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post #1 of (permalink) Old 05-08-2007, 12:20 PM
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Engine shuts off

Hi to all and thanks in advance for any possible help.

1985 Jeep CJ7 4.2L 6

My problem originally was the exhaust manifold was glowing and the idling seemed high, but engine would stall if idle was lowered. I was able to find some insight by finding Off-Road.com, but since I am a newbie dont really get all of it.
Reason being due to no understanding some of the verbage. Does ECM stands for the computer or ECU, what do the abreviations stand for I have ideas but they dont seem to match. Here is the original help tread that suggest what I am going through.


1989 YJ 4 cylinder 192K miles, 30K on ‘rebuild’ I added: 2” body lift 32x11.5 tires (good-by 5th gear!) When I recently purchased the vehicle it would not pass our state’s emission test. After replacing the EGR (physically damaged) and having an exhaust shop install a new catalytic converter, muffler, and pipe from the header pipe back, it passed the test. I thought things were going pretty well at this point. After about 2000 miles of mostly highway driving, I noticed some new exhaust noise and discovered that the muffler was cracked and discolored. The grease was also being slung from the adjacent u-joint. Things appeared to be heating up. The muffler shop warranty’d the muffler and I was back on the road. After another 1500 miles the same thing happened. Now the shop is claiming that my engine is running too rich, and that un-burned fuel is reaching the cat where it is igniting, and will have to be repaired prior to their next attempt (of which I will have to pay half of). They recommended a new O2 sensor, which I promptly installed. I failed to measure cat temperature prior to this replacement, but it now hits the mid to high 700 F (just behind the cat) when subjected to 15 miles of up hill highway driving. The muffler shop claims that this is excessive, and they don’t want to replace until I can ‘prove’ that the car is not coding, and is running cooler at the cat. The local Chrysler Dealer service rep said this older model does not store codes for retrieval, and that cat temperatures could run as high as 800F normally. The muffler shop disagrees; they feel that temps should not exceed 600 F. After purchasing a (Chrysler) manual, I’ve begun the testing procedures for the emission sensors (MAP, MAT, EGR/evap canister purge solenoid, TPS, WOT, etc.). So far I’ve only found one fault in the ECU from MAP sensor diagnostics: open circuit between terminals 2 & 17. The manual recommends replacing the ECU if the ground connection is solid. I’m trying to pry the $100 out of my wallet, but would like to be more assured that this is the problem. Is this a common failure? Is it true that I should not need to flash the memory for this older model? I also made a slight adjustment in the TPS to bring the voltage ratio up to the recommended range 0.925-0.935 from its pre-adjustment state of 0.89. I believe that the temp is still upwards of 600 F (my borrowed infrared thermometer maxes out in the high 500’s). Do you know of a document that states normal catalytic converter temps for this vehicle? Any thoughts, advice appreciated,


Hi Lowell, Before you go any further, refurbish the grounds: · Battery to engine · Engine to frame · Frame to tub Also at night look at the Converter/downpipe and exhaust manifold after the Jeep's been run a while. Are they glowing a dull red? LEVE


The reply giving to this post at the end asking if the manifold is glowing and I do have that problem. But now as of a week now the engine will not stay running. I have change the fuel filter it was a little clogged but the problem still the same.

I have no idea if I post correctly here and hope didnt put to much. I have never had a Jeep got it and love em. Just would like to have it back to the norm
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post #2 of (permalink) Old 05-08-2007, 05:03 PM
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Hi Troc...welcome to the board.

First off, ECM = Electronic Control Module, ECU is Electronic Control Unit...basically the same thing. (more on this later)

The problems you are noting are consistent with a very lean air/fuel mixture...
The most common problem is vacuum leaks....one of the reasons for the high idle....This is a common problem on the 82-86 years.......

There are several causes for the vacuum leaks...I'll try to list most of them...chances are you have several leaks..some worse than others.

1. Intake - The intake and exhaust manifold share the same bolts...they come loose all the time. If you are getting a 'ticking' sound from that part of the engine...you have some loose bolts. Tighten up those bolts...you may have to replace the gasket.

2. PCV Solenoid - There is a solenoid between the PCV and intake. Below a certain RPM this solenoid energizes and blocks the PCV for better manifold vacuum. If the solenoid is not working it can be either a bad solenoid or on of the diodes in a diode pak on the firewall. To see if the solenoid is working, pinch the hose with a pair of pliers to see if the RPM's drop.

3. Cracked or misrouted vacuum lines. Inspect all the vac lines for cracks and leaks.

4. Bad Brake Booster - Pinch the line going to the brake booster. If the RPM's drop, you have a leaky brake booster...which will also explain why your brakes are hard.....

5. Charcoal Canister - That black cylinder on your drivers side fender well is a charcoal canister that sucks up gas vapors and then sends them to the engine to be burned up. Hurts nothing...helps a lot. If the control valve on it is bad, it could be sucking all the time. The engine should only be able to draw gases from it when the RPM's are up high enough and the engine temp is right.

As you may have figured out, pinching a vacuum line is a good way to see if that line is letting a lot of air in. But just because the RPM's drop, it does not mean that it is a problem...some lines are supposed to such air.

If you don't have a vacuum gauge, I would suggest getting one. It's a cheap useful tool.

Now...ECM or ECU. You have a computer in the jeep...see the big wire bundle going through the firewall just to the left of the battery? There is a computer on the other side. It controls the carb and ignition timing (to some extent). Down on the drivers side inside fender well is another module. That is your Duraspark module (Ford design). It controls the spark (with minor input from the computer). If you are running at all, the Duraspark module is ok. The computer will not cause vacuum leaks or a real high idle.....don't worry about them.

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Last edited by JeepDawg; 05-08-2007 at 05:10 PM.
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post #3 of (permalink) Old 05-08-2007, 06:35 PM
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Chances are John nailed it. It has been so very long, but I remember all of that on my '85 until I went fuel injection, what a great thing (But expensive and a good amount of work). How long have you owned the Jeep, and how long has this been happening? If you respond "not long" and "since/soon after owning the Jeep" I would recommend replacing all the vacuum lines. Just go down to a local parts store and get 4' of each (yes you will need them again) and replace them one at a time, believe me, they get confusing !

When you figure this one out, best to ground your old '85. Get some of these, and attach to the block to the frame, block to the fenders, block to the front clip and frame to the cab. I am sure Leve will give you some more ) You can get these at most auto parts or home depot.

1985 CJ7 T.H.O.R

"He brought me up out of the pit of destruction, out of the miry clay, And He set my feet upon a rock making my footsteps firm."
-Psalm 40:2
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post #4 of (permalink) Old 05-08-2007, 09:18 PM
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It's also likely that if the manifold is glowing, the cat is now plugged w/raw unburned fuel. The backpressure builds up and halts the engine.
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post #5 of (permalink) Old 05-09-2007, 03:08 AM
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Thanks alot guys!!!!!

First of all man this forum is great. So many helping one stumbling guy. You guys are great. A lot of info to divulge so will read over and try these tips on the weekend.

I also notice while drive it today it lunges as if its not getting fuel and seems to be missing.

As to the vaccuum lines only 2 years old had them completely replaced but will do all that was suggested.

The cat is also about 2 years old replaced it when manifold was glowing before. After replacing the glow went away but only months later returned. At first thought this was ok since replaced the cat, but then I read the question here in the forum and discovered I have a problem.

thanks again guys, just receiving your replies got me excited. lol yes I have a life but I love this jeep living in Cali is great to have and fun, really would like it back to norm
post #6 of (permalink) Old 05-09-2007, 02:27 PM
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Get some carb cleaner and lightly spray around the base of the carb at idle, if the rpm's change, you need a new manifold gasket.

1985 CJ7 T.H.O.R

"He brought me up out of the pit of destruction, out of the miry clay, And He set my feet upon a rock making my footsteps firm."
-Psalm 40:2
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post #7 of (permalink) Old 05-10-2007, 02:25 AM
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Much Appreciated

Thanks for all the support and help will try those suggestions
post #8 of (permalink) Old 11-17-2007, 03:41 PM
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Thank God for the site and more help needed

Thanks guy for all the help previously given you guys nailed it. Have been away for awhile so didnt get to do alot of work on it as I wanted but back now.

My question now is after taking all that great insite in everything you guys said was wrong or the problem was. So I stripped it down to the block. While I was checking the freeze plugs since seems like the original after cleaning I notice one was leaking. I want to change to brass is this a good Idea? If so my next question is how many plugs are on the block because I didnt remove the engine just too off the exhaust manifold. I can see from facing the front of the engine right side 3 freeze plugs and two smaller one seems rusty but didnt want to touch them too much until I was sure what they are.

So what I am asking you pros are how many plugs are there and what are the 2 smaller one.

Thanks guys love the site
post #9 of (permalink) Old 11-17-2007, 06:22 PM
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The six-cylinder block has four 2" plugs - three on the left side and one in the rear. The head has three 7/8" plugs on the left side and one 2" plug in the rear. I don't know what the smaller ones are unless you're looking at the head and missing one.

My advice is to replace all of them you can get to. It's cheap insurance.

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Last edited by Jim_Lou; 11-17-2007 at 06:22 PM. Reason: Spelling
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post #10 of (permalink) Old 11-19-2007, 03:03 PM
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Thanks alot with my luck the one in the back that hard to get to will be bad also. A lot of good info on the site love all the support.
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