As some of you know, I often maintain that problems can exist in spite of a no-DTC situation, multiple testing methods, etc. This problem occurred with my Lincoln a week ago Saturday. The car is a 1996 Lincoln Mark VIII with a 4.6 DOHC.
SYMPTOMS. Ran fine. Started 2 hours later and ran like garbage. My wife insisted it would clear up; I wasn’t convinced. Two miles of bucking later I pulled over, took the inexpensive code reader out of the console and it showed nothing. No CEL illuminated either. Two miles of bucking back home and we drove another car. On the trip that evening I picked up a new set of plugs as I knew I would be going into that area although the plugs (20k miles) and wires (30k) are comparatively new. Plugs are mildly difficult to access and upon initial removal of the plugs last Sunday I was 99%+ certain where the problem was after looking at the plug tips.
While in there I did a few other checks on a whim although some would have no bearing on this particular incident. Here’s the results.
No DTCs set and no CEL at any time; steady or flashing.
Compression - 180ish PSI all 8 cylinders.
Fuel pressure -35 PSI.
Fuel pressure regulator good and operative.
Manifold vacuum - 20" rock steady even with the poor running and no vacuum leaks.
All injectors ohm out at 14.7 and pulse.
Plug wire resistance as follows with short wires (15-16") in the top bunch and and long wires (24-26") in the lower.
There is one thing about the symptom I’ve omitted so as to cut down the odds of a lucky guess by anyone.
Just posting this as a minor mechanical brain exercise more than anything and the question would be; what is your line of thinking as to the cause of the problem and what would you do?