My 94 4.0L has developed a cough and sputter between 2100-2500 rpm. It sometimes clears after 2500 rpm other times not at all. Does this cold or warm. No codes shown. New plugs, wires, ignition module, CPS, cleaned MAF and throttle body and even swapped the old injectors back without a change. Any ideas?

 

Aj6 or AJ16? If AJ6 since you mention plug wires… Cap and Rotor are shot.

 

its the 6 cylinder. New cap and rotor and fuel pressure unit too.

 

there are two versions. AJ16 and AJ6. One uses plug wires with cap and rotor and the other uses coilpacks. You should familiarize yourself with the difference so that when you ask for help, you get the right help. Your AJ6 doesnt use a MAF sensor, it has an airflow meter. So we need to get some proper details. A dirty TPS will cause stalls and rough running at times, or an air leak

 

I have the AJ6.

 

My firs thought is that the fuel pump may be getting old and it will give up the ghost at some point. I experienced a similar thing before the pump gave out. When you fill up, use Shell gas only for a couple of weeks fo see if it makes a difference. It used to make a difference with the old pump in place. My second thought is an air leak somewhere in the system. Smoke test it

 

The first thing I did 9 months ago was put in a fuel pump. (not very fun). Since then I've gone thru the emissions system and just about every sensor including the Engine ECU and harness. Finding the connection to read ALL the codes I was getting was a watershed moment. I tackled the TPS today. Cleaned and recalibrated it. That seemed to do the job. I'll take it on a long test drive tomorrow to confirm. Removing the throttle body wasn't too bad. It was black on the manifold side.
In a past life I was an MG/Triumph/VW mechanic back in the 70's. that's where my relationship with British cars started. Getting to know how things have changed has been a learning experience. Until you mentioned it I did not realize the 4.0 came in two versions. Thanks for your guidance.

 

Excellent, what I did was drill two small holes on the underside of the TPS housing. This allows me to insert the mini hose on a spray can in one of the holes and Im able to spray in there while it drains through the other hole. Once the fluid comes out clear, its done and I dont have calibrate it. It dries out within seconds.

 

Where did you drill the holes. Don't want to damage anything inside. I started having the same problem after about 45 minutes of driving around town.

 

You drill on the lowest point of the housing, the housing covers the electronic component, holes should be facing toward the ground. This allows oil from the intake to not pool inside, causing erratic TPS issues. TPS issues tend to trigger CELs and sometimes limp mode.

 

OK, I did that and a bunch of black goo came out. I drove it agin and it improved but I believe their is a bad spot on the wiper part. I'm getting faster at pulling the throttle body off now.

 

Wiper part?

 

I'm guessing this is late 80's technology in a mid 90's car. Something Im a little familiar with from my past life as a USCG engineer. So I'm also guessing that there is some kind of contacts inside the TPS where there is a physical contact between switches. Otherwise cleaning it would not have any affect. If that's not the case and this is a "solid site" electronic switch I need a "new" one, because a resistor or some other electronic thing beyond my knowledge has failed. I know from reading, this TPS controls the injection system and transmission shifts. Thats why there are 6 wires verses 2 or 3 wires as there are on other Jags. After cleaning the original three times there really is not much improvement. I have two used ones coming as a new one does not seem to exist anymore. Once I replace the original Im going to try and take it apart and confirm my original guess. l'll post what I find.

 

The inside of the TPS.

 

So the inside is a potentiometer. The outer wire corresponds to the GY wire that controls idle and I believe throttle control.

 

Ive never removed one. But its great to see you do it. I hope this clears up your issues

 

Replaced the TPS but still had fueling problems. So back came the fuel tank and removed the fuel pump. I was sure the check valve was not working and I was correct. I replaced the check valve with an inline one. I also found the return hose completely collapsed and a tear in the supply hose (most likely the problem). These were self inflicted wound because I did not check the hoses thoroughly when I replaced the fuel pump 6 months ago. The car now drives live I put a new engine in it!
Brewtech you called this one right when you said my fuel pump was failing.

 

Well done! and a terrific lesson here for us all: ENSURE the basics are 100%!