# Chevy 3500HD (GAS) fuel pump(s) question



## Alan Letts (Jan 12, 2008)

Hi Folks,

I have a question on my 99 C3500HD dump with plow hookup. I have the 454/auto powertrain with a dual tank system. It seems my rear tank is not pumping although the unified dash fuel gauge states 1/2 full. Can I safetly assume the combo pump/sending unit is bad in that tank, or is there another "brain" in the truck pump harness that should perform a "switchover" when the forward tank runs dry? I have been surprised by this happening a few times now. I never see any gas usage from the rear tank.

I understand this was/is a common problem with 3500 series dual tanks with individual intank pumps and sending units. Seems my manual states there is a porportioning valve somewhere that controls the "flip" from one tank to another.

Any one out there that's had this experience? I don't want to be buying a bunch of suspect parts if only one will fix it. BTW The combo fuel pumps are avail thru www.rockauto.com internet parts house for alittle over 220.00. I've heard stealers charging more than twice that.

Hoping someone can help narrow this down quickly.

Al Letts
Cincinnati Oh
[email protected]


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## ticki2 (Jan 10, 2006)

My understanding is that it doesn't use one tank at a time . The rear tank automatically pumps into the front tank . If the gauge is reading 1/2 full it means that both tanks are 1/2 full. And yes they have been problematic.Some have found that you need to fill the front tank first or it throws the gauge off. Try filling both tanks.


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## Sawdust Bob (Oct 16, 2004)

I have a 98 3500 dually. I filled both tanks and went out to plow. Early morning truck quiet running and I looked at gas gauge i had a half tank of fuel. Had truck towed to garage(thought it was fuel pump). Their is a pump that pumps fuel from back tank to front tank. No fuel in front tank,back tank full no way to get it their =1/2 tank of fuel truck won't run :crying:


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## Alan Letts (Jan 12, 2008)

*gas tank faults*

Bob,

Same problem here. Both tanks fulled, go down the road for 150 or so miles. get two notches on fuel gage below a half tank marking, and the engine shuts down with a full tank in the rear and nothing in the front. Rear tank doesn't supply the front as it's always full. When the indication of empty comes up and the truck stops there is NO fuel in the line at the fuel filter location.

There is a porportioning valve switch shown on the factory manual BUT I have never found it. I do know there are two seperate pumps and they share the connective wiring harness between them.

?????

Alan


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## Alan Letts (Jan 12, 2008)

Bob
I have a GM SI manual on my PC here at home. For the side by side (L+R) tanks for the 3500, there is a porportional valve shown in the harness shared by both tanks. Both tank sending units/pumps seem to be the same PN. I have to suspect the selector or rear pump. I will be tracing lines on my 3500HD tomorrow and try to make a determination which is which. Anybody else out there with this problem? Seems it has surfaced in a few TSB's in the past. 
Alan


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## ticki2 (Jan 10, 2006)

My '02 had the same problem ( with previos owner)so I did not deal with it . Work order says they replaced the transfer pump PN 15161174 , list price $ 98.52 . This is on a diesel , hope this helps.


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## Alan Letts (Jan 12, 2008)

*Transfer Pump*

Hi Ticki2:waving:

Well been crawling under the truck dump body today on a rainy day. I believe you're right in your suggestion. THe rear tank has only a two conductor wire connector going to it which is prob the sensor circuit only, and that rear tank does seem to feed thru a remote frame rail rmounted pump to supply the fwd tank. That fwd tank has a 4 wire connector I assume to power both the in tank fuel pump/sending unit combo. I'm prob going to drain the fwd tank to induce the aft tank to fill it. If the rail pump is getting 12 volt DC power and not pumping I have the culprit then. Thanks. This high priced GM-SI service manual didn't show that.

Alan 
[email protected]


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## Alan Letts (Jan 12, 2008)

*The Fix!*

A finale...

Replacement transfer pump 15161174 ordered thru www.rockauto.com for ~70 dollars. Whoopie..

I really reccomend these guys!

Alan Letts
[email protected]


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## Alan Letts (Jan 12, 2008)

*Final Story*

Ticki2,

You're the man!

Received the pump from Rockauto in three days. I just installed it yesterday. A easy job. Raised the dump body and it was right there behind the forward fuel tank mounted on the frame rail. 15 minutes later, I gave the truck a start and that new pump gurgled into life emptying the rear tank into the forward tank and raising my fuel level. Yippee.

I'm so happy I fixed this fuel curse I've been shouldering for a few months.

Remember www.rockauto.com BEST INTERNET PARTS REPLACEMENT HOUSE.

Alan


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## ticki2 (Jan 10, 2006)

Alan

Glad to hear it , I love it when that happens.


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