Any jeep savants out there? 4.0 1990 cherokee


#1

I m looking for a magical solution to a problem.

I m hoping that your combined wisdom will allow me to fix my better half s jeep , with as little effort as possible on my part.

I have had to have it towed home twice in as many days…

yeah… embarrassing, and expensive.

here is the deal… the jeep will not start when it has been driven for a while and is then cut off. three hours later, after it has cooled completely, it will fire right up

it turns over fine, but will not start.

there is fuel at the feul rail, I don t know how much pressure is there tho…

and no, I have not yet checked to see if it has spark when it is not starting.

the problem seems to be heat related and I m hoping that you guys will point me to some famously failing relay or part that is notorious for such failures.

hopefully the guilty part will be cheap and easy to change.

I will report back with the results…

…and anyone who magically points me to the problem will win my undying gratitude and an imaginary giant cookie!

thanks, wes…


#2

ok guys…

she is looking at me funny…

like I should be out working on her jeep…

…but I have confidence in the old cartalk magic…

and my truck is broken too, I ll have to ride my bicycle to the parts store… so please try to get it right the first ime, will ya?

please write the answer to my jeep question on a new power steering gearbox for a 75 ford truck and send it to me at 222 moron avenue, the eastern shore, USA

thanks again!!!


#3

Not a Jeep savant but this sounds like a classic failure of an electronic part. Even if you didn’t say it was getting fuel, I’d guess ignition module or crankshaft position sensor.

A little internet search showed a number of reasons why this happens on GC’s. The 2 I mentioned plus old and failing relays, a harness short from a rubbed-through wire routed over the bellhousing, a screw through the ignition module that was shorting, a power wire to the starter (not the battery cable) that corroded, ignition coil and a few others.

The CPS sensor is cheap and relatively easy to replace as are relays for fuel and ignition. I’d start there and look for rubbed wire along the way. Bike Friendly part size, too. Good Luck, Wes!


#4

thanks mustangman…


#5

Not magic, but you might want to check the fuel pump. The fuel pump on my wife’s 91 Taurus would quit after an hour or so of driving back in 1998. We found this out crossing the Delaware river heading into Philadelphia. After 2 hours I was able to restart it and take it to my Philly mechanic. They had to leave it running and connected to diagnostics for an hour or so to determine it was the pump.

Good luck,

Ed B.


#6

thanks edb1961…

I guess I would have to get a pressure gauge and connect it to the fuel rail shraeder valve and simply observe the pressure for an hour if it is the problem that you describe.

does that make sense?

I think that I will go over the wiring for shorts and bad connections and maybe change a relay or two first but I knew that the fuel pump would be suspect too…


#7

Don’t forget about divide and conquer approach. Starting spray can be very effectively used to eliminate (or prove) fuel related issues. I’d get it toasty on a drive and arrive back home. Try starting it, if it fails to start, then break out the spray. If it momentarily tries to start or runs briefly, you can start looking at fuel delivery issues. Otherwise, it likely electrical. Then simple plug or timing light test will help there to isolate…


#8

good idea TT… thanks.


#9

alright guys… thanks.

at least I ll have a night light on and won t be fumbling around in complete darkness now…

time to get off of this 'puter and under the hood.

thanks again,

wes

I ll report back later…


#10

Crankshaft sensors are notorious pattern failures for the 4 liter Jeeps.


#11

thanks ase…

I have new info!!!

so…, I took it out and got it toasty hot, and picked up some starting fluid…

when I got it home I cut it off and tried to re start it immediately after shut off…

…it started fine three times in succession…

…then I let it sit for ten minutes and tried again…

it failed to start. turned over fine, but did not start…

I then sprayed some starter fluid into the intake and tried again…

it fired up, hesitated a bit, but then ran fine.

I let it sit for five more minutes, and it is now starting again on it s own, tho it is still hot.

I m flummoxed as this doesn t make sense to me.

any thoughts?


#12

…and, the CPS seems to be high on everyones list, including the guy at the parts store, but I m not sure that it jibes with the results and symptoms from my post above…


#13

…I m gonna start checking for bad wires now.

any further thoughts, before I start spending money, will be greatly appreciated.

thanks again,

wes


#14

well, if it is the cps…, I don t know how, on god s green earth, that I m gonna be able to reach it…, but maybe…, just maybe…

the TPS is a lot easier to reach…


#15

The CPS was a particulary troublesome part on Jeeps of that era. And if you decide to replace it look closely at the brake master cylinder and consider detaching it from the booster and moving it forward. I seem to recall gaining some access that way. It’s been a few years though so decide for yourself.


#16

thanks rod, I will consider that. I m not famialiar with the master cylinder attachment to the jeep yet but I saw that the MC was in the way of accessing the cps from the top.

I was thinking of trying to reach it from underneath, but I m not yet sure if I can do that either.

the fact that it started, with starter fluid, and continued to start after that, while still hot has me flummoxed.

I may road test it til hot again and see if I can repeat the above results, before I start taking stuff apart. idk.


#17

I need to get on my bike and buy a multi meter…

I m too hardheaded. someone stole my fluke multi meter years ago and I m too stubborn to go buy a new one…

:slight_smile:


#18

and now, oh joy of joys…, I can t get it to repeat the failure…

I did go buy a cheap meter and I tested the CPS…

it is supposed to have 200 ohms of resistance , plus or minus 75, on a hot engine…

…I read 267…, which within the acceptable parameters…

but…, that is not in a failing situation…

I wanted to repeat the failure to start, and re test it, but I am unable to get my vehicle to fail, which is unusual for me…

I did feel and fiddle and caress all wires that I thought might be pertinent, and may have re jiggered something…, who knows, but that would not explain why it fired up with starter fluid, in a failing situation earlier.

flummoxed, I tell you…, flummoxed!

I m thinking ignition module and pretending that the fuel pump is not at all the problem…

but I want to test the darned CPS in a failing situation first…

maybe I should let holly drive it…, she is better at breaking it than I am :slight_smile:


#19

still won t fail.

flummoxed.

declare victory and call it fixed is my feeling…, she who must not be named disagrees…


#20

It could be a classic case of coil failure. Fill up a 2 liter bottle with water and put it in your Jeep. If it quits on the road, pop the hood and pour the water over the coil to cool it and see if it starts. In the old days we used to cool the coil with any …um available liquid.