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  #16  
Old January 19th, 2022, 12:40
Lost_Wrench Lost_Wrench is offline
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Re: Fuel Pump Check Valve or leaky Injectors?

I did, I picked up a set of Standards FJ682 from Oreilly and that's what is currently in the Jeep. I scrapped those cheap Bosch injectors. There was likely nothing wrong with my original injectors.
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  #17  
Old January 19th, 2022, 12:57
RCP Phx RCP Phx is offline
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Re: Fuel Pump Check Valve or leaky Injectors?

That's yet to be seen but good injectors don't come from Checker!
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  #18  
Old January 19th, 2022, 13:49
Lost_Wrench Lost_Wrench is offline
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Re: Fuel Pump Check Valve or leaky Injectors?

The Standards were the closest to OE that I could find on short notice, and at least they are made in USA.

My plug wires all seem to be working based on the fact that when I unplug each one my check engine light comes on and tells me which cylinder has had the circuit interrupted. This is also how I verified that each connector was on the right injector which they are.

Regardless, I'm fairly certain my problem is a head gasket due to my findings. Compression test is next.
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  #19  
Old January 19th, 2022, 14:21
Lost_Wrench Lost_Wrench is offline
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Re: Fuel Pump Check Valve or leaky Injectors?

^^ by plug wires I mean fuel injector wire harnesses, not spark plug wires.
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  #20  
Old January 23rd, 2022, 09:06
Lost_Wrench Lost_Wrench is offline
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Re: Fuel Pump Check Valve or leaky Injectors?

UPDATE: Well I'm back to the drawing board. I replaced the head gasket, it took me 14 hours by myself and that was the first one I've ever done so all in all not too bad just time consuming. My old head gasket didn't look bad meaning there were no holes or blemishes that I could see. After putting back together it still ran bad. Long cranking times to start, rough low idle at first, and backfiring. Having a brand new clean exhaust manifold gasket made one thing apparent right away. Fuel was completely filling up cylinder 2. I watched as it slowly became more saturated in front of my eyes. Apparently what I thought was white smoke and condensation coming out of the tailpipe was actually straight gas coming out of the tailpipe. So I switched out that injector with one of the old Chrysler Mopar injectors and the idle immediately improved and sounded normal at 800 rpm. I took it for a test drive and after being sluggish at first it ran great, had plenty of power and was running fine even up to 75 mon, but upon restarting I've got the same old symptoms of long cranking stumbling and backfiring. I did notice that my oil pressure is higher now according to the gauge, I'm not sure if that's a result of the new head gasket improving compression or if I need a new sending unit for some reason even though it was not touched during the head gasket install. It goes all the way to 80 psi at WOT whereas before it maybe went to 60 at WOT. Now for those of you who warned or advised against cheap injectors, please tell me what good injectors are. I replaced my original Chrysler Injectors with cheap Bosch injectors, then went to much more expensive USA made Standard injectors of which at least one was stuck open right out of the box I learned. Should i order a set directly from mopar next? Also, after researching I think my fuel pressure is in question and my fuel pump may be faulty as well. I was getting 28-30 psi on the fuel gauge while idling. But turning the key to "on" only made the gauge jump to maybe 2 psi for a second or two and then drop to zero. So it seems a check valve is faulty since the rail isn't staying primed, or I have 1 or more stuck open injectors. I've still read conflicting information regarding the correct fuel pressure for a '96. I don't have a pressure regulator on my fuel rail so it's on the pump assembly. Apparently these are supposed to have 39-49 psi, while the ones with the regulator have 31 psi and both types were made in 1996. There are a lot of things I could have done different or better to this point but I'm still at a loss for the most part.
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  #21  
Old January 23rd, 2022, 09:28
RCP Phx RCP Phx is offline
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Re: Fuel Pump Check Valve or leaky Injectors?

Your '96 should be 49psi and you want a company that match test/flows their sets. I have purchased 3 sets of Jeep injectors from these guys and they warranty them for life. https://precisionautoinjectors.com/c...fuel-injectors
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  #22  
Old January 23rd, 2022, 10:19
lawsoncl lawsoncl is offline
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Re: Fuel Pump Check Valve or leaky Injectors?

Getting the correct CEL codes when unplugging injectors is a good sign, but I'd still recommend opening up the loom and inspecting the wiring from the injector back along the head and where it crosses over to the firewall. If the wire from the injector to the PCM is damaged and even partially shorting to ground, it will cause the injector to stay open. The other possibility is a blown injector driver in the PCM, which typically manifests as the injector not firing and a CEL, but could short through to ground as well.
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  #23  
Old January 23rd, 2022, 12:54
jhenke jhenke is offline
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Re: Fuel Pump Check Valve or leaky Injectors?

Did you perform a compression check ? You may have a cracked head.
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  #24  
Old January 31st, 2022, 15:15
Lost_Wrench Lost_Wrench is offline
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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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