Fuel Pump Questions??

1990 4.0 AW4
Ive got quite a large number of questions/comments here because I'm trying to see if my fuel pump is going out on me.

1. Im getting a whirring noise from the back end near the gas tank but it is only after the car has been driven for like 45 minutes. (been doing this off and on for a week or so now)
2. I was reading other posts and it seems like when the gas tank is full I dont hear it(although Ill have to check again) Other people posted saying the same thing.
3. My engine starting time is really getting bad(especially cold crank)
4. I dont know if this is tied to it or not but since it has been making the noise my acceleration has been severely suffering.

The only reason that leads me to believe maybe it is something else is the fact that when I just turn the ignition on right after its been making the noise, the noise is absent. However, if I shut the car off and start it right away again it will make it.

First off do these symptoms sound like a worn fuel pump? Otherwise what could it be? Any help? Thanks

Sounds fuel pump related. Your ballast resistor (white ceramic thing) on inner fender drivers side controls fuel pump noise. The long crank when cold is classic check valve in fuel pump going bad symptom. The poor accellaration also suggests a bad pump or fuel filter. I would change the fuel filter first of course. Use a fuel pressure gauge (cheap from autozone) and attach to schrader valve on fuel rail. Pressure should be approx. 31 psi w. vacuum line attached to regulator on end of fuel rail and approx. 39 psi w. the vacuum line disconnected. Note the vacuum line disconnected psi is the one that happens w. wide open throttle (accelleration). Re long crank when cold - your check valve is probably bad if your pressure gauge shows pressure has dropped considerably over 20 psi after sitting for over 30 minutes after shutdown and before restart and if the drop is approx 20 psi then suspect your pressure regulator on end of fuel rail per my 89 fsm (note your renix fuel injection sys on a pre 91 4.0 is the same). If you replace your fuel pump I recommend using the bosch oem type pump only. Many report odd issues with non oem type aftermarket pumps myself included. Good Luck. Greg

Thanks, anyone else?

in 1990 jeep had a problem with fuel pressure bleeding back after sitting for a while. if you have access to a fuel pressure gauge, you can see how long it takes to get operating fuel pressure while cranking.

jeepguy1990 said:

1990 4.0 AW4
Ive got quite a large number of questions/comments here because I'm trying to see if my fuel pump is going out on me.

1. Im getting a whirring noise from the back end near the gas tank but it is only after the car has been driven for like 45 minutes. (been doing this off and on for a week or so now)
2. I was reading other posts and it seems like when the gas tank is full I dont hear it(although Ill have to check again) Other people posted saying the same thing.
3. My engine starting time is really getting bad(especially cold crank)
4. I dont know if this is tied to it or not but since it has been making the noise my acceleration has been severely suffering.

The only reason that leads me to believe maybe it is something else is the fact that when I just turn the ignition on right after its been making the noise, the noise is absent. However, if I shut the car off and start it right away again it will make it.

First off do these symptoms sound like a worn fuel pump?

Click to expand...

Yes. It's only a matter of time before it craps the bed completely and leaves you stranded so replace it before it does.

mine crapped out on saturday night on a date... unfortuneately, it caught on fire and nearly killed us both.

everythings ok though...

There's a date you're not likely to forget! Bummer to hear it burned though...did you get another date out of it?

yeah actually, I really kept my cool and played the poker face the entire time. I pulled off the highway and coasted through a red light into a gas station and borrowed an extinguisher, put out the fire, got a tow, and was sitting at dinner with her by 11. a late night, but I was definately the fearless hero. Overheard her tell her roommate i was "certainly not a boring guy"

on the whole, a priceless night.

:bunny:

I should add, I had it at the shop today, and they were shocked to hear it had been on fire... said they saw the extingisher dust, but didn't see much charring, and they started it up and it ran!

I couldn't believe it...

anyway, I had them replace the pump, filter, and wiring/hoses, while it was there and the tank was out. I'm interested to see how it runs when I pick it up... Three weeks ago I got a new Jasper 4.0 and it's been great, with the exception of a slight stumble at idle, which I attribute to the pump. So, this will be the first time running it with a fresh fuel pump and filter.. and it's just now seasoned with 1100 miles... it's finally ready for a nice little beating!