Question about 1994 Jeep Wrangler
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Posted on Jan 02, 2017
Here are some things that I have run into.
First any sensor cam/crank/tps etc..) that has a reference voltage from the pcm can cause this issue these sensors,(ESPECIALLY THE CRANK SENSORS or CAM Sensor) CAN SHORT OUT INTERNALLY.
THIS WILL CAUSE A NO START CONDITION AND A "NO COMMUNICATION" ISSUE
WITH THE PCM causing stalling. here are some things that I have run into. This condition has caused numerous unneeded pcm replacements. It gets difficult to diagnose when its an intermittent problem.sometimes a tech will install the pcm and let
the jeep leave. Then when temp is right, the sensor shorts and it all
happens again. Often by the time the jeep shows up on the hook the
engine has cooled and the short is gone. In this case the tech has
nothing to go on. YOU MOST LIKELY WONT HAVE A CODE HERE.
THIS IS HOW I DIAGNOSE THE ISSUE. WHEN THE CONDITION IS PRESENT (NO COMMUNICATION") with THE KEY ON, START
DISCONNECTING EACH SENSOR THAT HAS A REFERENCE VOLTAGE. START WITH THE
CRANK SENSOR. IF YOU SEE THE SCANNER GET COMMUNICATION, THEN YOU FOUND
THE SHORTED SENSOR.this CAN BE A PAIN IN THE @** IF THE CONDITION IS INTERMITTENT.
PLEASE NOTE: IT IS EXTREMELY RARE THAT THE PCM ITSELF HAS CAUSED THIS CONDITION. 99% OF THE TIME ITS A SENSOR SHORTING OUT, WIPING OUT ALL COMMUNICATION. ALSO NOTE:I HAVE NEVER SEEN THIS CONDITION ACTUALLY DAMAGE THE PCM. ONCE THE SHORTED SENSOR IS REPLACED, THE PCM IS FINE. THERE IS A RESISTOR IN THE PCM THAT PROTECTS IT FROM THIS. Good Luck and I Hope this will help resolve your issue. Please Rate Me. For any further assistance you can always ask me
Posted on Apr 25, 2009
If the problem began before you changed the plugs that they are likely OK...Some engines "like" certain brand plugs better than others. You may have a weak ignition coil. Poor spark will generally show up at higher rpm's. Spark should be blue and have good "snap" to it and should easily bridge a 1/4" gap or better. If fuel was contaminated, it should show up at lower rpm's as well. System cleaners sometimes work but often are added far too late to do any good. (tank can hold up to a gallon of water without noticing it.) I use 3oz of acetone and one oz marvel oil per 10 gallons of fuel about once a month...cheaper and more effective than most cleaners. (and does not "melt" gaskets and seals as legend has it) The vehicle speed sensor can also give you problems but needs testing to determine if it's got any problems.
It's difficult to diagnose by remote control, but I hope you benefit form something here!
Posted on Jun 12, 2009
Oil gauge may be bad, you said you changed the oil sending unit, and tried a aftermarket which worked, so the other option is to have you oil gauge checked. The sending unit may be good but you gauge is not reading proper.
Posted on Jan 12, 2010
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