Opinion needed do i need new fuel pump, jeep 4.0

[RegDunlop]

I'll try and keep story short:

Jeep is 97 GC 4.0 I 6 engine

I've had it about a year, 125,000 on clock

Since I have owned it, it always took 2 turns of the key to start, I would turn it, wait a few seconds then turn again and it would fir right up.

The last 2 months it began to stall, then not start.

So i gave it tune up, new plugs wires rotor cap and it was good for a few days.

Then began stalling again, but always starts up almost right away. Also has not had problems starting from cold since tune up.

The battery and alternator have both been tested and are in good shape.

I tested the fuel pressure from a rent a tester auto-zone, what that showed me was when I first turn the key the fuel pressure gets primed fro 0 to about 15 PSI, the second turn starts the car and puts it in spec at around 50. That explained the odd starting it has had since I got the car one year ago..

After shutting down the fuel pressure drops quickly to about 15 , then a few minutes later goes to 0.

I changed the camshaft sensor ( part that is under distributor rotor ) , and again was much improved for a few days. When it began stalling again , it stalls then quickly restarts , sometimes on its' own ( which to me felt almost like some type of electrical ground loss ) Would a fuel pump do that?

Then it began again yesterday. I realized I may need to change the crankshaft position sensor. When I started the car and moved the wire near he wiring harness the CKS plugs into I could get the car to stall, so I assume the CKS needs to be changed. I also noticed that the sensor wire was under a lot of tension so I rerouted it ( but now it is close to the engine block and will get hot so I protected it with a piece of fuel line) .

Any ideas if the fuel pump is the culprit, or some othe electrical gremlin?

 

[rshaw125]

Have you changed the fuel filter??

 

[gomes512]

My '94 needed the pump primed before starting, accomplished by key on and off a couple times... New pump took care of that issue.

Your stalling is likely the crankshaft sensor and not the fuel pump. Not sure why but they usually always go out after a 100k-150k. Changed 2 in my 4.0 and a few others in family and friend's Cherokees. Just make sure the replacement sensor is the same depth as the original otherwise the flywheel will shear it right off.

 

[RegDunlop]

Originally Posted By: rshaw125
Have you changed the fuel filter??

It is integrated into the pump, so not possible to do.


That is to say, to change the pump/filter etc, the entire tank must be driopped as the pump is on TOP of the tank( why do they effin engineers do this?!).

So if I change the filter I will do pump at the same time.

 

[SwampSurvivor]

The pump itself may not be bad, but there is a check valve in the non-serviceable unit as a whole that often goes bad and drains off the fuel pressure.

 

[RegDunlop]

Originally Posted By: Miller88
The pump itself may not be bad, but there is a check valve in the non-serviceable unit as a whole that often goes bad and drains off the fuel pressure.


I assume that is bad, based on my readings.

But the car has been running for a year like this.

Trying to figure out if it woukld suddenly caus eth stalls or if that is from the CKS?

 

[Bgallagher]

Originally Posted By: gomes512
My '94 needed the pump primed before starting, accomplished by key on and off a couple times... New pump took care of that issue.

Your stalling is likely the crankshaft sensor and not the fuel pump. Not sure why but they usually always go out after a 100k-150k. Changed 2 in my 4.0 and a few others in family and friend's Cherokees. Just make sure the replacement sensor is the same depth as the original otherwise the flywheel will shear it right off.



+1 This was my thoughts as well.

 

[440Magnum]

My best guess:

The fuel pump is fine, the check valve is leaky. Stalling is due to the crank sensor wiring or the sensor itself

FIX the crank sensor- that intermittent will become permanent at the worst possible time. Bad crank sensors are a common 4.0 thing at high mileage.

If you can live with the slow starting, then I would wait on replacing the fuel module until a convenient time (run the tank empty so its light and easy to drop). There are tricks to improve starting too. Try this sequence: key on... wait 3 seconds... key off... wait 1 sec... key on...wait 3 seconds... start. I bet doing that lets it fire right up as it will run the fuel pump twice before you crank it, allowing it to pressurize the fuel rail fully.

 

[RegDunlop]

Originally Posted By: 440Magnum
My best guess:

The fuel pump is fine, the check valve is leaky. Stalling is due to the crank sensor wiring or the sensor itself

FIX the crank sensor- that intermittent will become permanent at the worst possible time. Bad crank sensors are a common 4.0 thing at high mileage.

If you can live with the slow starting, then I would wait on replacing the fuel module until a convenient time (run the tank empty so its light and easy to drop). There are tricks to improve starting too. Try this sequence: key on... wait 3 seconds... key off... wait 1 sec... key on...wait 3 seconds... start. I bet doing that lets it fire right up as it will run the fuel pump twice before you crank it, allowing it to pressurize the fuel rail fully.


Thanks

That trick is basically what I learned through trial and error, and was using it.

I will do the Cranshaft position sensor first, and see if that stops the stalling.

I got the car very very very cheap so I do not mind sp[ending on parts, I just hate having to pay a mechanic, becuase i know a lot of jobs are near impossible without a lift.

 

[Chris142]

There is a check valve,pressure regulator,filter on top of the pump. Replace it all so your not pulling it again when the pump dies in 3 months.

 

[dlundblad]

Originally Posted By: RegDunlop
Originally Posted By: rshaw125
Have you changed the fuel filter??

It is integrated into the pump, so not possible to do.


Are you sure about that?

I think you may be confusing the strainer with the filter.

 

[RegDunlop]

Originally Posted By: dlundblad
Originally Posted By: RegDunlop
Originally Posted By: rshaw125
Have you changed the fuel filter??

It is integrated into the pump, so not possible to do.


Are you sure about that?

I think you may be confusing the strainer with the filter.


I am sure. For a 97 it is inside the tank with the pump.

Hard to believe, but they did it.

 

[dlundblad]

Very odd design indeed.

 

[Chris142]

Originally Posted By: dlundblad
Very odd design indeed.
Chrysler/dodge/jeep/ford/gm has been doing that for decades

 

[mk378]

Like the other guy said, crank sensors are an almost universal problem on these. When they quit, engine is instantly dead as a doornail. I don't think the cam sensor will cause stalling or prevent starting.

 

[440Magnum]

Originally Posted By: RegDunlop
Originally Posted By: dlundblad
Originally Posted By: RegDunlop
Originally Posted By: rshaw125
Have you changed the fuel filter??

It is integrated into the pump, so not possible to do.


Are you sure about that?

I think you may be confusing the strainer with the filter.


I am sure. For a 97 it is inside the tank with the pump.

Hard to believe, but they did it.


That practice is EXTREMELY widespread among manufacturers now. I'm not sure what the thinking behind it really is, but my guesses are:

1) the fuel PUMP itself at least as sensitive to fuel contamination as anything else in a modern system, so it needs the protection of the filter and will last longer if the filter is upstream... and the only way to do that is put it in the tank.

2) Fuel supplies are far cleaner now that underground tanks have to be regularly inspected and are made of/lined with non-corroding materials and are more vapor- and water-tight than in past years, so the filter traps less gunk per mile driven than it did years ago. The life of a filter before clogging is probably close to the life of the pump itself, so why not pair them.

Its probably a bit of both factors. I don't think its necessarily cheaper than a downstream filter, so I suspect there's actual engineering (as opposed to mere bean-counting) going on behind that choice.

 

[Nick1994]

Yeah that is weird that the filter is in the tank.

My 96' XJ has the filter easily accessible outside the tank. And the tank in an XJ doesn't need to be dropped to do the filter. Just crawl under and take it out. I've had mine taken out before.

 

[dlundblad]

They (WJ's) have a strainer before the pump. I am not sure I'd call that a "filter."

My Jeep has the strainer, pump then the fuel filter/ pressure regulator. I am not sure on the ZJ's.

I'm on my original pump knock on wood. Currently using a WIX filter.

 

[Killer223]

having not read the whole thread, have you changed the crank shaft positioning sensor? mine went out on my GC a few times. as did the fuel pump.

By what the first post stated i'd bet it's the Crank sensor. i could be driving along and it's just shut off. sometimes it'd restart sometimes not.

when it dies does it turn right off or spudder n quit?

edited to add, you might well have an access in the floorboard of the jeep to get to the fuel pump. my 87 GC did but my TJ did not. worth pulling some carpet back to find out. better then dropping the tank.

 

[jeepman3071]

The taking two tries to start is 100% the fuel pump. The check valve in the fuel pump to be exact. The check valve will stick open causing the fuel lines to lose pressure. Cycling the key twice before starting will pressure the lines back up again. The check valve failure will not cause the Jeep to run rough or stall, it will just take longer cranking time to start. I'd put some fuel cleaner or Marvel's Mystery Oil in the fuel and it might help the valve get unstuck. I've done this with a few Jeeps and it worked. The only way to permanently solve this problem is to replace the whole pump assembly.

With that said, I believe the crank sensor is your problem. Every crank sensor I've seen on a Jeep 4.0 that failed has failed in that manner. They will cause the Jeep to stall, then run rough and "catch itself" when stalling, and eventually it will not start at all. Sometimes they even fail sporadically where they will run fine for weeks then act up again. I would definitely buy a MOPAR ONLY crank sensor. I've seen non-OEM sensors cause even more problems and lead people on a wild goose chase thinking that something else is the problem because the new sensor continues to fail.