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Old 11-29-2011, 11:24 AM   #1
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Smile Electronically challenged

Hello folks, I am a new owner of a 1990 Jeep Wrangler 4.2 ltr 6 cyl. Recently I had to change the fuel pump because as it was idling in the drive the fuel was leaking out of the side of the manual fuel pump, and then just shut off
I replaced the fuel pump but the Jeep will not start. I look into the carb and it is getting fuel. I sprayed starter fluid in the carb just to see if I could get it to run, and you guess it, it would not start. I pulled one of the spark plugs to see if I was getting spark…no spark was found.
So being that I am an electronic idiot, I am really lost and I hope someone can help me.
Thanks to Google, because I do not have a manual for this jeep, which I will be getting, I was able to determine at least four things that could be my problem. Ignition switch, ignition module, Coil, and distributor. I don’t have a diagnostic computer checker, so I have to check things manually.
My question is, how do I determine what is casing the jeep to have no spark. I wanted to work my way up from the spark plug, so I took a light tester to the yellow wire going to the coil, and it lit up, so I know we have a flow to the coil. Question is if we have power to the Coil when we crank over the motor, does that mean the ignition switch, and ignition module are working, so the problem has to be at the distributor? Is there a way to determine if the distributor is getting flow from the Coil…..Please help.

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Old 11-29-2011, 12:52 PM   #2
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mrnascar30,

If you are getting spark to your coil and your starter is turning over, then your ignition switch is fine. Are you sure your spark plug wires are plugged all the way in? Mainly I am concerned about the Coil wire going to the distributor.

Electricity flows from the coil, to the distributor cap, to the rotor (underneath the cap) to the spark plug wires. These are the things you need to check (in order) to locate your problem.

If the coil wire checks out fine, I would check the distributor cap and the rotor (located under the distributor cap). You are looking for worn contacts or, more likely, corrosion on those contacts. It is simpler to just replacer the rotor and the distributor cap... it has been a while so I am not sure how much they cost. However, if it is only an issue with corrosion, you can gently sand off the corrosion from the contacts and retry. If that is not the answer, I would suspect the computer. Does your local auto parts place have a coil tester? If not, let me know and I will explain how to test it. It is more than using a "light tester"... but that is a good start!

Also, I read where you have a jeep manual coming in, GREAT!! I joined ALLDATAdiy.com. For $20 a year PER VEHICLE, you get all the manuals and information available for your vehicle, which includes all technical bulletins. You download it anytime. It helps me ESPECIALLY WITH MY WIFE'S GRAND CHEROKEE.

Oh I forgot to ask, are there any engine codes showing? Is the "check engine light" on?

I hope this helps.

Take care,

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Old 11-29-2011, 12:58 PM   #3
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Did you check that all the wires are connected to the coil and distributor? It seems like a simple thing but something may have come loose as you were changing the fuel pump.
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Old 11-29-2011, 01:34 PM   #4
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You said that you have no spark so the test on the coil doesn't mean that it is functioning properly. With a carb'd 4.2 and no spark the usual suspects are a bad coil, then bad Ignition Control Module, given that your rotor and cap is good. Forget about trying to test the ICM. I haven't seen that it could be tested to replicate a real world situation yet. It will cost you about $70. Chances are that's your problem, but at this point also replacing the coil means you're less likely to get stuck because of that. They're not that expensive.
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Old 11-30-2011, 10:24 AM   #5
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1SAS, no engine light coming on showing a problem. How do i test the coil. Do I just uplug the coil wire for the distributor cap and see if I get spark against the metal? I would like to test the coil first, then if that is not that work on the distributor. Beast master, I can't see any wires that were could have come loose. KIK, what is the ICM?
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Old 11-30-2011, 10:25 AM   #6
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And thank you guys, you are least helpful....lots of people I have talk to don't know jeeps.
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Old 11-30-2011, 12:37 PM   #7
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Quote:
Originally Posted by mrnascar30 View Post
1SAS, no engine light coming on showing a problem. How do i test the coil. Do I just uplug the coil wire for the distributor cap and see if I get spark against the metal? I would like to test the coil first, then if that is not that work on the distributor. Beast master, I can't see any wires that were could have come loose. KIK, what is the ICM?
You're not going to get a check engine light for that. My 89 4.2 doesn't have one. You might have a maintenance light on a 90. Anyway, you can try that to see if there is any spark. If there is no spark then I would replace the coil and the ICM. One or both can cause these problems outright or intermittent. The ICM is located under the coolant expansion tank. Just unbolt, unplug and replace it. Chances are alot greater that one or both of these are your problem instead of the distributor.
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Old 11-30-2011, 02:49 PM   #8
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Unless you are the most unlucky person in the world to have some ignition component go out just as you changed the fuel pump, I would suspect that in changing the fuel pump you either broke a wire or inadvertently loosened or disconnected something.....
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Old 11-30-2011, 04:28 PM   #9
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I am going from memory about what coil your jeep has. So here it goes...

TESTING A COIL

(A) Checking Coil's Primary Resistance:

Connect an OHM meter to the two little brass "nipples" on top of the coil. These are the threaded rods with nuts on them. Thin wires connect to them. (Use the "low scale" on the OHM meter.) Coils using ballast resistors or resistance wires should have approximately 1.0 resistance. Coils with internal resistors should have approximately 4.0 resistance. (You should be able to call your local Auto parts store to see which coil your jeep has.) If the resistance is much higher than stated, you should replace the coil. (Generally, all Chrysler products have used ballast resistors in the past.)

(B) Checking Coil's Secondary Resistance:

Connect an ohmmeter across the distributor side of the coil and the coil tower. (The "distributor side" of the coil is the thin wire that connects the distributor to the one of the coil nipples. The "coil tower" is the center part of the coil where the "high lead spark plug cable" connects to the center of the distributor cap.) Read the resistance on the "high scale" of the ohmmeter.
The resistance of a satisfactory coil should be between 4,000-10,000. If the resistance is considerable higher (example: 40,000) replace the coil.

This test is not for "high performance" coils. Only OEM units.

Most of this information came from an old "Chilton's" manual.

I hope this helps.

Take care,
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Old 11-30-2011, 09:11 PM   #10
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Quote:
Originally Posted by Garyk
Unless you are the most unlucky person in the world to have some ignition component go out just as you changed the fuel pump, I would suspect that in changing the fuel pump you either broke a wire or inadvertently loosened or disconnected something.....
That is what I thought, but I can fine no lose or broken wires. Just before the fuel pump issue it shut off on two separate occasions so think the problem was already happening
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Old 11-30-2011, 09:14 PM   #11
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Quote:
Originally Posted by kik

You're not going to get a check engine light for that. My 89 4.2 doesn't have one. You might have a maintenance light on a 90. Anyway, you can try that to see if there is any spark. If there is no spark then I would replace the coil and the ICM. One or both can cause these problems outright or intermittent. The ICM is located under the coolant expansion tank. Just unbolt, unplug and replace it. Chances are alot greater that one or both of these are your problem instead of the distributor.
I think your right on the ice, the coil is brand new. I think i'll just replace both coil and ice, then make sure the rotor in the dist is ok.
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Old 11-30-2011, 09:16 PM   #12
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Quote:
Originally Posted by 1SAS
I am going from memory about what coil your jeep has. So here it goes...

TESTING A COIL

(A) Checking Coil's Primary Resistance:

Connect an OHM meter to the two little brass "nipples" on top of the coil. These are the threaded rods with nuts on them. Thin wires connect to them. (Use the "low scale" on the OHM meter.) Coils using ballast resistors or resistance wires should have approximately 1.0 resistance. Coils with internal resistors should have approximately 4.0 resistance. (You should be able to call your local Auto parts store to see which coil your jeep has.) If the resistance is much higher than stated, you should replace the coil. (Generally, all Chrysler products have used ballast resistors in the past.)

(B) Checking Coil's Secondary Resistance:

Connect an ohmmeter across the distributor side of the coil and the coil tower. (The "distributor side" of the coil is the thin wire that connects the distributor to the one of the coil nipples. The "coil tower" is the center part of the coil where the "high lead spark plug cable" connects to the center of the distributor cap.) Read the resistance on the "high scale" of the ohmmeter.
The resistance of a satisfactory coil should be between 4,000-10,000. If the resistance is considerable higher (example: 40,000) replace the coil.

This test is not for "high performance" coils. Only OEM units.

Most of this information came from an old "Chilton's" manual.

I hope this helps.

Take care,
Cool I will check this. Can I take the coil to the auto parts store to see if it is good
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Old 11-30-2011, 09:18 PM   #13
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Auto parts places used to check coils. I don't know if they do anymore, but a phone call will tell. I hope this is your problem or something simpler.

Take care,
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Old 12-12-2011, 12:17 PM   #14
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So I checked the Coil, and we have good spark, still no spark at the spark plug. I checked the distributor, the rotor and cap look brand new, no problems that I can see there. Trying to understand this, like a fuel sytem you have the tank, fuel pump, filter than carb, would the same apply to the ingnition switch, ICM, Coil, Distributer, spark plug? If the ICM failed, would the coil have no spark? are is that independent of each other. I guess I am trying to determine if it is the distributor, or the ICM. Also, on the Distibutor, what would cause the spark plug to have no spark if the rotor or cap are good?

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