Jim Grant's Tech Tips
'96 Ford Windstar, 15 Second Misfire
Q: I have a misfire in one of my cylinders on my 96 Ford Windstar. Each time the misfire occurs, the engine runs rough for about 15 seconds. Do you know what might cause a misfire to last for fifteen seconds each time it occurs? The diagnostic says cylinder #4 but I changed the plugs and wires and it still happens and reports cylinder #4. I know it could be wrong info from the diagnostic tool regarding which cylinder.
- John L.
A: Just because your vehicles computer is reporting a misfire (skip) doesnt mean that it is a spark related problem. A misfire code is only the computer reporting an incomplete combustion event. Incomplete combustion can be caused by spark, fuel or mechanical engine problems. I also have to warn you that the computer does not know all and can even be wrong in identifying which cylinder is the problem cylinder. On more than one occasion, I have seen the computer report the wrong cylinder when there was a misfire. So you have to first prove which cylinder is misfiring. Once youve proven which cylinder it is, you have to check the spark and fuel. If both are good, you then have to check the mechanical condition of that cylinder. Items such as a vacuum leak, worn valves or guides, low compression or even a weak valve spring can cause a misfire that will come and go. It all depends on what stage the failure is in. The solution to the problem could be as simple as a bad spark plug with a confused computer. Alternatively, as difficult as a mechanical problem, that will require disassembly of the engine.