TJ cranks but won't start
- Thread starter Anger57
- Start date
Checked ASD relay. Looks like i got my power to post 30 and power to post 86 and 85 with key on but no power to 87 with key on. I noticed injection fuse #28 has no power. Also checked power, grounds, and signails on cam sens and crank sens. Seems good there.
Ok, now im following a path here in my wiring diagram. Fuse with no power for injec is also on the same power grid for power for my o2 sens fuse that also has no power and same wire going to my ASD relay coming from the PCM. Would this have anything to do with my exhaust leak on the cat with the o2 sensors and engine light i had years for it?
Exhaust leaks have nothing to do with anything electrical unless it's blowing hot exhaust on a wire or electrical component and melted it.
Ok this is what a i figured. Thought maybe the o2 sensor would not let the ASD relay power up everything seeing how to the o2 sensor goes threw the pcm. I am guessing o2 sensor dont even respond anyhow till after engine is running. So i was right on this one. 3 things start a engine. Fuel, Spark, and o2. Lol
Fuel, Spark, Compression, and (more correctly) air. The results are especially nice when the first 3 occur in the appropriate sequence.
The 02 sensors do absolutely nothing until things are warmed up. You could unscrew them and leave them hanging off the connectors, plug the holes in the exhaust, and nothing would change with respect to starting the engine.
The ASD relay should momentarily come on (about 2 sec) then off again when you turn the key from off to run.
Is that happening? If so, verify that the “ASD Sense” voltage is getting back to the PCM.
Without that signal present the pcm will not activate the ASD relay during startup and the engine subsequently will never start.
Is that happening? If so, verify that the “ASD Sense” voltage is getting back to the PCM.
Without that signal present the pcm will not activate the ASD relay during startup and the engine subsequently will never start.
Asd relay pin 87 gets power for a couple of seconds then pin 86 gets power on relay. This is with ignition on. I also bench tested relay and check wires from asd relay to pcm. I check wire pin 3 asd relay and wire on pin 12 asd relay output.
I theory yes, but unfortunately a standard multimeter isn’t quick enough to actually see the pulse, if you want to verify an accurate signal you’ll need an O’scope.
You can remove the sensor with the key in the run position and pass a screw driver over it and watch the 5v on your meter if you want to verify that the sensor works.
The ASD relay supplies power to the coil, injectors, and fuel pump, and must be closed during cranking or running. In order for the relay to activate during those two conditions the pcm must receive a valid crank, cam, and ASD sense signal.
That would be the easiest way, you should be able to sort it out pretty quickly with that tool.
So didnt hook up scan tool yet. I just wanted to inspect teeth on the flywheel for the crankcase sensor before i ran the scan tool. I removed the starter for the teeth inspection and broke the bolt head off of the lower starter bolt. So im down right now now till i get the seized bolt out. Going on vaction next week so going to have to take a brake on this no start issue. Thanks for the help and ill be back after the holidays. Happy holidays all and thanks for the help so far.
Nick B
Member
My friend forgot to turn his lights off and his battery died in his 1999 Wrangler. We jumped the jeep but it would only crank and would not start. Battery gauge on the dash showed 13 volts when we turned the ignition on. He ended up being towed and the shop said that multiple fuel injectors had failed. You have spark and air so the only thing missing is fuel. I'm not sure if this is relevant to your issue but I figured I would throw it out there.
Thanks for the advice Nick. Im running out of things to check here. My asd relay is shutting the power off for my ejecters. There are some checks im still working atm.
Ok so ran ran alot of other checks for cpu wiring and sensors. Guessing it may be a bad pcm. So i towed it over to a good shop i know. They came up with the same diagnostic after checking for 2weeks. Put in a new pcm, jeep started but ran rough like before when i first started with issue. My first isssue was run rough wont stay started. So mechanic fix my exhaust and replaced the cats. Jeep runs like new again. Now this post has closer. Thanks all who tried and help respond with some good suggestion on checks to do.
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