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Chris
Chris, Shop Foreman
Category: Jeep
Satisfied Customers: 9956
Experience:  Jeep and ASE Certified Master Tech
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92 jeep no spark, new coil, cam sensor, ignition switch, and

Customer Question

92 jeep no spark, new coil, cam sensor, ignition switch, and cps help?
Submitted: 5 years ago.
Category: Jeep
Expert:  Chris replied 5 years ago.

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.

 

Chris

Customer: replied 5 years ago.
Yes, thats the C.P.S. as mentioned in the heading...
Expert:  Chris replied 5 years ago.

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?

 

Chris

Customer: replied 5 years ago.
Yes I can hear the fuel pump, there is a constant supply to the fuel rail and it would appear to be getting fuel (haven't checked the filter yet). This is a jeep I bought as is last week and thought it would be just a quick crank sensor replacement, it ran fine for the previous owner but just stopped one day. After replacing that (Wich he had already done) I started checking for my fuel, air, spark. Thats when I noticed no coil spark. The coil has been replaced as well as the o2 sens @the exhaust. and the ignition switch. all but the computer itself. I do notice when turning the key to start the temp gauge goes nuts....oh and yes the engine light is on.
Expert:  Chris replied 5 years ago.

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.

 

Chris

Customer: replied 5 years ago.
nothing @all......
Expert:  Chris replied 5 years ago.

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.

 

Chris

Customer: replied 5 years ago.
Just did that, plus cleaned all the rust off of my tester, now I have a 2 second light when I turn the key on.
Customer: replied 5 years ago.
plus all the fuses seem fine.....
Expert:  Chris replied 5 years ago.

Ok,

Since you swapped the relay do you now have a spark when cranking?

 

Chris

Customer: replied 5 years ago.
When I turn the key on the fuel pump and the coil run for 2 sec. then they both shut off, is there some thing I can do to test the computer to see if it works properly, or is there something i can test or look for that might be telling the computer to cut power to the coil and pump???????
Customer: replied 5 years ago.
Hello?......Marco?............Pollo?........Is there any body out there?
Expert:  Chris replied 5 years ago.

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.

 

Chris

Customer: replied 5 years ago.
More input, need more input.....Have volt meter, light bulbs, ninevolt batteries, wire the works.....Just not a mechanic shop w/ its very own scanning center...Please let me know what I can test and Where....
Expert:  Chris replied 5 years ago.

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.

 

Chris

Customer: replied 5 years ago.
hayes manuel is in my hands, looking @ wiring now......
Expert:  Chris replied 5 years ago.

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.

 

Chris

Customer: replied 5 years ago.
Both read 6.94...
Expert:  Chris replied 5 years ago.

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?

 

 

Customer: replied 5 years ago.
Well unfortunatly Im not a mechanic or an electrician, hence the reason im @ this site, but with the multi meter im using, when I plug it into the harness for both components thats the reading that was consistant...........Maybe Im doing it wrong, can you be more specific where the "SRVT" is @? I do know that both those components are new. And have power. What else can I do or check.................Soooo frustrating...............
Expert:  Chris replied 5 years ago.

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?

 

Chris

Customer: replied 5 years ago.
92 jeep cherokee sport, 2door, hard top, four wheel drive, 4.0 inline six, white, half tank gas, 32 psi in all 4 tires. im in Hawaii with a local time of just after noons, and I wont be avaliable for comment till after 6:00 my time on monday.....Dont they have wiring diagrams on this magic picture box? (like www.pdfoo.com or www.wire diagram.com/jeep? or couldn" you Just google it?????)
Expert:  Chris replied 5 years ago.

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.

 

 

Chris

Customer: replied 5 years ago.
Thank you very much for your help, I do appreciate the info.....I dont have much time left in my weekend. Any info, clues, hints, rumors, or legends of what could be styfeling my spark would be great. Thank you again.
Expert:  Chris replied 5 years ago.

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.

 

Mahalo,

 

Chris

Customer: replied 5 years ago.
All parts were purchased @ carquest, I have two new ones( one the previous owner tried and one I treid) how would I test it??? Oh and no the tach does not move...... What next?????
Expert:  Chris replied 5 years ago.

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.

 

Chris

Customer: replied 5 years ago.
Yes it works....What does thiis mean? as far as the not moving tach thery, why does my 96 jeep tach stay still while cranking when you say it shouldn't??? They are both Identical in symptoms when cranking (except for the obvious 92 doesn't get spark...).
So I would like some more diagnostic prociedures if you have any....
Thankyou for your time......
Expert:  Chris replied 5 years ago.

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,

 

Chris

Customer: replied 5 years ago.
Is there any thing else at all I can check, poke, plug, shake, beat, or pry on before I start dropping any more Benjamin Franklins into this?...... I hate to sound skeptical but I've already got more new plastic parts then Cher does, ( at what feels like the same prices). Any other diagnostic clues would sure be swell....
Thank you.
Expert:  Chris replied 5 years ago.

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.

 

Chris

Customer: replied 5 years ago.
sweet. Thankyou for your information Chris. I'm gonna kick it with my wife and son for the day but i'll try that when I can. What say shall I do next if the screwdriver wand works and I get a signal? Thanx again for your time, talk to you soon.
Expert:  Chris replied 5 years ago.

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,

 

Chris

Customer: replied 5 years ago.
Got a signal. But still for some reason the coil and fuel pump keep getting shut off after about two seconds, wich leads me to believe that something isn't regestering, or working long enough to even get cranking spark.......what to do......
Expert:  Chris replied 5 years ago.
That may be a normal response from the PCM when doing that last test. Is there any way you can get hold of a scan tool?

Chris
Customer: replied 5 years ago.
Sounds like I'm on a mission........ . . . .
Expert:  Chris replied 5 years ago.

Any luck getting a scan tool for your Jeep?

 

Chris

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