87 XJ cranks no start, fuel delivery issue

Ok, I've got this somewhat narrowed down, here's what I know. Next 2 paragraphs are background, last one is the important details.

Picked up this 87 XJ a while back, it ran fine. I didn't have much time to work on it at that point, next time I went to drive it it wouldn't start. Figured out the fuel pump was bad (87s don't have the ballast resistor, it's easy to tell when the pump is running!). Changed fuel filter and then fuel pump, went through some self-induced wiring stupidity, figured out I had the pump wired backwards so I fixed that and everything was great. Had a little fuel leak around the return line O-ring, so I bought the *proper* kit and fixed it. It started, ran great, I moved it outside.

Again, didn't have much more time to work on it, I went to start it again recently and it would crank and crank but not fire. Eventually it would stumble like it wanted to start, but still nothing. I knew it was getting fuel fine before, so I made a bad assumption that it was ignition. I changed CPS with a new one (bought a while back, why not). Did all the diagnostics for TPS, sync signal generator (distributor cam sensor), ignition coil, etc. Everything checked out so I went back to looking at the fuel system.

The test port on the fuel rail always lets air out. I can turn the key, prime the pump, and hit the test port and get air. Turn it off and retry, more air. No matter what I do I'm getting air out of the test port. I don't have fuel in the vacuum line of the regulator, what else can I check to determine if it's the FPR or not? Otherwise what else am I looking for? Another bad O-ring letting in air? Cracked fuel line? I doubt there is a cracked fuel line inside the tank as it is a new pump, however I cannot find any fuel leaking out from any of the fuel lines or fitting though. Which makes me wonder if the pump is picking up air.

Thanks in advance for any help you can give me! :worship:

If you're only getting air out of the fuel system, I'd suspect the fuel pick-up in the tank. If the fuel pump has somehow worked loose from the assembly, it might be "floating up" in the tank and pumping air instead of fuel. Worth a quick check at the tank.

Since the pump is pressure from the pick-up...no leaks in the system from the tank to the engine could introduce air (they're all under positive pressure)...would show a leak if anything.

Let us know what you find.

I'd suspect either the pickup in the tank or the pump itself. But the problem is most likely not related to the regulator. Your 87 4.0 needs 31 psi or close to it to fire. Go back and check your fuel pump work. And also know that it is not that rare to get a bad fuel pump out of the box. Especially if it is an Airtex, not known for stellar reliability IMHO. I will not purchase anything from that mfg.

And when you get that resolved and the engine fires, again use a fuel pressure GAUGE to verify that fuel delivery is where it should be. 31 psi at idle; then disconnect the vacuum line leading to the fuel pressure regulator and the pressure should jump to approximately 39 psi.

Good luck and be sure to check back to let us know what you find!

Thanks for the advice guys... very good point on the fuel system being positive pressure after the pump. So with the problem narrowed down to "inside the tank," I pulled the pump today and here's what I found:



The rubber rings around the fuel pump are so swollen that they popped out of the assembly. Bingo. I got another Airtex pump under warranty, but who cares? I still have my OE pump assembly, so today I will put the Airtex pump in the OE assembly with the OE rubber pieces and see what happens.

And as an added annoyance, as if the sender gasket wasn't enough of a pain to hold in place while the retaining ring is installed:



The gasket has swollen and is now way larger than the original ring. Of course I can't find the original O-ring from the OE pump, but found on another forum that Dorman/Motormite 55812 is a suitable retaining ring / O-ring.

At any rate, thank you everyone for the help and advice! I will get everything back together today and see if everything works as it should!

Good news: it runs!

Bad news: I'm somewhat of an idiot. When I changed the pump originally, the tank was close to empty but I put 5 gallons in it when I was done. When it wouldn't start again and I started fooling with the pump, I heard gas sloshing around so I assumed I was still good.

I don't know if one of my quality neighbors siphoned it or what, but after I swapped the proper rubber rings and a new pump in and it wouldn't start, I finally poured a few gallons of gas in it and it fired right up.

So... I feel kind of dumb for that, and it probably means it was lack of fuel the whole time and not the pump. I guess the lesson learned is don't assume anything!