I have a 96 grand cherokee 4.0 that will crank but not start. With key in run position i get no fuel gauge, volt gauge, and no check engine light. The red light on the dash turns on solid, and the on board diagnostics test does not work at all. A 20 amp mini fuse under the hood blows as soon as i turn key to on position. I replaced the crank position sensor but no change. Do I need to change the PCM?
Jeep cranks but does not start. No check engine light.
- Thread starter Nucks
- Start date
SteelHeadz
Super Moderator
Which fuse is blowing? check the fuse cover for the location of the fuse in question, let us know what that fuse controls.
SteelHeadz
Super Moderator
Ok, i'm not sure about this bit it's worth a shot. i'll be more definitive tommorow when i get to work and look for a service manual for your jeep. anywho, i think that you may have a shorted O2 sensor that may blow that fuse. If that's the Fuse 20, that controls the PCM, ASD circuit, 02 sensor circuit and IPC. Check the 02 sensor wires and make sure they are not burnt to the exaust manifold pipe. if they are, disconnect it and install a new fuse and try to start the engine.
SteelHeadz
Super Moderator
IT IS fuse# 20. Swap the ASD relay with a known good one. Test for the concern. still evident?, remove the fuel pump relay and retest.
toaday i checked the o2 sensors. Wires looked ok, but I unplugged them both anyway, replaced fuse, and turned key. The Relays went crazy for a few seconds then settled. Problem went away. So I ran a on board diagnostic test and came up with 12 and 55. Jeep started. Took it for a test drive, all was good right up until I hit a speed bump. Fuse blew again. Replaced it and fired back up, parked her back in garage. I've swaped the relays around before today and got no change, but I belive you are right and there is a bad relay or two in there. Might explain the dead Jeep when i hit a big bump. A bump was the cause of the problem in the beginning as well. So I am going to change all the relays with new ones and try again.
SteelHeadz
Super Moderator
Well, i would have to say that's good news that your getting somewhere on this issue. the fact that the fuse blows when you hit a bump, that could be the best diagnostic tool to have. Get a bunch of extra 20 amp fuses. Do the bang and bump test. bump one component at a time until the fuse blows again. wiggle the wiring harness around as well. this should help you narrow it down.
SteelHeadz
Super Moderator
Although 02 sensors Create's Voltage as they heat up, the PCM has the capacity to tolerate failures by shutting down circuits internally but still let the other sensors function and let the engine keep running. so, no worries here. it's actually more likely to Fry the PCM by disconnecting the PCM connectors and reconnecting it back without disconnecting the negative battery cable.
Found it!!!!! In the mix of banging and wiggling things while the truck was running I saw a arc flash near the the top of the manifold. Sure enough there is a black wire feeding the injectors, I believe this it what the wire is doing, that is completely fried. Arcing out on manifold. Checked fuse and sure enough blown and the cause of all my problems. I will upload a picture of this wire to show it's location. Hopefully save others from buying PCM's or CPS sensors in the future. Thanks SteelHeadz.
Dragon5126
New member
reply to old thread: O2 sensors in Jeeps don't just create a voltage (thermocouple) they are also heated so that they set a reference point for the PCM to start at. This speeds up the time frame in which the system can get accurate readings, since it doesn't have to wait for the exhaust stream to do the heating of the thermocouple in the O2 sensor.
Similar threads
