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Hi Folks. I have a nice 1985 Deville. Last summer I dropped the gas tank, cleaned it, sealed it and put back into the car. The tank is ok now but my gas gauge is crazy. When I have used about seven of the sixteen gallons of gas, the gage goes very quickly from nine gallons left in the tank to 8,7,6... to E and the car stalls. I fill it up and it takes only seven gallons. Am I supposed to reset something in the ECM or do I have a mechnical problem in the tank? Thanks.
 

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88 Sedan Deville, 89 Eldorado, 11 SRX, 18 CT6
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sounds like a bad ground. even with guage saying E, the car will suck whatever gas is in there. pump runs regardless of how much gas is in car... if you have a bad ground, the sensors are reading voltage from the fuel pump as it spins down and cuts car due to no pressure. i'd check for a bad wire, ground, dirty anything, etc.
 

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2003 STS w/BoseNav, 1993 Deville, 1985 Deville
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You might also have a bad sender unit. Get one from the junk yard for cheap. While you have the tank off the car, test your current unit to see if it's bad or not. I had a similar problem, but it would read almost empty even when there was plenty of gas.
 

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Thanks for your suggestions fellows. But, I don't think that the problem is a bad ground. If I didn't have a good ground the pump wouldn't work and the sending unit wouldn't report correctly from F down to 9 gallons left in the tank. Also, my car actually runs out of gas and stalls when there is still 9 gallons in the tank. When I add gas it starts right up and runs well untill I use about 7 gallons. I'm thinking that I must have screwed up something when I put the pump and sending unit back into the tank. I think that I'll get a sending unit and pump from a junk yard. When I drop my tank, I can compare what's in my tank to the unit from the junk yard. I was hoping that I wouldn't have to drop the tank again. But I guess I will. Thanks again.
 

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1926 Model T street rod, 2000 Jaguar XJ8, 1999 Corvette.
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This style of sender mounted fuel pump has a short piece of fuel hose joining the sender to the pump, usually this hose is cracked, has a pin hole etc. when the fuel gets below this hose the lines suck air instead of fuel, car quits! Replace this hose and new clamps. Might not be related at all to reassembly , just age! Good luck!
 

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Discussion Starter #6
Thanks for the advice, Carnut. I plan on dropping the tank in the spring. I'll be sure to replace the hose and clamps when I have it apart. :worship:
 

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carnut said:
This style of sender mounted fuel pump has a short piece of fuel hose joining the sender to the pump, usually this hose is cracked, has a pin hole etc. when the fuel gets below this hose the lines suck air instead of fuel, car quits! Replace this hose and new clamps. Might not be related at all to reassembly , just age! Good luck!
HOLY CRAP!

I think you just solved MY problem! My '85 gets down to 7 gals and starts quitting and then hard-cranking. I knew there was a fuel problem, just didn't know where to look.

Thanks Soooooo Much.

Brix:worship:
 

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1996 Deville Concours
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I have had a problem that's been annoying the **** out of me for 2 years, which may be related to this... Mine's a 90 Fleetwood, mind you. I recall my 85 having a bit of a dodgy fuel data system, but this takes the cake. The fuel used is always about 1.5 gallons less than I've actually used (per tank or little less). Except my fuel tank and sender unit have been replaced with new, and didn't change a thing. Fuel filter, plugs, wires, distributor, rotor, ignition coil have all been replaced. I just yesterday did the FPR. I've heard FPR and/or injectors causing this gauge discrepancy (and the injectors are practically the only thing in the entire bloody fuel system I have not yet replaced), but I did a fuel pressure test (before and after the pressure regulator), and it's just behaving too normally in that area to lose 1.5 gallons as far as I can tell. The pressure will all bleed off after I turn the car off, but it takes a couple hours.

Aside from the discrepancy, it behaves similarly to what was described here...once it gets down to somewhere in that 9-gallon range, the speed at which I lose gallons is noticably increased.... I supposedly have an 18-gallon tank, and it does indeed take about 3 gallons worth of driving before "F" goes to "15." However, I let it go practically out...E flashing and about 10 minutes later it was low enough to stall at a light. I filled it up and it took 15.9 gallons... So basically it seems the last 2 gallons are useless...and the sender unit is barely a year old. That, or I somehow have a 16-gallon tank...and yet F to 15 still...well you get my frustration lol. The mileage isn't quite what it should be on this car according to ratings. I seem to get 22 or so on the highway and I'm supposed to get 25, and I've heard others with this engine boast of more. If anyone has a clue...I'll be grateful. If anyone knows how to fix it, I'll mail a steak or something...
 

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88 Sedan Deville, 89 Eldorado, 11 SRX, 18 CT6
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tthere is a screen type tube that is supposed to attach to the bottom of the sender unit, and it SHOULD be touching the bottom most portion of the pan. the screen keeps air from getting into the tube, and keeps it wet so it's always sucking in gas. it also keeps sludge out of the hoses. if that last piece isnt at the very bottom of the tank, then how would it get the last two or so gallons out of the bottom mold of the pan? other then that, that's the last item that i can think of. i replaced that screen, i believe it came with a new fuel pump if im not mistaken. though the sender units on those arent the best... ive got two of em, and both are flakey lol. hope that helps
 

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1996 Deville Concours
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Well it may or may not help lol...but I appreciate it all the same. The thing is...like I said, my tank AND sender unit were replaced not all that long ago... The place I took it to seemed reasonable about not trying to suck it up or invent work... Could this screen have been omitted somehow? Blah... I've never taken a gas tank off...and it doesn't sound fun...but if that's what it takes...then I'll look into it...later :rolleyes:

In any case, the discrepancy with the fuel used gauge occurs WELL before the tank gets low as well. I had "used" 6.4 gallons, and it took 7.2. I got some Bosch injectors at the junkyard today, and I'll install them...that's the last thing I can think of.
 
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