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Need help. '94 4.0L 2wd auto died and won't start.

91Heep

NAXJA Forum User
Location
North Louisiana
1994 2wd Xj 4.0L engine 2wd with auto trans 157,xxx miles.

I'm trying to figure out what happened.
Previous owner replaced crank position sensor and ignition coil about 10k miles ago.
Has ran great until I hit a big bump.
I'm thinking there is a short somewhere but have exhausted myself searching for it.

Hopefully someone will know what parts to look at.

Here's what I do know.

-20 amp engine control fuse was blown.
-Fuel pump works, have pressure.
-No spark.

Information that I'm getting from scanner:
- tps above maximum allowable
-charge temp too high
-short in radiator relay circuit
-short in a/c clutch circuit

Where/what is the radiator relay?

Anyone have a clue as to what I may have going on here?

Any help is appreciated.
 
Alright so I started questioning myself on the radiator relay deal.

Here are the real codes of the last two
Code 33-Air conditioner clutch relay circuit-open or short detected in the air conditioner clutch relay circuit. If vehicle doesn't have air conditioning ignore this code.
Code 35-Radiator fan control relay circuit-open or short detected in the radiator fan relay circuit
 
sounds like the ground is disconnected. the tps, charge temp, and coolant temp all ground to the same point. check for ground on all the connectors it should be black with light blue.

also you may have a fuse burned out. its listed as F6 its a 15Amp. do your back up lights work?
 
Going back to look at it today.
I will check backup light function for sure.
That should indicate NSS function correct?

I checked battery to block ground but not the manifold area ground strap.

Will also check sensors for ground, studied the Haynes manual last night looking for management sensors common and see what your talking about.
 
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well the fuse that i think may be blown also looks to be driving the reverse lights. assuming the nss does work. if the nss was at fault it would not enable the starter.
 
Reverse lights do not work.
All other lights work and function correctly.
The interior fuse block doesn't have a fuse provision for 6 it's just a single female spade.
If it's under the hood, mine aren't numbered

I removed ground on engine block, at fire wall to manifold and near the computer, cleaned and made sure there was bare metal connections on the body.
The battery to engine ground had some green inside the wire group so I replaced it.

The tps and charge sensor have 4.9 volts positive power on all pins?
 
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After that I lost the a/c clutch and radiator fan relay codes but
The rest remain.
Although now they read:
Tps senor input above maximum allowable input voltage
Charge temp sensor input above maximum allowable input voltage
 
sounds like the ground is disconnected. the tps, charge temp, and coolant temp all ground to the same point. check for ground on all the connectors it should be black with light blue.

also you may have a fuse burned out. its listed as F6 its a 15Amp. do your back up lights work?

The ground from the pcm to the sensors?
 
Ok so looking in the manual again (I'm working nights this week so plenty of time to obsess over this) I see the 15 amp F6 from pdc.

According to the manual, there is a f15 30A and a F6 15A.
This is the fuse box I have: (figure 2)
http://www.cherokeeforum.com/how-tos/a/jeep-cherokee-1984-1996-fuse-box-diagram-398207

Neither fuse matches up.

I now see that the coolant temp sensor I've been focusing on was the wrong one, the pcm is connected to the thermostat housing sensor.

Is this black/light blue wire a pcm ground wire or the +5 volt feed?
I'm trying to figure out the common between them since I have the sensors all showing in the diagnostics.

I'm going to focus on this wire for the time being.
I don't understand the grounding of these these sensors to be honest.
 
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Ok I found a diagram of the PDC under hood thay had number labels for the fuses, someone made this themselves.
F6 was the small ignition system 15a and F15 was the large 30a engine control.
If this is correct, F6 is indeed good.
 
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probe f6 terminals to verify 12v is present.

also the charge temp sensor should be the incoming air temp. and it is located on the intake manifold.

its a grounded sensor but black with red is the ecu signal side.(pin 21) the black w/light blue runs to all the sensors and back to the ecu on pin 4.

if you can temporarily ground the black with light blue and see if all the codes go away you have a broken wire.
 
um... does it start? and now i would check where the original wire broke. might be rubbing on something and could damage more wires
 
No it doesn't start :(
But I feel you've helped me get pointed in the direction of fixing it and removing alot of guess work on my end.

This wire will get a thorough inspection asap.

Had it towed back to my shop today.
 
so it looks like your input systems are working but output systems might not be. also crank sensor will not throw a code on that system. so that might still be faulty. that whole ground circuit could be broken.
 
I did ground this stuff to the body btw, Idk if it will function doing it this way.
Perhaps I should try to go from where I spliced at to the pcm and bypass the wiring loop?

The upper bolt for the CKPS is missing and came from Autozone, atleast the ign coil did as it has the duralast symbol on it.
The original is in the glove box, I'm going to test it against the replacement.

Happen to know the bolt specs for the ckps?
If not I'll remove the other one and try to find one to match.
 
if the CKPS is the one on the bell housing if its to far away from the tone wheel it will never see the engine turning and will not fire the injectors or the spark. so you may have knocked that lose in the process.
 
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