Have Jeep Questions? Ask a Jeep Repair Expert for Answers
Hello and welcome to just answer Jeep. Have you changed the crankshaft position sensor? This is the most common cause of a no spark on these vehicles.
Ok, I am sorry I guess I missed that. Lets start diagnosing this. First of all, when you turn on the ignition, do you hear the fuel pump come on for about 2 seconds and then go off? And does the check engine light come on after turning on the ignition?
Ok, good. If you can get a test light (12 volt) disconnect the coil wire 2 way connector, and probe both of the wires. One of those wires should show voltage for about 2 seconds after turning on the ignition. (have some one in the vehicle turn on the ignition while you check this). Let me know what you find.
Ok, that is a problem. The ASD relay supplies voltage to the coil's power circuit. Try this next: Swap out the ASD relay (in the under hood fuse/relay box) with another relay like the horn, or ac clutch relay and then do that test again. Also, check all of the fuses in that box with your test light. Let me know what you find.
Since you swapped the relay do you now have a spark when cranking?
Well here is how it works. When you first turn on the ignition, the PCM (engine computer) energizes the fuel and ASD relays for a couple of seconds and then turns them off until it sees a cam and crank signal, then turns them on again. You have proven that the PCM is capable of turning on the relays so then the next thing we need to check is whether or not the PCM is getting the cam and crank signals. The best way to check this is through the use of a scan tool. I recommend trying to do that next. If you do not have access to a scan tool, then check and see if your auto parts store will rent/loan you one. If not, then we will have to do some individual circuit tests on the cam and crank sensors using a digital volt meter.
Ok, the only problem I have at the moment is my on line wiring diagrams only go back to 1996 Jeeps. I have them in book form at my shop, but will not be able to access them until Monday. Do you have a diagram for this vehicle? If so I can probably help you.
Ok let's start at the crank sensor. Disconnet the connector and measure voltage at the wiring harness "sensor reference voltage terminal" With the key on there should be 5 or 8 volts on this terminal, and then the "signal wire" should have 5 volts. Do this same test at the cam sensor. Let me know what you find.
That does not seem right. So you are saying that the reference and signal circuits both read 6.94 volts on the crank and cam sensor connectors?
Well, at this point I would really like to have the diagram for your Jeep here so I can look at it and tell you what color the wires are that I want you to test. If you can wait until Monday, I can do that for you. By the way, I know that we are working on a 1992 Jeep, but what model and engine?
I have access to a Chrysler data base that I use. I have tried other online sites but they usually make you pay for the use of them. Let me look around and see if I can find any diagrams that will help us.
No problem. I have been looking for diagrams but have come up with nothing yet. I was thinking about one thing you can check, and that is when you are cranking, does the tachometer needle move a little bit? If it does not, then that is confirming that there is no am or crank signal getting to the PCM. Another thing is this. I have seen many crappy after market sensors out there. If the crank sensor you installed is not a Mopar one, keep in mind that you may have a bad one. If I come up with any more ideas I will let you know.
There really is no way to test the sensor itself, but let's try this: Disconnect the crank sensor, and get a paper clip. then touch the signal terminal of the harness connector to the ground terminal of the connector (ground will probably be a black wire with maybe a blue tracer). Make and break this connection a few times. If the wiring and PCM are ok, then the fuel pump and ASD relay should click on. Let me know if this works.
The '92 and '96 have different type PCM's. The main thing is you have verified that the wiring and PCM on the '92 are ok, and that you may still have a bad crank sensor. I would really like you to try a Mopar sensor if you can,
Try this next. Remove the crank sensor, plug it into the harness, turn on the ignition and then take a large screwdriver and pass it back and forth across the face of the sensor. If the sensor is good, your PCM should see a signal and turn on the relays.
Well if the screwdriver test gives you a signal, then there is ether a problem with the sensor not sitting close enough to the flexplate/tone wheel, or a problem with the flexplate itself (cracked,bent, etc.).
Have fun with your wife and son today, and I will talk to you later,
Any luck getting a scan tool for your Jeep?