Hi All,
Here’s the problem.
1996 Cherokee. Stock 4.0L.
Fuel pump with Pressure Regulator in the tank.

I was having a problem with the fuel pressure.
The pump was working normally.
However the engine would not start normally.
If I got a helper to squirt starting fluid while cranking, it would start and run.
The problem seemed to be that after the first “priming”, when the I ignition switch was turned to start, the fuel pressure would bleed off and it would not start.
Fine.
New fuel pump module.
For reasons too many to post here, I left the problem for a year.
Now to my effort to get things going.
Well, of course, the battery died.
I managed to get the battery up to about 50%.
I turned on the ignition to position 2 and the fuel gauge showed ¼ tank.
I was happy.
With a year to think about it, I rationalized that the problem was not the pressure regulator as I first thought but the check valve in the pump.
New fuel pump module, right?
So I got hold of an inline check valve and installed it upstream of the filter.
When I turned on the ignition, I did not hear the pump run for the few seconds I expected.
I did give it a crank but, of course, no start.
I left it for a few hours for the battery to charge.
New problem.
When I tried to start for a second time there were new symptoms.
The pump is running continuously but now the fuel gauge is reading below empty.
There is no “Check Engine” light. (I did not notice that before)
No start.
I did not do anything with the harness from the tank.
Before I pull the PCM, I was wondering if anyone has any ideas.
Thanks
Joe

 

Did you ever actually replace the fuel pump or just think about it and instead install a check valve?

 

I did not replace the pump.
It is now running.

 

If you have further troiuble with it, check your fuel pressure. With a gauge, not a thumbnail in the Schraeder valve.

 

Fuel pressure is really not the big deal right now.
I have no "Check Engine" light when I turn the ignition switch to position 2.

 

Update:
I replaced the PCM/ECU and it started.
Still have a problem with the fuel gauge reading below empty.

 

I got the check valve on Ebay. Cheap.
3/8" connections to fit the upstream line to the filter.
Many Auto supply stores will carry that.
Fuses and relays all checked.
The Check Engine Light is now on continuausly.
I had not seen/noticed that there was no "CEL" the time before when I turned on the ignition.
No CEL= dead PCM/ECU.
As I said, I did not hear the pump run for the few seconds I expected in the first instance.
The problem was originally no fuel pressure unless the pump was running.
As I said, "With a year to think about it, I rationalized that the problem was not the pressure regulator as I first thought but the check valve in the pump."
The pump only runs for a few seconds during the start cycle and comes back on after the engine starts.
The pressure regulator is attached to the pump/sending unit inside the tank on this model.
A real pain.
The check valve is in the out side of the pump and that is inside the tank.
After I installed the check valve, it would not start and I then noticed that there was no CEL light when I turned on the ignition.
Any way, I pulled out a spare PCM (rebuilt) and the engine started right up.
Not bad after 18 months of laying idle.

But my problems are not over.
The fuel gauge is reading below empty.
The CEL is now on continuously.
The "flash codes" feature is not working.
I got a code P0340 with a scanner but cannot erase. Not a code normally expect on a 1996 Cherokee.
The engine is running great.
Idle, acceleration and driving is fine.

I will get to the PCM later.
I took her out yesterday for a 60 mile drive with several stops.
Ran like new.
At one stop, the fuel gauge was reading correctly when I returned to the car.
Short lived.
Plan to put a can of injector cleaner in the tank.
I suspect that the sending unit is gummed up after 18 months of no use.

The PCM:
This Cherokee was built with a special PCM.
It was built to run on "Leaded" gas for export.
The "chip" is programmed to do that.
When I got the the first rebuilt PCM, the shop had to transplant the chip from my original PCM to a regular USA type PCM from 1996. (1296)
I had several done.
The one I put in two days ago was rebuilt 7 or 8 years ago and had the heart transplant.
I suspect there is a problem with it.
I have another spare PCM but I will not put that in at this time.

What I would like folks to take away from this Post is this.
There is a difference between "
Fuel pressure" and "fuel supply".
The fuel pressure is provided by the pump and controlled by the regulator.
The supply at the fuel rail is maintained by the check valve in the pump.
If the pressure in the fuel rail is bleeding off, it's the check valve. (or a fuel injector)
If you get pressure while the pump is running and the pressure is normal, 49 psi for this model, the pump and regulator are working.
If the pressure bleeds of as soon as the pump stops, it's probably the check valve. Need a new pump.

What I did was put a check valve in the fuel line to hold the pressure after the pump stops.
I put it just upstream of the filter. (on the line coming from the tank before the filter)

Very cheap ($6.00 to $7.00) and 25 minutes work.
There is a lot of information in my original Post.


Check Valve
About 2 1/2" long.
So, I'll be driving it around for a while with the CEL light on.