91 Fuel Starvation

We have tested and replaced many parts on this '91 with 4.0. Got back on the trail yesterday and after a few hours it went back to it's old ways of cutting off. It will sometimes start right back up and sometimes take several tries. We have replaced PCM, most sensors, fuel pump and filter, etc.
At this point we are thinking the gas tank is not vented properly so we did take off the cap but it was after the issue started and it did keep cutting off, but maybe not as bad. we were able to get out of trails and loaded up. So we are thinking that the cap is bad but at this point the pump too from working under a strain and high demand.
Is the cap the only method of vent for the fuel system? I thought there was a return line.
We can test pressure in the driveway but the problem doesn't happen except under trail use.
Please give me your input.
Thanks

Unless you replaced the fuel pump with a Bosch, it's probably a bad pump. Take the pressure gauge on the trail?

Might be good to check The relay and ballast resistor.the resistor you can bypass with a fuse or something.

Don't know much about venting, there are two vent lines that the top of the tank which run eventually to the purge canister at the front and from there to the intake someplace.

I agree about the Bosch pump, if you have to replace it again that's the brand I'd go with.

How clean is the tank? Any chance rust or other junk is clogging the sock and filter but only when the sediment is stirred up bouncing on the trail?

Unless you've got a kink in the metal lines someplace restricting the flow, I dunno.
Not sure what bad injectors would do, or if they'd do it intermittently.

Be interesting to know if it is a fuel pressure issue on the trail.



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I see this Bosch pump for $166.97
https://www.summitracing.com/parts/bch-9580810019/overview/year/1991/make/jeep/model/cherokee

And this one for $81.97
https://www.summitracing.com/parts/bch-69302/overview/year/1991/make/jeep/model/cherokee

Whats the difference?

RQqqqq said:

I see this Bosch pump for $166.97
https://www.summitracing.com/parts/bch-9580810019/overview/year/1991/make/jeep/model/cherokee

And this one for $81.97
https://www.summitracing.com/parts/bch-69302/overview/year/1991/make/jeep/model/cherokee

Whats the difference?

Click to expand...

$85 ?????

The cheap one is listed for the 4 and 6 cylinder and the expensive one is only for the 6. I'd check with Bosch to make sure the flow rates on the cheap one are correct for the I6 before buying it. Just a guess as I know nothing about the 4 but assume the injectors don't need as much flow as the I6's ones will.

I think Bosch 69302 is the one I used. Rock auto has it for $60.79


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