Noah911

You can get a fuel psi gauge loaner tool. Check psi in run, but not with engine running yet for normal psi, that does not drop any significantly over a 5 - 10 minute timeframe. Check the psi next with the engine running to see if it holds pressure when the fuel pump continually operates. See if the psi goes up with increased RPMs.

If the psi drops, it has to be determined wether it is a problem aft at the pump, regulator, check valve... or, if it is leaking loosing psi forward internally at the injectors. There are ways to test for this when using the fuel psi gauge.

Alexr54

I do have a fuel psi test gauge. I tested the psi both while not running and while running. Both showed ~45-50psi. Maybe a little less then 50. I probably could have kept it on longer.
I already removed the fuel injectors and they all looked to be in really bad shape and very very dirty.

Noah911

Curious what was your tps voltage readings at the closed throttle position, and at the wide open throttle position?

New injectors should help with getting things running more optimal, no matter..

Alexr54

I don’t remember exactly. I think closed was a bit below 1 and wide open was about 4.5 or so. I also tried taping it to see if it would fluctuate and it didn’t.
Just need to wait on the delivery for the injectors now. So the Jeep is out of commission for a while.

Eventually everything will be new... I won’t give up until this gets solved.

Noah911

Wide open at 4.5V sounds good.

At closed throttle idle position, the TPS output voltage should be greater than .26 volts, but less than .95 volts.

The closed throttle at idle voltage is an important value. If it is too high at near or over 1 Volt while reading at the closed throttle idle position.. The PCM may see this as a partial throttle application when you have not pressed on the gas.

Alexr54

Thanks for the awesome info. I will check it again when I get the injectors in.
i felt bad about putting in a cheapo TPS so before I tested it I went and got a mopar one from the local auto shop.

It also seems like it can be a vacuum leak somewhere causing the issues. Although the codes I get have nothing to do with that.
The rough idle happens mostly in reverse and drive. In park it stumbles a little - but nowhere as much as in reverse or drive, while at idle.
Driving at higher RPMs feels and sounds great.

While I was at it I also replaced the idler pulley since it started making noise recently.
Also plan on replacing the AC compressor and accumulator in a couple weeks. And the exhaust system...

Its a huge work in progress.

Noah911

Yes definitely; also make sure..

The distributor work having been done is a suspect. Double check the entire area, looking to make sure it is all together correctly, and that you did not pinch or disturb the 'Pick-Up.. Cam Sensor wiring, and other wires and hoses and stuff near where you were working.

Vacuum lines... Once it is running you can check those, spraying around in the engine compartment with carburetor cleaner spraying onto the gasket areas and vacuum hose lines. They are not hard to figure out to see them to do.

Did the new Mopar TPS improve the performance any? Maybe getting your Jeep closer back to how it was performing prior to replacing the TPS with the aftermarket one, and before the tune-up? (not sure if you were able to change it out to see yet, before you pulled the injectors or not?)

Just as a piece of advice that may or may not mean something. I hear it does! Maybe someone will verify this if they have personally experienced it, or witnessed it with another 4.0L? I have heard many times from what I percieve as reliable sources, the 4.0L does not do well on any type of fancy spark plugs. The spark plugs that it does the best with are the inexpensive copper core Champion RC12LYC plugs. Super inexpensive plugs that just need changed a little more frequently. They are without a doubt, the reccomended single best possible spark plug you can put in a 4.0L Jeep. These are all I have ever run in my Jeeps, so I cannot say otherwise how it runs on the different type and brand of spark plug... I know 100% with certainty, many many people have written about and complained of poor running performance conditions when they switched putting in other spark plugs in a 4.0L Jeep. It might be a good thing to do, or at least to be aware of while you are having running issues that you are trying to chase down? So, that way you know this is not a possible reason contributing to make the running issues you are having to chase down from being worse, or exagerated.

I always gap the plugs before I install new spark plugs in a vehicle. I just replaced mine in my 4.0L. Only one of the new pre-gapped Champion spark plugs was initially set correctly at a gap of 0.35" new out of the box. I had to set the gap on 5 of the six new spark plugs that I got this time, before I went to put them into my Jeep.

Alexr54

So after all is said and done I found my problem.
it was either one of 2 things. I fixed both at the same time.

I replaced the ignition coil and I redid the ground for a better connection.
After this was done the jeep works better then I can ever remember.

I found it had had a weak spark which led me to do those things. The codes from the diagnostic tool was completely irrelevant and led me down a rabbit hole.

Noah911

How about that. I am glad it is running good again for you, and you found the problem!

In a perfect world.. The DTC's would tell you exactly the problem. Then, technicians would not need to go through hours and hours of training, followed by years and years of hands-on experience...

Misfires that are below the vehicles threshold often pass unnoticed, but a constant misfire is hard to be overlooked by you or the engine. Therfore, the PCM generates generic OBDII codes to do what they do best. In your case, all cylinders constant misfiring was pointed out for you in this way. They should never be considered an end all/be all with their information.