Fuel Pump Issue

[robbie95]

So, I'm trying to find an electrical issue, that's what I'm assuming it is. I was driving home last Sunday and all of a sudden, the truck just shut off, I did a little investigating before I decided to have it towed home. 

 

1991 2.5 Jeep Comanche 5spd manual

 

When I got it home, I realized that the fuel pump does not cut on/prime when I turn the key into the "ON" position like it usually does. So, I figured the fuel pump had gone bad. I put a multimeter on the connector that you hook up to the fuel pump and saw that it's only reading 6-6.5v instead of the 12v I'm assuming it should get. I took the fuel pump relay out and tried a jump wire the relay. Still didn't get anything, so I put the multimeter on that, from what I've read, pin 30 should be grounded, and 87 should have constant 12v, I'm not getting anything on pin 87, however on pin 85 and 86 I get 12v. I've checked all my grounds, cleaned them up etc. What else should I check?

[Pete M]

were you checking for power while the key was turned to "start"?  power to the pump is not available with the engine off.  were you checking for power at the fuel level sensor wire instead of the power wire?  did you check the ground wire at the pump for ground? 

 

if you disconnect the power cable running to the starter you can have someone turn the key to "start" without the engine actually cranking and making a bunch of noise.   

[robbie95]

58 minutes ago, Pete M said:

were you checking for power while the key was turned to "start"?  power to the pump is not available with the engine off.  were you checking for power at the fuel level sensor wire instead of the power wire?  did you check the ground wire at the pump for ground? 

 

if you disconnect the power cable running to the starter you can have someone turn the key to "start" without the engine actually cranking and making a bunch of noise.   

I have the key turned to where it usually would kick on the pump and prime before I try to crank it.

 

I could have been, my fuel level sensor is working fine, just can't get the pump to power up. I haven't checked the ground there, no, how would I go about checking the ground at the pump? I already redid the ground behind my driver's tail light, so I know that one is good.

[Pete M]

the ground is one of the wires in the harness coming off the truck. there should be 3 wires.  ground, power and signal.  the ground runs all the way back to the taillight.

 

the pump only gets power for a couple seconds if the key is turned to "run". 

[eaglescout526]

Ground is where I would check but if it’s been driving fine and suddenly cuts off, I wouldn’t put it past the fuel pump to have died. 

[robbie95]

14 minutes ago, Pete M said:

the ground is one of the wires in the harness coming off the truck. there should be 3 wires.  ground, power and signal.  the ground runs all the way back to the taillight.

 

the pump only gets power for a couple seconds if the key is turned to "run". 

I've been looking around for a wiring diagram, I'm guessing the black is going to be the ground?

[robbie95]

5 minutes ago, eaglescout526 said:

Ground is where I would check but if it’s been driving fine and suddenly cuts off, I wouldn’t put it past the fuel pump to have died. 

I thought so too, but I tested my old fuel pump with running 12v through it, and it kicked on

[Pete M]

yes, black is ground   if the middle wire is skinnier than the others, that's your signal wire.

[Eagle_SX4]

Since you have a 91 have you checked the codes?

 

 

 

[robbie95]

8 minutes ago, Eagle_SX4 said:

Since you have a 91 have you checked the codes?

 

 

 

For some reason, my check engine light doesn't work either...so I can't check codes, it's crazy

[Eagle_SX4]

Just now, robbie95 said:

For some reason, my check engine light doesn't work either...so I can't check codes, it's crazy

It may be that the bulb is just burned out. It doesn't take to much effort to pull the 91+ clusters (no speedometer cable to deal with). You don't even need to buy a new bulb just to check it you can just swap one of the others in its place.

[robbie95]

12 minutes ago, Eagle_SX4 said:

It may be that the bulb is just burned out. It doesn't take to much effort to pull the 91+ clusters (no speedometer cable to deal with). You don't even need to buy a new bulb just to check it you can just swap one of the others in its place.

Tried swapping bulbs from one that I know work, and it didn't do anything.. maybe I just have a giant electrical problem on my hands lol

[Eagle_SX4]

That's not a good sign. I know that on the 91-95's the check engine light is operated by the computer grounding the circuit. Maybe your computer isn't grounded. Definitely check all the grounds you can find. Take them apart clean them and use some ox-gard when putting them back on.

[robbie95]

16 minutes ago, Eagle_SX4 said:

That's not a good sign. I know that on the 91-95's the check engine light is operated by the computer grounding the circuit. Maybe your computer isn't grounded. Definitely check all the grounds you can find. Take them apart clean them and use some ox-gard when putting them back on.

Will do, I know I had problems in the past with grounding, thought I had them all solved.. I appreciate all of the help!