Fuel problems?

[ccnova]

I have a 1990 Cherokee Laredo with 105,000 miles. I have owned it for 9 years with no problems. I dont drive it much in the summer but do use it in the winter. Yesterday I started it after it had been sitting for a couple weeks and as usual I had to crank it for 5-10 seconds before it would start. Today I went to move it again and it wont run. If I pour a little gas down the throttle body it will run for a few seconds. Is there anything I should check first or is it the fuel pump? I did change the fuel filter and it does have fuel in the tank. Any help is appreciated.
Thanks,
ccnova

[MagicRat]

Thump the bottom of the gas tank with a piece of wood or rubber mallet, then try to start it. If it starts, then your pump is bad.

[ccnova]

Sorry ive been busy. Ok it will ocassionaly start and run for about 15 20 seconds on hi idle then just run out of fuel and die. If I can quickly "feather" the throttle it will keep running as long as I keep it up. Its seems as though it is only getting fuel when I 'hit the gas' When I turn on the key I can hear the pump build pressure but its like it only gets fuel when I call for acceleration?
Any ideas are appreciated,
Thanks,
ccnova

[fredjacksonsan]

So it sounds like the fuel pump is running.

Throttle position sensor? Idle air control valve?

Is it giving you any codes? [ok I don't know if the 90 had OBD or not]

[ccnova]

Tried it again just now and it started right up and ran for 5 to 10 seconds then dies. It starts goes to hi idle @1500rpm then starts to idle down then just stops as it runs out of gas. It will start right back up and do the same thing. Would this be the throttle position sensor as suggested? Should I check for fuel pressure also and if so what should it be and when? Does anyone know of a way to test the tps?
Thanks for all the help.
ccnova

Sorry forgot no obd.

[ccnova]

Ok sorry everyone life got busy and this thing has just been sitting in the garage every since. So I put in a battery today and poured a little fuel down the throttle body and turned the key and after a cough and sputter it started and ran on hi idle for about one minute no problem then it just started losing rpm's and died.
Now it will start if I pour a small amount of fuel in but then I have to pump the gas to keep it running above 2500 rpm or it will just drop rpms and die?
I really dont want to just throw parts at it. Can anyone tell me where to start diagnosing and how?
Thanks,
ccnova
Sorry to refresh its a 1990 Cherokee Laraedo 105000 miles 4 liter

[LittleHoov]

Sounds like a sensor issue, you have a "Renix system" on your Jeep, which among other things means it has no on-board diagnostics system.

The sensors on a Renix Jeep have to be tested manually using a multimeter, and thats about the extent of my knowledge on it, so start searching for "Renix Jeep" and things of that nature. Google is your friend.

[ccnova]

Ok, I turned on the key and can hear the fuel pump build pressure and stop but when I check for fuel at the test port on front of fuel rail nothing comes out at all. Does this mean for sure that it is my fuel pump? I did just change the fuel filter as soon as I found there was no pressure at the fuel rail and that made no difference. and yes for sure there is fuel in the tank just added about 2 gallons to be sure.
Thanks for the help.
ccnova

[ccnova]

I crawled under the jeep and checked voltage at the pump. with my wife turning it over one wire has 12 volts or more at the pump the other wire only has 2 to 3 volts. can anyone tell me if this is right or does it point to a bad pump?
Thanks
ccnova

[ccnova]

Well I was just gonna drop the tank and change the pump but the j-bolts on the strap are so rusted I cant break loose the nuts. I know I can twist them off or cut them but none of the parts stores have replacements. So I'll go to the dealer tomorrow. But can anyone tell me what voltage to the two wires to the pump should be before I go any farther?
Thanks,
ccnova

[Rmbodie]

If you have 4 wires to the pump harness. the larger wires are for the pump, the smaller are for the gauge. Sounds like you have sediment in the tank clogging the screen. It can draw enough fuel to build pressure when there is no demand. another option: buy or borrow a fuel pressure tester for about $40. It can save you alot of time on your back trying to drop the tank. It will help you check the regulator and the pump.

[Rmbodie]

Oh yea the 12 volts on the larger wire is right, and 5 volts or less on the other one

[ccnova]

Ok thanks for the help! There are only three wires to the pump. one has 12 volts one has between 2 and 3 volts and the other is a ground. If my voltages are correct I will probably just take out the pump and check the screen before buying a new pump. Then go from there. I can hear the pump run and stop when you turn on the key theres just no fuel at the rail. Thanks again for the help. I'll try it tomorrow.
Thanks,
ccnova

[mastertech1964]

the fuel pump in these models has a rubber hose that connects the pump to the fuel pipe ive frequently seen them develop a hole in them or the clamps loosen up and you have long crank time and insufficent fuel volume at cranking the pump gets 12 volts which makes the pump run faster but once the key is released and in normal run mode there is a ballast resistor on the left fender which reduces pump voltage to about 9.5 volts reducing pump speed and volume if theres a leak at the pump you could have a car which will start but dies out or runs very poorly when the key is released

[mastertech1964]

also you should be able to change the pump without removing the tank simply loosen the locking ring which is actually on the front of the tank not the top and pull the pump and sender assy out and inspect it make sure to use a new sender oring so you dont have a fuel tank leak when your done