Padre70

Hey Everyone, new user here. I have an 1988 Cherokee 4.0 with fuel problems. I took it to a mecanic and he replaced the ground wire to the computer and said it was fixed! I drove it for 3 miles, shut it off and after sitting for half an hour it coughed and sputtered and finally started. I took it back and he said I needed a new fuel pump as it was not holding pressure when the encine was turned off. I replaced the fuel pump and had the same problem - he said I got a bad fuel pump from the dealer, so again it was replaced, and same problem. I was the otls the injector pigtails were bad so I replaced them, guess what?? So now I have replaced the fuel pump, pigtails, injectors, plugs, plug wires, rotor & cap, and crank sensor. Still fires right over when cold and if you start it right after shutting it off, but hesitant to start after sitting when warmed up. Sounds like its loading up, if it were carburated I'd knoe how to fix it but with TBI Im lost. I have had this Jeep since 1995 and am not about to give up on making it my daily ruuner. Any suggestions? maybe coil? ignition sensor? new paint job? Holy Water?:

Black89

Test your TPS make sure it's working correctly. Test when cold then drive it shut it off and see if the readings are the same. See post #8 here: https://www.cherokeeforum.com/f51/cr...x-tips-153657/

Black89

cruiser54

MAP sensor tube
There is a brittle little tube. It comes out of a rubber plug, low on the engine side of the throttle body. It runs back to the firewall, then up to your MAP sensor, behind the valve cover, higher up on the firewall. It has one vacuum line as already mentioned, with a 3-wire plug in the bottom.
CRUCIAL!! The MAP sensor will tell the ECU to dump fuel with little to no vacuum to the MAP. Any crack or blockage and it will be pig-rich. ( black smoke, fouled black plugs, must hold your foot to the floor to keep the engine running). You can pull the line off the MAP sensor and feel for vacuum with your finger. If it runs!
A visual inspection usually reveals any issues with the line from the throttle body to the MAP sensor.

And, you can do this yourself:

Renix Ground Refreshing
The Renix era XJs and MJs were built with an under-engineered grounding system for the engine/transmission electronics. One problem in particular involves the multiple ground connection at the engine dipstick tube stud. A poor ground here can cause a multitude of driveabililty issues, wasted time, failed emission tests, and wasted money replacing components unnecessarily.
The components grounding at the dipstick tube stud are:
Distributor Sync Sensor, TCU main ground, TCU "Shift Point Logic", Ignition control Module, Injectors, ECU main ground which other engine sensors ground through, Oxygen sensor, Knock Sensor, Cruise Control, and Transmission Sync signal. All extremely important stuff.
The factory was aware of the issues with this ground point and addressed it by suggesting the following:
Remove the nut holding the wire terminals to the stud. Verify that the stud is indeed tightened securely into the block. Scrape any and all paint from the stud’s mounting surface where the wires will attach. Must be clean, shiny and free of any oil, grease, or paint.
Inspect the wire terminals. Check to see that none of the terminals are crimped over wire insulation instead of bare wire. Be sure the crimps are tight. It wouldn’t hurt to re-crimp them just as a matter of course. Sand and polish the wire terminals until clean and shiny on both sides. Reinstall all the wires to the stud and tighten the nut down securely.
While you’re in that general area, locate the battery negative cable which is fastened to the engine block just forward of the dipstick stud. Remove the bolt, scrape the block to bare metal, clean and polish the cable terminal, and reattach securely.
Another area where the grounding system on Renix era Jeeps was lacking is the engine to chassis ground. There is a braided cable from the back of the cylinder head that also attaches to the driver’s side of the firewall. This cable is undersized for it’s intended use and subject to corrosion and poor connections at each end.
First off, remove the cable end from the firewall using a 15mm wrench or socket. Scrape the paint off down to bare metal and clean the wire terminal. Reattach securely.
Remove the other end of the cable from the rear of the head using a 3’4" socket. Clean all the oil, paint and crud from the stud. Clean the wire terminal of the cable and reattach securely.
A suggestion regarding the braided cable:
I prefer to add a #4 Gauge cable from the firewall to a bolt on the rear of the intake manifold, either to a heat shield bolt or fuel rail bolt. A cable about 18" long with a 3/8" lug on each end works great and you can get one at any parts store already made up. Napa has them as part number 781116.
A further improvement to the grounding system can be made using a #4 cable, about 10" long with 3/8" terminals at each end. Attach one end of this cable to the negative battery bolt and the other end under the closest 10mm headed bolt on the radiator support just forward of the battery. Napa part number 781115.
For those of us with Comanches, it’s very important to remove the driver’s side taillamp assembly to access the ground for the fuel pump. Remove the screw holding the black ground wire. Scrape the paint from the body and corrosion from the wire terminal. Reattach securely.
If you want to upgrade your grounds and battery cables in general, contact Jon at www.kelleyswip.com. He makes an incredible cable upgrade for a very reasonable price.
　
Revised 03-04-2013

Padre70

Thanks everyone for the very informative answers to my post. Looks like I'm in for a day with a multi-meter and can of electrical parts cleaner. I'll keep everyone informed of my progress. The mechanic that worked on the car did tear the main elecrical terminal apart in order to install a new ground from the block to the ECU, so that will be the first thing I check out. Thanks again.

Bustedback

Time to find a new mechanic.

asuderma

x2

The first thing I did when I moved here was find a good honest mechanic that does what I ask and nothing more. This way I save money doing the work that I have time for myself, and don't have to worry when I do take it in.

Good luck!

Bustedback

Try and bypass the fuel pump ballast resistor on the left front fenderwell.

Padre70

After a day of testing, I accidently found that the vacuum tube from the Fuel Line Pressure Regulator was full of gas. I replaced it with a new one and it wouldn't run at all. Put the old one back in and it ran (for a while). It shut off and now stutters trying to start, but no luck. Somehow I think its in the starting circuit (maybe the neutral safety switch?) I drove it this morning prior to changing the regulator, and it ran OK, I just didn't want the vacuum lines accumulating all that gasoline and then maybe exploding in the carport. Thats the only reason I changed it. I'll try again when it's cooled off and see if it starts.

I want to thank everyone for the information i've gotten. You have saved me many hours of frustration and dollars at the mechanics. (By the way, Iv'e gotten a new one now.)

tjwalker

Padre, if the vacuum line leading to the fuel pressure regulator has raw fuel in it, the diaphragm in the original fuel pressure regulator is shot. What you are seeing is one of the primary symptoms of a bad regulator.

It is not impossible and in fact very probable that the new regulator you put in is faulty. I find new parts faulty more than you would think. I'd try a new regulator in there. They should replace it on warranty. Buy the best regulator you can get your mitts on if you have to change brands.

Good luck and keep us posted!

Padre70

IT RUNS !!! Replaced the old regulator with a new one and then retraced all the vacuum lines to make sure they were where thry were supposed to be and attached correctly. It still wouldn't start, so I went back to my electrical concept. traced all the elctrical ground lines and they were OK, then I went to the positive lines and found one small line connected with a cluster of other lines right behind the where the positive cable connects to the battery. The insulation was gone aNd the wire broken. I soldered in a new line with a shrink wrap covering and it started right up. Ive driven to the store and back, once around the lake and have had no problems on start-up (hot or cold). Don't know if the wire was the problem all along or probably all things considered, a little bit of everything. Now I,m off to do the 3" lift, see you all in the hills!!