89 Cherokee 4.0 no fuel

[Edge]

Fuel pump works with secondary power source,but not otherwise.Problem went from intermittent to permanent over 800 miles or so.
Relays have all been changed out(I have piles of extra parts)no change.

I am no electrical troubleshooter(color blind)but picked up a meter anyway,not sure if its a good or bad(Ex Tech),and am going thru the manuals page by page.

Checked the fuel presure @ the mpi rail and get 31 psi(under secondary power)so I'm fairly sure the pump is not the problem.........


Any ideas??

Thanks in advance,

Edge

 

[SteelHeadz]

Is there Power from the Power distribution Center under the hood? Check the fuse circuit from the fuse box for power and ground..

 

[Crazy4diesels]

Are these like some of the older injected vehicles in that they need a valid oil pressure signal to keep the pump running? If the ECM does not see oil pressure in time it might be shutting off the fuel pump relay??? Just a thought. I remember some early 90's Fords had a "crash switch" which shut off the fuel pump. It tripped if the car was hit (not even hit really hard) and had to be manually reset. Best of luck - John

 

[Edge]

No joy.

All fuses in the box are good,power *from* the ECU is present.Had an undervolt to the fuel pump relay,replaced that and it all worked for about 14 miles,then,same problem.

Not sure where to look from here.

In its 14 mile journey it gave me the opportunity to change its thermostat in the Auto Zone parking lot.

Regardless,I still love my Cherokee,just wish the feeling was mutual.Sure wish I could speak Jeepanese.

Edge

 

[SteelHeadz]

Do a wiggle test on the Power distribution center. where the Relay you replaced, install a voltmeter ant test the circuit for a battery voltage, if it's below battery voltage, then start wigling some wires or harness on the PDC and see if the voltage changes as you do this. if it fluctuates or intermittently drops, you might have a loose or corroded terminals under that PDC..

 

[Edge]

**Do a wiggle test on the Power distribution center. where the Relay you replaced, install a voltmeter ant test the circuit for a battery voltage, **

Funny you should mention that.......I did a wiggle test throughout the harnesses,and when I was finished,it fired and ran......I ran it for an hour but couldnt duplicate the problem,the second time thru I neglected the PDC wiring....

i'll get back after it tomorrow am,and focus on the PDC......

On a brighter note,while wiggle testing I noticed a ?vaccuum? line snapped off its moors right by the passenger side axle going into something I havent had to relace so I dont know what it is.My guess would be something with the 4wd....was able to drill out the broken line and reinsert it.......one less surprise next time I head up to Brianhead in a blizzard.

Thanks a bunch for your help!

Edge

 

[Edge]

No wiggle failures.

Finally broke down and took it in for diagnostics;

1) The "emissions maintenance" light was on......under a strategically placed piece of electrical tape(not placed by me).

2)Regular diagnostics guy was gone so had a rather green tech.....he said intake manifold gasket was bad....causing all my problems....not sure I'm buying that one.

3)Module under coil looks like it got whacked........should I try a swap out or is it unrelated?

4)Sight unseen,my regular tech said CPS.............

Ready for any and all opinions,and thanks for your patience.......


Edge

 

[SteelHeadz]

No wiggle failures.

Finally broke down and took it in for diagnostics;

1) The "emissions maintenance" light was on......under a strategically placed piece of electrical tape(not placed by me).**** Set this one on the back burner, emmission DTCs will not cause a No start condition..****

2)Regular diagnostics guy was gone so had a rather green tech.....he said intake manifold gasket was bad....causing all my problems....not sure I'm buying that one.***Technically, if you spray a Carburator cleaner on the intake manifold gasket while cranking on it , it should start, granted that there is spark on the plugs.***

3)Module under coil looks like it got whacked........should I try a swap out or is it unrelated?
*** I'm not sure what you mean by "Module under the Coil"***
4)Sight unseen,my regular tech said CPS.............
*** CPS or CKP would mean no Fuel and spark, besides, i think the cps is the pickup in the distributor.***
Ready for any and all opinions,and thanks for your patience.......


Edge

No Biggie..

 

[Edge]

Module under the coil.........goes to the distributor from there,........cps ( i think) he meant crank position sensor......

And by "whacked",I mean the module looks like it took a rock.Not sure where I would have found a rock in Utah,but stranger things have happened.........


Edge

And yes,I'm getting spark all the time,good spark.

Also threw in a can of ether just in case to test the intake manifold theory.Gonna drive it tomorrow to see if I can get a duplicate failure.

 

[SteelHeadz]

Module under the coil.........goes to the distributor from there,........cps ( i think) he meant crank position sensor......

And by "whacked",I mean the module looks like it took a rock.Not sure where I would have found a rock in Utah,but stranger things have happened.........


Edge

And yes,I'm getting spark all the time,good spark.

Also threw in a can of ether just in case to test the intake manifold theory.Gonna drive it tomorrow to see if I can get a duplicate failure.

Haha, I've been to Salt lake, Roosevelt and if i remember correctly, your rock there is just as hard as the rock here in Texas..

 

[Edge]

Yeah....rocks is rocks.....

Changed out the module,still cant duplicate engine cut off.Let it get plenty warm too.

Since all failures have been while hot,should I put say,a heat gun to the cps(while the jeep is running) and see if I can cause the glitch?

I'm glad its running now......but I dont like not knowing *why* its running.....most of my romping areas are well outside cell phone range and I really hate walking.

Edge