I have a dead miss (1994) on cyl #4 at idle. Have spark at the spark plug, have pulse at the injector(noid lite), have 160 psi on all cyl dry, O2 code fault, but have new O2 sensor. Haven't check rail pressure yet. Let truck sit unused for about a month and wife drove it for a day. First engine lite ever in 100,000 miles. I'm not blaming her ... yet. Any ideas would be appreciated.

 

If you have compression (you say you have 160 psi dry on all cylinders), ignition (spark plug on #4 is firing), and power to the injector (the noid light says it's firing) then about the only thing it can be is a stuck injector. It won't be missing only at idle, however, but the miss is harder to detect at higher speeds. I have an unmentionable SUV (a C*E*Y BL*Z*R) where I've had a stuck injector happen twice.

Short of removing the intake manifold and fuel rail and and physically removing the offending injector, you could try a bottle or two of a GOOD injector cleaner (I use "Redline") in the gas tank. You may have to drive the car for several hundred miles before the injector loosens. This assumes the injector isn't 100% stuck closed, because some gas has to be getting through the pintle orifice so the cleaner can work.

Other than the cleaner, you may need to remove the injector and manually clean it. Use a "turkey baster" and manually pump injector cleaner through it while activating the injector with a 9-volt battery. Trigger the injector frequently while pumping the cleaner through it in both directions. Be careful of sparks from the 9V battery, because the cleaner is flammable.

Have you pulled the codes from the ECM? I'd do that first, just to make sure there's not some other problem. Removing an injector can be a several hour job, and no use wasting time if the code tells you something else is wrong.

Please post back as to what you've found.

 

Found the problem. After approx 25 hrs of testing, just before I decided to take the intake off and check for gasket or more serious problems for # 4, I was in the middle of taking ohm readings for all the underhood wires and found a broken wire on the inside of the insulation. Went to the coolant temp sensor.. Soldered it and it runs like brand new. Can't figure it out. Didn't get a code for that, just the o2. Don't understand why just #4 missed. Just guessing that the pcm leaned out the mixture so far that #4 was missing. Just glad I found it. Was ready to do something really stupid.

 

An "open" coolant temp sensor (wire) should make it run too rich....