Help us help you. By posting the year, make, model and engine near the beginning of your help request, followed by the symptoms (no start, high idle, misfire etc.) Along with any prevalent Diagnostic Trouble Codes, aka DTCs, other forum members will be able to help you get to a solution more quickly and easily!
I have no idea on what to do next. Parts thrown at it already… - New upstream and downstream o2 sensors replaced on bank one. All the voltage’s were displaying correct numbers as the vehicle was running. - New purge valve installed regarding a different issue. Was a small evap leak that was actually fixed with a new gas cap. But I noticed the old purge wasn’t holding vacuum like it should either and replaced it. Misfire still exists. - New spark plug installed. Actually 2 plugs. I thought maybe the first one I bought was shitty so I got another better brand the misfire still exists. - New fuel injector replaced on # 5. Still misfire. Changed them around to see if I got a bad part, still misfire on #5. - New spark plug wires on all cylinders. Still misfire. - *** Coil packs have not been changed. But I moved them around to see if misfire changes to another cylinder. No change. Still misfire on #5. Tests conducted: - Stethoscope verified all injectors on bank one had a good ticking pulse sound - fuel injector balance test on all injectors on bank one. All injectors passed. The amount of psi that was lost during the pulse testing were all the same. - noid light pulsated correctly on each bank one injector. - fuel injector resistance test showed all injectors were the same and to spec - inline spark tester lighted and pulsed when connected from plug wire to plug. - new plugs were tested to have spark on my bench top spark plug tester to verify before installing. All passed - smoke machine test at the intake showed no leaks anywhere in the system. - smoke machine at tail pipe showed no leaks. - compression test was conducted on all bank one cylinders. All showed the same psi at 205 with no leaks. - leak down test was conducted on all bank one cylinders. No leaks - removed bank one valve cover. Saw nothing out of ordinary to my eye. Cylinder 5 is non afm/dod. -Misfire is mostly occurring at idle. While watching misfire counts on my scanner, the count stops after giving it a little throttle. - Fuel trim on bank 2 are usually very close to zero for both short and long. Bank one short is usually around negative 2 to negative 3% and long is usually anywhere from negative 8-12 - oil is good and has been recently changed. - added some SeaFoam to the gas about a week ago but no change. Any thoughts on what to test or look for would be greatly appreciated. This particular cylinder 5 is not afm/dod. I know a lot of folks may say it’s an afm issue but that’s not on #5. Can it be a bad ecm? I was thinking maybe, but if it was a bad ecm, wouldn’t it show on the noid light test?
Although it is a non DOD cylinder, it is still possible to have a failing lifter. If you don't have a scope and pressure transducer, a running compression test (with the Schrader valve removed from your compression gauge hose) is the next best thing. Expect about half the cranking compression and compare to known good cylinders.
It may also be worth moving the fuel injector even though it passed well the tests. I have spent many hours chasing a misfire that ended up being an injector with what I suspect was poor spray pattern. It passed the fuel pressure drop test with all the other injectors, scoped perfectly but when no other problems could be found I resorted to moving the injector, and much to my surprise, the misfire followed.
Sorry, I should have been more clear.To perform a running compression test, the Schrader valve must be removed from the hose that you thread into the spark plug hole. Otherwise it works as a one way valve and will freeze at maximum compression. Removing the Schrader valve from the compression gauge hose allows the gauge to react to every compression change in the cylinder. (In hindsight, holding the pressure relief valve of the gauge should do the same thing). Which does make it tricky to interpret, it will move around quite a bit. That's why I suggested comparing to a known good cylinder. Once you know how the known good looks, you'll hopefully be able to tell if there's funny business going on in the misfiring cylinder that would indicate a mechanical issue.As far as the fuel rail and pressure drop test, i dont think you need to modify anything there. I just wanted to let you know that the results of that test, in my experience (all be it one time only) can be misleading if an injector still flows the same amount of fuel, but doesn't spray it in a pattern that allows for proper atomization. Thinking pour instead of mist. So in that scenario, it may be worth your time to just move the injector on the missing cylinder and see if the misfire follows.
Topic Author
