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99 Suburban Fuel Pump Voltage

Old April 5th, 2008, 12:47 PM
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Default 99 Suburban Fuel Pump Voltage

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?
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Old April 5th, 2008, 1:17 PM
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Default RE: 99 Suburban Fuel Pump Voltage

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.
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Old April 5th, 2008, 6:25 PM
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Default RE: 99 Suburban Fuel Pump Voltage

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.

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Old April 6th, 2008, 1:55 PM
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Default RE: 99 Suburban Fuel Pump Voltage

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...
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Old April 6th, 2008, 11:22 PM
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Default RE: 99 Suburban Fuel Pump Voltage

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 otheroptions? 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!!!

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Old April 7th, 2008, 5:25 PM
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Default RE: 99 Suburban Fuel Pump Voltage

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.
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Old April 7th, 2008, 11:34 PM
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Default RE: 99 Suburban Fuel Pump Voltage

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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Old April 16th, 2010, 8:40 AM
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Hey Smitty,

Did the new wire do the trick?
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Old May 31st, 2010, 2:42 PM
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Default Suburban Fuel Pump Woes

1996 Suburban;
After 3 fuel pumps, numerous harness upgrades, fuel pump relay and new grounds installed, the problem was discovered during the 4th pump install.
Had to replace the sending unit. The connection on the bottom side of the mounting plate (black wire to pump), was weak and caused loss of power, ( it had even gotten hot enough to start to melt the pigtail on the underside of the plate). Hope this helps alot of you out there!
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Old June 16th, 2011, 8:43 AM
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shawnvw, did you ever here from smiitygj on the problem where he was getting only 4-5 volts dc at the fuel pump?
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