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Old January 31st, 2022, 15:15
Lost_Wrench Lost_Wrench is offline
NAXJA Forum User
Join Date: Dec 2020
Location: CO
Posts: 94
Re: Fuel Pump Check Valve or leaky Injectors?

SOLVED! It was the fuel pump.

Here's where I got tripped up. The first time I checked my fuel pressure it was about 30 psi. I read conflicting info in more than one place about the fuel pressure in a 1996 XJ. Some have the old style fuel pump system with the pressure regulator on the fuel rail and those systems apparently are supposed to get 31 psi. Sometime in 1996 the fuel pump was updated and the fuel pressure regulator became part of the fuel pump module assembly and these systems are supposed to get 49 psi.

The second thing that tripped me up was my exhaust. After putting in the second set of new injectors (Standards from Oreilly) it still ran like hell, backfiring, running very rich, and thick white exhaust with lots of condensation dripping from tailpipe. Turns out that one of those Standards was stuck wide open right out of the box and I confirmed this with multiple tests of it. So I put all my old original Chrysler injectors back in and it ran better but I was still getting white smoke from exhaust and even though my oil on the dipstick was clean, I had a little bit of bad looking milkshake like oil under the oil filler cap leading me to believe I had a head gasket problem and was getting coolant into one or more of the cylinders and causing the thick white smoke. So I changed the head gasket. First time doing it but I took my time, cleaned all surfaces well, followed correct torque specs and patterns and all went well. Except that it helped nothing. Finally I researched more about the the fuel system and the correct pressures for my 1996 and got ahold of a tech with Crown Automotive (Adam?) Who was super knowledgeable about XJ's and confirmed that I needed to be at 49 psi. Some on this thread were also correct about that but again I had read a lot of conflicting things about the 96 XJ fuel pressure due to the change that was made to that system. So I ordered the entire new fuel pump module assembly from Crown Automotive via Quadratec. It took me maybe 35 minutes to swap out the old fuel pump and man what a difference 49 psi makes! The old fuel pump looked like the original module with a newer pump attached whose serial number I traced to be a cheap AutoZone model. After the pump was installed and she was running good again I also put in yet another set of injectors, this time a set of matched Siemens from Precision Auto Injectors - thanks for the suggestion RCP phx! Wojtek (hope I spelled his name right) with precision auto injectors is very knowledgeable and suggested these to me on the phone after I told him my issues with other cheapo's and faulty injectors.

Chased my tail on this one quite a bit unfortunately and a lot of it boiled down to me missing or misinterpreting diagnostic clues and then guessing. In the end though, I now have a new fuel pump, fuel filter, fuel injectors, head gasket, valve cover gasket, exhaust manifold gasket, thermostat, spark plugs, new coolant, and an oil change. Most importantly though, that Jeep has never started faster, idled better, or run smoother since I've owned it! I've put 150 miles on it so far including charging up a large mountain pass here in Colorado. I just wish there was a check engine code for low fuel pressure! Maybe there is but I wasn't getting it, it would have saved me a lot of time and guessing.

Thanks for everyone's help and suggestions! I learned a lot more about XJ's the past several weeks that's for certain.
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