1995 Jeep YJ Dies and Won't Start

[Marv46534]

I have a 1995 Jeep Wrangler YJ with MPFI.

The problem is it will instantly die on the road, no missing or sputtering, then won't start. Cranks fine. Does start when it is good and ready.

I thought it was happening when it had been running and was really warm. It would start after maybe 30 minutes. But yesterday it wouldn't start the next morning. After I towed it home, it started right up.

This has happened 4 or 5 times in the last 2 years. Always in the worst possible place. Otherwise it runs great. Here's what I know.

Trading fuel pump relay didn't help.
Jumpered contacts on relay socket and could hear fuel pump working.
Checked for spark and was good.
Checked for fuel pressure at tire valve like cap on fuel injector. Seemed ok without a gauge.

I did have a Datsun pickup years ago that would do the same thing. Turned out to be a small piece of foil floating around in the fuel tank. It had an access cover in the truck bed, and I could see inside. I would hate to have to take my Jeep's tank all the way off.

My question is could low pressure due to a bad fuel pump cause it to just instantly die? It seems like that would cause sputtering and bucking first. This sounds like ignition, but I don't think so.

 

[Saddle Tramp]

As always with electrical, check your grounds to make sure they aren’t loose or corroded.

 

[superj]

dumb idea, thinking of something else

 

[jfrabat]

I would guess a lose connector is your issue. Possible even the battery connector. but since all the other electrical components seem to be working properly (you mentioned spark, fuel pump, etc.), it could also be the ECU, I guess... I would start by checking connections, though (that's free, after all!).

 

[Marv46534]

It looks like I've fixed my problem. As it turned out, sometimes the fuel pump wasn't working. Sometimes the ignition wasn't firing. The key was the check engine light wasn't coming on when it wouldn't start. I found a thread on another forum (jeepforum) that hit the nail on the head. My PCM (computer module) wasn't working right.

jeepz won't let me paste a link here (haven't been a member long enough), but you should be able to find the thread by searching jeepforum for "91+ Hard or No Start/Long cranks in the cold explained" for the cause and "Crash Course In Brain Surgery Replacing Capacitors On ECU" for the fix.

It was a real pain working on the circuit board, and I've been an electronics technician for 30 years. It really isn't designed to be taken apart and fixed. It's encased in some kind of rubber compound to protect it from the elements. So, it's a throwaway. Trouble is a new one costs $650 or more. Used ones are hard to find, because there are so many types. There were several types for just my 1995 YJ. It has to match the engine, transmission, etc. I think PCM's after 96 or 97 are programmable, so the same one can be used for many models.

Anyway, I followed the instructions. Bought 3 capacitors at Radio Shack part # 272-1029 for $1.29 each. These are 220uf 35wvdc capacitors. Took about an hour to replace them once I had the module on my work bench. I was doubtful this would work. But much to my surprise, my YJ fired right up and hasn't failed since.

2 of the capacitors I took out were swollen and leaking. Electrolytic capacitors do have a life in hours. Someone on the above thread said this particular one is only designed to last 10 years. I'm not sure the Radio Shack ones will last that long, but the price is right.

BTW, I used a silicon dielectric compound to seal the openings I made on the circuit board. It never hardens and is designed for electrical connections.

I have a 1995 Jeep Wrangler YJ with MPFI.

The problem is it will instantly die on the road, no missing or sputtering, then won't start. Cranks fine. Does start when it is good and ready.

I thought it was happening when it had been running and was really warm. It would start after maybe 30 minutes. But yesterday it wouldn't start the next morning. After I towed it home, it started right up.

This has happened 4 or 5 times in the last 2 years. Always in the worst possible place. Otherwise it runs great. Here's what I know.

Trading fuel pump relay didn't help.
Jumpered contacts on relay socket and could hear fuel pump working.
Checked for spark and was good.
Checked for fuel pressure at tire valve like cap on fuel injector. Seemed ok without a gauge.

I did have a Datsun pickup years ago that would do the same thing. Turned out to be a small piece of foil floating around in the fuel tank. It had an access cover in the truck bed, and I could see inside. I would hate to have to take my Jeep's tank all the way off.

My question is could low pressure due to a bad fuel pump cause it to just instantly die? It seems like that would cause sputtering and bucking first. This sounds like ignition, but I don't think so.

 

[SteelHeadz]

That's good to know.