99 Suburban Fuel Pump Voltage (Full Version)

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99 Suburban Fuel Pump Voltage

smittygj -> 99 Suburban Fuel Pump Voltage (4/5/2008 10:47:42 AM)
1999 K1500 Suburban Fuel pump went out on me in Feb 2007, and I replaced it without any problem. March 2008 (1 month after the warranty expired on the pump) Sitting in parking lot with engine running, and engine dies. Got under truck while having wife turn key on, and cannot hear fuel pump come on, so assume it is fuel pump gone out again, so had it towed home. Removed fuel line from input side of fuel filter and turned key on. Expected result would have been fuel to come out if pump was working. No fuel came out, so that verified that pump was not working. Dropped gas tank, and replaced pump, which came with a new wiring harness, which I spliced in. Put everything back together, and tried to start it, still won't start. Removed fuel line again from input side of fuel filter and turned key on. Expected result would have been fuel to come out if pump was working. No fuel came out, so that verified that pump still was not working. Replaced fuel pump relay, and rechecked all fuses again, and it still didn't work. Dropped fuel tank again, and cut and respliced all the wiring on the replacement wiring harness again, just to rule out a bad splice. Hooked up the wiring harness, and had key turned on. Fuel pump should have come on for 2 seconds, but did not. Checked voltage to grey wire in wiring harness back at fuel pump, and with key turned on, get approx 4 to 5 volts for 2 seconds, so it is getting voltage, however what I do not know is should I be getting more voltage at the pump, or is 4 to 5 volts correct? If voltage is correct, then I have to assume that the replacement pump is bad. If voltage is incorrect, then I do not know what to check next.... Any suggestions?

RonH -> RE: 99 Suburban Fuel Pump Voltage (4/5/2008 11:17:12 AM)
I think you should be getting 12v at the grey wire. Power comes from the underhood fuel pump fuse to the fuel pump relay, then on to the fuel pump on the grey wire. You might want to check the voltage to the fuel pump relay, and also check your grouind connection (black wire) out of your fuel pump.

shawnvw -> RE: 99 Suburban Fuel Pump Voltage (4/5/2008 4:25:12 PM)
yea definately should be getting 12 volts....Sounds like there may be a corroded wire somewhere. Use your multimeter to see what kind of voltage you have at the fuse(ecm B in the underhood fuse box). If you only have 5 volts there, then there a bad connection between there and the battery. 1st place to check would be where the cable bolts to the fuse box. Have seen these get so hot it melts the plastic from a poor connection. If this was the culprit, you should have more problems than just fuel pump. If you do have 12 volts there, test for 12 volts at the relay with key off. If you do have 12 volts, then you either have a bad relay, or a poor connection somewhere on the grey wire from the fuse, to the tank.

smittygj -> RE: 99 Suburban Fuel Pump Voltage (4/6/2008 11:55:20 AM)
Results of checks: Input to fuzebox = 12.44V ECM-B = 12.44V Input to Relay = 12.44V Guess I'll have to start tracing the wiring on back from there...

smittygj -> RE: 99 Suburban Fuel Pump Voltage (4/6/2008 9:22:53 PM)
Added note. I DID have a bad replacement fuel pump. Hit it with direct 12v line, and nothing happend. Returned it, and received a new one since it was still under warranty. They gave me a different brand this time, but basically it is the same pump with the same replacement wiring harness. Plugged it in while holding it underneath the suburban just to see if it buzzed on, and it did not. Hooked it up direct from battery with good ground, just tapping it a little to see if it would buzz on, and it did, so this pump is good. Now, back to the wiring. I bypassed the relay with a jumper, and took a multimeter reading at the fuel pump wiring harness, and I still get 5 volts. So relay is definately good. Aside from unwrapping all 10+ feet of conduit that is taped up from the fuze block to the wiring harness connector to search for the faulty connection, are there any other options? I'd probably need 10 rolls of electrical tape just to tape it all back up. Here are my thoughts. How about just running a new hot wire for the pump from the output in the fuel pump relay and just running it all the way back and splicing it in place of the grey wire? I still don't understand what could be causing me to get the 5 Volts at the pump wiring harness. I've searched various boards, and have seen this problem numerous times, but never a definative cause. What is weird about it is that it is almost always approx 5 Volts when it is encountered, on cars, trucks, vans, etc. But no one has ever posted back as to what the cause was. This thing is really kicking my butt!!!

shawnvw -> RE: 99 Suburban Fuel Pump Voltage (4/7/2008 3:25:38 PM)
If i wire you, I would just run a new wire from the relay to the pump. No sense in wasting time trying to find a bad spot in the wire when you could run a new one in less time, and you know that the entire length of wire is fine and won't give you more problems in the future.

smittygj -> RE: 99 Suburban Fuel Pump Voltage (4/7/2008 9:34:05 PM)
That is what I did this evening. I opened up the fuseblock, and took a voltage reading at the grey wire (hot wire) at the fuze block, and got 12V for 2 seconds when key turned on. Double-Tripple-Qaudruple checked the voltage back at pump wiring harness and it was still 5V. Went and bought the splices I needed for the fuseblock, and put in a new wire in place of the grey wire. Ran it back to fuel pump wiring harness and spliced it in. Tested voltage, and got 11.96V at the harness. Going to put it all back together tomorrow and try it out, and I'll let you all know what happens!!!

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