1990 xj doesn't like to run

We are dealing with a 90 xj 4.0/AW4/231. Well, here is the story.

I was taking it on a country cruise and started to get low on gas. So I stopped to fuel up. After fueling up I started the jeep up without a problem. I started to drive away and the jeep started to buck and miss. It finally shut off, it would crank over but would not start.
I checked for fuel pressure at the rail and there was nothing. So I got the tools out and took off the fuel line between the pump and the filter. The pump was kicking on but not pushing anything out. So, onto the trailer it went.
Now that it is home I can investigate. I tried to start the jeep and it fired right up after sitting on the trailer for a week. So off the trailer and took it for a ride. It would run without a problem until you tried to give it a good amount of the skinny pedal. Then it would just start to miss and want to die. If I apply more pedal it makes it worse and almost dies. If I leave it alone when it starts to die, it will recover on its own and drive without a problem, kindof like it's building fuel pressure in the system again.
So, the first thing I tried was taking out the fuel pump and replacing the screen. I was just going to replace the pump with one I have on the shelf but I would figure I would try this first, as the one on the shelf is a little different. Changing the screen filter did not fix the problem. The next thing I am going to do is replace the pump. I don't know if something clogged it to prevent full operation of the pump.
Any other ideas out there to this problem. Sure would like to go and play in the snow again.

Kim

Without knowing the acrual fuel pressure, it's hard to tell. Could be as simple as a new pump.

Except for the part about the pump kicking on and not pushing anything out, kind of sounds like a flaky CPS.
Not your normal electrical fault, but kind of a one off, that may be relevant to your problem or may not. I had a pump that wouldn't build much pressure, even tested fine for voltage at the pump wire. On a hunch I ran a hot wire all the way back to the pump from the battery, it ran fine. I started checking the wiring and found a really crispy connector near the drivers side rear wheel well. I figured it was getting voltage, but not enough amperage. I've never heard the same again from anybody else, so I'm guessing it was a one time event. Check your pump ground.
If you do have to check the wiring, there is a middle section that changes colors from yellow/black, to pink/black (I think) and back again, between connectors in the center of the harnesses someplace. I remember that gave me some aggravation.
Another off the wall possibility is the rubber line, as it exits the pump. My filter was full of little rubber chunks, that hose was in pretty sorry shape.

Just a couple of odd ball ideas, if the normal stuff doesn't work out for you.

Another quick tip, I picked up a freon low pressure gauge (R-12) to test my AC, same fitting as the fuel rail. Worked just fine for a fuel pressure test, gasoline didn't seem to hurt it any, I've had it for decades.

Thanks for the replies. I am going to check the wiring today along with the ground. I will check out the CPS just in case also. If all seems good, I will spend the $10.00 on a new filter that's mounted on the frame, and if that doesn't work, then a new pump.

Looks like I will be replacing the CPS. The wiring is SHOT. So, I will have a new one tonight and see if that cures the problem.

85xjwoody said:

Looks like I will be replacing the CPS. The wiring is SHOT. So, I will have a new one tonight and see if that cures the problem.

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If the crank sensor isn't making it to the computer, you won't have spark. Easy enough to verify that by pulling a spark plug, keep it attached to the plug wire, place the plug electrode near a good engine ground, have a buddy crank the engine while you watch.

Certainly makes sense to repair any wiring issue within the crankshaft position sensor issue, but if you have spark, the problem is not likely the crank sensor itself.

In your original thread, you mention that the fuel pump is energizing, but there is no output. Unless the filter is completely clogged, that means you have a fuel delivery issue.

This sounds a lot more like a fuel pump problem than it does a crank sensor issue.

With the two wires exposed on the CPS wiring, it is touch and go with starting. Moving them around helps it start. So I will start by replacing the CPS first. If the problem still is there, then I will be swapping out the fuel pump. I checked all the wiring and it is fine front to back. I will be changing out the fuel filter also. Updates tomorrow.

Glad to hear of your progress. BTW, your avatar creeps me out.

X2^^ on both counts

if all else fails, I've heard rumors that the small section of hose between the pump and sending unit can fail and cause similar symptoms-- make sure it's good an tight if you end up in the tank for anything.

Shorty said:

X2^^ on both counts

if all else fails, I've heard rumors that the small section of hose between the pump and sending unit can fail and cause similar symptoms-- make sure it's good an tight if you end up in the tank for anything.

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I agree. That avatar should be on a gay site, not here.

I thought this was a gay site? Bunch of haters around here.

85xjwoody said:

I thought this was a gay site? Bunch of haters around here.

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LOL @ Kim.

Got the jeep back Friday and all is good. The CPS was the problem, not fuel related. Also had the entire exhaust replaced. Not to replace all the crap I broke on the front D44 Saturday.