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fuel system [message #223479]

Mon, 23 September 2013 20:25

mickey szilagyi

Messages: 273
Registered: January 2013

Karma: 0

Senior Member

We have several problems with our fuel system and are looking for a schematic of the entire system and an explanation of how it all works. I've checked the forum and can't find some of the things I've read in the past or specifics that addresses what we are looking for.

First of all our fuel gauge works sporadically. And when it does work it may work only for the main tank and not the auxiliary tank. We're trying to determine if the sending unit is bad or if there is a ground problem in the wiring. My understanding is that if the gauge shows empty then the ground is OK. And here's the strange part. With the ignition on it seems that if I play with the shift selector, from park to reverse and so forth the gauge will suddenly work.

We figured we'd just live with this oddity until we needed to deal with the fuel tanks. Well, for the first time since purchasing our coach, we filled the tanks almost full and found that we have a leak when the rear of the coach is lower than the front. So now we're about to deal with the tanks to find the leak. It's not a fuel line leak as it doesn't leak when the engine is running. This just appeared when we put more fuel in the tanks. And we'd like to know just how the fuel system works.

Is there a good detailed diagram that shows the two tanks, how they are connected to each other, where the sending unit is and if there is a sending unit in each tank. We understand the fuel pump is in one of the tanks but we aren't sure. What exactly is happening when we switch the dash board fuel switch from main to auxiliary tanks?

We are having this work done at a repair facility and these are some of the questions we have as well as the mechanics have asked. We have a parts book and maintenance manual. There is one schematic in the parts manual but it's really hard to figure out what is what. Since the tanks will be down we are considering having the insides coated, all the lines checked etc.

Any help with these questions and a reference for a good diagram of the fuel system would be much appreciated.

Thanks again to everyone, you have been a great help as we proceed with our restoration.

Mickey 1977 Kingsley, 403, Lansing, MI

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Re: fuel system [message #223489 is a reply to message #223479]

Mon, 23 September 2013 22:16

Carl S.

Messages: 4186
Registered: January 2009
Location: Tucson, AZ.

Karma: 13

Senior Member

Mickey,

Try looking through the GMC photo site. Here is a link to a search of "gas";

http://www.gmcmhphotos.com/photos/search.php?searchid=56953&cpage=1

Quite a few of us have redone our fuel tanks and lines/hoses and documented the work there.

There is also this on Gene Fisher's site:

http://gmcmotorhome.info/list.html#fuel

I'm sure the Maintenance Manual has all the info you might need.

The tanks do not (unless the system has been modified) have fuel pumps in them. They have numerous lines/fittings/hoses on top of them, any one of which could be leaking. Dropping the tanks is not a difficult job. Just make sure you get all the fuel out first, otherwise the tanks will be really heavy.

Carl Stouffer '75 ex Palm Beach Tucson, AZ. Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles, Solar battery charging. GMCSJ and GMCMI member

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Re: [GMCnet] fuel system [message #223493 is a reply to message #223489]

Mon, 23 September 2013 23:29

Bruce Hart

Messages: 1501
Registered: October 2011
Location: La Grange, Wyoming

Karma: 5

Senior Member

Look at the liquid/vapor separator in the rear wheel well just in front of
the mid boggie on the drivers side. If that is stuck or malfunctioning then
raw gas can leak out. These units can leak after filling to the max, the
plastic gets brittle and cracks.

On Mon, Sep 23, 2013 at 9:16 PM, Carl Stouffer <carljr3b@yahoo.com> wrote:

>
>
> Mickey,
>
> Try looking through the GMC photo site. Here is a link to a search of
> "gas";
>
> http://www.gmcmhphotos.com/photos/search.php?searchid=56953&cpage=1
>
> Quite a few of us have redone our fuel tanks and lines/hoses and
> documented the work there.
>
> There is also this on Gene Fisher's site:
>
> http://gmcmotorhome.info/list.html#fuel
>
> I'm sure the Maintenance Manual has all the info you might need.
>
> The tanks do not (unless the system has been modified) have fuel pumps in
> them. They have numerous lines/fittings/hoses on top of them, any one of
> which could be leaking. Dropping the tanks is not a difficult job. Just
> make sure you get all the fuel out first, otherwise the tanks will be
> really heavy.
> --
> Carl S.
> '75 ex Palm Beach
> Tucson, AZ.
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>

--
Bruce Hart
1976 Palm Beach
Milliken, Co
GMC=Got More Class
51st State? Northern Colorado!
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
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Bruce Hart 1976 Palm Beach 1977 28' Kingsley La Grange, Wyoming

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Re: fuel system [message #223498 is a reply to message #223479]

Tue, 24 September 2013 00:02

Matt Colie

Messages: 8547
Registered: March 2007
Location: S.E. Michigan

Karma: 7

Senior Member

mickey szilagyi wrote on Mon, 23 September 2013 21:25

Mickey,

I don't know where the good diagrams are. I know I have a great set lodged in my cerebellum. There are numerous good diagram in the photo archive, but I can answer most of you questions in a few minutes on the phone and we will be back in striking range of Lansing about Oct 3.

Please send an e-mail to matt7323tze at Gmail dot come with a number and a good time to call and we can talk about this. The fuel system is not well described in any of the GM publications.

I need to burn some minutes anyway.

Matt - it's only midnight in Branson

Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit

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Re: fuel system [message #223522 is a reply to message #223489]

Tue, 24 September 2013 11:50

mickey szilagyi

Messages: 273
Registered: January 2013

Karma: 0

Senior Member

Thanks to everyone that offered advice on our fuel problem. I spent a number of hours reading the respective links on Gene's website and a bunch of pictures on the photo forum. We're beginning to understand what the system entails. The leak seems to be low and not at the liquid/vapor separator as it's dry there, no signs of fuel leaking there.

We had good results with a repair shop near us, A&D repair in Haslett MI, and will be taking the coach in tomorrow, Wed, 9/25, to have them look for the leak we are experiencing. Hopefully the leak and the fuel gauge problem is related or can be remedied a the same time. If the tanks are OEM and need cleaning we're thinking of biting the bullet and having them cleaned and coated inside and out. There's a place in Lansing, MI that does the Gas Tank Rene procedure.

Again, thanks to all. We've relied heavily on the information provided by this forum.

Mickey 1977 Kingsley, 403, Lansing, MI

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