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I'm killing myself. '93 YJ won't start

2K views 7 replies 4 participants last post by  Austin93YJ 
#1 ·
I'm dying over here! So here's the scoop:

I've been having fuel pressure problems. My jeep would sometimes begin to stall when any throttle was put into it. Sometimes it wouldn't start at all. Sometimes it runs no problem. But recently it's been not firing after turning over so I rented a fuel pressure gauge. When it has pressure the pressure is good. Occasionally I'll watch the gauge and it'll slowly start to lose pressure. And sometimes it wont have any pressure at all. It was running really lean when it wouldn't pass smog so knowing it was having these problems I replaced some stuff:
Fuel Pressure regulator
Throttle Positioning sensor
Crankshaft positioning sensor
Idle Air control sensor
Manifold Air pressure sensor
Intake Air temperature sensor

The O2 sensor was changed about a year or so ago. I replaced the entire sending unit (Including the pump) two years ago and thinking it was the pump again I bought a bosch one and last week rereplaced just the pump to see if it changed anything. It didn't. I will say that it is idling at a nicer rpm, sometimes... When it won't start I've disconnected the hose from the back of the fuel filter and either nothing or a small drip will come out. I am running out of things to try. I thought I'd bring it to the experts! :)

The only thing that is weird to me is that when I pull the gas tank cap off there is a large release of pressure, after its been running. Is that normal? My truck doesn't do that. Also, I don't know if this is normal or not, but is the fuel pump sending unit supposed to be pinned in between the top and bottom of the gas tank? I was rear ended so my skid plate back there is a little warped but I seem to remember having to pull the tank up to the sending unit gasket before the accident as well. The other thing I can think of is when I dropped it recently I discovered that the longer fuel tank vent hose was pinched. But I replaced it and put it back up doing my best not to pinch it this time. I just can't think of what else to try. Could it be the ECU taking a dump? I have tried resetting it (Leaving the battery disconnected for 8 hours) and it started up after doing that, but it wasn't a long term fix. Why would it be so spotty?

Any troubleshooting you guys can help me with would be amazing! Thank you so much!
 
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#2 ·
Isn't there a fuel return line? Odd pressures like that I would take a stab in the dark and say if you have one, make sure it's not kinked or clogged. It seems to me that a vent hose is clogged/ kinked. As you use fuel you may be causing negative pressure forcing the fuel pump to work harder until it gets to a point it's not overpowering the neg pressure. That's my theory and I'm sticking to it.
 
#3 ·
It's not too much a negative pressure though. It nearly blows the gas cap off when I loosen it.

The only thing I can see with the return line being an issue is, you know how the sending units have that rubber boot on the return spout? Last time I was in the tank I removed the plastic cup in the bottom of the tank (it was all warped and causing my fuel gauge to stay at half-mast) and I think the rubber boot might be now pinned to the bottom and causing the return fuel not to flow into the tank? I should have left the boot off in hindsight because I had a small feeling this could be a problem. I had the starting issues before and after taking off the plastic cup so I didn't really think that it was that.
 
#5 ·
There is a tank vent line that runs up front the charcoal canister, then to atmosphere. If you are building pressure I suspect that vent line is kinked or the canister is plugged.

There should be a line from the intake to pull vacuum on the canister and the vent line from the tank. Disconnect the vent line and see if that makes any difference. If not trace the line back to the tank to see if it kinked somewhere. Unfortunately it may be on top of the tank or cross member making seeing it difficult and fixing it requiring you to drop the tank.
 
#6 ·
Just an update but when I drove the Jeep to work yesterday it wouldn't start right away but after a couple tries it fired. Then, on the way home it started to stall out whenever I gave it juice and then rev back up when I took my foot off the gas. It eventually died and would not restart. I hooked it up to my truck and towed it home. It will only started now when I pushed the gas while turning it over. It would stall out if I took my foot off the pedal. I revved it up to 4500rpms and now it idles like normal now.. I plan on dropping the tank when I get a day off and we'll see what I can find up there. I think that's where any kinking would come from there.
 
#7 ·
I've read that my resting fuel pressure should stay around 20 psi but it drops to 0 psi instantly. Then when I start it up again it idles at 1500 rpms for around a minute. Could I have an injector leak? Would it make sense that my pressure was releasing into a cylinder and causing the high idle to burn off all that extra gas in the cylinder? Does that make sense or is that crazy talk?
 
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