Mechanics

ELECTRONIC FUEL PUMP

1999 GMC Jimmy

Computer problem
1999 GMC Jimmy 6 cyl Four Wheel Drive Automatic 200000 miles

I can crank over the engine but won't start! I don't hear the fuel pump coming on anymore when I turn the key on. I checked all fuses and looked for loose wires. Checked my security system to make sure its working right. I thing there's something wrong with the power going to the fuel pump, but that's my guess and I don't know how to check it! Help!


http://www.2carpros.com/forum/automotive_pictures/432803_P6120244_1.jpg

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Jimmy99
November 9, 2009.




Welcome, do you have spark at the plugs, engine cranking? Also, use a gage and check fuel pressure. There should be a fuel pump relay in the power distribution center, under the hood. Voltage for the load side of relay is hot all the time, voltage for the coil side of relay goes hot with engine cranking and a couple of seconds when you first turn key on, no crank.

JDL
Nov 9, 2009.
There is a Fuel Pump module (fuse). ECM B in the fuse distribution box under the hood. I don't see a relay that deplics anything to do with fuel control.
Isn't there a fuel pump Re-set button anywhere on this truck? Still lost!

Tiny
Jimmy99
Nov 9, 2009.


http://www.2carpros.com/forum/automotive_pictures/170934_99_gmc_jimmy_1.jpg



My info showed the above for underhood fuse block. no reset that I'm aware of.

JDL
Nov 9, 2009.
I am having the exact same problem. The manual says to first listen to the whirring sound of the pump when ignition is first on.

If pump does not come on, check the fuel pump fuse which governs the fuel pump relay, the fuel pump, the injectors, the ignition system and the PCM.

If fuse is good, check for an open circuit between the relay and the fuel pump. With the ignition key on (engine not running), check for battery voltage at the relay connector. This is located behind the glove box inside the relay control box.

(I am having problems determining what the relay looks like behind the glove box. I see a large harness that I believe connects to the ECM, and to the right of this is a black box that may or may not be the relay I'm looking for. I am wondering if I need to remove the relay in order to test for power to the relay, if this is actually the relay at all). I digress.

If battery voltage exists, replace the relay with a known good relay and retest. If necessary, have the relay checked by a qualified automotive parts store.

If the fuel pump does not activate, check for power to the fuel pump at the fuel tank. Access to the fuel pump is difficult but it is possible to check for battery voltage at the electrical connector near the tank.

If oil pressure drops below the specified pressure level, the oil pressure switch will act as a feul pressure cut off device.

Tiny
Jhub65
Jan 24, 2010.
I know this is an older thread, but I am posting this for those that stumble upon it.

As previously stated, the manual says the fuel pump relay is behind the glove box. Mine was actually in the fuse panel in the engine bay. I went online and after appxomately 1 hour, I was able to understand how to test the relay to see if it is working. An easier way is to put your finger on the relay itself and have someone turn the ignition on (engine not running). You can feel the relay click if it is working properly. You can also hear the click. If the relay is in close proximity to another relay, it may be difficult to hear if the relay you are trouble shooting is the one that you clicking. That's why it is good to follow up with the feel method.

Once I was sure my relay was working properly, I was able to reach above the fuel tank at the back end of the tank and reach the connector at the fuel pump. I unplugged the connector and was able to place a multimeter on the pins to read voltage. Use your manual to determine which of the four pins are power and ground. The important thing to remember is that when the ignition is on (engine not running), the fuel pump relay kicks on and provides temporary voltage to the fuel pump to prime the lines. If the fuel pump works properly you can hear this momentary prime. The relay only provides power for a couple of seconds. You cannot turn on the ignition and then crawl under the car to test the connector for power. There will be no power by the time you get there. You must be under the car with the probes from the multimeter hooked up while somebody else turns on the ignition for you. You should see near 12v of power momentarily and then no power. If you have power, and your fuel pump does not work, drop the fuel tank and change the pump. If the voltage is excessively low (more than.5 volts lower than what your battery is giving), a relay could still be the problem.

If you check the connecting harness and see 5 volts of power to the pump, be certain you are reading the correct probes at the connector. The connector for a 2001 GMC jimmy has 4 terminals. Two are for the fuel pump and two are for the sending unit. The sending unit should read 5 volts with the ignition on at all times.

Word of caution when changing the fuel pump. There are three feed ports on top of the pump assembly. They are very brittle. If you are not careful you can break one of the plastic ports when attempting to connect the fuel lines to it. Be sure the tank is high enough and only attempt to connect the fuel lines from the fuel lines to the pump ports. This means you should connect the flexible fuel lines to the rigid fuel lines along the body of the car first, then once the tank is high enough, reach up and connect the flexible fuel lines to the pump ports. When connecting them the other way around, when you pull on the flexible fuel line from the port nipple, in an effort to connect to the rigid line along the body of the car, it takes very little force to snap the port clean off and will likely have to replace the pump.

Hope this helps.

: )

Tiny
Jhub65
Jan 31, 2010.
What should you check if there is no power to the fuel pump fuse next to the relay?

Tiny
Demodaryl
Mar 4, 2010.
Are you talking about 99 Jimmy? ECM B fuse, goes hot when you turn on the key. I can't say if ignition switch is faulty? I'd have to check the feed to and from the switch.

JDL
Mar 4, 2010.
It's a 98 but same set up

Should have constant power per the wiring diagram
Get nothing from either side of the fuse, but when I pull the fuse and check the hot side it barely lights up the circuit tester
Isn't there a wire somewhere along the fire wall that goes directly to the pump to test it?

Tiny
Demodaryl
Mar 4, 2010.
Mod shows fuel pump test connector, if there is one, in the underhood bussed electrical center. I don't know why the ecm B fuse isn't hot, have to track the circuit. There is a 175 amp mega fuse, one of the positive battery cables, lead to it, Don't have exact location. That fuse serves several circuits, including ecm b fuse.
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JDL
Mar 4, 2010.
Where is this located. I'm looking at the picture in the Haynes manual and it says it's on the block behind the intake manifold, but I don't see it. Could it be on the valve cover? I see something there that looks like it.

Tiny
Demodaryl
Mar 8, 2010.

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