Stumped! 4.0L AX15 OBD1

[CHIEFWAHO]

Having issues with dad's old daily driver. 1981 with a 4.0L AX15 swap we did back in 2011. OBD1

Jeep started acting up (bucking, sputtering, dying) before dad's passing and has just sit the last couple years.
I've been trying to get it back on the road.

It intermittently loses the injector pulse. So first thought, CPS, changed that out with a know working Mopar sensor. No change.

What really baffles me is when the injector pulse goes away, I can dump a bit of gas in the throttle body and it then starts every time. Sometimes runs great for awhile until it's shut off or dies, then you have to wait awhile (for injector pulse to return) to restart without gas to the throttle body.

Fuel pressure is always good.

Always have spark when injector pulse disappears.

I am getting the 5V ref from computer.

Other components swapped with know working parts:
(3) different computers, map sensor, coil, CPS

Swapped auto shut down relay out.

My OBD1 scanner took a dump, so no help from that.

4.0 fuel pressure regulator & flywheel

I have installed a 1995 Grand Cherokee 4.0 eng in my 81 Scrambler. This eng does not have a fuel pressure regulator on the fuel rail and does not have a return line to tank. I want to mount an inline fuel pump, regulator, and filter (or filer/regulator combo) at the tank area. I believe I will...

www.cj-8.com

The original computer harness plug was broke, I thought maybe it was not keeping good connection to the computer so I pinned it out and replaced.

 

[spankrjs]

Maybe the camshaft position sensor/thingy in distributor has an intermittent fault??

 

[CHIEFWAHO]

Maybe the camshaft position sensor/thingy in distributor has an intermittent fault??

That's about the only thing I have NOT changed out yet.

I did unplug the cam sensor while it was running and it did not kill engine.

It was also receiving the 5 volt ref from the PCM

And the cam sensor is the style you have to pull the distributor to change it.

 

[spankrjs]

That's about the only thing I have NOT changed out yet.

I did unplug the cam sensor while it was running and it did not kill engine.

It was also receiving the 5 volt ref from the PCM

And the cam sensor is the style you have to pull the distributor to change it.

Yeah, pretty sure that how it is on my red Scrambler with the Mopar MPI based off 94 OBD1 Wrangler.

I just remember that the MPI instructions were adamant about putting the distributor exactly at TDC, not to try to adjust timing by twisting it around. I figure the distributor on the OBD1 is just a cam sensor that shares a housing with the plug wires, stop gap before they went coil packs and cam position sensors.

 

[Belizeit]

Your dad sure had a nice looking Scrambler. Beautiful

 

[CHIEFWAHO]

Your dad sure had a nice looking Scrambler. Beautiful

Thanks, but it is a little worse for the wear now.

We did a frame off resto mod back in 2006.

Dad flat used this Jeep between daily driving, wheeling and a work utility wagon.

Tub is about due for another frame off. The worst thing we ever did to this Jeep was spray bed liner inside the tub.
IMO opinion it seals one side and does not allow it to breathe, thus we now have some rust issues.

We will continue to use it as dad did. I really hope I get it going to take to this years National Scramble as this Jeep has been to several over the last 20 years.

 

[Belizeit]

Yeah I’m really glad I never put the spray liner in mine when I bought it new. I thought about it, we get a lot of rain, but someone I knew talked me out of it.

 

[CHIEFWAHO]

I believe I have finally tracked down the culprit causing the issues.

Was able to borrow a scanner that has capabilities way above my skill set.

Not knowing what I was really looking for, I noticed the "Throttle angle %" was reading 100 %
So that got me thinking, was that telling the PCM throttle was wide open?
While cranking with the TPS plugged in, I was not getting any injector pulse.
While cranking with the TPS unplugged, the injector pulse came returned.


With replacement TPS, the "Throttle angle %" was now reading 0 % at idle.


After installing a new TPS it has not once died on it's own and has restarted every time after shutting it off.
Now to get some time and miles on it to confirm a definite fix. Fingers crossed!

 

[mtruckstuff]

Having issues with dad's old daily driver. 1981 with a 4.0L AX15 swap we did back in 2011. OBD1

Jeep started acting up (bucking, sputtering, dying) before dad's passing and has just sit the last couple years.
I've been trying to get it back on the road.

It intermittently loses the injector pulse. So first thought, CPS, changed that out with a know working Mopar sensor. No change.

What really baffles me is when the injector pulse goes away, I can dump a bit of gas in the throttle body and it then starts every time. Sometimes runs great for awhile until it's shut off or dies, then you have to wait awhile (for injector pulse to return) to restart without gas to the throttle body.

Fuel pressure is always good.

Always have spark when injector pulse disappears.

I am getting the 5V ref from computer.

Other components swapped with know working parts:
(3) different computers, map sensor, coil, CPS

Swapped auto shut down relay out.

My OBD1 scanner took a dump, so no help from that.

4.0 fuel pressure regulator & flywheel

I have installed a 1995 Grand Cherokee 4.0 eng in my 81 Scrambler. This eng does not have a fuel pressure regulator on the fuel rail and does not have a return line to tank. I want to mount an inline fuel pump, regulator, and filter (or filer/regulator combo) at the tank area. I believe I will...

www.cj-8.com

View attachment 113792

The original computer harness plug was broke, I thought maybe it was not keeping good connection to the computer so I pinned it out and replaced.

put a '99 Cherokee 4.0 in mine. did a port match for the original 258 intake and put Howell fuel injection on it. Davis ignition. Runs like a champ and I got away from the Mopar junk injection. Uses 1985 OBD-1 GM throttle body system off 4.3 V-6. (all parts available at O'Reilly's/autozone/napa/advanced) I live in Colorado and changing elevation 5,000/10,000 ft used to be an issue. Howell system is self learning and I can go to any elevation and it compensates quickly. Just a thought.