homestd

Hey all. Well it's happened. My 90 refuses to start. It's been running great for a while now, but today she left me stranded 30mi from home, without my cell phone! I managed to get home, but here's what happened: She has had 2 bouts of running BADLY for a few miles before getting over it. After driving 30mi and sitting for a little while it would have a mushy (closest thing I could think of) start but would run OK after that. Once, it ran so badly I didn't think I would make it home, but after 10mi. it straightened up up an ran well the rest of the way. The next time, I stopped at a friend's house on the way home and it refused to start (for the first time). The next day I changed the fuel pump relay and jumpered the ballast resistor, thinking I was having fuel pump problems, it started OK and ran fine for a few days before dying from idle while I was out of the jeep.

I know I have leaky injectors, It's getting fire (seems a little bit weak) and gas at the rail. I'll have to have it towed home so I can hopefully get it straightened out. OK guys...Where do I start???

exasemech

Endless possibilities but if it actually has reliable spark when it doesn't start that helps.
"Fuel at the rail" doesn't mean much. As a place to start I would measure the fuel pressure when it's not starting.
I would also check the battery voltage and cables/clamps....do the easy stuff first.

Sig220

Don't forget to clean and refresh your ground wire locations. Good Luck and Happy Thanksgiving!

lawsoncl

Leaking externally? Full stop. Replace those with some refurbished Bosch injectors before you really do have fire.

and what he said. Check whether you have spark first and then fuel pressure. "Gimme fuel, gimme fire, gimme that which I desire...."

homestd

Thanks all y'all. This is going to be a journey as she's my only ride and I live 30mi from civilization. As soon as I get her home (after the holidays) I'll do the whole routine. Happy Thanksgiving to All and please stay tuned.

cruiser54

www.cruiser54.com Tips 1,3,4 and 5.

homestd

OK gang, she's in the garage. Tomorrow I start checking everything. Cruiser, which sensor grounds in particular should I check first?

cruiser54

CRUISER'S MOSTLY RENIX TIPS

RENIX GROUND REFRESHING

OCTOBER 30, 2015 SALAD 72 COMMENTS EDIT

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.

All the components listed below ground at the dipstick tube stud:

Distributor Sync Sensor, TCU main ground, TCU “Shift Point Logic”, Ignition Control Module, Fuel Injectors, ECU main ground (which other engine sensors ground through, including the 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. If the whole stud turns, you can use a 7/32″ six point socket or wrench to hold it so the nut can be removed. Worst case, cut the wires and remove the stud and nut. Install new terminal eyelets on the wires when going back together. Scrape any and all paint from the stud’s mounting surface where the wires will attach. Surfaces 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. Apply a liberal coating of
  OxGard
  OxGard
  , which is available at Lowe’s and other stores. Reinstall all the wires to the stud and tighten thhttps://i0.wp.com/cruiser54.com/wp-content/uploads/2015/10/dipstick-stud.jpge 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, apply , 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 its intended use and subject to corrosion and poor connections at each end.

• 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. Apply
  OxGard
  OxGard
  . 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 with a liberal coating of
  OxGard
  OxGard
  .

2 STRONG suggestions regarding the ground system:

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 tail lamp 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. Add a 10 gauge wire, with an eyelet on each end, from that grounding point to a bolt on the frame. Better yet, on both Cherokees and Comanches, complete Tip 29 for the best fuel pump grounding. Be sure to scrape all mounting points to bare metal and apply also.https://i0.wp.com/cruiser54.com/wp-content/uploads/2015/10/Fuel-Pump-Ground-Comanche.jpg
If you want to UPGRADE YOUR GROUND AND BATTERY CABLES with custom made parts, contact Paul at www.jeepcables.com



Revised 02/04/2017

homestd

OK, I guess I was right. The first thing that entered my mind was the fuel pump. There is zero fuel pressure at the rail when trying to start (thanks Exasemech). I'm going to check the 12v connector at the fuel pump after I get it up on the stands. At least I have a new one ready to install.

Well, it's on the stands and only has 5v on the center terminal of the fuel pump connector with the key on, but it has a hot 12v at the relay on two pins. I assume one powers the relay and the other goes to the pump. I'm digging through the FSM to see where to look in the wiring.

homestd

Does anyone know the pinout for the three conductor plug going to the fuel pump?

lawsoncl

Looking at the 1990 wiring diagram:

(A) Black = Ground
(B) Violet = Fuel Gauge
(C) Orange=power to the pump

homestd

I saw in an old post that the fuel pump only gets 12v for a brief time then drops to 5v (which I measured). Do you know if that's correct?

lawsoncl

Yes, that's the purpose of the ballast resistor. While cranking, the starter relay sends full voltage to the pump and otherwise send it through the ballast resistor. Also note that with the key in run position, if the computer doesn't see the engine turning, it will turn off the fuel pump after a few seconds. So you need to watch the pressure and voltage while cranking. The resistor was Jeep's fix for complaints about the pump being noisy. See https://cruiser54.com/?p=35 and https://cruiser54.com/?p=249. Actually, go through all of his tips, but especially the one on improving the grounds. Check the connections to the resistor, and try bypassing it with a wire jumper and see if that helps. You can leave it permanently bypassed. That's also a handy place to stick a meter and see if you've got voltage and how much current the pump is drawing.

homestd

Thanks Lawsoncl, That agrees with what I've read. My problem is, I live alone with no neighbors or anyone to help. I don't know how I can read the meter, etc, while turning the engine and I'm really hard of hearing and unable to hear the pump running when it does work. I'm a one man show, if I can't figure it out I have no one to call. Any suggestions?
BTW what does the clutch relay have to do with the fuel pump?

exasemech

[QUOTE=homestd;3685942]Thanks Lawsoncl, That agrees with what I've read. My problem is, I live alone with no neighbors or anyone to help. I don't know how I can read the meter, etc, while turning the engine and I'm really hard of hearing and unable to hear the pump running when it does work. I'm a one man show, if I can't figure it out I have no one/QUOTE].

I do about 95% of my work solo these days. a jumper cable, cut up an old extension cord if you have to, for your meter leads works fine.
Edit: a perhaps more modern approach occurs to me for such occasions. Hook up your meter. Prop up your phone and make a video of the meter display.😀

All this sorta reminds me of a task a couple years ago when I was "recalibrating" the back pressure transducer on a not Jeep EGR system. Had to be under load to work so was driving around the neighborhood with a vacuum gauge duct taped to the windshield.