Help with 4.0

336wheeler

Well-Known Member
Joined
Sep 9, 2006
Location
Boone
So it comes down to the time to actually get the YJ moving without me pushing it around. I'm having a problem. The motor will roll over all day, and I get fire to my coil, but I'm not getting any ohms off of my CPS. I had to cut and crimp my own CPS for it because the harness end was correct, but it has the TF999 in it currently and it needed the tall round sensor end, so I cut both and got both ends right. Unless the factory changed the wires around on me, the wires are black/white/black, and the white wire is only white on one side. The sensor is new, came with the paper on it, pushed it down until the paper made contact, and tightened it up. However, it just won't do anything. Anyone with an OBD 1 computer around the Asheboro area want to come check it out? I will pay for it, no worries, I just need some help to get the electronics squared away.
 
I believe that I've narrowed it down to the VSS not being hooked up, which will make the circuit incomplete. Will hooking up the VSS (splicing in a harness plug and then putting one in the D300 from a CJ-7) work?
 
And you have no problems with getting fire from your CPS?
 
Well, I've never actually tried testing my CPS, so I'm not entirely sure what is SUPPOSED to happen there, but my engine runs fine. :)
 
You DO NOT need the VSS to fire a 4.0. You DO need to to complete the logic circuit for the AW4, but that is not your problem.

Jeep DID NOT change the sensor or the wiring of the CPS.

1. Make sure you have fuel pressure. I know it sounds stupid, but I have seen worse.

2. Make sure your ground to the computer is good. They get real touchy with a bad ground.

3. Does it try and fire/run for a little bit? It is possible to get the key on power and the constant power crossed so it only runs for a couple of seconds, and there is also the encoded key deal. but it will start/run for 5 seconds or so.

4. The plug end has signal/ground/5v power. You can find the ground and 5v in other plugs on the engine to check to make sure you have a good contact. You can trace the signal wire back to the computer and check the pin there to make sure the signal wire has continuity.


MOST 4.0 problems I have run into involve either a bad splice, bad ground or bad fuel pressure. There is not too much else to mess up.

I really can't emphasize the fuel pressure thing enough - I have burned up three pumps that made the noise/squirted fuel/etc but only made ~20 psi at the rail. 4.0's need at least 30-35psi to run.

Any 91-95 4.0 computer will work for diagnostic purposes.

Good luck,

Gavan
 
Well I was gonna try the VSS thing last night, but a)ran out of time and b)apparently it's not needed. It will roll over, but never cranks. I'm not getting anything off of the CPS unless I turn it from ohms to milliamps.
 
Do you have the check engine light hooked up? Even if you do not, you can check the codes with an analog ohmmeter. Ground one end of the ohmmeter, other side to the check engine lead (black/red of I am not mistaken)

Cycle the ignition 3 times and watch the blips on the ohmmeter.

Good luck...
 
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