My 1993 Deviile 4.9 liter engine with 120K miles has developed a misfire/stumble problem and no diagnostic codes are present. When the engine is cold it starts and runs fine for about 25 miles then the engine begines to misfire or stumbles all the way through the speed range. The problem is most pronouced at low engine speed under load. At highway crusing speeds or acceleration under light load the "misfire" is less pronounced. If the car sets for a few hours it is hard to start and after starting idles very rough (Almost like in the old days when carbs would "Load up") The ignition wires, ignition module, coil, rotor, cap and spark plugs have been replaced. The fuel system has been flushed. The EGR valve was sticking and has been replaced. The fuel injectors seem to be operating (Stethescope test) on each injector. Fuel pump pressure within specs. I am out of ideas. Any suggestions?

Probably time for a new distributor cap. See if the 8 contacts are badly spark eroded.

You might want to check your fuel pressure regulator.

Make sure you don't have any loose boots (mine kept popping off after I replaced them) and pull a plug, check for gap (my ht4100 is 0.6 - mine were gapped WAY too much, around 2.1, and I had major performance problems). Never assume they come pre-gapped.

Thanks for the suggestions guys. I have checked the plugs. fuel regulator and replaced the distributer cap. Same problem. A former Caddy mechanic said that an intermittant Cam Sensor(Hall Effect switch) located in the Distributer(?) could give those symtoms. Anyone have experience with the Cam Sensor?

Thanks

When my cam sensor was going, it would cut out intermittently. At highway speed, I could put it in neutral shut the ignition off, without locking the steering column, start it back up. I would run well again for 30 min to 1 hr.
It never threw a code until it got real bad. When I looked itnto the distributor, I saw the wire going to the cam sensor was rubbing on the cam and was down to bare copper.
It was one of my more challenging Cadillac adventures. I was on a road trip in Northern Maine at the time.

When my cam went ou t it set a code. Oh how fun it was replacing it.