All my cars have carbs, actually. Hm ... kid's taking a nap break right now, this would be a good time to test 87cv's claim.
![]() |
Announcement
Collapse
No announcement yet.
Gas Gauge
Collapse
X
-
Back from the garage. Big surprise, the potentiometer behaves like a potentiometer. Fuel gauge reads the same given the same armature position when wires are reversed, provided that the body of the sender is not grounded. When the body of the sender is grounded, the gauge reads correctly when connected correctly, and reads Full regardless of armature position if connected backwards.
Fact: Sender plug consists of two wires, one signal wire and one ground.
Fact: Fuel gauge reads over Full if signal wire is connected directly to ground.
Observation: on at least some older Ford fuel level senders, only the signal wire was used. This is because that in most installations, the steel tank is effectively grounded to the steel chassis (such as in first-gen Mustangs where the tank bolts directly to the trunk floor), and the steel sender body is in turn grounded to the tank. Hence, no theoretical need for a redundant ground wire going directly to the sender.
Postulate: The ground wire was added to the normal sender circuitry to make the fuel gauge more reliable, in the event that a tank attached by straps (such as ours) happened to be inadequately grounded or there happened to be an inadequate electrical contact between the sender body and the tank. It's simpler to connect a ground wire directly to what needs to be grounded, rather than worry about whether the sender is adequately grounded via its retaining ring.
Prediction: If your sending unit happens to be adequately grounded to the vehicle chassis, reversing the wires to your fuel level sender will cause your fuel gauge to read Full regardless of how much fuel is in the tank. If your sending unit happens to be not grounded at all, your fuel gauge will read Empty. In some cases, the resistance between the sender body and chassis ground could conceivably be between 73 and 10 Ohms, and in such cases the gauge will read somewhere between Full and Empty. There is NO correlation between gauge reading with the plug reversed and the position of the armature, and this procedure does not test the function of the sending unit.Last edited by 1987cp; 04-15-2009, 12:02 PM.2012 Mazda5 Touring | Finally working on the LTD again!
Comment
-
nice write up! Allright well thats what i needed to know, at the very least i can test to make sure my fuel gauge will go all the way to full. and from there I can begin taking the sending unit out. Thanks to both of you!-Phil
sigpic
+1982 Ford LTD-S Police Car. Built 351w, Trickflow 11R 190 Heads, Holley Sniper EFI, RPM Intake+ Hyperspark dizzy, WR-AOD, Full exhaust headers to tails. 3.27 Trac-Lok Rear. Aluminum Police Driveshaft. Speedway Springs+Bilstein Shocks, Intermediate Brakes, HPP Steering Box.
+2003 Acura CL Type S 6-speed
Comment
-
very nice 1987cp~David~
My 1987 Crown Victoria Coupe: The Brown Blob
My 2004 Mercedes Benz E320:The Benz
Originally posted by ootdega
My life is a long series of "nevermind" and "I guess not."
Originally posted by DerekTheGreat
But, that's just coming from me, this site's biggest pessimist. Best of luck
Originally posted by gadget73
my car starts and it has AC. Yours doesn't start and it has no AC. Seems obvious to me.
Comment
-
Originally posted by 1987cp View PostBack from the garage. ....86 Lincoln Town Car (Galactica).
5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley
91 Lincoln Mark VII LSC grandpa spec white and cranberry
1984 Lincoln Continental TurboDiesel - rolls coal
Originally posted by phayzer5
I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers
Everything looks like voodoo if you don't understand how it works
Comment
-
Originally posted by 87_crown_vic View Postif anything, it would let him know if there was a bad wire or gauge was bad... when reversing it it will at least show that things still work and narrows it to the sending unitGive a man a fish and he will be fed for a day. Teach a man to fish and he will promptly forget that he once did not know, and proceed to call anyone who asks, a n00b and flame them on the boards for being stupid.
Comment
-
Well I was driving around yesterday and I looked down and my fuel gauge is working all of a sudden....so im now guessing its wiring, I allready bought the float and stuff, i wonder if i can return it. I'll have to check it out, haha. Opps-Phil
sigpic
+1982 Ford LTD-S Police Car. Built 351w, Trickflow 11R 190 Heads, Holley Sniper EFI, RPM Intake+ Hyperspark dizzy, WR-AOD, Full exhaust headers to tails. 3.27 Trac-Lok Rear. Aluminum Police Driveshaft. Speedway Springs+Bilstein Shocks, Intermediate Brakes, HPP Steering Box.
+2003 Acura CL Type S 6-speed
Comment
-
keep it..you may never know when it will actually shit the bed....but it is sure nice to have money in the pocket.~David~
My 1987 Crown Victoria Coupe: The Brown Blob
My 2004 Mercedes Benz E320:The Benz
Originally posted by ootdega
My life is a long series of "nevermind" and "I guess not."
Originally posted by DerekTheGreat
But, that's just coming from me, this site's biggest pessimist. Best of luck
Originally posted by gadget73
my car starts and it has AC. Yours doesn't start and it has no AC. Seems obvious to me.
Comment
-
Like I mentioned there should be some orange box under the glove box that should work with the gauge, or maybe it's just the light. If it's only for the light, which you don't have a fuel light, that box won't be there. Could someone verify this for me??
Comment
-
The box is for the light. It should actually say Low Fuel Module or something to that effect. Mine is actually black, and lives next to the gas pedal though.86 Lincoln Town Car (Galactica).
5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley
91 Lincoln Mark VII LSC grandpa spec white and cranberry
1984 Lincoln Continental TurboDiesel - rolls coal
Originally posted by phayzer5
I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers
Everything looks like voodoo if you don't understand how it works
Comment
-
Must be different on a Grand Marquis too because I looked behind the dash and couldn't find it. Does anyone know where it is on an '88 GM?Nick
88 Colony Park LS
G-pa's old car, but he's cruisin around heaven in his 69 wagon now
Future plans:Semi HO conversion, or Explorer motor swap, shift kit, PI springs and sway bars, KYB-GR2 shocks
Comment
Comment