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98XJ stumbling/loading up/cutting out...HELP!!

XJ&CHZ4ME

NAXJA Forum User
Location
Unionville, MO
OK gang, I am here to ask for help this time instead of to give it :D I have searched until I am about ready to fall asleep.

This is the rig I am working on:

1998 XJ/4.0/AW4/NP231

The rig will fire right up and idle perfect, and even in park or neutral you can rev it to the rev limiter and it runs perfect. Once you put it in gear and get going and try to accelerate under power, it loads up and wants to sputter and try and die. I have put a fuel pressure gauge on it and it holds a constant 46# of pressure at the rail. We replaced the TPS and there was no change, then we replaced the CPS and there was still no change. We took both items back off and put the original ones back on and still no change. We also did a quick cleaning on the sensor (like an air intake sensor of sorts on the side of the TB). We have not replaced or messed withe the MAP sensor....I am at a loss at this point. I am at my brothers working on this rig w/ his very limited tools, so it is even more frustrating that I am 6 hours from my shop with everything I need. Any help is greatly appreciated...HELP !!!!!!!

Thanks in advance.:thumbup:

Cheeseman-OUT!
 
i have a friend with a '95, it did pretty much the same thing. everything "tested" fine, just screwing around we threw in a known good ignition coil. fixed it. just throwing that out there... sounds like a spark-breaking-down-under-load issue.
 
it could be trying to take off in another gear other than 1st.

Could be, unplug the TCU and see.

Bad cap/rotor/coil, been a few reports of cracked rotors.

What was happening before this problem occurred?
 
A failed or lazy Coolant Temp Sensor will cause bogging. It may run well at light throttle and at Wide Open Throttle, but bog and sputter in between.

A failed or lazy O2 sensor can cause bogging, stumbling, and will have very poor MPG's.

Consider that an O2 sensor wire or other sensor wire has chafed or melted insulation and may be shorting out or shorting to ground, causing the symptoms. A physical inspection of the wires is a good idea.
 
Can we assume there is no check engine light? If so, you must pull codes for guidance.

Other than that, there is some good suggestions above from the others.....Test your way to a solution and keep us posted.
 
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Could be, unplug the TCU and see.

Bad cap/rotor/coil, been a few reports of cracked rotors.

What was happening before this problem occurred?

I should have added, it has a recent tune up w/ cap, rotor, wires and plugs. It was running fine he said until he was wheeling and stuck it in some deep mud (water more then anything) and it ran ok the rest of the day on the way home but started acting up later....I am going to check the items mentioned again to see if the cap or rotor might be to blame.

A failed or lazy Coolant Temp Sensor will cause bogging. It may run well at light throttle and at Wide Open Throttle, but bog and sputter in between.

A failed or lazy O2 sensor can cause bogging, stumbling, and will have very poor MPG's.

Consider that an O2 sensor wire or other sensor wire has chafed or melted insulation and may be shorting out or shorting to ground, causing the symptoms. A physical inspection of the wires is a good idea.

It runs great at all levels while in park or neutral, but when in gear w/ any type of load applied to the motor it starts chugging and bucking. The check engine light is not on, so I did not evenn think about checking the O2 sensor yet...I will physically inspect the sensor and wiring tonight.

Can we assume there is no check engine light? If so, you must pull codes for guidance.

correct, there is no check engone light on at this time. When I was driving it I was hoping teh light would come on so I could pull a code and chek it that way...no such luck yet!


Thanks for the input guys, it is easy to overlook the obvious sometimes when ya get to close to a project. I will hit it again later today and see if we come up with anything. Thanks again!

Cheeseman-OUT!
 
It runs great at all levels while in park or neutral, but when in gear w/ any type of load applied to the motor it starts chugging and bucking...


same thing on mine, to an extent. everyone here said the same thing to check. even got motor mounts and trans mount.

my plugs were worn to 1mm, compared to what? 6-8 new? and the gap was at .075+ due to this. .035 is the correct gap. check plugs, 1 minute job.
 
...was running fine he said until he was wheeling and stuck it in some deep mud (water more then anything) and it ran ok the rest of the day on the way home but started acting up later....

This would point directly to a failed Throttle Position Sensor (TPS). TPS and water do not play well together Test the TPS. Several of the local XJ's have had TPS failure from deep water crossings that resulted in stalling in the middle of a hood deep pond. The CEL did not turn on with any of these failures.
 
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This would point directly to a failed Throttle Position Sensor (TPS). TPS and water do not play well together Test the TPS. Several of the local XJ's have had TPS failure from deep water crossings that resulted in stalling in the middle of a hood deep pond. The CEL did not turn on with any of these failures.

I had the same experience when I soaked my TPS in some deep water crossings. It felt almost like transmission failure driving back; thank God it wasn't. Try a third TPS - oh, and grab a replacement IAC while you're at it; the one in the throttle body may have gone bad before you cleaned it out. May as well pull the IAS out of the manifold and give that a clean as well while you're in there.

Here's an off-the-wall suggestion: is the catalytic converter OK? You say the XJ was in mud; is it possible that some of that got sucked back into the exhaust and plugged the cat? I know that seems counterintuitive given that it'll rev in park/neutral but won't pull in gear, but I have seen plugged cats cause weirdness that only shows up under load a couple of times. There's a chance this might not throw a code, so could be worth checking into.

Also, did any water get into the cabin? You didn't mention if this was the case or not, but I'm almost wondering if the TCU didn't get a soaking and as a result isn't working properly, leading to bogging the engine down under load when the tranny's in gear. Might want to unplug it and see if things get any better; at least it's a quick & easy check.
 
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Something similar happened to me a few years ago. Got stuck in a huge mud puddle, then couldn't get over 50 MPH on the way home. It ended up being the header/exhaust gasket. We sprayed some starter fluid around the manifold and the engine would rise, that's how we figured it out.
 
Something that gets water in it before the TPS is your distributor. Check for condensation under the cap and on the rotor.
 
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