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Fuel Pump Check Valve or leaky Injectors?

Lost_Wrench

NAXJA Forum User
Location
CO
My 96' XJ is taking too long to start at times and the symptoms seem backwards from most people's issues with check valves and leaky injectors. If the Jeep has been sitting overnight or long enough for the engine to be cold, it fires right up on the first try but then shakes and stumbles for a minute or so (or until I give it some gas) before idling smoothly. Once the motor has started and warms up though, it takes 2-4 crank/prime cycles to start and it seems to be slowly worsening over time. Isn't this backwards from most check valve issues where people have to prime the key several times after its been sitting due to the fuel in the fuel line slowly draining back into the tank?

This Jeep runs great otherwise, no check lights or trouble codes. About a year and half ago (approx 5k miles ago) it got a new fuel tank, fuel pump, and fuel filter.
 
Sounds like the injectors going bad, get a new "matched" set and be done.
 
I had the long start issue, replaced the fuel pump assembly, then ended up with the same problem youre having. I guess maintaining fuel in the lines caused the injectors to leak into the cylinders. Replacing with new injectors fixed the issue for me.
 
UPDATE: I replaced my injectors with a set if Bosch 4 hole injectors (serial # ending in 710) that cost me $60 total on EBay. The Jeep - which had been running fine with the old injectors but had long cranking time sympoms - ran like hell with those Bosch injectors. And i mean hell. Hard starting, rough idle, backfiring, stumbling. So I put the old original Chrysler injectors back in. It ran better but not the same as before. Running it down the highway it would bog down and then suddenly pick back up. Then it sat overnight. Now it runs like hell just like with the Bosch injectors.

I tested the fuel pressure on the rail today and it's at 30 psi. Apparently some 96 XJ's are supposed to run at 31 psi and at some point in 96 they went from a fuel rail mounted regulator to one attached to the actual fuel pump in the tank and that setup is supposed to run at like 49 psi. Seems like my pressure is low according to that, anyone have knowledge of this or a Chilton manual they could check for correct pressure for me? This Jeep does not have a fuel pressure regulator on the rail and my FP is not very old and maybe has 5k on it. Previous owner replaced the fuel tank, pump and filter, due to it having sat with old gas in it for too many years. I believe him I guess, the gas tank and fuel filter still look brand new.

Today I also bought new Standard Injectors from Oreilly for $300 total but I need to figure out if I have the correct fuel pressure before I install them for no reason. I'm perplexed at how swapping out injectors and resetting the pcm could suddenly make the Jeep run so terribly when it ran pretty great before, aside from the long cranking time to start (which only did so after it warmed up, it cold started right away every time). None of the injectors are leaking onto the manifold or anything. Could I have fouled the heck out of my plugs with those crappy bosches? Still no check engine light curiously. Well I'm really confused now, and rambling. Thanks for the responses thus far everyone!
 
UPDATE: Just installed the new Standard Fuel Injectors and started the Jeep. Ran terribly again and the exhaust was super rich. I pulled all of the spark plugs and cylinder 2 was completely full of fuel, the electrode was even fully submerged it was so flooded. The other plugs all looked fine, no noticeable fouling that I could tell. I don't think the new Standard injector I just Installed in cylinder 2 is the issue because when I Installed the crappy Bosch injectors I could pull the wire harness off of the cylinder 2 injector and there was no difference in the way it idled. So something is up with cylinder 2 that's making it dump fuel in there.
 
Here is what I've learned today.

1) Cylinder 2 is flooding badly
2) Cylinder 2 has a brand new fuel injector
3) Cylinder 2 has spark and a new champion plug

Why is cylinder 2 flooding even after I let it dry out?
 
Switch that injector to another cylinder. If the flooding moves its the injector, if not there is a mechanical problem with the engine; valve not seating, bent pushrod, broken rocker, etc.
 
Ok thanks, I'll do that tomorrow.

Any chance it could be an electrical issue such as a bad ground or the wires that go to that particular injector? When the engine is running and I unplug the wire harness from the cylinder 2 injector there is no change in the motor's idling or in the performance of the motor, it's like it doesn't exist even though it's getting air, fuel, and spark. The cylinder 2 injector meanwhile, is still dumping fuel despite being unplugged, which it shouldn't be right?
 
BAD NEWS! Today I reset the PCM..again. No change.

THEN I checked my oil, which looked fine at first glance but smelled kinda sweet and seemed "runny" so I took the oil filler cap off and looked at the underside of it and it's the dreaded milkshake. So looks like what happened is the head gasket failed and coolant was getting into cylinder 2 which is why it was so saturated and wouldn't fire normally despite having air + fuel + spark. Examining my exhaust and it was running really rich and dripping way too much out of the tailpipe leaving a small puddle every time.

Tracing this back to my original symptom though which was long cranking to get started and stumbling for a matter of seconds before giving it some gas, and I think the head gasket was already beginning to allow some coolant in, and the stumbling was that coolant getting cleared out of the cylinder. Once the engine sat for a long time it started right up but still stumbled a bunch so maybe whatever coolant was in there overnight evaporated some? When I changed out the injectors something must have happened to worsen the failed head gasket. Perhaps fresh injectors made better combustion and blew out the hole more, Idk. Thanks for all of your comments and help so far, I'll update as I make progress with my head gasket in the coming weeks.
 
2 things, you never got a good set of injectors (I don't think so), if you think you did then you've got to do some major wiring checks.
 
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.
 
That's yet to be seen but good injectors don't come from Checker!
 
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.
 
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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