4.0 stalling, need advice

BigClay

BigClay

Knower of useless ZJ things
Joined
Sep 24, 2008
Location
Winston-Salem
1998 TJ with 4.0, AX15, Rubi 4:1 tcase

This is a little long but I need some help with what is wrong with the 4.0.

For a long time I have had a problem with the jeep stalling when climbing anything in 4 high. Started back at Big Creek way back in the day trying to climb the huge hill: would be in 4 high and in 1st or 2nd, start hammering down going up the hill and then would lose my pedal (I could even have it to the floor and high RPMs) and engine stalls, and then takes a long time to crank but always re-cranks. This happened all the time on the trail in 4 high, so I stopped using 4 high, would have to run 4 low in 4th gear sometimes but never had a stalling problem.

Now this weekend at GER it started doing the same thing in 4 low and 1st gear. I will come up to an obstacle and start climbing it and then stalls even though I am still in the throttle.

Jeep takes a long time to crank and have to give it some throttle usually. Assuming that is related.

Give me all the thoughts.
 
I can't imagine it being gearing related. What are the engine RPM comparisons? Clearly higher RPM demands higher fuel flow rate, so do you have a collapsed, pinched, plugged or otherwise restricted fuel flow? You mention at angle, Have you dropped the tank to inspect the pick up tube and sock? I'd start at the tank and work my way forward inspecting all fuel lines, I've even seen where a soft line was fitted to a hard line and a little of the soft line tore away and created a flap that restricted flow. Or on my YJ, the PO put a larger poly tank in and didn't change the skid plate. They pinched the soft line between the tank and the tub restricting flow. Inspect all lines all the way up.
 
run a compression test and a leak down test on the engine.
 
Based on the symptoms, sounds like a sensor issue (Crank position most likely, or possibly cam). The slow restart sounds like an overheating Crank position sensor, the having to give it throttle sounds like an IAC (Idle Air Control) module that isn't working properly or the ECM isn't properly storing the value. My TJ used to do that when it sat for a long time and the battery died and the ECM forgot what the correct idle position was for the IAC. Now, ever since I put a new battery in it a couple years ago, it won't start until the second try. If you turn the key to crank, it will turn over a hundred times and not crank. As soon as you turn it off and back on again, it cranks right away. If you got to start it and just turn the key on, then off, then back on, it will crank immediately.
 
jeepinmatt said:
Based on the symptoms, sounds like a sensor issue (Crank position most likely, or possibly cam). The slow restart sounds like an overheating Crank position sensor, the having to give it throttle sounds like an IAC (Idle Air Control) module that isn't working properly or the ECM isn't properly storing the value. My TJ used to do that when it sat for a long time and the battery died and the ECM forgot what the correct idle position was for the IAC. Now, ever since I put a new battery in it a couple years ago, it won't start until the second try. If you turn the key to crank, it will turn over a hundred times and not crank. As soon as you turn it off and back on again, it cranks right away. If you got to start it and just turn the key on, then off, then back on, it will crank immediately.
Click to expand...
ya, I could definitely see it being one of those sensors or even the wiring to them.
 
I chased a similar problem in my TJ for a couple years replacing sensors and fuel lines.... Ended up being a dying fuel pump.
 
I would check fuel pressure running and the CPS and Cam position sensor. Also since it's a 98 clean all the grounds on the regular. Our 98 XJ died and it ended up being dirty grounds. My 94 ran an idled fine but would stumble driving and accelerating. I put a fuel pressure gauge on it and found that the pump was failing but it wasn't consistent. Just my .02 and experiences.
 
Check for fuel leaks from tank to carb, efi, whatever.
I wheeled with a guy having the same issue.
Ended up being a cheap glass fuel line filter sucking air.
 
Check for pinched wires. Buddy had same problem when he would climb stuff his chassis would twist and would pinch wire between frame and tub and shut off
 
This should help the stalls…

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rcalexander105 said:
This should help the stalls…

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Click to expand...

The ole 220k mile stock 4.0 may decide to stall indefinitely with that little add on
 
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