Fuel gauge accuracy ??

[j7l2]

How accurate is the fuel gauge in your trucks? In my 1995 Chev Ext cab p/u, I can run 200 miles before the gauge needle gets down to the full mark. Then I go another 200 miles until I fill up at the 1/4 mark. Is there an adustment that can be made in the the float apparatus that is in the fuel tank? Or are these units just that inaccurate? Any one who has experience or suggestions about this is welcome to comment.
Thank you,
JimO

[Barry Nave]

Same here, If I take the time to keep filling while foaming goes down I can get 5 more gal.

[a5150nut]

Bout the same on my 94. First half lasts for ever and the second half goes fast. I just figure fuel at 400 miles when empty.

[j7l2]

So does the lack of response mean only 3 of us have inaccurate fuel gauges? Or doesn't anyone know if there is an adjustment? Has anyone had the float unit out of the tank? Can the float become fuel soaked? Is there a float arm that can be adjusted {bent} to calibrate it better? Anyone?
Thank you,
JimO

[95-6.5]

mines the same way.lst half lasts forever,2nd half goes bye bye fast.
I think they may have used the same guage and calibration for all the trucks.1/2 ton with 20gal tank has the same as 3/4 with 38gal tank ect..I can tell you this...when the needles gets in the red you better be at a fuel stop.I was driving when it moved in the red.went about 10mls and stopped running...Put in more fuel,opened the fuel filtervalve to let the air out cranked it over for about 5 seconds and she was running again...I thin the gauges are accurate there just claibrated the same for all trucks.If i fill it up then after it shuts off,i wait about 5 min then if i fill real slow i can get it all the way to the top of the neck.takes about 30min total to do this though,The guage doesnt move for like three days.I only do that when im going on long trips though..

[whatnot]

I think is because the tanks are so long. The float is stuck to the top till it gets down a ways.

They should have marked the 3/4 marked 1/2 instead.

[Barry Nave]

My wife's GM safare van does this also. 91 year

[freddys]

My truck is the same

freddy

[sturgeon-phish]

Same as the rest. Goes way past "full" when full.

[G B Sisson]

Me too. Coming home from Canada yesterday a sign said check fuel ,next service 140 km.I figure Im on 1/2 no problem....well it was deep in the red when we got there.Course I was driving about 75 so mileage (kilometerage?) wasnt the best...Anyhow the 2nd 'half' is much smaller on my 94 burb 3/4 ton with 46 gal. tank. G.B. ps what a pleasure to drive on a long trip with this rig!

[gwaidman]

Yup, same thing here gents. First half makes me think I get 30mpg, .... and 3 on the other half.
My F**D truck was similair.
tongue.gif

[Beedee]

My truck is the same, My F**d that I got rid of to buy the chev was the same and my 92 Geo Metro is the same. Must be a plot by the auto makers ;) , when you take a new vehicle out for a test drive, the fuel gauge never moves, you only find out the truth after you buy it :D :D

[Marty Lau]

same here :confused:

[j7l2]

So, it seems as a lot of us do have inaccurate fuel gauges. Now, does any of TDP members know of a fix for this problem? My GM shop manual says for inaccurate fuel gauges to replace the sending/float unit that is in the fuel tank. But my feeling is that the new one may be the same as the old one. Has anyone replaced their sending/float unit in the tank and if so did it correct the problem?
Thank you,
JimO

[pannhead]

yes...if i remember it was like $300....within 8 months i was back in this boat,and still am :mad: ...i just fill-up when i hit 500 miles....i wish i would have kept the old float to see actually went wrong...shoulda,coulda,woulda..oh well :confused:

[Beedee]

I use both the fuel gauge and the trip meter. Reset the meter everytime I fill up and keep an eye on both

[busman]

j7l2, in a fleet of 90 99 & newer express & savana mini buses, about 8 have had sending unit problems. One other had a bad "fuel buffer module". Flow chart for proper diagnosis for either is found in the GM repair manual. As for what the sending unit looks like, it's the same as a gas motor unit minus the pump. I am curious about the "soaking" issue described earlier in the thread. I would believe that diesel fuel would react differently than gas to the float.

[KingNuzz]

The fuel guage on my '93 barely moves for the first 150 miles, as well. Think it's a couple of design features that do this.

We've had the fuel system apart on my 6.5 extended cab with the 31 gallon tank. The sender/float units for both the gas and diesel are similar, maybe even for smaller tanks. They have a one-size-fits all unit. The gas unit has a pump on a bracket in the tank, while diesels use the lift pump outside on the frame.

The tank is long, almost 5 feet. The longest part of the tank averages about 6" high, mostly due to the low front end that extends under the cab. This bottom part of the tank looks like it holds about 1/3 of the fuel. The rearmost 3/4 of the tank is around 12" high, including the middle, at the sender/float unit, which rises to just over 14" high.

When the is tank full, the float swings up in an arc, and looks like it would take a while to rotate much when the tank is between full and 2/3 full. That might explain the slow action of the gas guage starting out with a full tank.

John

[j7l2]

busman,
I will have to see what the fuel buffer module is. No one has mentioned that before. Do you know where it is located at? As you said I don't know if soaking is a problem with diesel fuel like it is with gas. I know that there must be a way to correct this problem, because I know owners of these trucks that have very acceptable accuracy of their fuel gauges, and they have never required any servise or adjustment. I wander if something isn't quite right in the sending unit itself even when new. It seems if they start out okay they stay okay. The dealer usually says all fuel gauges are like that and doesn't want to get involved. Thanks for everyones input and maybe one of TDP electrical problem solvers can comment.
Regards,
JimO

[Turbine Doc]

Chalk up another 200 mi 1st qtr tank, and 200 on the last 3/4, when I'm full fuel/foam spitting back at pump nozzle, I'm what appears to be 1/4 tank over full mark.

[j7l2]

No suggestions for how to correct this? I am not into electronics at all, but, I was wondering why some type of adjustable "pot" couldn't be put in the wire that feeds the fuel gauge. This way you could adjust the electrical signal or current going from the sending unit to the fuel gauge. This would allow for calibrating. Is this possible or am I over looking a basic electrical principle? Hopefully one of TDP members that understands electrical gauges could explain.
Thank you,
JimO

[Polar Diesel]

if you look closly at the gauges on 93, 94 style, the increments are different before and after half mark. so the guage is correct.

[bnmccoy]

My gauge has worked as most have described since day one. I have been filling to the brim every fillup as well. I typically pump about 3.5 gallons extra after the pump initially shuts off.

My tank is a 26 gallon tank.

Like someone else said, I typically know that around 400 miles I need to fill up. I do happen to know that the gauge is accurate when it indicates empty!

Bob

[Randee of the Redwoods]

I'm gonna take a stab at this and see if I've figured out what you're complaining about.
Gas gauges are calibrated in a specific way. They are set by auto manufacturers to read about 2/3 tank capacity to the right of 1/2 tank, and about 1/3 capacity to the left of 1/2 tank. This is for your convenience and protection. If the gauge was truly linear, you'd be constantly looking at to check your fuel level. That's not safe. Safest place to look while driving is at the road. So, fuel gauges were calibrated to put most of the fuel, about 2/3 of it, between 1/2 and full. As your drive, you glace at the guage to check level and see it had moved very little. Eventually your perception is altered(unknowingly to you). If you see the needle leaning towards the right, your brain will determine that less glancing is needed since the fuel level is falling so slow thus more time to keep eyes on the road. The gauge drops quickly after 1/2 tank because you actually have about 1/3 left. Well, after driving as much as you have, your brain has been trained not to worry about fuel level until below 1/2 tank. It's all a mental perception thing that's been programmed into you over the years. I found about this when I had my 86 Taurus. It's not inaccurate. You just noticed something not everyone else does. Car designing is as much mental as it is physical.

[gmctd]

GovernMental brain washing, huh?

Man, I saw that stuff on the X-files, and it's scary!

Hope the rest of them gages ain't messing with me!

Keepin' an eye on that temperature gage is about all I can stand!

;)

Good stuff, Randee - I remember seeing something about that, a long while back.

[catmandoo]

my 92 hits the full mark at about 150 miles,3/4 at about 275 miles,half at about400 miles and 1/4 at about 500 miles,this is with a brimful tank,that last 3.5 gallons takes as long to get in as the first 20.randee you bring up a good point there,but in my youth when i was low on money(girls and beer) took most of it and was constantly on empty i could drive my 66 chevelle home at night and shut it off and it would not start in the morning cuz it was out of gas,god my old man used to give me s#*t about that,said it's just as easy to keep it above 1/2 as it is to keep it on empty.but did i listen hell no thats another 10 bucks i could spend on beer.

[moondoggie]

Good Day!

My 95 pickup has the 35 gallon tank. When I fill up, I fill it all the way up, & I can get almost exactly 5 gallons in after the pump shuts itself off. That

[gmctd]

It's really quite simple to make the fuel gages indicate the way they do - non-linear resistive wire.

The few that drop to 1/4, then hang forever would indicate the resistive element was mechanically reversed during stamping\swaging operations, which would then be electrically reversed upon installation.

Other than that, the gage element itself is more accurate than you might suspect, and is used in the tachometer and speedometer, as well.

VSSB tweaking results in whatever speed DOT radar speedo-check station indicates, the Delco gage nails it every time, and exactly matches Tech-II Vehicle MPH indication.

My tach, off the PCM Crank Position Sensor input, consistently reads 200 rpm higher than the Tech-II Engine RPM indication.

That's fairly accurate.

Later - reason the tach is off? When installing replacement pointer, ign should be on, engine stopped, set new pointer to zero.
I attempted to 'zero' pointer with ign off - which seldom works.

[ 04-21-2004, 02:59 PM: Message edited by: gmctd ]

[moondoggie]

Good Day!

Actually, I have found that my fuel gauge is quite linear: as noted above, I get the same # of miles on three of the four 1/4 tanks (I don

[skip460]

My '95 has always been inacurate since new,going way over full then staying there for 150 or so then lazely fluctuating an 1/8 gal or so depending on direction an velocity. But E means E, just ask my wife. I never trust the acuracy of the guage to the gallon but I do trust them to show the general amount left. I always watch mileage and amounts at fill up.I figure as long as it works I am happy.