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Old 11-13-2013, 09:39 PM   #1
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Cool Run, Die, Repeat: What's wrong?

I've had my carbureted (Weber double barrel) 1990 YJ 4.2L since late March and have had relatively small problems along the way. As of about a month ago, it was starting up just fine then cutting out without warning. After it dies, it won't start again for anywhere from 10 seconds to 15 minutes. After it starts up again, it idles very rough for around 20 seconds and is fine...unless it happens again - as it often does.

When I start it for the first time in a while (in the morning or on way home), I have usually let it warm up for a minute or two then go on my way. It shows no sign of strain/stress while driving until when it dies. It just shuts off as if the spark is gone, no fuel, that sort of thing. Even though it is a manual transmission, it still rolls without any wheel locking afterward.

As soon as it stops running, the battery voltage registers on the border between OK and red. It does not usually turn over on the first attempt of restarting. This is regardless of radio, lights, heat, etc. When it is cranking, it sounds normal.

When it does start again, the whole thing shakes (sometimes hard, sometimes soft) and the idle hangs around 700-1000 RPM for about 20 seconds or until I apply throttle. At this point, I wait a minute more then start driving. Sometimes that's it, but more often it's the first of 2+ times that it'd happen.

Also, it will sometimes stops on its own if I let it warm up with the choke on or off without touching the gas at all while its running.

This started happening when the temperature started dropping, so I've come up with a few hypotheses:

1) "It needs to warm up for longer because it's carbed, otherwise it won't run well." I tested this and have little to say to support it. I let it idle for a good 15 minutes one time and there was no problem. I've also let it go for 5-10 and it still stopped. That amount of time seems like it would be adequate for everything to be at operating temperature - maybe not.

2)"I never changed the spark plugs/wiring/cap since I bought it because the plugs were in good condition, so something must be quitting in that department." I have nothing supporting or against this, but it seems likely that there is a bad connection somewhere or enough cylinders may not be firing in a row to merit a shutdown while the oil is still cold. Who knows...

3) "It's cold and I've never tested the battery, maybe that's it." Maybe there's a bad connection or it is flawed in some way. Like I wrote before: the meter reads low voltage after the engine shuts off, so that could be something right there. If so, that's a very simple fix.

4) "There are goblins inside the engine f***ing everything up." Highly likely - yet to be disproved.

Recap: This started when the cold started and increased in frequency as it got colder out. It only happens when engine is NOT totally warmed up.

Thoughts? Anyone? Bueller?

Thanks everyone!

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Old 11-13-2013, 10:00 PM   #2
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There are several things that could cause this issues. Since you said it seems like the spark just quits, I think I would have the ignition module tested. An auto parts store will do it for free. Tell them it's for a ford. I had similar problem in a chevy truck. I say start here because it's easy and free.

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Old 11-13-2013, 10:05 PM   #3
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Before you do that check your battery cables. Make sure the ground looks good and has a good connection. I just remembered I had yet another chevy truck that would die and then not turn over at first. I replaced the ground cable and it never did it again.
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Old 11-13-2013, 11:44 PM   #4
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I had something similar on my 95 4.0 . tracked it down the "pigtail" on the coil was loose/broken had to relocate the coil by making a bracket to move it away from the back of the Alt.
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Old 11-14-2013, 10:55 AM   #5
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Thanks for responding so fast fellas!

I checked the battery cables this morning and they were solid. I'll look into the ignition module and pigtail when I get a chance. How expensive do you expect it to be?
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Old 11-14-2013, 05:14 PM   #6
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Pigtail about $5. Module 50-60.
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Old 11-14-2013, 06:02 PM   #7
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One of the wires on my coil came loose, it would stutter and jump, then die. Once it shorted and sounded like an explosion. I redid the connectors on the trai, and it's ok now, but I'm upgrading to the TFI setup this weekend. If you have a YJ, it's probably worth doing. The mc1250 gave me an extra 4 mpg from the carter. I hope the hotter spark helps.
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Old 11-14-2013, 06:05 PM   #8
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Is go for the TFI, it's only $98 on eBay! $140 at Napa, $110 at autozone. TFI ignition upgrade
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Old 11-14-2013, 07:29 PM   #9
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Quote:
Originally Posted by Cseistrup View Post
Is go for the TFI, it's only $98 on eBay! $140 at Napa, $110 at autozone. TFI ignition upgrade
Do this for the ignition control module, cheap but far better replacement, I have this with the TFI Civilian Jeep.Info "Stealth HEI" so I know it works with stock or after market ignitions.
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Build Thread: http://www.wranglerforum.com/f330/fi...ld-385106.html
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Old 11-21-2013, 05:46 PM   #10
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I'm planning on taking care of the problem this weekend and have just been dealing with it until then. However, it has been shutting off way more often than it was before. This is regardless of the temperature too.

Is this an expected result from the faulty ignition module/coil? What is actually going on inside the box if it is the ignition module? I can't find any solid pattern either. Very confused.
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Old 11-21-2013, 07:13 PM   #11
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Quote:
Originally Posted by MikeMikeMikeMike View Post
I'm planning on taking care of the problem this weekend and have just been dealing with it until then. However, it has been shutting off way more often than it was before. This is regardless of the temperature too.

Is this an expected result from the faulty ignition module/coil? What is actually going on inside the box if it is the ignition module? I can't find any solid pattern either. Very confused.
It just stops receiving and sending out voltage to the distributor and ignition coil check out my link from a few posts up if you want to try a cheaper replacement.
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Build Thread: http://www.wranglerforum.com/f330/fi...ld-385106.html
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Old 11-25-2013, 10:30 PM   #12
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I've shared the same issue for years.
1988 YJ , HEI upgrade, rest is stock .
Replaced : ICM several times, new plugs, coil, distrib pickup coil,redid connections primary at coil, dielectric grease across terminals.
symptoms= cruise at 30mph--> sudden cutout ignition. tach drops to zero.
This issue plagues many folks on YJ forums. I lean towards the MCU behind glovebox. I replaced mine 6 years ago for a different reason. Tried to do Nutter MCU bypass ;Jeep sounded like it would explode/ back fired /rough. Undid the modification .
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Old 11-27-2013, 05:20 PM   #13
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Believe it or not, I've still managed to not fix it yet haha.

So, it looks like the best route to follow is obviously the ignition system. TFI/HEI hybrid mod and MCU tinkering may have the best results. I'd also have to guess it'd take the better part of a day to do all of that.

Since my last posting here, I have been running seafoam and it seems like I have more power/smoother with it, thoihh that may just be the placebo effect kicking in. I was hoping that $10 of stuff dumped into my jeep would magically fix everything. (not quite)

Also, I'm going to replace the battery since it has given me problems in the past and am unsire how it will do with subfreezing temps. Any chance this solves the problem?

Has anyone else had MCU problems or done anything to it?
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Old 11-27-2013, 06:12 PM   #14
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Change out the cps (crank positioning sensor) that was my problem
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Old 12-03-2013, 06:00 PM   #15
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here in wv I am having the same problem with my 1987 YJ hoping to find a cure looking at the pickup coil in the distributer hope this takes care fo it.
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Old 12-08-2013, 04:40 PM   #16
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I found out what it isn't. It's not:
-battery
-loose cables
-coil
-distributer
-spark plug wires
-spark plugs
-gas
-fuel lines
-fuel pump
-ignition module (Advanced auto parts says it's good. reliable source?)

Symptoms:
-sudden shut off (no sputtering)
-occurs more often when cold (weather/engine)
-takes a little while to start again

Suggestions:
-MCU
-CPS
-ICM

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Old 12-08-2013, 07:33 PM   #17
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I found a great diagram of the ignition system if anyone wants to use it for anything.
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Old 02-23-2014, 06:51 PM   #18
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For anyone reading this, it was the Ignition Control Module that went bad. I replaced it with an HEI ICM from a '78 Impala and stuck a heat sink to the back of it. It's still good.

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