96 XJ stumbles then shuts off when warmed up. P0171

The one at the front is the sender for the computer, might try unplugging that one and seeing if the problem persists. The one at the back of the head. (If applicable, ) is the sender for the gauge.

Unclewolverine said:

The one at the front is the sender for the computer, might try unplugging that one and seeing if the problem persists. The one at the back of the head. (If applicable, ) is the sender for the gauge.

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Well, the gauge doesn't work, so maybe there's a dependency there? I'll go look for the one at the back of the head shortly.

If you have the rear sender it's my understanding that it only serves the gauge so it should have no effect on operating parameters. But if you unplug the front sender, the computer *should* default to warm up mode and stay there. That should tell you if its something in the computer that switches over once it hits operating temp.

Unclewolverine said:

If you have the rear sender it's my understanding that it only serves the gauge so it should have no effect on operating parameters. But if you unplug the front sender, the computer *should* default to warm up mode and stay there. That should tell you if its something in the computer that switches over once it hits operating temp.

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so if i fire it up cold and just unplug that sender on the thermostat housing, it should replicate the behavior? Am i reading that wrong? It'd be real cool if that's an easy way to test.

When i bought my 96, I had issues with it bogging down and dying when hot. It wouldn't re-start until it cooled off a bit. CPS turned out to be fine, but the bolts holding it in were finger tight at best. I guess when everything was hot and heat soaked, the sensor would move to a less than ideal position.

Confirmed on the two temp sensors. The rear one goes to the gauge and i do not believe it has anything to do with engine management.

Unplug it then start it. The cooling fan should default to on, since the computer can't read the temp it will try to cover all its bases. Drive normally. If it stays running its either in that sender or the computer. If not, it's elsewhere.

Numbers said:

When i bought my 96, I had issues with it bogging down and dying when hot. It wouldn't re-start until it cooled off a bit. CPS turned out to be fine, but the bolts holding it in were finger tight at best. I guess when everything was hot and heat soaked, the sensor would move to a less than ideal position.

Confirmed on the two temp sensors. The rear one goes to the gauge and i do not believe it has anything to do with engine management.

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Another valid point, most of the nuts and bolts on this thing weren't even hand tight when I picked it up. Looks like the project stopped midway and got sold. As far as the CPS, I replaced it last night, and I know for a fact that those bolts are tight.

Just as a stretch, check the wiring for the CPS, as in the the harness before the plug.

'96 is known as a bastard year (I have no complaints about mine, but I may share traits with it), and especially as regards sensors. Folks have trouble matching them up. When I went to the stealership to get a CPS they gave me one with the wrong plug. I am probably not the only person to whom that has happened. If you are dealing with a winner of a half done project it might be the case that someone tried to change the plug to match a wrong sensor.

That would just be one possible cause of a wiring problem.

It doesn't cost anything to inspect the wiring.

The other thing to check out is the quality of your ground connections. The resistance inherent in the wiring does not improve with age. Add a deteriorating connection and you could have your root problem. See this for an example of what I dealt with on my own '96 XJ: https://www.naxja.org/forum/showthread.php?t=1148570

Edit to add: I forgot that was done in order to resolve an intermittent stalling issue. (Yes, I have CRS) A bad ground or bad wiring to a ground could be exactly what you are looking for.

Anak said:

Just as a stretch, check the wiring for the CPS, as in the the harness before the plug.

'96 is known as a bastard year (I have no complaints about mine, but I may share traits with it), and especially as regards sensors. Folks have trouble matching them up. When I went to the stealership to get a CPS they gave me one with the wrong plug. I am probably not the only person to whom that has happened. If you are dealing with a winner of a half done project it might be the case that someone tried to change the plug to match a wrong sensor.

That would just be one possible cause of a wiring problem.

It doesn't cost anything to inspect the wiring.

The other thing to check out is the quality of your ground connections. The resistance inherent in the wiring does not improve with age. Add a deteriorating connection and you could have your root problem. See this for an example of what I dealt with on my own '96 XJ: https://www.naxja.org/forum/showthread.php?t=1148570

Edit to add: I forgot that was done in order to resolve an intermittent stalling issue. (Yes, I have CRS) A bad ground or bad wiring to a ground could be exactly what you are looking for.

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I think I'm going to go over the grounds tonight. Also tried to find a camshaft position sensor and am finding that you can't get it without replacing the whole distributor. Might do that too. I have the pcm that it came with, now repaired, might put that back in first and test it out. Every road I'm taking right now leads nowhere.

Don't know about the 96 model but my 98 you could replace the cam sensor I got mine at Napa.

Napa echlin calls it a distributor pickup MP 833 is this what you need?

jeep ride said:

Napa echlin calls it a distributor pickup MP 833 is this what you need?

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Possibly, I’ll call them in the am. Thanks!

So on the cam sensor, even with heat soak failure it should throw a code, right? Wondering if it would be good to just replace the distributor in its entirety for good measure. Looks original.

When the cam sensor failed on my 2000 it never threw a code, I'm assuming because it was a "intermittent" failure with it sometimes starting right back up after stalling out.

Anak said:

The other thing to check out is the quality of your ground connections. The resistance inherent in the wiring does not improve with age. Add a deteriorating connection and you could have your root problem. See this for an example of what I dealt with on my own '96 XJ: https://www.naxja.org/forum/showthread.php?t=1148570

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Once again Anak - great stuff - really appreciate your excellent, clear narratives with pics. All have been a great help for another '96 owner over the years

fenns7 said:

Once again Anak - great stuff - really appreciate your excellent, clear narratives with pics. All have been a great help for another '96 owner over the years

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Picked up the cam sensor this morning.
Ground refresh is definitely on the list for today. Well, once I can escape this desk...

fenns7 said:

Once again Anak - great stuff - really appreciate your excellent, clear narratives with pics. All have been a great help for another '96 owner over the years

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Thank you.

It is nice to hear that it helps someone.

So after replacing just about every sensor and checking every wire I can get to, it's down to the fuel pump.
Recently read somewhere that early '96 xj's with the regulator on the rail should have a pressure of something like 31psi, and later without the regulator on the rail, 49psi. Wasn't exactly sure which I have, since build date is 5/96. I cannot find a regulator on the rail, and the filter is in the location specified as that for the later iteration with the regulator in the tank.

I've been hoping it wasn't the pump, but I'm resigned to the strong possibility that it is.

Right now, when it starts, the needle on the pressure gauge fluctuates between 26-31 so fast it appears as a blur. Occasionally, it dips to 10. (likely where the lean code originates)

I'm considering replacing the tank as well as the pump all at once, as it's likely that I'll find 26 years' worth of sediment in it which will likely cause problems going forward.

Checked the grounds, they all look good, but going to follow guidance and refresh them anyways. Waiting to do so until pump and tank come in so I can make good use of borrowed shop space. (doing this in my driveway basically makes me a feast for mosquitoes and horse flies)

Any recommendations for things to change out while I'm at it?

If you are going to drop the tank now would be the time to do the vent tube mod so you can carry an extra 5 gallons of fuel if you so wish.

I would not necessarily replace the tank. I would check the condition of the tank first. The OE tank is constructed substantially better than the cheap replacement tanks.

It would be a good idea to get a pair of new grommets for the vents (be careful with the vents themselves--I think you would have to pull another tank in a junkyard if you were to need to replace them), new hose for the fill tube and the vent tube, new vacuum lines for the two vents and new fuel injection rated fuel line for the run to the fuel filter. Now is the time when you will be disconnecting most all of those lines, and being over 25 years old odds are good it will be due for replacement. Oh, and make sure to get a new seal (big honkin' O-ring) for the fuel module.

Anak said:

If you are going to drop the tank now would be the time to do the vent tube mod so you can carry an extra 5 gallons of fuel if you so wish.

I would not necessarily replace the tank. I would check the condition of the tank first. The OE tank is constructed substantially better than the cheap replacement tanks.

It would be a good idea to get a pair of new grommets for the vents (be careful with the vents themselves--I think you would have to pull another tank in a junkyard if you were to need to replace them), new hose for the fill tube and the vent tube, new vacuum lines for the two vents and new fuel injection rated fuel line for the run to the fuel filter. Now is the time when you will be disconnecting most all of those lines, and being over 25 years old odds are good it will be due for replacement. Oh, and make sure to get a new seal (big honkin' O-ring) for the fuel module.

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This is amazing info, thank you!

Just got called out of town, again. Will see what I can source in my travels so I can put some time into this on Sunday.