Hello i just acquired a 1981 corvette and i decided to test the mpg. After the test i concluded that i only get 5.8 mpg. Car is stock besides new edelbrock filter and msd system. since i got it last week the right headlight was always slow to go up and just today it stopped going up, could it be a vaccum leak? maybe some hoses in the engine? the car has a check engine light since i bought it. To me the car runs great i can get it up to 65 mph at around 2,400 rpms. I also had my uncle test it because he also owns a 81 vette and he said it drives well. Any suggestions appreciated.
edit; i should add that i have adjusted the idle screw a couple of times and the idle seems to change by itself

 

If it's running well but only gets 5.8 mpg then you have a fuel leak! No way would it run nicely using that much fuel. Check the fuel lines, specifically at the pump, which might not leak until the engine is running.

 

Although these cars are not noted for there wonderful fuel economy. That really is bad.
81's came with computer controlled carburetors and ign. systems.
Stock computer controlled carb not being controlled by a computer, aftermarket ignition system unable to work with factory computer.
Sounds like you need to look further into what is factory and what isn't.
Then get rid of factory stuff and install 1980 and earlier parts. Then tune. Then let us all know how happy you are now.

 

You have a check engine light and don't know what it means?
Could that maybe indicate what the problem is?

 

While I haven't bothered to check the mileage on my 81 in many years, I'd say it averaged 13-14 in local driving and 16-18 highway driving. The EPA rating for 81's was 15 MPG combined mileage. If you used an Edelbrock filter, I assume you have an Edelbrock carb too, and not an original Q-Jet? If so, that could be part of your problem.

A slow or non opening headlight is likely a vacuum issue, either a hose issue, a bad headlight door vacuum actuator or a bad relay valve.

If you pull the ashtray out of your console you'll find a 5 post terminal underneath the ashtray. If you place a jumper wire across the "D" and "E" terminals your Check Engine Light will flash the fault code(s). If your carb was changed to an Edelbrock, and the computer not removed/bypassed, this is likely why you have a lit Check Engine Light.

Welcome to the Forum!

 

Welcome, if you plan to do the maintenance on you vet, invest in these two items, Assembly Instruction Manual (AIM) for your specific year. The GM service manual for your specific year. NOT the Haynes or Chilton. They are too generic. Also reach our to papawana, he will give you the electrical drawings for you year. I've attached the vacuum troubleshooting guide I used. Worked great.

 

This is confusing.

 

uh, sounds like no orig carb or dist?
so, no torque verter lockup?
going to need more info, pics

 

I'm not familiar with 81. But definitely check the fuel lines on the passenger side by the fuel pump. Should be a straight hose and an "S" shaped hose at the fuel pump. Don't forget to check metal fuel line from fuel pump to carb. Carb gaskets can seep fuel, easier to see on a cold start. A hot engine will cause the gas to evaporate and make it hard to see. And their are rubber hoses at the fuel tank.

My 77 smelled bad with a full tank of gas. The fuel pump was leaking. The leak slowed with low fuel in the tank.

If you don't know the history of your car, I'd start replacing all rubber lines in the fuel, brake, steering, cooling and transmission.

Remember it's not "miles per gallon"... its "smiles per gallon".

 

Post a picture with that "Edelbrock filter" removed.

If you have a new dist, and the stock carb, your car might be in some limp mode where it's dumping extra fuel.

There are lots of threads on the peculiarities of the 81-only system, but first some photos please!

 

Hmmm that's about what I usually get in mpg's on my 78 SA

JJ78

 

The computer is giving me code 51 which is bad calmem. I already unplugged and plugged everything and even eprom. Is this the cause of my bad mpg?

 

carb would be full rich
timing adv would be minimal.
that means no economy

 

You have another thread going of "what mods to make first", where you say you have an MSD.

Post some photos! I bet ditching the computer controlled carb is the correct next step.

There are a few people who keep the stock 81 system going. But why would you?

 

I would like to ditch the computer controlled carb but doesn’t the computer control the torque converter lockup? Or do I just replace the carb and just leave the computer plugged in to still control the lock up? Also what carb do you recommend? Something with a little more power
edit: also does code 51 affect mpg?

 

 

Thanks I didn’t see your prior reply

 

Uhhhhhhh that's what I get with this:

Something is very wrong, my guess bubbazised & not stock. You should get about 3x's that hwy !

 

What I got going on under the hood. I already have that msd thing so I can just get a another carb and everything should work fine right?

This thing also appears to have gas on it. Does it need a new gasket?

 

The '81 had a one-year-only ECM/electronic carb/distributor system that would only work properly if all items were in good shape and used as a system. If you 'modified' engine system no longer uses the ECM, it also MUST use a 'standard' distributor and carburetor...it cannot use those items which came from the factory.
If the ECM (and other components) are still operational, you need to diagnose the problems with the engine controls system via info contained in the 1981 Chevrolet Chassis Service Manual. To my knowledge, there are no qualified mechanic shops (or dealerships) who have adequate capabilities for working on an '81 C3 engine control system. In this case, yes, your OBD-I trouble codes will help to guide you toward the cause of your problems.

What has the previous owner told you about this issue? Surely, he/she had similar problems...maybe why the car was sold. But, if the PO knows that the fuel mileage was not a big issue in the recent past, the problem could be solved with a rebuild of the metering solenoid in the carb and/or a new O2 sensor. This control system is not "complex". It just needs to be diagnosed to identify the problem area[s] needing resolution. If the engine seems to run OK, odds are that the issue is somewhere in the engine controls system.