xjmuddigger

my xj was misfirin and i put new wires,cap,and rotor and now its misfirin when im in drive and goin,its fine in reverse,neutral,park,i need to get this fixed tomorrow,what do i do?

Basslicks

Sounds like the timing is off... did you re-time it with a light after you replaced everything?

- Justin <><

xjmuddigger

i put the wires and cap in the exact same spots as they where before they were changed

Basslicks

Yeah, but you said it was mis-firing before too right? Doesn't happen all the time, and may even be rare, but hitting a potholes just right every now and then has the ability to knock a motor out if time...

- Justin <><

xjmuddigger

well i was told it may be my O2 sensor but im not sure but i dont see how the timin changed cuz the distributer is very tight,and it cranks up very easy but just misfires when i accelerate

Basslicks

I would think checking the timing would be cheaper than changing an o2 sensor... I had a 91 s10 with a 4banger that would start up in less than a second in hot or cold weather... but the timing was advanced just enough that I had to run premium in it to keep it from knocking... and we couldn't time it with a light because there was a ground wire that needed to be undone that we didn't know about till after (i was too lazy to have it re-timed once we figured that out).


I'm just saying, try it... that's all... vehicles aren't perfect and crazy stuff happens sometimes that isn't designed to happen... so might as well cover all the bases. If you need a timing light, autozone will loan you one for free...

- Justin <><

xjmuddigger

ok well ill do that tomorrow,but could a bad TPS cause this as well?

Basslicks

Not sure... I would think if it was that, it would do it whether under load or not... also, check your vacuum advance on the distributor as well... if you have a leak I'm the line, the spark timing when you accelerate won't advance... usually makes it sluggish, but it may make it misfire.

- Justin <><

xjmuddigger

whats the vacuum advance thing? i dont know much about electricals or whatever,im more fabbing kind of guy

Basslicks

Just check to see if there is a vacuum tube connected to a fitting on the distributor... if there is, check the tube for leaks...

- Justin <><

xjmuddigger

ok,i will do that tomorrow and im also gonna do the top dead center thing and get the timin right as well then check my O2 sensor and my TPS

SNIDELYWHIPLASH

Since it hasn't been mentioned, I should point out that the timing on a 4.0 is not adjustable.

quote:
"The 4.0L engine's timing is 100% under control of the engine computer and cannot be adjusted. Even rotating the distributor as was done on older engines will not change the timing, the computer will override if you attempt to change it by rotating the distributor.

There is no need to worry about the timing, the computer actually does a vary good job of setting the timing where it needs to be."

source:
Answers.com - How do you set the timing on a 4.0 liter jeep

xjmuddigger

then what could cause this?

xjchase

I would check to see if your coil is getting weak and not sure if 91 has CPS (crank position sensor) but if it does check that as well. Mine is doing the same thing but I also only have 30 psi of compression so mines getting a rebuild!

xjmuddigger

so my CPS may be doin this?