96 4.0 still stumbling at startup and in reverse/1st gear
Been going on for a while. I replaced the crankshaft position sensor (twice), fuel pump (twice), and idle air control, but no dice. Sometimes it just wants to turn over forever without starting, then I switch it off, then back on, and boom, start. Stumbles, but starts. I have no engine codes. Might go for plugs and wires as the PO didn't bother to gap the plugs, which I did after I bought it. Trans fluid is at the correct level, also.
I had forgotten that it cut off on the wife the other day and she mentioned that the oil pressure gauge was kind of erratic. The dude at advance said sometimes the sender can be the culprit, and cause it not to start, and once cranked, even tough it's reading good on the gauge, might not e letting enough electricity through at idle or super low speed causing it to stumble. What do you think?
It's possible the sensor is bad. Low tranny fluid can do the same thing, I'm told.
First check under your distributor cap for oil and debris. Then make sure the PCM ground wire at the coil is clean and tight. Dont just look at it, take the nut off, clean it with a wire brush or pocket knife and re-install it.
I am assuming you cleaned the throttle body as well as the IAC area?
Tranny fluid level is good. Distributer rotor and cap were replaced by PO and I replaced the Hall Effect sensor, and all that is clean. IAC and throttle body are clean. I just backed out the 2 screws on the PCM just in case they were shorting it out. I've been reading all night. Blah. Would a faulty throttle position sensor possible cause this, too. Mileage has been pretty crappy for a wile. Not entirely horrible, but not like it would be. I'll also check that ground in the morning.
Yeah, screws didn't work. Went to Advance and the dude ran a full diagnostic test. The only blip was when he tested tha MAP sensor, but no codes at all. Could it be possible that the MAP sensor is not reading or rectory, but not throwing a code? I checked and cleaned the ground by the coil. It was pretty clean, but just in case. TPS was fine. Everyone seems dumbfounded. The guys at our Advance actually know their stuff, which is nice.
Most of us here have been through this more than once on our own Jeeps.
It's like this....it throws codes, like map sensor, coil, etc. But what it's really saying is that "something" is jacking with the PCM at a certain point, therefore, the PCM isnt willing to send the signal to fire the coil....or maybe it did, but another issue caused a fault which belayed that order..so to speak. It's frustrating, I know. ( reminds me of certain annoying women)
My latest episode was caused by one of two things. ( fixed them at the same time, so I dont know which !)
1. Crud and oil inside the distr. cap....AND UNDER the cam sensor plate. I sprayed contact cleaner on and wiped down the rotating metal piece UNDER the cam sensor plate as well as the edge of the cam sensor itself.
2. As I replaced the distrib cap, I noticed that the center ( coil) lead was crossing a spark plug wire as it left the distr. cap. I repositioned it so that it came straight out between two plug wires and made sure that none were touching. ( this isnt easy to do sometimes)
I think I also might have removed the PCM connectors, re-sprayed them, using a 12/ can of contact cleaner, let them dry for 20 min, applied a little dielectric grease and re-installed them on the same day...but it may have been a day earlier. I've slept since then.