89 cherokee new pump is 125 psi. why? - Hot Rod Forum : Hotrodders Bulletin Board
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Old 06-27-2010, 05:15 PM
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89 cherokee new pump is 125 psi. why?

workingon an 89 little cherokee 4x4 with 4.0L

for some reason they give you a universal 125 psi pump as a replacement. the specs for these was 31 psi

why do they do this?

we tried to run it but it just explodes hoses and run so loud you cant cover up the noise with the sterio even

gonna go with a 4cyl one thats around 40-50 psi


im just curious...

also since these cherokess dont have a FP relay they must be wired directly through the ign switch or whatever like the toyotas etc were, right?

it does not prime up with key in run, and only powers the pump while cranking,.

this is factory correct right?

i found voltage drop in the wire and i had to connect it to the ACC port in the fuse panel because the original way it was wired it only had barely over 10 volts and rapidl dropped after firing it up and it would just run out of fuel and die.

normally the FP wire either is perfectly fine or is totally dead such as with the s-10 trucks and blazers and such,

not these jeeps apparently...


thanks

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Old 06-28-2010, 06:33 AM
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Somebody Stop Him! Please Relay This Information Before Someone Gets Hurt.

Quote:
workingon an 89 little cherokee 4x4 with 4.0L

for some reason they give you a universal 125 psi pump as a replacement. the specs for these was 31 psi

why do they do this?

we tried to run it but it just explodes hoses and run so loud you cant cover up the noise with the sterio even

gonna go with a 4cyl one thats around 40-50 psi
Whoa! First of all I am guessing you got this number from the manufactorer specs. Manufactorers rate their pumps at dead head pressure and no restriction flow rate. Second, the volume of the pump is the most important apsect and that secod pump is gonna have a lot less volume. I am gonna venture and guess that you have a blockage; ie either pinching the return line, or the return and feed lines swapped.

Quote:
also since these cherokess dont have a FP relay they must be wired directly through the ign switch or whatever like the toyotas etc were, right?

it does not prime up with key in run, and only powers the pump while cranking,.

this is factory correct right?
Yes this is factory correct. The ecm commands the fuel pump on only during cranking and running. Yes there is a fuel pump relay; it is on the fender with three other relays.

Quote:
i found voltage drop in the wire and i had to connect it to the ACC port in the fuse panel because the original way it was wired it only had barely over 10 volts and rapidl dropped after firing it up and it would just run out of fuel and die.

normally the FP wire either is perfectly fine or is totally dead such as with the s-10 trucks and blazers and such,

not these jeeps apparently...
Stop! Pleased rewire the vehicle back to original condition! That fuel pump wiring has a ballast resistor in-line near the fuel pump. This resistor is there to keep the "electrical noise" down. You could perform an overlay from the relay to the pump and bypass this circuit to test for faulty conditions. Also, with the fuel pump wired to acc the pump will only have power when the key is in the acc or run position. Therefore, there will be no power to the pump when cranking. Also, the pump will run continuously if the key is left on. This could be a fire hazard! Further, you will be overloading that acc circuit. The wiring in the dash is way to small to feed the fuel pump! Please correct this before someone gets hurt! You are endagering your life and others!!!!

I know you ignore me; but I hope someone will relay this information before anybody gets hurt.
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