Hey! Okay. So I finally fixed my 85’ corvette. Many wires were corroded.
that problem is fixed.

heres what I need help with. The car is getting - on average - 12-13 mpg. It should be around 17 mpg.

i believe this is because the vacuum hoses are broken? How can i fix this? Would it also help if I replaced the air filter?

and the car also seems to not accelerate as fast as it should, too. Could this also cause this?


I really love the cars, and im thinking about selling this one. I want to try to get a 1990+ (because of the airbags )

also so do you think I would be able to get around $5000 for it?
it has 112,000 miles on it. Besides that the car does run pretty well. The paint is really good, just a few scrapes here and there. The interior isn’t too bad, just the carpet a little messed upz

 

https://www.autozone.com/fittings-an...ent/426017_0_0

I forget the size but one of these is the perfect fit, takes 20 seconds assuming you have easy access to the hose. I just had to repair one I broke when replacing the thermostat.

 

City stop start driving will give you bad gas mileage C4's hate slow stop start traffic, highway is really good 18 - 22mpg
330 to 380 miles a tank on highway and around 200miles city driving.

First check your throttle position sensor, the top and middle wire set it to 0.54VDC factory however 0.6 volts DC works great.

Check your air filter is clean and make sure there are no gas leaks, the biggest killer to fuel economy is timing.
It can easily drop a 100 mile range if running a lot retarded, so set it to 6 degrees advanced.
DO not rely on harmonic balancer first check No1 piston is at top dead center when the harmonic balancer is at tdc.
The outer ring can slip.

I would recommend resetting the ECM, it can get in knots compensating a perceived issue.
Whenever something doesn't seem to run right i reset the ecm, pull the ecm wire near battery or just disconnect battery for 10 secs and reconnect.
Solves most poor running issues, it will take a few miles to relearn the engine management and gets better.

 

Also check each exhaust manifold with the squirt test. yhe water won;t evaporate on a dead cylinder. Those symptoms are exactly as mine when my #7 injector came unplugged.
I even put a tie wrap on my vacuum hose ends and it seems to work great.
Good Luck

 

Give it a tune up. Plugs, wires, cap, rotor. Ignition module replacement wouldn't be a bad idea but not necessary unless you think its never been done.

If the mileage then continues to be bad, its probably the Oxygen sensor. O2 sensors rarely give SES light until they are completely dead.

 

Generally, a doggy c4 is due to TPS or timing.....although lots of other reasons.....like Vader says, Tune it......vac leaks are easy to find....spray TB cleaner up / down the lines.....rpm will pick up at the leak...(no smoking!!!).....

 

As O2 sensors age they get lazy and respond more slowly. You can check your O2 Sensors out put if you desire to, but if it is older than 12 months then I would replace it right away. A slow responding 02 sensor will really mess up the cars performance.

The other thing to check is your fuel pressure regulator, disconnect the vacuum line and smell inside the hose, if there is a presence of the smell of gasoline then you should change the FPR as well.

The EGR valve has a vacuum solenoid that activates the EGR valve, it is very common to find a vacuum leak in this area. On my 1988 C4 it was a bad solenoid and broken vacuum lines that made the engine run poorly. The solenoid on my car was bad as well. I replaced the parts and have a car that passes the emissions testing here in Virginia.

If your gasoline is over 30 days old top it off with fresh gasoline. If you car sat for any long period of time you might want to verify that you don't have a blockage in your catalytic converter. A Blocked catalytic can be determined by removing the 02 sensor, if the exhaust pressure blows out the O2 sensor hole then it would indicate a blocked catalytic converter. A little leakage is okay but too much indicates a blockage downstream in the exhaust system.

I have an old 1988 C4 with the basic options and the 3.07 rear end ratio and the automatic transmission I have been able to break into the above 30 mpg with my 103,000 mile C4. In the city you loose but on the highway my cars gets great mileage. I do however have very good compression numbers so I believe that my motor is healthy and happy.

Last but not least, if available try a can of BG 44K Fuel injection cleaner, it does wonders for a dirty fuel system.

Regarding selling the car for $5k that might be a challenge, there are plenty of C4's out there and the prices depend on where you live and how many potential Corvette owners there are around where you live. I have seen several 1990's C4's with LT1's going for less than $5k in the Craig's list

Good Luck!

 

I wonder if you could help me. I need to see a picture of the oil temperature sender and the wiring to it. I cannot find the wire that goes to the oil temperature sender and the coolant temperature on the drivers side of the motor. Even the color of the wires would be a big help. I don't know what these guys did to these wires. thank you