Redwolf624

So i have a 1996 XJ 4.0. I cracked my exhaust manifold late into 2016, probably about September. Ever since then i have been having a check engine like for P0420, replaced the exhaust manifold around Christmas time and reset the light. however the light came back for the same code. Since the manifold issue i have been having a really hard time starting my XJ when she warms up; no problem on a cold start or a warm start, but when she has been driven for a prolonged period of time she doesn't wanna start back up until about 15-30 minutes after i shut her off. I can't think of anything it would be. smells like fuel when i try to start her, coughs a lot and stalls. No fuel leaks, no vacuum leaks that i can tell so far. If anyone has any ideas and how to test for the issue i would greatly appreciate that!

Thanks in advance,
Redwolf

alpine.adrenaline

I'm almost sure you need a new rear O2 sensor. Once your vehicle warms up that O2 sensor is looking for the right combo of fuel and air- and probably making too rich of a mixture which is where the fuel smell is coming from. Sometimes the wires fall out of their loom and can get mangled by the driveshaft, but I'd recommend disconnecting it under the vehicle to see if it changes the startup behavior.

nujeepguy

i had a bad 02-2 on the cat, rear. got check eng lite and code
?, i think 705?
2000 ran great, no symptoms other than lite on.
got new o2. the only change was the lite went out, no code.
still runs exactly the same??? both o2s look good on scanner.

bluejeep2001

Is this an early 96 with the rail mounted fuel regulator and do you have a sensor at the back drivers side of head for coolant temp gauge

BurtGummer

My Jeep does this same rough startup too from the sounds of it. But only when it's hot outside and usually on the first startup of the day. Well it's done it a few times this fall and winter but when my rig has been running for a while. First it was a misfire in cylinder 1 & 2, so I switched my spark plugs to 3 & 4. And the next time it happened the problem did move to cylinder 3 & 4, so I changed all four plugs. That worked but only for a while. Still doing it but it only happened once or twice a month in the cooler months..

Redwolf624

the downstream O2 sensor is 2 years old, i don't see how it would be bad already. i had the wires wrap the driveshaft 2 years ago and the preformance never changed
i don't know if it's an early or late model, i just know my fuel rail goes to injectors and straight to the head, i have a fuel line that comes off the front side of the fuel rail but no regulator.

Update:
the other day i tested the spark plugs and coil pack and they're all good, so i'm gettin spark, i'm gettin fuel, i know i'm gettin air because she fires up. I'm leading towards either the cat or the charcoal canister,

Redwolf

BurtGummer

Hey, so my Jeep did it yesterday. It was pretty cold outside so I don't think that's a factor anymore. Last spring I replaced the coilpack to see if that would do it. I talked to a guy I know that works in a shop and he said he worked on a Jeep with the same problem, and the coilpack was it. For them.....
Well it's still doing it. It started up and bogged at about 500rpm's so I turned it off. Tried once more and it did the same thing but I wanted to see if it would even out like it does sometimes. It died on it's own. I went into the Library with my girlfriend for an hour or so and let it cool down. it fired up just fine, idol was good. Drove away...
It rarely ever happens, but when it does...........

Redwolf624

I tested the fuel pressure yesterday and normally XJs are supposed to push 49 PSI give or take 5 PSI. Mine is pushin 30 PSI. I'm gonna replace the pump as i've already replaced the fuel filter....see what happens,

Redwolf