A couple months ago, my 1990 XJ 4.0 started running like crap, started losing power and became completely undrivable. It would start and idle, but if you blipped the throttle it would stumble before revving. And sometimes it would die. Sometimes it would backfire. Even from when i bought it, it had a little stumble at throttle tip in. Also, after running a compression test, found two cylinders down a lot lower than the others. But still better than 100.
I ruled out timing and timing chain issues by hitting it with a timing light, held steady despite the crappy running. First thing, replaced the plugs, cap and rotor (at this point, I might have even swapped wires, but not sure...) I replaced the Throttle Position sensor after looking at the Renix manual. No change and decided to change the O2 sensor, no change. Unplugged everything and replugged. Checked vacuum again and again, no change.
Went back and did the compression test, and decided to replace the headgasket. Again, no change. I replaced the injectors, fuel rail and fuel pressure regulator with those from the parts XJ I picked up, no change. I start thinking the cam sensor might be the problem. Someone suggested MAP sensor, swapped that with a spare, no change. Someone suggested EGR, swapped the solenoid and valve, no changes. Checked the vacuum lines AGAIN!
Again I consider the cam sensor, but someone convinced me the CPS could be the culprit. You guessed it, no change. On a whim, grabbed the ignition module and coil from the parts rig, no change. So I finally pull the distributor from the parts rig, and swap it over, no change.
Decide to swap fuel pumps.
When I get the fuel pump out, hmmm, the hose between the pump outlet and the tank fitting is really bad looking and loose... Easily pulled it off both fittings without loosening the clamps. And its cracked/rotted like crazy. So I get a piece of fuel injection hose, and a new strainer, and put the pump back in the tank.
By this point I don't expect much. But it started and settled into a NICE smooth idle. Let it warm a couple minutes. Blip the throttle and it revs and settles back to idle. Hey, it didn't die... It revs nice, and doesn't do anything like it did before...
So I slip it in gear and doesn't die. Let off the brake and roll forwrd, and back on the brake. Still runs. OK, out into the street, and it drives nice. Like it should. And no more stumble at throttle tip in.
Run it HARD around the block. Runs nice. Smooth. Strong. I'm a happy man. Ran it around town again this evening and am still pleased. Runs good and strong and idles nice and smooth.
I'm convinced the hose was soft and loose enough that most of the pumps output just flowed out around the fittings. Enough fuel made it to the rail to run the motor, but that was it. So now I need to add a new tool, a fuel pressure gauge.
At least I have a box full of spares for trail repair if needed. I'm glad I had spares on hand thanks to the parts XJ I got form a guy on the list...
So, if your fuel pump is running, but you don't have pressure, check that stupid little hose. I'm just saying this is a weird problem that made things seem like a couple other problems. I've seen pumps go bad, but can't recall ever thinking that hose could be the problem...
Thanks for reading...
I ruled out timing and timing chain issues by hitting it with a timing light, held steady despite the crappy running. First thing, replaced the plugs, cap and rotor (at this point, I might have even swapped wires, but not sure...) I replaced the Throttle Position sensor after looking at the Renix manual. No change and decided to change the O2 sensor, no change. Unplugged everything and replugged. Checked vacuum again and again, no change.
Went back and did the compression test, and decided to replace the headgasket. Again, no change. I replaced the injectors, fuel rail and fuel pressure regulator with those from the parts XJ I picked up, no change. I start thinking the cam sensor might be the problem. Someone suggested MAP sensor, swapped that with a spare, no change. Someone suggested EGR, swapped the solenoid and valve, no changes. Checked the vacuum lines AGAIN!
Again I consider the cam sensor, but someone convinced me the CPS could be the culprit. You guessed it, no change. On a whim, grabbed the ignition module and coil from the parts rig, no change. So I finally pull the distributor from the parts rig, and swap it over, no change.
Decide to swap fuel pumps.
When I get the fuel pump out, hmmm, the hose between the pump outlet and the tank fitting is really bad looking and loose... Easily pulled it off both fittings without loosening the clamps. And its cracked/rotted like crazy. So I get a piece of fuel injection hose, and a new strainer, and put the pump back in the tank.
By this point I don't expect much. But it started and settled into a NICE smooth idle. Let it warm a couple minutes. Blip the throttle and it revs and settles back to idle. Hey, it didn't die... It revs nice, and doesn't do anything like it did before...
So I slip it in gear and doesn't die. Let off the brake and roll forwrd, and back on the brake. Still runs. OK, out into the street, and it drives nice. Like it should. And no more stumble at throttle tip in.
Run it HARD around the block. Runs nice. Smooth. Strong. I'm a happy man. Ran it around town again this evening and am still pleased. Runs good and strong and idles nice and smooth.
I'm convinced the hose was soft and loose enough that most of the pumps output just flowed out around the fittings. Enough fuel made it to the rail to run the motor, but that was it. So now I need to add a new tool, a fuel pressure gauge.
At least I have a box full of spares for trail repair if needed. I'm glad I had spares on hand thanks to the parts XJ I got form a guy on the list...
So, if your fuel pump is running, but you don't have pressure, check that stupid little hose. I'm just saying this is a weird problem that made things seem like a couple other problems. I've seen pumps go bad, but can't recall ever thinking that hose could be the problem...
Thanks for reading...
