URGENT HELP - 95 YJ 4.0L Shutting Off

Stryder106

Explorer
Hi All - I need some urgent help with my daughter's 95 Wrangler YJ 4.0L. We are literally getting ready to leave on a Mojave Road run Monday at 0400 and her Jeep decides to start acting up. Here's what it is doing: Starts fine, idles fine, runs fine - but then, it will shut off. Electrical stays on, but the engine shuts down. This is happening sporadically but seems to be more when it is under more of a load (uphill roads). Looking at the Chilton's book, there is an ASD (Automatic Shut Down) relay that controls the power to the Fuel Pump fuse. I've checked the relay and the fuse - they are fine. Any ideas as to what can trip that ASD relay? Or could it be something else? 02 sensor was replaced in April. Catalytic converter was replaced in April. Brand new Odyssey battery one week ago.


She is only 17 and this is our first big multi-day overlanding trip. She was sooooooo looking forward driving her Jeep on Mojave Road. Any help is appreciated.
 

NatersXJ6

Explorer
I don't know about YJ specifically, but many vehicles have an impact sensor that is supposed to shut off the fuel pump in case of an accident. I would check there for a loose wire or other issue. It might just be a mercury switch? If your issue really only happens uphill maybe jack the front up while running and see if it stalls? That would support a bad mercury switch thought.

Also, you could just have a bad fuel pickup tube, plugged in-tank pickup sock, or clogged fuel filter.

Does the pump still run when it stalls? Listen for it closely when it stalls.

I don't know if that is helpful, but it might be?
 

charles.atcher

New member
Crank position sensor.
Second that. Mine would randomly die as well. Sometimes not start, other times run for a few hours fine. Or start and then die after a few minutes. Then restart and drive for 30 minutes fine.

Replaced the crank sensor, and so far it seems to be perfect again.

Somewhat easy to replace, the trick is a wobble socket, or u-joint, and a good long extension. Helps if you have midget hands to reach up there as well!!
 

Stryder106

Explorer
I hope it isn't the crank position sensor as I just replaced that a year ago. It had thrown an 02 sensor code - so I checked down there (I replaced it in April of this year) - and found on all four of the harness wires - the insulation was pulled back at the pin connector. So, given they are so close together - I figured - it stalls under a load - and when under acceleration - the engine torques over a bit - tah dah - the bare wires get really close together and could just touch with some vibration. So - to confirm my suspicion I had my daughter start the Jeep and I rotated the connector to make the wires touch - it instantly died. Found it - so taped them up since we are heading out on a trip (will fix it correctly when we get back). Go to fire it up - NOTHING!! It will crank but not fire. So, I blew something when I grounded the wires. Checked the fuses and relays in the control box by the battery - all are fine and working. Swapped some around - still won't start. Put a multimeter on the pins using the negative battery terminal and get 12V, 4V, 0V, 0V on each of the wires - spot on. Try them using the engine block as a ground and get 0V on all 4. I blew something - I just don't know what (hopefully not the computer). Any chance I fragged the crank position sensor when I did that?
 

Fursphere

Observer
I thought a CPS would throw an engine code - maybe not though?

Pull a spark plug and crank it over with the electrod grounded to the block - you should see spark. Maybe the ignition coil is dead.
 
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Curly

Adventurer
ASD doesn't get 'tripped', its is a poor description of a relay that controls power to the injectors, ignition and fuel pump. When the pcm sees a crank sensor and Cam sensor signal, it powers the ASD. It also powers it for 2 seconds at key on. If the pcm doesn't see a rpm signal from the cmp and ckp within 2 seconds of key on, it shuts the ASD off. It will also turn off the ASD if either one of the 2 signals goes away while the engine is running. This prevents the fuel pump from running in case of an accident where the driver may be unconscious and the key is on.
Turn the key to the run position (do not crank the engine) and listen, you should hear the relay click or the fuel pump run for 2 seconds. If so, the ASD is not the problem. Looking at the wiring for the o2 sensor, I see the DKGRN/Org wire comes off the injector power feed. I see no fuses on any of the wires attached to the o2 sensor. I think you may have burned out your PCM. Check for power at any of the injectors with the key on. They are fed off the PCM w/o any fuse (that I see, using Mitchell wiring diagram). There is a 5 amp fuse under the dash that feeds the pcm. Check that also.
 

Stryder106

Explorer
ASD doesn't get 'tripped', its is a poor description of a relay that controls power to the injectors, ignition and fuel pump. When the pcm sees a crank sensor and Cam sensor signal, it powers the ASD. It also powers it for 2 seconds at key on. If the pcm doesn't see a rpm signal from the cmp and ckp within 2 seconds of key on, it shuts the ASD off. It will also turn off the ASD if either one of the 2 signals goes away while the engine is running. This prevents the fuel pump from running in case of an accident where the driver may be unconscious and the key is on.
Turn the key to the run position (do not crank the engine) and listen, you should hear the relay click or the fuel pump run for 2 seconds. If so, the ASD is not the problem. Looking at the wiring for the o2 sensor, I see the DKGRN/Org wire comes off the injector power feed. I see no fuses on any of the wires attached to the o2 sensor. I think you may have burned out your PCM. Check for power at any of the injectors with the key on. They are fed off the PCM w/o any fuse (that I see, using Mitchell wiring diagram). There is a 5 amp fuse under the dash that feeds the pcm. Check that also.
OOoooooooooooooooo - I did not see the 5amp fuse under the dash - dang it. I just had it towed this morning to a shop who specializes in this sort of thing. Hopefully - it is just that fuse (I had checked all of the others and the relays). Thought I checked everything under the dash, but a PCM fuse is not ringing a bell. Many thanks for the info.
 
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