Jeep YJ is kicking my ass

ltrpilot9

ltrpilot9

Well-Known Member
Joined
Oct 15, 2012
I have a 1994 Jeep Wrangler YJ with a 4.0 and a 5 speed. The jeep is parked outside and it was wet and cold this morning before work. It ran fine this morning, but the engine died today on the way home from work like I shut off the key. No sputter, just instant stop. It will crank, but it wont fire. I checked the fuses and the 30amp fuse for the ECU was blown. I pulled the one out of the headlights and put it in to see if I could limp it home, and it instantly blew when I tried to crank it. I did some more checking while I waited for my wife to pick me up and it looks like theO2 sensor, the ECU, the crank position sensor, the auto shutdown relay and the fuel pump are on that circuit. I picked up 4 new fuses and went back to troublshoot. I disconnected the O2 sensor and auto shutdown relay for the first test to see if either of those was the culprit. The first try with both unplugged the Fuse stayed good on crank. I plugged the O2 sensor back in and tried it again and the fuse stayed good. I plugged the auto kill relay back in sure that this would be my problem, but the fuse stayed good. So now it is not longer blowing the 30amp fuse, but still wont start. I am thinking fuel pump, when I turn on the key I cant hear it run. I don't know if I should be able to or not, I have never really paid attention or listened for it. I really don't understand why it would blow the fuse one minute, and not a half hour later. I need to preface your comments with the knowledge that the electrical system is not my strong suit. Assume I don't know anything and proceed from there. ANY advice is welcome.
 
I am still working on this, I have been checking wires for the better part of the day. I found a couple wires on the O2 sensor near the alternator bracket that had broken insulation. I fixed those, even though the O2 sensor should not give me the symptoms I have. Still no spark. Just for fun, I also hung test a known good crank position sensor. Still no spark. The jeep guys at work all say they think it is a short in the fuel pump, or the wiring between the pump and the computer. I have checked the wiring between the pump and main harness junction near the battery. Both of the dark blue and green with grey tracer wires looked good and tested good. I looked at the wiring under the power distribution center. Both the wires that run from the 30 amp fuse for the ECU are red and white. One goes to the fuel pump relay, and other joins the main harness that runs toward the PCM. I don't know if I should keep testing the wires for the fuel pump towards the PCM, or the red and white wire that runs from the 30 amp fuse. Has anyone ever been down this road with a Wrangler YJ and could point me in the right direction? I am also not finding much on a method to test the fuel pump with a multimeter. I REALLY don't want to drop the tank if I don't have to, but I am just about out of ideas. Any help or advice is appreciated.
 
Will it fire/run on starting fluid?
 
Some of North Carolinas leading techs are floating around this site. If you could provide some data from the ecm there's not a doubt in my mind it could be solved very quickly.
 
Thanks for the advice, I really appreciate it. First, I don't have a diagnostic tester, so I don't know what the codes are. How would I go about getting one? I did check for power on both sides of the coil and there was none, still isn't. I also checked all the fuses and they are all fine. I should also mention, that it is still not blowing the 30 amp ECU fuse like it initially did. I checked all the wires coming from the O2 sensor, and found 2 that had broken insulation near the alternator bracket. I fixed that but none of the symptoms changed. Just for fun, I also put in a new fuel pump relay and a new ADS relay. Neither did anything for my plight. Next I disconnected the fuel pump at the plug on the top side of the fuel tank, and inspected all 3 wires all the way to the main grey plug next to the power distro center. They all looked good, and had good continuity. I did a quick power check with the key on, and the dark blue wire, which the center wire in the plug has 3.45 volts. The other two are 0. Does this indicate a power draw somewhere in the engine harness, a problem with the computer, or something else entirely?
 
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To check engine codes get a pen and paper ready. Turn the ignition switch to the on position,off,on,off,and back to on. The check engine light will begin to blink. Count the # of blinks, pauses between will be separate codes. Once you get the #'s Google the answers.
 
I really appreciate the help. I just went out and tried this, but the check engine light does not come on. None of the advisory lights come on when I turn on the ignition. When I try to crank it the brake light come on. Weird?
 
The ignition switch feeds pcm pin 9 do you have voltage here koeo? Pin 5,11 &12 are pcm grounds. What is the koeo & koer (or cranking) here? Pin 86 of the of the fuel pump relay, what's the voltage there? On pcm pin 51 back probe does it go from 12v to 0v(or close) when the key is turned to on and start positions?
Missed one, pin 3 in pcm is b+. Do you have voltage here.
Make sure you test everything you can plugged in and using a paperclip to back probe (make sure it doesn't have plastic on it)
 
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Connector view to help
 

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mysterync, you are my new best friend, and I would like to offer you a steak and all the beer you can drink if you are brave enough to take me up on it. I checked pin 51 and did not have voltage. I checked the voltage at the ignition fuse on the firewall and had 11.83 volts. I started following the wire and found it broken about 6 inches into the harness. I repaired it and the jeep fired right up. Its running a little rough, so I am not finished yet, but I am breathing much easier now. THANK YOU
 
ltrpilot9 said:
mysterync, you are my new best friend, and I would like to offer you a steak and all the beer you can drink if you are brave enough to take me up on it. I checked pin 51 and did not have voltage. I checked the voltage at the ignition fuse on the firewall and had 11.83 volts. I started following the wire and found it broken about 6 inches into the harness. I repaired it and the jeep fired right up. Its running a little rough, so I am not finished yet, but I am breathing much easier now. THANK YOU
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Glad I could help. If I ever get down your way I'll take you up on it!
 
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