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Old August 25th, 2022, 16:42
californiadreamin californiadreamin is offline
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Could bad fuel-pump check valve cause stalling?

I have been suffering the last couple months with an insidious problem with my 91 4.0: Every time I take it up in the mountains, far from home it starts stalling. After about 1 hr of uphill freeway, it stalls. Repeatedly for 2-5 seconds at a time, requiring a roll start or use of the starter if I was going slow enough. Issue will persist until I leave the jeep to calm-down/cool offer for 6 more more hours. And the problem does not happen with regular around-town driving. Only long-sustained uphill drives.

At first I thought it was heat related, so I installed an e-fan (since my 91 Sport didn't have one stock) and insulated some things. That didn't help. Yesterday, I thought to check the fuel pressure. While the fuel pump makes the right pressure at idle (32 psi) and with vacuum disconnected (39 psi), it won't hold fuel pressure. (pressure totally goes away in 15 or 20 seconds). I verified that it's not leaking through the injectors or back through the fuel regulator.

So my question is: could a bad fuel-pump check value cause an an engine to stall when it's at medium-heavy load?

Sigh. Thanks so much for any input you have. This problem has thrown a monkey wrench into my last 4 wheeling trips and I'm really hoping this could be the problem.
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Old August 30th, 2022, 22:30
HeyAwesomePeople HeyAwesomePeople is offline
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Re: Could bad fuel-pump check valve cause stalling?

No, the fuel check valve failing would only cause a hard-start. Once the pump is running, there should be constant fuel pressure to the engine.

Most likely, your fuel pump is overheating or wearing down under sustained load. What you're experiencing is a common issue with failing fuel pumps. My 01' Jeep did this with an aftermarket pump. Would work great around town, but during long drives the fuel pump started to die and stall out the vehicle. The most fun was when it died halfway up Big Bear Mountain!

I would start with replacing the fuel pump. It sounds like the culprit. Luckily in pre 97 vehicles it's a lot easier since you don't have to drop the fuel tank!
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Old August 31st, 2022, 05:42
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Anak Anak is offline
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Re: Could bad fuel-pump check valve cause stalling?

I agree that the fuel pump is your most likely culprit.

The other possibility would be the fuel pressure regulator. I am not sure what sort of failure mode this would be. The only problem I have ever had with a fuel pressure regulator was a disintegrating diaphragm. Your temperature dependant problem doesn't sound like it would be FPR, but I would keep that option in the back of the mind, and would certainly do a visual inspection on it and the vacuum line that connects to it.
Project "Scope Creep": 1996 4wd 4.0L, AX15

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Old August 31st, 2022, 05:47
Unclewolverine Unclewolverine is offline
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Re: Could bad fuel-pump check valve cause stalling?

Another possibility is the fuel pump pick up sock is getting clogged and while sitting the crud slowly falls back of. Seen that cause similar problems.
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Old August 31st, 2022, 18:13
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Runnin'OnEmpty Runnin'OnEmpty is offline
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Re: Could bad fuel-pump check valve cause stalling?

Since your fuel pressure is leaking down,
also suspect cracks in the in-tank fuel hose.

They tend to crack around the clamp.

When replacing the pump, use submerged
rated hose, I think it's 10R, and fuel injection
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