Expert: Sean Halliday - 1/13/2007

Question
My truck started running slugish about two weeks ago. Last week the check engine light came on so I took it to Auto Zone and scanned it. Cylinder # 6 misfire. Replaced the plugs still there. replaced the wires, still there. replaced the coil for cylinder 3 and 6, still there. the only things left are fuel injector, valve, compression,... I keep the oil changed regularly so I dont think the valve is an issue. the fuel injector seems a likely candidate but the prospect of removing that entire manifold assembly freaks me out. is there another way to like clear that injector? I have a full tank of fuel with a bottle of redline fuel cleaner in it now. Whats weird is sometimes, while accelerating, the problem clears and the check engine light goes out. Then I'll pull to a stop and it starts all over again. HELP!!!!

Answer
Eliminate the valve by doing a compression test on that cylinder.If the cylinder is ok you will have 100psi or maybe more but below 70.or a poor reading is a burned out valve and so a valve job.Read all the cylinders pressure and take the average reading.Should be 100/110.Or more. As for the injector,if you get a noid light and test the power is going to that injector but to be sure you must replace it if the cylinder checks out ok for compression.Thats if all electrics are ok,wires ,plug,coil.The other possibility is a leak at the intake manifold and the fuel/air mix is out of range for that cylinder.Then you can test with a vacuum guage for leak at the manifold.Or spray some WD40 around the intake and watch what the engine does as it idles .If the idle differs then you have a leak.Alternatively you can use carb cleaner but be careful as its flammable and dont use too much just enough to hit that one cyl and if its leaking then the intake of cleaner will make the idle level out.So hope this helps.