Need help with fuel pump resistor test

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97 greenmonster

97 greenmonster

10 Year
Joined
Dec 7, 2013
Threads
14
Messages
490
Location
Canonsburg pa
so I've been having running issues on my 97 fzj. I have another post about it. But I just tested my fuel pump resistor as per the fsm and its reading 1.7ohms when it's suppose to be .70-.76omhs. Problem is from reading some posts it seems checking such low resistance meters can be inaccurate. So I ask any nice member out there with a min of time a good fuel pump resistor and a multi meter could you please quick test the resistance of it at around 68 degrees to let me know if what I'm getting in my test is right and I need a new one. Thanks in advance.
 
Yes, your typical multimeter can't measure low resistance very well since the meter test leads have resistance too.

Some meters allow you to zero the ohms reading, so touch the two probe tips, push to zero and then measure your load.

If no zero function, then just touch the probe tips and note the displayed resistance (call it offset error). Then measure your load and subtract the offset error due to the test leads.

That should get you pretty close.

cheers,
george.
 
Were it my truck and I suspected the FP resistor I would jumper across it and see if that was a fix. I believe that all it does is make the pump run slower and therefore produce less noise. The pump should be able to handle 12-14 volts continuously.
 
so just jump the two wires on the plug where I unhooked it from? I ask because I made a jumper out of paper clip with some tape on the end and starred the truck and it got crazy hot.
 
What multimeter model/brand are you using. Seems very unlikely you get zero ohms. Even a 6 1/2 digit fluke won't give that without either zeroing or using 4 wire mode.

cheers,
george.
 
Ha - so you're trying to use a cheap pos meter to do some low resistance measurements. Good luck :) I'd treat a HF meter as a basic go/no go tester, versus something I'd believe the actual readings of...

cheers,
george.
 
New update while I had fuel pump resistor out I figured I'd jump the wire and take it for a ride. I can say the truck has never run so strong. No issues so what would this point to? Remembering Fuel pump resistor checked out fine
 
There is a relay that shorts around that resistor when it demands more fuel pressure, which delivers the full 12V to the fuel pump. That relay has fried contacts probably. It's on the other side of the engine bay, up behind the ABS stuff.

Don't run it shorted for extended periods as you will probably burn up the pump prematurely.
 
Well the only time the pump runs full voltage is at start and under high load and hard acceleration. Your running higher psi at all times now and sending more fuel to the injectors. The ecm will continue to lean out the mixture to make up for the Xtra fuel. I don't think the pump will cap out sooner but running lean isn't a good thing either.
 
Just the fuel pump resistor jumped out everything else is how it should be. I ask how long I can drive it jumped to test it again later to make sure it wasn't just fluke it running better. Thanks
 
So what is the jumpering of the resister masking? Clogged fuel filter, dirty "sock" at the pump, failing FPR, injectors? Time to make a list of suspects and start crossing them off.

EDIT: IMO there is no danger to the pump running it full voltage but it is masking something else that could bite you. I wouldn't run less than a 1/4 tank of gas while you've got it jumped for more than test drives, however.
 
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