armymedic120

Hey all. I have a 1989 Cherokee that's driving me up the wall. Recently it started stalling when I would slow down or stop at intersections. Now it just won't run. I can get it to start but immediately shuts off. What I have done:

Replaced vacuum lines
Replaced broken knock sensor
Replaced air filters,
New wire set
New distributor (entire distributor)
New tps
Cleaned throttle body.

Still no improvement. I can get it to stay tuning if I keep my foot on the gas, but the second I let off it will idle for a few seconds then die. I can't run a computer on it because it's a remix era jeep. I really need to get this going soon it's my daily driver and I'm running out of cash buying parts people tell me it will fix

tjwalker

First thing you need to do is to stop throwing parts at this on a hunch. Terribly inefficient and as you have found, gets expensive in a hurry!

You need to adopt a "testing based" strategy. It is the only way to go.

I see no testing of fuel pressure mentioned. It is one of the first things that would be done if you had this vehicle in a shop. You must use a gauge; there are NO shortcuts. Many big box parts stores will rent you this gauge inexpensively; call around. It's easy to test. Just screw on the gauge adapter to the schrader valve on the fuel rail.

For an 89, you should have 31 psi at idle. Then disconnect the vacuum line leading to the fuel pressure regulator and the pressure should jump to approximately 39 psi. Be darn sure that the vacuum line leading to the FPR is pulling good vacuum and is not wet with raw fuel (ruptured fuel pressure regulator).

Start with that. Proper fuel delivery needs to be ruled in or out early in the troubleshooting process.

Also, did you ADJUST your new throttle position sensor? Adjustment is necessary for your TPS.

A parting point. be sure that all of your grounds are good; Renix vintage XJs are very susceptible to ground issues! More on that below.

Here is a link to testing many things on your XJ. Bookmark it and use it if you get stuck here.

http://www.lunghd.com/Tech_Articles/...iagnostics.htm
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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, and wasted money replacing unnecessary components.

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.

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.

armymedic120

Thanks that's a lot of great info!, unfortunately I can't even get the jeep to idle, do you think the short amount of time that I've been able to get it to idle will be enough to get an accurate reading?

stev-o

Replace your cps sounds like cps to me

Fsher21

Swap out the battery if you have access to another one and see if it runs. Have it load tested if you can 2 pedal it to a place like autozone. Don't throw yet another part at the problem as suggested above until you at least eliminate the battery as the problem lol

cruiser54

Doesn't need to run in order to do what Mr Walker suggests.

armymedic120

I put a new battery in it when I bought it

armymedic120

I assume thats the crank position sensor?

95grc

The fuel pump.

caged

check your ballast resistor. it's that little white ceramic thing on the drivers inner fender with two wires going to it. they are only about 5 bux new.

you can unplug it and jump those wires to test.

if it's bad, your jeep will only run in the start position, when you release the key to the run position, it will die.

i used to keep a couple spares in my glove box from my old mopar days.

armymedic120

If I jump the two wires it will run right?

caged

it should, but if that's the problem, i would replace that resistor as soon as you can.

i know back in my mopar days, you wouldn't want to run it long or it would burn out the points, but with these electronic ignitions, we don't have points.

i know the newer jeeps don't have this ballast resistor, but i think the new coil has it built in, but i'm not sure...

but yeah, you'll be fine to run it jumped for a bit. just be sure to cover the leads so they don't short out.

cruiser54

That particular ballast resistor on the Jeeps is not for the ignition system. It's there to reduce the voltage to the fuel pump so it won't be noisy. In Start mode, the pump gets battery voltage. In Run mode the pump gets about 10 volts.

That said, it is still a rock not to be left unturned. Make sure the connectors are tight at each end and jump it for testing purposes.

armymedic120

Thanks guys it looks like it was that ballast resistor

cruiser54

Did you bypass it, fix the connectors, or replace it?