- Location
- Rainy side of Washington
My 98's been having some issues for a while and they are starting to get worse, so I figure I should probably fix it. It's a 98 XJ 4.0L/AW4, nothing else is relevant but it's got an NP231, a d30, and a 29 spline 8.25 for the curious. Around 150k miles on the motor.
Temps: fine. takes a minute or two of driving to come up to 210 and stays there.
Oil pressure: fine. 40psi cold idle, 20psi hot idle, 40+psi hot running.
volts: around 14 running, and the factory gauge usually lies on the low side so I'm not afraid of issues here, it's been like this for months so the battery would have gone flat by now.
What it does - it idles extremely roughly, and cylinders 3 and 4 are effectively doing nothing. I can unplug the injectors and the idle doesn't change at all. Unplugging the other injectors causes it to run even worse. If I goose the throttle I get some pretty awesome loud backfires through the intake. Trying to drive it, it basically has no guts at all, makes some interesting pop/backfire noises that almost sound like loose control arm or track bar bracket bolts until you hear it do it a couple times in quick succession. It strains and bogs down and runs horribly till around 2500rpm, at which point it picks up a little, then completely falls on its face at around 2700-2800 and you have to floor it to get it to downshift so it picks up the revs and runs again. If you can baby it downhill till it gets to 3000rpm it'll take off and go, and almost feel normal, but it still lacks power and sounds extremely rough/throaty. Check engine light is sometimes off, sometimes on, sometimes flashing :scared: before my code reader decided to take a vacation I pulled the codes and there were so many I couldn't really tell what the hell was going on.
I've searched till I'm blue in the face (kinda like that scared guy a line or two up...) and it looks like it could be O2 sensor (replaced a few thousand miles ago), cam sensor (need to check this), fuel pump (it was fine a while ago, need to find my gauge and check this but I'm expecting it to be fine since it runs ok above 3000rpm), MAP sensor (doubt it, but might toss my spare on to verify), plugged catalytic converter (I have a new one on order, going to cut the junk muffler off it tomorrow and shine a light into the cat to see if I can tell if it's disintegrating, bad head gasket between 3 and 4 (I hope not, I don't feel like doing another motor swap right now), burned/cracked valves (see above), wiped cam (see above)... basically "hey dude it's something to do with the motor and the sensors attached to it!"
What say you? I am going to try the cat first since I already have the replacement on order and the muffler's beyond junk anyhow, no loss there. I don't think it's the cat though because that generally causes bogging down ABOVE 3000rpm, not below it... If it's not that, fuel pressure then probably the sensors. At some point I need to check compression but my crappy gauge's adapters won't screw into the 4.0 head so I have to make one myself. I really don't want to turn this into a "throw expensive sensors at it till it runs again" session, even if it just means swapping them off parts vehicles. If it's the motor I have a spare in storage but will be sorely tempted to toss a gas can and a road flare in it and collect my insurance money on the damn thing, it's been fighting me since last October or so. Every time I thought I had it fixed and went to get it inspected it would flip the CEL back on, or burn a bulb out, or otherwise fail me, and I've gotten tired of explaining to the police how many things I've replaced on it and why I'm still test-driving it around with a rejection sticker from last fall on the windshield.
Oh yeah - this all started when I replaced plugs 2-5 but not #1 (since some chucklehead previous owner had mickey moused the heater bypass tube screwed into the water pump and I was afraid to bend it till I had a new one sitting around spare, last time I did that it broke and I was pretty much boned.) It started giving me a lot of check engine lights, replacing the last plug (checked the others and they are still fine) and resetting the computer improved things for about 5 minutes but then it went back to its new tricks again. It's been all downhill from there.
EDIT: holy crap, wall of text. Hopefully someone actually feels like reading that mess.
Temps: fine. takes a minute or two of driving to come up to 210 and stays there.
Oil pressure: fine. 40psi cold idle, 20psi hot idle, 40+psi hot running.
volts: around 14 running, and the factory gauge usually lies on the low side so I'm not afraid of issues here, it's been like this for months so the battery would have gone flat by now.
What it does - it idles extremely roughly, and cylinders 3 and 4 are effectively doing nothing. I can unplug the injectors and the idle doesn't change at all. Unplugging the other injectors causes it to run even worse. If I goose the throttle I get some pretty awesome loud backfires through the intake. Trying to drive it, it basically has no guts at all, makes some interesting pop/backfire noises that almost sound like loose control arm or track bar bracket bolts until you hear it do it a couple times in quick succession. It strains and bogs down and runs horribly till around 2500rpm, at which point it picks up a little, then completely falls on its face at around 2700-2800 and you have to floor it to get it to downshift so it picks up the revs and runs again. If you can baby it downhill till it gets to 3000rpm it'll take off and go, and almost feel normal, but it still lacks power and sounds extremely rough/throaty. Check engine light is sometimes off, sometimes on, sometimes flashing :scared: before my code reader decided to take a vacation I pulled the codes and there were so many I couldn't really tell what the hell was going on.
I've searched till I'm blue in the face (kinda like that scared guy a line or two up...) and it looks like it could be O2 sensor (replaced a few thousand miles ago), cam sensor (need to check this), fuel pump (it was fine a while ago, need to find my gauge and check this but I'm expecting it to be fine since it runs ok above 3000rpm), MAP sensor (doubt it, but might toss my spare on to verify), plugged catalytic converter (I have a new one on order, going to cut the junk muffler off it tomorrow and shine a light into the cat to see if I can tell if it's disintegrating, bad head gasket between 3 and 4 (I hope not, I don't feel like doing another motor swap right now), burned/cracked valves (see above), wiped cam (see above)... basically "hey dude it's something to do with the motor and the sensors attached to it!"
What say you? I am going to try the cat first since I already have the replacement on order and the muffler's beyond junk anyhow, no loss there. I don't think it's the cat though because that generally causes bogging down ABOVE 3000rpm, not below it... If it's not that, fuel pressure then probably the sensors. At some point I need to check compression but my crappy gauge's adapters won't screw into the 4.0 head so I have to make one myself. I really don't want to turn this into a "throw expensive sensors at it till it runs again" session, even if it just means swapping them off parts vehicles. If it's the motor I have a spare in storage but will be sorely tempted to toss a gas can and a road flare in it and collect my insurance money on the damn thing, it's been fighting me since last October or so. Every time I thought I had it fixed and went to get it inspected it would flip the CEL back on, or burn a bulb out, or otherwise fail me, and I've gotten tired of explaining to the police how many things I've replaced on it and why I'm still test-driving it around with a rejection sticker from last fall on the windshield.
Oh yeah - this all started when I replaced plugs 2-5 but not #1 (since some chucklehead previous owner had mickey moused the heater bypass tube screwed into the water pump and I was afraid to bend it till I had a new one sitting around spare, last time I did that it broke and I was pretty much boned.) It started giving me a lot of check engine lights, replacing the last plug (checked the others and they are still fine) and resetting the computer improved things for about 5 minutes but then it went back to its new tricks again. It's been all downhill from there.
EDIT: holy crap, wall of text. Hopefully someone actually feels like reading that mess.