1996 Jeep Cherokee pcm

  • 4.0L
  • 6 CYL
  • 4WD
  • 140,000 MILES
How can I tell if my c p m is bad on my 1996 jeep cherokee 4.0 4x4 will not start, no spark, no power to fuel pump, replaced with new pump, replaced with new cam sensor, replace with new crank sensor, new battery, all fuses, and relays check good, fuse links all ok, what else could it be?
Do you
have the same problem?
Sunday, January 19th, 2014 AT 7:52 PM

1 Reply

You've added new problems by disconnecting the battery. The idle speed is going to be too low for starting unless you hold the accelerator pedal down 1/4". Most importantly, you erased any diagnostic fault codes that were stored in the Engine Computer. Without that valuable information, there is no way to know which circuit has a problem. At this point the best approach is to find a mechanic with Chrysler's DRB3 scanner to view live data. The crankshaft position sensor and camshaft position sensor will be listed as "present" or "no". If either one is missing, the computer won't turn on the automatic shutdown (ASD) relay. That's what sends current to the ignition coil and fuel pump.

The only thing you can do without a scanner is to check for that 12 volts from the ASD relay and check the voltage feeding those two sensors. Look for the wire that is the same color at the ignition coil and all of the injectors, usually a dark green / orange. You should see 12 volts there for one second after turning on the ignition switch. What's important is if that voltage comes back during cranking. If it does not, check for 5.0 volts on the feed wire for those two sensors. If it is missing, unplug both of them and measure it again. If the voltage comes back after cycling the ignition switch off and back on, one of them is shorted. If the voltage doesn't come back, the feed wire is broken or grounded.
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Sunday, January 19th, 2014 AT 9:00 PM

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