1990 Cherokee No Start

[zsnoopy1225]

As the title states, the jeep won't start. It cranks well but thats about it, except for a very occasional cough.

A bit of history/information:
4.0L 6 cyl, 313K miles, original engine; Problems started with the fuel pump, driving along, began to lose power, could 'limp' it along at max 25 mph, almost made it home - plenty of gas. Determined it was the fuel pump (original) changed it out, drove it about 100 miles, parked it overnight & would not start the next morning. Checked fuel rail - no pressure, forced pump to run by jumpering across starter solenoid, no fuel pressure - detemined pump was defective from factory (NAPA Bosch), replaced with a second pump, which appears to be doing the same thing except that occasionally have pressure at fuel rail, however not enough to start/keep running.

Replaced fuel filter - both internal and external to pump; Have checked the CPS, resistance is 225 ohms (acceptable range 200+/- 75), part of this included twisting, bending, etc to try to get the CPS to fail,; Checked ballast resistor on drivers side - 1.5 ohms, compared to brand new, same resistance; checked starter solenoid - determined that not getting voltage where requried, replaced with new solenoid - voltages OK all about 12.5V. (May be part of the problem). Fuel pump runs when key turned, but does not provide sufficient pressure to fuel rail.

With both fuel pumps, I was able to start and drive it for about a week and then one morning it would not start again. Have checked all connections related to the pump - fuel lines, power, etc - all OK.

Jumpering across the starter solenoid, - SOL to batt +, a solenoid (EGR solenoid??) on the drivers side fender behind the ballast resistor clicks. No idea if this is suppoed to happen.

Also, the injectors were replaced about 2 years ago, recently, within the timeframe of the two fuel pumps, have changed the cap, rotor, wires, plugs (4-point Bosch Pt), and the Jeep was running really good.

Any suggestions would be greatly appreciated as I have run out of ideas.

Thanks in advance.

[wwwildman]

When you replaced the fuel pump in the tank, there is a rubber hose from the pump to the line leaving the tank, did you check to make sure that the hose clamps were tight?
When I had the fuel pump replaced on my sons 89, it worked for about four months then would not hold pressure at the fuel rail, so I went off to get a new fuel pump, but when I removed the one from the tank I found that the rubber hose was loose and it was losing prime and dumping most of the fuel back into the tank. This caused it to lose fuel pressure at the rail and it would not start.

Try checking on that and make sure that all fuel lines are not kinked or clogged. Also the fuel pump could still be bad, even it is pumping fuel. Try a leakdown test to insure that the pressure is not leaking down faster that it should.

[G.A.S.]

5 bad brand new pumps right out of the box in one summer. (4 months).
Went to a different supplyer and not a problem sence.
Make sure you do the tests and inspections of lines per wildman.
and just for chitz and giggles I wounder about the new filter. I dont know if you can install it backwards or not. some filters have a anti flow back valve and should be installed per the arrow, only flows one way.
Just a thought

[wwwildman]

Originally Posted by G.A.S.

5 bad brand new pumps right out of the box in one summer. (4 months).
Went to a different supplyer and not a problem sence.
Make sure you do the tests and inspections of lines per wildman.
and just for chitz and giggles I wounder about the new filter. I dont know if you can install it backwards or not. some filters have a anti flow back valve and should be installed per the arrow, only flows one way.
Just a thought

G.A.S. is right, I forgot that, make sure that the filter outside the tank has been installed in the right direction, or the fuel may not flow correctly.

[dwendt1978]

Lol. This happened to me on my jeep! Had the blasted filter backwards and burnt up a fuel pump. Funny thing is it will actually run a while that way.

By the way, it wasn't me that installed the fuel filter!!

[zsnoopy1225]

Thanks for the suggestions.

I'm hoping to do some more troubleshooting and confirm that the external fuel filter is installed correctly this weekend.

If the problem is the pump losing its prime, how do I insure that the hose is tight. Is there some type of compound that could be placed around the tubing/pipe to help prevent the loss of prime?
(When installing the pump, I made a point of tightening both clamps extremely tight because I had heard one problem, although unlikely, was that the hose could acutually come off the fitting.)

I will post more info if I get to work on the jep this weekend.

Thanks in advance.