incredibly well with outstanding power/fuel economy. I'm kinda hoping You've heard of this or seen this before and I'd be ok if you'd tell me i have a bad sensor (lol). I'm just about ready to give this car the buckshot salute. Any help would be greatly appreciated. (for the records I am a truck/coach/equipment mechanic for 10 years)
Thanks,
Chris Woods
P.S. Anything you need to know I can tell you as much as you need about this car
ANSWER: Hi chris:
weel I would do a compression test on the engine and see what you have on #3 if that doesn't show much of a difference the do a cylinder leak down test. If that doesn't reveal a issue then I would start looking at fuel delivery possably a rich injector on #3. the fact that it's only 1 cylinder misfiring would rule out an ignition issue for the most part being that this usues companion cylinders for the coil so if it was a bad wire or coil it would affect 2 cyliners not just 1. That is where I would start looking. Good luck :)
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QUESTION: ive done the compression/ leakdown test and all cylenders are equal in that sense. Ive put new injectors in since and the problem remains. What gets me is there is no MIL light on which tells me a sensor is either weak but still in range, or its a mechanical problem. That being said what are the chances of having an intake manifold leak on the third cylender port causing that kind of problem, or a bad cranks sensor reluctor, and last but not least, this car has 1 O2 sensor pre cat, can a "slight" exhaust leak (after the sensor) affect engine performance/fuel economy? I know that this wont be the perfect case in this situation but if it does affect it, i can diagnose that then see about the one cyl misfire. DOes the O2 sensor only affect engine timing in closed loop or at all times?
Sorry, and Thanks
Chris Woods
P.S. I owe you a coffee
AnswerAn exhaust leak before the O2 sensor will cause a fule delivery issue yes. It will not effect timing per say. A vacuum leak can cause an misfire on 1 cylinder but not all that common on this engine. do you have a scan tool to look at fuel trim rates? if the fuel trim is in the -% you have a rich condition if it's in the +% a lean condition. + or - Up 5% is normal but once you gte over 10% there is an issue.. You could have a contaminated Pre converter O2 sensor that could be you issue but it will not effect just 1 cylinder.. As for a reluctor on the crank being bad I doubt it!
