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93 Jeep yj 4.0 automatic. Had an intermittent no start issue for a couple months. Sometimes I would turn key and the asd/fuel pump would close and engine would start. Other days I’d turn key and no relays. I tried wiggling some of the usual suspects(crank sensor, battery terminals) but never could nail down a specific culprit. Battery grounds clean, new crank sensor as well as fuel pump none of which had any real effect on the issue. I did notice however as the condition went from intermittent to complete asd circuit failure that the last few times it started, the asd closed very weak. The sound the relay makes as it closed was significantly at a lower volume. To the point where I had to physically touch the relay to feel the “click”. After approximately 5 attempts to start the Jeep after the weak click began, the relay completely failed to operate any longer. I have power to the relay but that’s about the extent of my electrical knowledge. Also the pump works when power is applied directly. Where the Jeep is 30ish miles from my home right now so going there to check one thing at the time is time prohibited. I’m looking for a process of elimination but haven’t found any videos that deal with this issue and the obd1 Jeep system. Any help would be greatly appreciated
I could tell you a whole bunch of things to check with an O-scope, but if you don't have one then it wouldn't do much good.
A volt meter can go a long way too.
Based on your description, it sounds either a failed ASD relay, a bad connection to the coil of the relay or maybe a failed driver circuit that is driving the relay.
You can check coil terminals on the ASD relay for signal. It will need 12v ( most likely ) to power the coil to activate the relay. It will also need a good ground, so check the ground terminal too.
The next thing that it will need is supply voltage to one of the switching terminals (12v most likely ).
If the coil terminals have both power and ground, then the relay should close. You can test to see if it is closed by checking for supply voltage on both of the switching terminals. If you find 12v on only one of them, it's not closed. if you find 12v on both of them, it is closed and your problem is somewhere else ( though maybe not far away... it could be a bad connection or loose/worn wire ).
If it is a bad ASD relay, you can bypass it to get you home. Just take a single strand of copper wire and wrap it around the two switching terminals 3 or 4 times. Make sure you get the right terminals. If you get the wrong terminals you'll be shorting the coil driver signal to ground, which can damage the driver circuit. Bypassing it this way will allow you to plug the relay back to the same socket and limp it home. DON'T leave it like that! That's definitely not safe for long term use. It's just good enough to get you home where you can do a better diagnostic.
If you find that bypassing the ASD does not allow the car to shut off, you'll have to unplug the ASD relay to shut it down ( because you by passed it ).
Last edit: 5 years 7 months ago by hakachukai. Reason: Adding detail
