4.0 cuts off............. need help

PUNK

Active Member
Joined
Jan 11, 2006
Location
Elkin
I have a buggy with a 4.0 jeep engine in it. After its been running for a little while, it just sputters and cuts off. It will fire back immediately, but will do it again shortly after that. It sounds like it's running out of gas.
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how close are the fuel lines routed to the radiator hoses/tubes/whatever? I wonder if it could be vapor locking? I didnt think about this until you said it sounds like I'm running out of fuel...

edit. just realized how unlikely that is with a fuel injected engine, unless the pump has been relocated.
 
The fuel filter/strainer in the tank could be clogging with garbage. When it shuts down it stops pulling fuel the garbage drops away and it will start up again for a while. This is what happened to my ZJ a few years ago.
 
It has a fuel cell, and an inline pump and filter. It ran fine for years, and just dcided to start doing this one day.
 
Does the cell have foam in it? Mine started that and the foam was breaking down and clogging the prefilter
 
Its gravity fed from the bottom. I pulled the old foam out until i can replace it. Next thing I'm gonna try is to put a few wooden clothes pins on the fuel line, near the engine. I know that sounds stupid, but it's an old redneck fix for vapor locking. They act as a heat sink to cool the fuel back down. it's crazy, but it works....... if thats the problem. Gasoline boiling point is just over 100 degrees, so vapor locking is highly possible. Im gonna try that next.
 
Ive chased this little evil demon around for a few eeks now, and still havent figured it out. Any input from some of you die hard jeep guys would be great. If it were aToyota engine, I could shove my hand up the tail pipe, and pull out the broken parts, but I dont know much about the 4.0, or its strange quirks.
 
what year is the engine/ecm? renix or chrysler injection? how warm is the engine when it happens? try putting a fuel pressure gauge on it to see what you're working with & determine if it's fuel or spark.
just a wild guess, but from jeep experience, i'd look at the crank position sensor first.
 
I had similar issues when my throttle body position sensor was on its way out. I would be going 80 and the engine would cut power. Also had a terrible idle
 
Misfit runs like a race car............... then just sputters and dies. It has no other issues, and gives no warning. It wont do this until the engine gets up to good operating temp.
 
It has no regulator. It just has an inline pump, going straight to the fuel rail. It ran fine like this for quite a few years.
 
Went around and around with one doing this and found finally caught the coil and injector signals going completely crazy when it stalled with the oscilliscope. Turned my attention to the computer and found the screws on the front of the computer (94-97MY only) were digging into the board. Backed them put and it quit for a while. Started doing it again and replaced the computer and no issues sense. I think that issue was limited to pcms produced 94-97, but it did stall and back fire the exact same way. Might restart fine, next time might not start for an hour.
 
cj777 said:
What year 4.0 is it? You should have a pressure regulator on the fuel rail itself.
Click to expand...

It's a 94 model engine and ZJ harness. I know because I wired and built that engine when @35xj owned it. There is a regulator on the rail on that year model.
It's a long shot, but I once had to re-wired the crank sensor and make one out of two at the top of Guardrail at Tellico. May wanna inspect that wiring to be safe.
The harness is a cut down 94 ZJ harness with a YJ PCM if I remember correctly.

Like everyone else said, check the obvious like TPS, see if the fuel pump is running hot or is running noisier than normal, check the inlet to the pump for debris from the cell, etc.
 
Last edited:
No pressure regulator on the rail. I hooked a fuel pressure guage to the rail today and let it run. The pressure drops to roughly 2 or 3 pounds when it cuts off. I will fire back immediately, and holds around 30 psi for a few minutes........... then fluctuates between 10 and 25........... then drops to 2 or 3 and sputters out.
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