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Renix fuel issues maybe?


NAXJA Forum User
I have a 89 4.0 aw4 that's been sitting last two minutes months cause of case problems, but that's a story for another time. Tried to start the jeep today and it didn't have no fuel pressure at the rail. And yes I had a gauge hooked to it in case y'all are wondering. Thought maybe cause the battery was dead and charging it might not have nuff juice to pull fuel up. Skip ahead like two hours and still no pressure, she'd hiccup and that would be it. So I poured a little fuel into the throttle body and after a couple revolutions she fired up and ran like garbage. Still wasn't showing pressure so I cracked the throttle body open a hair and sure as the sun sits in the east sge started to get pressure albeit it was only 20# I was thrilled. Tapped the throttle a couple times and she has factory specs concerning fuel pressure then all a sudden she'd start losing it and stumbling. Shut her off and pulled the filter and blew through it. Went and turned the key on......no pressure once again. So I "primed" the throttle body once more and same results as last time. Figured I'd check the injectors by pulling harness's while she was idling #1 #2 #3 didn't make any difference plugged in or not. So I'm thinking there might be a slight obstruction some where and the suspect injectors are also clogged, my question is how do I go bout back flushing the fuel system and being as my pump has the funky power ground where it can be reversed could I get say a container with fuel in it and back flush the pump like that. Taking the pump out isn't an option for me atm.
Sorry this was such a long thread for those two simple questions.
While cranking, the fuel pump will run at full voltage. With the key in run position, if the computer doesn't see the engine turning, it will turn off the fuel pump. So you need to watch the pressure while cranking.

When the key is in the run position, the fuel pump circuit runs through a ballast resistor to drop the voltage. That was Jeep's fix for complaints about the pump being noisy. The resistor is the ceramic thing on the drivers fender near the airbox. See https://cruiser54.com/?p=35 and https://cruiser54.com/?p=249. Actually, go through all of his tips, but especially the one on improving the grounds. Check the connections to the resistor, and try bypassing it with a wire jumper and see if that helps. You can leave it permanently bypassed. That's also a handy place to stick a meter and see if you've got voltage and how much current the pump is drawing.
The gauge says a quarter tank but I crawled under it yesterday and knocked on it and she sounded hollow so I'm throw some in tomorrow when the weather clears up.