YJ runs fine for 10-20 miles, then hesitates, sputters, and stalls

Zimic

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Jun 24, 2022
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Florida
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Hello,

I'm new here. I bought a 89 YJ 4.2l a few years ago. The body and chassis are in great shape (California jeep). the engine on the other hand needed work. I was able to get it running and driving good, until about a year ago. It has progressively gotten worse since then, on to the issue.

When it started happening it took a lot longer before it was a problem, now 10 to 20 miles is all it takes sometimes less. It starts and runs fine for the first 10 to 20 miles, then it hesitates, sputters, and will stall at idle. I can restart it and it will sit and idle fine, give it gas and it sputters or stalls. if I push it to far, I have to let it cool for 30 minutes to an hour before it will start again. it acts like something is getting hot and causing a problem.

What I have done:
replaced Distributor today
replaced cap & rotor, plugs, wires, coil (twice since I bought it, less than 10k miles)
replaced all fuel filters including in tank filter
removed the Howell EFI system I had installed, replaced with weber carburetor and problem still there, reinstalled EFI
replaced fuel pump for EFI
Added fuel pressure gauge to ensure proper pressure
I'm sure there is more I have left out.


I know it can't be fuel management, being I have the problem on EFI system and a carburetor with 2 different fuel pumps.

I finally decided to take it to a mechanic and first they fixed the rough idle issue (because I did a sloppy job putting the throttle body back on) and never look at the issue I brought it in for. After being at the shop for 2 months and they still hadn't looked at it, I brought it home and I'm going to try to fix it myself, again.

Any help and suggestions are greatly appreciated. I hope to get it fixed so I can drive it down to the local beach, but currently it may be come and artificial reef or meet the crusher.
 
Do you have the factory electronic ignition still? Have you tried replacing the ignition control module? Are you sure its not vapor locking or something like the tank venting is plugged off starving it for fuel. When it dies and wont start do you get a significant hissing if you were to remove the gas cap. When it dies are you still getting spark?
 
Do you have the factory electronic ignition still? Have you tried replacing the ignition control module? Are you sure its not vapor locking or something like the tank venting is plugged off starving it for fuel. When it dies and wont start do you get a significant hissing if you were to remove the gas cap. When it dies are you still getting spark?

I checked the tank vent when I had it out replacing the filter. Also, fuel seems to be flowing since when I pinch the return line while it's running horribly the pressure goes up. So, I'm pretty sure it's not vapor locking.

I located what I believe is the stock ignition module under the coolant reservoir. I haven't messed with it before, and it looks original. doing research on it now.

Thanks for your help.
 
okay, after researching ICMs I have more questions than answers. I read a lot about the nutter bypass, which I did not do when I removed the old bbd computer and installed the Howell FI kit. It ran good for a year or two after that. I didn't do it since none of the instructions (Howell's or multiple others I found online from people who had done it) said the nutter bypass was needed.


So now I'm going to do the nutter bypass and inspect the ICM.
 
okay, after researching ICMs I have more questions than answers. I read a lot about the nutter bypass, which I did not do when I removed the old bbd computer and installed the Howell FI kit. It ran good for a year or two after that. I didn't do it since none of the instructions (Howell's or multiple others I found online from people who had done it) said the nutter bypass was needed.


So now I'm going to do the nutter bypass and inspect the ICM.


Update. pulled the ICM to inspect and do the Nutter bypass. that's when I found that the Howell FI is wired into the ICM. I forgot that as part of the FI install, you have to remove one pin and replace it with a wire from the Howell harness, which would be why there is no need for the nutter bypass. it was replacing the purple wire by the way.

so, the ICM looks okay but I will head down to my local parts store today and get a new one, hopefully this solves it, but I'm not placing any bets.
 
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I had Howell on my 86 CJ and cant recall how it wired in, but you can get the manual on line if needed to verify whats been done to it with that install. Basically a bunch of Chevy 4.3 parts. Those modules do go bad like any other electronic part. Hopefully thats the issue and replacing it does the trick. Also i do recall Howell uses a frame mounted FI pressue fuel pump. Now that you back to the weber are you using a engine drive stocker or?? IIRC much of the "nutter bypass" eliminates the stock carbs variable main jet operations. I believe they operate kinda like Fords Variable venturi carbs. Pre FI emissions nightmare parts.
 
Sorry for the delay, busy weekend.

Replaced the ICM and the problem is not fixed. I have no other ideas, so it sits for now.

EDIT to clarify:

I installed the Howell FI. I have all manuals and guides. It ran good when I installed it and for about a year or so after. thinking it might have something to do with it I removed the FI replaced it with a Weber carb and replaced the fuel pump with a smaller one and a regulator ti ensure proper pressure to the carb and the problem continued, so after multiple test runs, I reinstalled the Howell FI.

The problem:

It runs great when you first start it idles smooth drives good everything. After 20-30 miles then the issue starts, it will start missing, sputter, if i stop it will hesitate sputter and even stall when i start moving again. the longer i drive it the worse it gets. Saturday i pushed it way to far and it stalled and wouldn't restart. luckily, I was by a buddy's house and only 2 miles from home, so he towed me back. I tried stating it about 2 hours later and it fired up.
 
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So when it craps out are you checking to see if you have lost spark or fuel pressure. What kind of coil are you using? I read several posts about accel,IIRC, coils crapping out in short order. Wiring in good shape? heat makes resistance makes for lost connections. Gotta be something overlooked as you have damn near replaced the entire electrical and fuel systems.
 
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So when it craps out are you checking to see if you have lost spark or fuel pressure. What kind of coil are you using? I read several posts about accel,IIRC, coils crapping out in short order. Wiring in good shape? heat makes resistance makes for lost connections. Gotta be something overlooked as you have damn near replaced the entire electrical and fuel systems.

So I had an Accel coil and replaced it (not sure brand) but unless it was bad out of the box it didn't change the problem. fuel pressure is always fine, i have added a gauge to the line to monitor it. I haven't checked spark while its acting up. All the plug wires are new since the problem started. I've checked the harness where I can, but not every bit of conductor. when i have time I will check more of the wiring harness for any problems.

Thanks for insight
 
Pull the plugs and examine, perhaps a head gasket or valves problem. Might do a compression check with engine warm.

have changed the plugs once and checked them a few times, they look fine everytime. Did a compression check cold and hot, pressures were the same. If i remember correctly, i had 3 that matched two 10 psi lower and one 20 psi lower. Removed the valve cover to check, did a visual and poked around everything seemed fine.
 
I would do what Gilaguy23 said before going any further. Check for spark after it shuts down and won’t restart. That way you can rule out the ignition system. Today just installing new parts means nothing. I have personally known of many electrical parts that have been brand spanking new and were junk. Remember, practically all electrical parts these days comes from china. A friend took 3 new coils back to Advance before getting a working one, sad but true.
 
That was my point with the coils. Somebody here went thru 3 and finally went back to the OEM one after they kept crapping out. I think 89 would be able to store codes on the OBD1 system. If so you should be able to pull them up and see if that helps pin point the issue. Dont boat anchor the thing, looks far to nice.
 
I have 30 years as in the electrical field, I've seen plenty of bad parts straight out of the box, so I understand it. When I get time, I will bench test the coil and do some spark checks.

It has been nothing but yard art for over a year, I'm thinking it might make a nifty section of artificial reef in the gulf.
 
Hi
I have the same exact problem and like you I have replaced a ton of stuff including the ICM and replaced the after market coil with a factory type one (Standard Ignition). I even took the Webber carb of and rebuilt it. The challenge is, like yours it dies but starts up and idles. Therefore, it is getting spark and fuel, and there is the little issue of being on the side of the road with people flying by you. I keep going back and forth on electrical and fuel. The funny thing is it was running fine (I bought it a year ago) then this problem started and every time I replace something I check it and find something wrong with it. For example when I replaced the ICM i drilled out the rivets (was an after market one) and found water and rust in it. So of course I gave myself a high five thinking I got it now, but same issue. Any other thoughts from the group. Oh it has a 4.2 w/5 speed trans.
Thanks
Ralph
 
Hi
I have the same exact problem and like you I have replaced a ton of stuff including the ICM and replaced the after market coil with a factory type one (Standard Ignition). I even took the Webber carb of and rebuilt it. The challenge is, like yours it dies but starts up and idles. Therefore, it is getting spark and fuel, and there is the little issue of being on the side of the road with people flying by you. I keep going back and forth on electrical and fuel. The funny thing is it was running fine (I bought it a year ago) then this problem started and every time I replace something I check it and find something wrong with it. For example when I replaced the ICM i drilled out the rivets (was an after market one) and found water and rust in it. So of course I gave myself a high five thinking I got it now, but same issue. Any other thoughts from the group. Oh it has a 4.2 w/5 speed trans.
Thanks
Ralph
When this thing shuts down and leaves you sitting, have you checked to see ”at that time when it is not running” if it has spark coming from the plugs?
 
Hi
I have the same exact problem and like you I have replaced a ton of stuff including the ICM and replaced the after market coil with a factory type one (Standard Ignition). I even took the Webber carb of and rebuilt it. The challenge is, like yours it dies but starts up and idles. Therefore, it is getting spark and fuel, and there is the little issue of being on the side of the road with people flying by you. I keep going back and forth on electrical and fuel. The funny thing is it was running fine (I bought it a year ago) then this problem started and every time I replace something I check it and find something wrong with it. For example when I replaced the ICM i drilled out the rivets (was an after market one) and found water and rust in it. So of course I gave myself a high five thinking I got it now, but same issue. Any other thoughts from the group. Oh it has a 4.2 w/5 speed trans.
Thanks
Ralph
Hey Ralph,

Sorry to hear your having the same pain in the A as me. Although it does make me feel more sane that I'm not the only one with this problem. I haven't been able to do more troubleshooting on mine for the last week but will try to get on it soon. I had some of the same issue I would pull off a part and see corrosion or something and think I found it but nope. I do have a very extensive set of back up parts unfortunately.
If I figure anything out, I will post it here. I would appreciate you doing the same. Maybe one of us will have some good luck soon.

Good Luck