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XJ left me stranded (again), after suddenly dying while driving

9

90Pioneer

NAXJA Forum User
Location
USA
I am really getting tired off the problems with this Jeep. Just yesterday I was thinking about how it's been about a month since something which prevents vehicle operation has happened.

Well, what do you know. Today while drivng home this afternoon my 1990 XJ AW4 suddenly turned off. I coasted to the side of the road and tried to restart. Cranked over fine, it would start, then suddenly die again. Did this three more times and got the same result. I sat there pissed off at it for about 20 minutes, and tried starting again. Everything seemed normal, and it was idling fine. After about 15 seconds I shut it off. Since I didn't want to risk it dying in a traffic circle, or such, I hiked about a mile home.

It has 4 or 5 gallons of gas in the tank. I replaced the original fuel pump at 167k, and changed the fuel filter. The new pump and filter have about 1,000 miles on them.

Any sensors or other things I could check? Any guesses as to what the problem is, or how I should find it?

Thanks
 
Crankshaft Position Sensor (CPS) is a likely culprit. Often it can help to break and make (disconnect then reconnect) the connector until you replace the sensor. The connector is near the back of the valve cover on the driver's side.
 
Pop the hood and check the ballast resistor located on the driverside fender by the air box. It is a white/tan ceramic looking thingy with a wire attached to each end. Pull each wire off and make sure they aren't corroded, clean them and put them back on. See if that works. That resistor allows voltage to your fuel pump once it's started. If it's bad or the wires are bad, you'll be able to fire it up but it will quit. Good luck.
 
I have been searching, and isn't the CPS usually the problem when you aren't getting spark? And isnt the CPS on the bell housing??

Is the ballast resistor the part hanging off the driver side fendor, sort of inbetween the headlights and the aux fan relay?

Thanks!!
 
Yes, bad CPS=no spark; however, it can be intermittant. Sounds like you found the resistor but if you hear the full pump running just before turning the ignition switch to the start position, then the resistor should be fine.
 
after market or factory replacement fuel pump?. I had the same problem with autozone and napa fuel pumps seams great for a couple of weeks then starts acting up. I replaced it with the mopar unit and never had the problem again. The mopar units are whalbro ten times better than the others and more pricy too!

Also check for bad connection at fuel pimp get under there and wiggle the wires around. they go bad quite often
 
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I know for a fact the connections on the ballast resistor are not that great. They have a bunch of corrosion on them. I looked at them before while doing some wiring, and I just didn't know what they did so I left them as is.

Carquest has the CPS in stock for only $35!!! I only called Carquest since no one else in town even listed the CPS. Carquest never has anything I need in stock, and if they do, it's always 25% higher than the next guy. I'm flabbergasted. I think I will replace the CPS just for good measure. What kind of socket extension did I need to get to the bolts?

The fuel pump was from Napa. I had to do some rigging to get the pump to fit the bracket that holds it.

It was running great until this. Hmm.. If I can catch a lift up to the parts store, before they close, I will pick up a gauge to test the fuel pressure.
 
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If it is the ballast resistor, can I just snip the two wires, and connect them together, to by pass it until I can get another one from Jeep?

What should my fuel pressure readings be with the ignition in the "run" position? What about when the XJ is running? It's a 4.0L.

Thanks
 
90Pioneer said:
If it is the ballast resistor, can I just snip the two wires, and connect them together, to by pass it until I can get another one from Jeep?

What should my fuel pressure readings be with the ignition in the "run" position? What about when the XJ is running? It's a 4.0L.

Thanks
Click to expand...

You can indeed just bypass the resistor. It quiets the fuel pump, and might prolong its life, but the 87 came without one (and the fuel pump in my 87 was still going at 235 thousand miles).

Fuel pressure should be 31 lb running, 39 with the vacuum line to the regulator disconnected.
 
OK, well I got the Jeep safely in my driveway. As of right now, she seems mostly normal. If I rev the engine up high, and back off sharply, it sputters like it's about to die, but catches itself. It does not do this all the time.

I bought a fuel pressure gauge ($45 ouch!), and my pressure reading was about 32psi, both while running, and just having the ignition in the "run" position. It remained pretty much the same while reving it as well. When I disconnected the vaccum line on the regulator, it when to 40psi, right on the dot. Does this mean it's running rich, and could possible account for my relatively poor gas mileage? Can I adjust it? How?


While the XJ was running, I fiddled around with the connections to the ballast resistor, but it kept on running. What would the negative effects be if I were to jump the wires? Is it ok to do perminately? If it is actually better for the pump, why did Jeep put one in?

Is it looking more like a CPS problem?


Help! Thanks!
 
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Red circle is the ballast resistor.

Yes, it sounds like a CPS problem.
 
Will I be able to access and change the CPS with just a bottle jack? Or will I need to borrow a floor jack again?

Thanks
 
If I rev the engine up high, and back off sharply, it sputters like it's about to die, but catches itself.
Click to expand...

Well now I wonder if you ought to check your egr. Since it doesn't cost anything, unplug the vacuum line to the egr, rev it and see if it still does the same thing. While your at it, check the line from your map sensor on the firewall to your throttlebody just to make sure it's not unhooked or cracked.
 
ACE said:
Well now I wonder if you ought to check your egr. Since it doesn't cost anything, unplug the vacuum line to the egr, rev it and see if it still does the same thing. While your at it, check the line from your map sensor on the firewall to your throttlebody just to make sure it's not unhooked or cracked.
Click to expand...


Stupid question, but what and where is the EGR?
 
Exhaust Gas Recirculation valve. It's on the exhaust manifold, below the throttle body on the intake.
 
90Pioneer said:
I am really getting tired off the problems with this Jeep. Just yesterday I was thinking about how it's been about a month since something which prevents vehicle operation has happened.

Well, what do you know. Today while drivng home this afternoon my 1990 XJ AW4 suddenly turned off. I coasted to the side of the road and tried to restart. Cranked over fine, it would start, then suddenly die again. Did this three more times and got the same result. I sat there pissed off at it for about 20 minutes, and tried starting again. Everything seemed normal, and it was idling fine. After about 15 seconds I shut it off. Since I didn't want to risk it dying in a traffic circle, or such, I hiked about a mile home.

It has 4 or 5 gallons of gas in the tank. I replaced the original fuel pump at 167k, and changed the fuel filter. The new pump and filter have about 1,000 miles on them.

Any sensors or other things I could check? Any guesses as to what the problem is, or how I should find it?

Thanks
Click to expand...

Your fuel pressures are normal and the ballast resistor is working fine. I can guarantee that your problem is a bad CPS so I suggest that you replace it.
 
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