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1996 Cherokee Country 4.0L, AW4
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Discussion Starter · #1 ·
Hello, fellow forum-ers.

I'm have a puzzling issue with my 1996 Cherokee 4.0L.

Problem:
The XJ will start quickly, it will run for a second or so, then it stalls. It will crank right back up and stall, again and again.

Things that have been done:
Scan for codes - no codes
Ignition side:
New cap, rotor, plug wires, and spark plugs - there is spark.
New crank sensor - MOPAR brand
New cam sync sensor
New PCM - preprogrammed with my VIN
Ground connections - removed, cleaned, reinstalled. I even ohmed the ground connections to the battery and found between 0.4 and 2.5 ohms. Two connections by the PCM that ground the harness, connection on firewall to the back of the head, two connections on the right front of the engine block to the battery, and right fender to the battery.
Ignition switch - removed and check for proper power in the off, run, and start positions. All tests good.
ASD circuit - relay is good. Powers the ignition coil and fuel injectors properly

Fuel side:
Found the wrong fuel pump installed and replace the fuel pump and fuel filter. I have 47-48 psi at the fuel rail, even after the stall.
Fuel tank is clean.
Pick up sock is new.
Fuel filter is new.
Fuel lines from tank to fuel rail are clear, no kinks, or other obstructions.
New fuel rail.
New fuel injectors.

Most of this was bought and installed by the previous owner. I did go through and verify the new parts.

I'm leaning toward some kind electrical issue at this point.

Does anyone have any thoughts?
 

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How many miles on the clock?
What engine?

The new PCM is a little concerning. Why was the original PCM replaced?
IMPORTANT Did the engine ever work ok with that new PCM?

Without knowing the exact fuel pressure spec. it appears to be in the ballpark but have you measured the pressure while trying to start the engine?
That will indicate if something is turning off the fuel pump or some problem with the pump or its fuel psi regulator.

Measuring ground cables end to end with an ohm meter could sometimes be useful but also check for any corrosion at the cable's connection to its spade or other terminals.
However the electrical connection from the cables spade terminal to the engine block, etc. cannot be reliable tested with an ohm meter. That ground connection must be cleaned.
For example:
Lets take that 2.5 ohm measurement with 2 Amps running through that cable.
From Ohms Law (V=IxR) that would be a voltage drop of 5 Volts across that cable.
Nominal battery voltage during a cold start is 12.6 Volts - 5 Volts = 7.6 Volts to what ever electrical load that cable is energizing.


Its unclear if you actually cleaned the ground connections if not:
Disconnect the Neg battery cable and then remove each and every ground terminal and burnish both the terminal spade and its mating surface bright with some fine grit sandpaper, wipe off any sand paper grit with rubbing alcohol and refasten.
Do not use dielectric grease on ground connections.

Some things to consider other than electrical are:
-a vacuum leak
-IAC valve is stuck or broke
-MAP sensor
-TPS sensor
 

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1996 Cherokee Country 4.0L, AW4
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Discussion Starter · #3 ·
272k on the clock.
4.0L

47-48 psi with key on, cranking, and when it starts.

The ohm readings were from the various ground connectors to the negative battery post. The grounds were and sand papered, cleaned, and reinstalled. No dielectric or any other substance used.

The old PCM was replaced because I thought there may be something in the PCM causing this problem. The problem still remains with the new PCM.

IAC is new.
No vacuum leaks.
MAP is working.
TPS is working.

Sensor operation was checked through the OBD port. I was able to log the crank start and then the stall of the engine. However, I cannot see all the PIDS with the software in using.
 

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But did you perform a fuel pressure test to see if the fuel pump shuts off after a start?
I'd eliminate that issue and then proceed forward.

If you're positive all those sensors are working i'd next concentrate on a vacuum leak somewhere.
Also make sure both the IAC and the throttle body gaskets are not leaking and intact.
A new IAC sometimes needs time to calibrate itself if its not bad out of the box.

Any chance of re-installing the original PCM and see what happens?

Worst case and I hope this is not the case but the engine could be semi-seized.
Pull the spark plugs and manually turn over the engine at the crank's vibration dampener's bolt to verify.
 

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Discussion Starter · #5 ·
But did you perform a fuel pressure test to see if the fuel pump shuts off after a start?
I'd eliminate that issue and then proceed forward.

If you're positive all those sensors are working i'd next concentrate on a vacuum leak somewhere.
Also make sure both the IAC and the throttle body gaskets are not leaking and intact.
A new IAC sometimes needs time to calibrate itself if its not bad out of the box.

Any chance of re-installing the original PCM and see what happens?

Worst case and I hope this is not the case but the engine could be semi-seized.
Pull the spark plugs and manually turn over the engine at the crank's vibration dampener's bolt to verify.
Yes. I did a fuel pressure test.

I plan to check further this weekend with the IAC and throttle body possibilities you suggested.

The Jeep does the same thing with the old PCM as it does with the new PCM.

The engine is not seized. It will start every time. It cranks easily. It just stalls after a second or two. I sounds great when it starts, but it does not stay running.

I did verify the timing with #1 at TDC and the timing mark on the harmonic balancer.
 

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One thing i forgot to ask is this a newly acquired XJ which had the problem out of the gate which could have stale or contaminated gas?

OK you replaced the IAC, CPS and injectors?
Its possible the new IAC is bad out of the box.
Did you replace the TPS? I could be wrong but replacing it on your year is plug 'n play with no calibration procedure.
Air filter?
At 270K miles the timing chain could have skipped a tooth or two or is worn way out of spec?
How did you determine again that the MAP sensor is good without replacing it?

This to me smacks as a fuel supply problem, a faulty air/fuel ratio after startup or a vacuum leak.
If the fuel pressure did not drop during startup or shortly after when the engine dies that pretty much eliminates a fuel supply issue.

Not to leave out a possible ignition issue or injector issue. When replacing the injectors its not hard to cross their connectors.

I'd double check the cam sensor replacement procedure.

If you didn't do this already, one quick thing to try is to 'prevent' the engine from starting by any means maybe pull the fuel pump relay then crank the engine continually and test for 'continual spark' at the each of the cylinder spark plugs.

Yeah not an easy thing to trouble shoot this without a diag. scanner tool but have to methodically eliminate possible culprits one at a time. Been there done that.
After changing all those parts with nothing new to try might even re-install the original PCM and see what happens.
 

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Discussion Starter · #7 ·
I did put a new IAC in today. I removed the throttle body and cleaned out the IAC chamber. Still does the same thing.

I logged the MAP and TPS on my HP Tuners software. The numbers look good.

The fuel in the tank is new. The tank is clean.

There is a fuel problem. I was able to keep the engine running, and it ran very well, by spraying carb cleaner through the TB. I have been over the engine and vacuum lines multiple times. I cannot find any vacuum leaks. The lines and gaskets appear good.

I'm wondering if the previous owner installed the wrong fuel injectors. 1996 was a transition year for the fuel system. I did find he installed the wrong fuel pump. My fuel system is 49psi +- 5psi. It is internally regulated in the fuel pump module. I bench tested the module and got 48 psi. I connected a fuel pressure gauge at the fuel rail and got 47 psi with key on, while cranking, and after it started then stalled. I'm not losing fuel pressure or volume. This is why I'm beginning to suspect incorrect injectors.
 

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No telling how, why or what the POer(s) did.
I would 2nd guess everything the POer did including all those replacement parts that were installed.

When you spray the starting fluid into the throttle body does the engine seem to idle smooth and at idle rpm's?

Far as the throttle body, i'd make absolutely sure its gasket is not leaking. Might want to spray the starting fluid around those gaskets instead of the throttle body air intake port.

Its still possible this could still be an air/fuel ratio problem even though the numbers look good.
I'd check the IAC, MAP and TPS connectors carefully for spread or corroded pins if not already.
As a last resort i would replace first the MAP and see what happens then the TPS.
Might be able to get them at a bone yard or cheap aftermarket just for testing purposes.

If you replace the injectors, i'd go with Dodge Neon or equivalent 4-hole injectors, they made a noticeable performance improvement on my 4.0. Stock 4.0 injectors are one holers with crappier fuel atomization.
I got my used 4-hole injectors for a reasonable price from this place:

Before replacing the injectors, check their wiring harness rail and where it bends at the firewall for anything suspicious like frayed melted wiring, broken wires, etc. My old '94 XJ's 4.0 had a problem in that harness.

Far as vacuum leaks, my current 4.0 out of the blue developed a rough idling problem.
I checked for vacuum leaks and found the culprit. It was an unused vacuum nipple on the intake manifold sealed off with a rotted enlarged rubber cap about ready to fall off.
 

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Discussion Starter · #9 ·
No telling how, why or what the POer(s) did.
I would 2nd guess everything the POer did including all those replacement parts that were installed.

When you spray the starting fluid into the throttle body does the engine seem to idle smooth and at idle rpm's?

Far as the throttle body, i'd make absolutely sure its gasket is not leaking. Might want to spray the starting fluid around those gaskets instead of the throttle body air intake port.

Its still possible this could still be an air/fuel ratio problem even though the numbers look good.
I'd check the IAC, MAP and TPS connectors carefully for spread or corroded pins if not already.
As a last resort i would replace first the MAP and see what happens then the TPS.
Might be able to get them at a bone yard or cheap aftermarket just for testing purposes.

If you replace the injectors, i'd go with Dodge Neon or equivalent 4-hole injectors, they made a noticeable performance improvement on my 4.0. Stock 4.0 injectors are one holers with crappier fuel atomization.
I got my used 4-hole injectors for a reasonable price from this place:

Before replacing the injectors, check their wiring harness rail and where it bends at the firewall for anything suspicious like frayed melted wiring, broken wires, etc. My old '94 XJ's 4.0 had a problem in that harness.

Far as vacuum leaks, my current 4.0 out of the blue developed a rough idling problem.
I checked for vacuum leaks and found the culprit. It was an unused vacuum nipple on the intake manifold sealed off with a rotted enlarged rubber cap about ready to fall off.
When I sprayed the carb cleaner it ran smooth.

I put a new TB gasket on, too. The old one was sealed well, no leaks.

I got a noid light and will be checking the injector wiring harness tonight.

I did check the connectors for the IAC, TPS, and MAP. The connector seals were good and there was no corrosion, bent or broken pins, and the voltage from the PCM was at 5v and the ground wires were grounded on the TPS and MAP.

I have the rubber cap on my intake, too. It is good.
 

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Discussion Starter · #10 ·
The noid light test indicates all the injectors are getting a consistent signal to fire from the computer.

Then I checked the injectors and found that they were intermittingly firing. The injectors are SMP FJ682 and appear in new condition. The inlet and outlet of each injector is very clean. It checked the resistance of each injector and measures 13.9 to 14 ohms across the coils on each of the injectors. I'm thinking the resistance is too high. Is the resistance supposed to be 8 to 12 ohms?
 

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I did a quick check on that Standard Motor Products injector part number and it looks like its the correct replacement for your engine.
Far as the coil impedance offhand no idea though i once knew it when i replaced my injectors but that was years ago.
Might want to search the specs. for that part number.

If the engine starts and keeps running by spraying startup fluid in the throttle body i sorta doubt its the injectors but i've been wrong before.
 

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Discussion Starter · #12 ·
I think I will remove my fuel injectors and have them tested and cleaned/repaired if needed.
 

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Discussion Starter · #14 ·
I ran a scan on the PCM and found one of the PIDs was labeled "Safety Fuel Cutoff." This PID had a value of "no" until the engine started, then the value changed to "yes." When this value changed to "yes" the engine dies. I cannot find anything about this anywhere. Does anyone have any knowledge of this? I do not have a factory alarm system, or any alarm system, and the VATS in the computer are disabled.
 

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Without knowing the exact CEL trouble code i'll take a wild guess, that could be the ASD relay acting up.
What are VATS?
 

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Discussion Starter · #16 ·
VATS = Vehicle Anti-Theft System

The ASD relay checks out good. I still have power to the ignition curcuit and the fuel injectors, even after the engine stalls.

There are no CEL codes.
 

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The symptom you're describing, at least to me at this point looks like its ASD related.
The PCM controls the ASD system which can shut power off to the injectors, fuel pump, etc. so the new PCM is a little concerning.
Do you still have the original PCM to try?
Who knows what other data the PCM needs in order to employ a ASD shutdown.

One thing you might try to verify is to monitor the ASD relay contacts and its coil with a multimeter and see what it does when the engine shuts down.
Not the easiest thing getting at those relay pins in their sockets and might need an electrical diagram or at least the ASD realay pinout.
One other thing if not done already is to check the ASD socket pins for spread or corroded and any associated wiring to the socket.
 

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Discussion Starter · #18 ·
I did monitor the ASD relay. When the engine stalled, there was no loss of power in the ASD circuit. The ASD circuit also powers the ignition coil. I can keep the engine running with carb cleaner. There is no loss of power at the fuel pump and no loss of fuel pressure, either. This is beginning to be a PITA. Hahaha

I'll start going back over everything, again.
 

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So you can keep the engine running with carb cleaner?
That tends to indicate no fuel supply with the assumption the injectors are working?
Have you done a fuel pressure test while spraying the carb cleaner into the throttle body?
 
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