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| Re: [GMCnet] rookie errors. [message #323964 is a reply to message #323941] |
Sun, 17 September 2017 21:16   |
cbryan
Messages: 451
Registered: May 2012
Location: Ennis, Texas
Karma:
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Senior Member |
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Quote:How would having 2 fuel gages reading the existing sensors work? From what
I have read there is a lot of confusion about reading the gages and
guessing how much fuel is left. Also, there seems to be a lot of unusable
fuel when going uphill. We may not run out of fuel as often if we only had
the main tank hand had to fuel ever 200 miles.
OK, as I understand the workings of the fuel system, over the years, the tank gets toward empty and the tank being relieved of the fuel weight, bends the fuel pickup up off the floor of the tanks. Add to that any pressure put on the tanks from running over debris, and my favorite possible cause, our own pushing on the bottom of the tanks to reinstall them. The tanks also are shallow like a stack of two waffles...if you get my drift, so the sloshing of fuel means less fuel is available at all times. Add this to the expectation that we think that if we run out of one tank, we can, like in an airplane, switch to the other tank and have a hundred miles or so to go. And, in my case, add a custom instrument panel with a poor ground as I bought it, and any time I wanted more fuel indicated, I just turned on the headlights.....
You know the tanks are cross connected at the inlet pipe, so that both tanks' gasoline are used until the tanks are at about 1/8 tank, and thus you theoretically have 1/8 tank left for the other tank that is not selected. Well, no, often the selector valve has failed and unknown to you the valve is drawing from both tanks, so when one runs out, that's it and you are out of gas. Or the selector valve doesn't operate to begin with, and you are limited to the operational tank and the surplus gas in the other tank, and then you are out completely. Or, as in my case, the selector valve was bypassed and I got some more miles out of the coach by taking some long nose vise grips and clamping one hose shut, so that gas could be drawn from the unempty tank. It involved guessing which tank was empty.
A help is to use two pumps, either in tank, or like Johnny Bridges, outside the tanks, one for each tank, selected by the selector switch on the dash panel. This helps in getting some more gas out of the tanks and having a redundant fuel pump situation. The other solution might be to put a flexible pickup in the tank so it rides up and down with flexure of the tank. (could be dangerous, wear on the bottom of the tank.) Get the grounds sure on the instrument panel, Ken Burton has a couple of posts on how to to that.
Or, just fill up every 200 miles. There's more technology available to help take care of this problem. Climbing a mountain or going down a mountain or hill with turns to the left means fuel sloshes toward the outside of the tank and there doesn't seem to be a reservoir inside the tank with a swinging door to keep fuel near the pickup, and this, too can cause fuel starvation at a dangerous time, just when you need power, power brakes, and power steering all at the same time, and by the way, the emergency or parking brake might or probably won't hold you on a slope when you break down. This means a solution becomes a matter of safety. Ken Henderson pumps fuel at low pressure from each tank into an external reservoir from which he pumps at high pressure for his fuel injected setup. He has never reported a fuel starvation issue, and he has reworked his fuel sending units to actually show all the "Delta fuel level" from full to empty, for the first time, he reports he now knows how much fuel he has in each tank. It might be the only GMC coach that is so accurate.
All this to say is that two fuel gauges are useless to solve this problem. JWIT.
Carey
Carey from Ennis, Texas
78 Royale, 500 Cadillac, Rance Baxter EFI.
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