Engine Sensors

OlyJeep · Feb 15, 2008

Hello. My trail rig is a '92 XJ with a 4.0L HO. It has almost 200k and I'm looking to replace the critical sensors for added reliability on the trial. I realize that some failed sensors may result in a completely dead engine (i.e. crank position sensor), while others may only cause a rough idle. Which sensors are most critical? Also, what is the life expectancy of the main computer? Thanks.

OlyJeep

JOOP · Feb 15, 2008

pay the money and have a shop scan it and pull the codes. Otherwise you just wasting money and throwing parts at it.

Wildman1 · Feb 15, 2008

OlyJeep said:
Hello. My trail rig is a '92 XJ with a 4.0L HO. It has almost 200k and I'm looking to replace the critical sensors for added reliability on the trial. I realize that some failed sensors may result in a completely dead engine (i.e. crank position sensor), while others may only cause a rough idle. Which sensors are most critical? Also, what is the life expectancy of the main computer? Thanks.

OlyJeep

The ones I would look at are as you said the ones that can kill the rig.
I would carry a crank position sensor, throttle position sensor, and maybe the map sensor. Or replace these and then carry the old ones. I have seen a CPS fail on the trail and the TPS if it gets wet fails pretty easy. The other thing I would do is get a code reader and carry it with you. I got mine at Shucks for about $60 on sale. It is a basic unit but does the job. On a 92 it might be a little harder due to it being an OBD I instead of OBD II.
The main computer should not fail unless you get a voltage spike or something like that. You should be able to find a used spare on Ebay. I got one for my Jeep for $50.

GaryTJ · Feb 15, 2008

Your system is one of the most reliable systems out there. Also, you can't cover for every eventuality.

Personaly, I would carry a Crank sensor and a fuel pump and thats about it.

Chrysler computers have an internal "substitute with known good value".
That is why they are hard to diagnose sometimes, because the value you are seeing might be a "replacement value" You have to read right after code clearing to get good values.

but, that also makes them reliable.

NotMatt · Feb 15, 2008

The 4.0 is a pretty reliable motor... crank sensor would be the big thing I would be wary of. If you feel you need to, swap it out and carry your old one as a spare. TPS can be finicky sometimes too, but you can still limp home with a non-functional TPS... if you wanted to, carry a spare for that one. Maybe a spare coil if you wish, I've never had one die on me though. Honestly, I've never had problems with any of the other electronics on any of my various 4.0 rigs I've had over the years, and that says something as far as problem areas. CPS is really the major one... and sometimes it's not the CPS itself but the connector to the CPS gets corroded and doesn't make a good connection, and simply unplugging and re-plugging or wiggling it will help.

As far as other good things to carry goes... In addition to what Gary said, I would also carry a spare serpentine belt and idler pulley, a spare upper and lower rad hose, some hose clamps and a length of heater hose. Cooling system failures will leave you dead in the water (no pun intended)... been there, done that... don't want to do it again, so I carry spares and enough water to refill the coolant if I should need to.