golfboy

So, for awhile now I have suspected that my gas gauge was not reading properly and I decided to see what is wrong. I have a 1978 Pace Car with a modified engine, transmission and exhaust system that runs great but it seems that I have to put gas in it too frequently. According to the manual, the tank holds about 23.7 gallons of fuel when full. The last time I filled the tank all the way up, I set the trip odometer to zero. I then drove until I had the gas gauge all the way to the bottom of the red zone by the E mark which should be empty. When I refilled the gas tank, I could only get 17 gallons in the tank and it was full. There is a difference of 6 and a half gallons of gas that I can't account for. Why would my gauge be that far off the mark? On a side note, I also checked my gas mileage during this experiment and was shocked to learn that I am only getting 9 miles to a gallon! It seems that I am driving a Hummer in regards to the gas mileage that I'm getting. Don't get me wrong, I really enjoy having over 300 horsepower to play around with but I had no idea that my gas mileage was that low. Does this seem about right for those of you who have modified engines in your Corvette?

hgoodwiniii

I have a similar problem with my 76. You can check this thread;

https://www.corvetteforum.com/forums...ding-unit.html

I have not gotten around to do all the checks recommended yet. Pretty close to next on the list.

golfboy

Thank you for your response to my thread, hgoodwiniii. I read your original thread on the same problem with your 76 Corvette. At this time, I'm not interested in removing my gas tank to find the root of the problem. I will just keep in mind that when my gas gauge goes to the bottom of the red zone and near E on the gauge, I still have over six gallons of gas in the tank, effectively giving me a 6+ gallon reserve. So, I should never run out of gas accidentally. LOL.

hgoodwiniii

You are welcomed; That's pretty much how I've been playing it as just a reserve; I just hate to have to keep stopping to fill up every so few miles; I am definitely going to run a boroscope down in there very soon.

NeverTooOld

When my gas gauge reads EMPTY I still have 7 gallons left which doesn't bother me in the least bit. I'd rather have extra than not enough.

0Willcox Corvette

GM listed the tank, 457999 as a 25 gallon tank. While I've never thought the tank would actually hold that much fuel, that's what's listed in the parts book.

78·82 Y ......457999 1 236.00 TANK (25 GAL) (NOTE 2) Note 2 only says the tank has a bladder made into it.

The issue may be a faulty sending unit and quite possibly is the issue. If the float has fuel inside of it it may be sinking too early. On your car you don't have to remove the tank to figure this issue out, you simply remove the fuel door and bezel and remove the sender (looks impossible but it's very possible).

Once out of the car you can check either the arm is bent and not getting full travel, and/or the output ohms of the actual sender.

Willcox.

golfboy

NeverTooOld, my thoughts exactly! Thanks for the input.