hi from belgium everyone
c4 -87 , drinking around 32liters/100kms
and today i compare with another one, and sadly , mine is a turtle.
i know it can be a lot of things, but can you show me the way?
fuel pump-filter-relay-air filter-sparkles are new
thanksssssssssss

 

….. Keep it simple … Is the Check Engine Light on ? Any Fault Codes ? ... If so , deal with them first … check the timing , there is a single wire connector near the windshield wiper motor that needs to be opened to prevent the Electronic Spark Control from automatically adjusting the timing … don't forget to re-connect it when you have the distributor locked down @ 6 degrees on the damper … check/set the minimum idle speed , there is a complex procedure that needs to be followed to do this … consult the Factory Service Manual or the internet … then set the Throttle Position Sensor … You might want to install a new Oxygen Sensor and Coolant Temp sensor … have the Catalytic Converter checked/tested … in rare instances , they can become a major restriction to exhaust flow and will kill power … same for the rest of the exhaust system ….. Good Luck ! …..

 

What C409 suggested makes good sense. He covered a lot of the bases very well.

Your O2 sensor is one that frequently gets ignored and as they age their signal gets weaker and slower which both affect the performance of you C4. Do you get your emissions tested in your Country? I replaced the exhaust on my 1988 C4 Coupe with a Catalytic-back system and while doing it I changed to a High Flow Catalytic Converter. The difference was close to 14 horsepower gain and the mileage will get up into the low 30 MPG range. Now my car is similar to yours but I have the automatic transmission with a 3.07 "Performance" Gear. The regular one is like 2.59 or something for the automatic.

How does your car "sound" drinking that much fuel? I don't know if my math is right but that means you are getting roughly 7.35 miles per gallon. Can that be right? I have never heard of any Corvette getting that bad a mileage. My 1968 C3 Corvette with the 427 engine gets double that mileage.

Your car has the Cold Start Injector to assist starting your car in the colder weather. Check to see if it is running all the time. I think there is a plug on it to disable the power going to it. If your CSI was running constantly then your Catalytic Converter will likely have to be replaced as the rich mixture plugs up the catalytic converter.

Is the car transitioning from "Closed Loop" to "Open Loop" when it starts? If your car was stuck in open loop it might be able to use that fuel but would run terribly. Check to see if there are any codes being displayed. If Not, verify that the bulb works and test again. What do your tail pipe exits look like? Are they black and sooty by chance? To get this kind of mileage the car might not be switching into "Closed Loop". In Closed loop the engine looks for the amount of air being ingested (The MAF), the coolant temperature and the Oxygen sensor to decide on how rich it should make the fuel mixture. If the O2 is not working that would force the car to use more fuel. If the O2 is slow that could do the same. I would get a new oxygen sensor and get it installed. Does the car drive okay or is it bucking and acting unusual?

There is a device that measures the coolant temperature mounted in the front of the intake manifold and the output of that sensor tells the computer what temperature the coolant is. If your is off and reading incorrectly it can activate additional fuel and make your mileage go down. If it thinks the engine is hot when you start it the engine might be harder to start as a result. The device is called the Coolant Temperature Sensor and the output can be compared to a chart in the FSM that shows the corresponding temperatures. They do go bad and can make the fuel consumption rise and can make the engine very hard to start.

Do you have a set of the Factory Service Manuals for the 1987 C4 Corvette? How about a scanner or code reader that works on the older OBD1 systems?

Something has to be REALLY WRONG to allow that engine to get 7 mpg. My 1988 gets three to four times that mileage regularly.

Tell us more about your Corvette.
Any detail may be important.
Is the quality of the gasoline you are using good?
Has anything been modified on this Corvette?
Do you remember the fuel pressure from when the parts were replaced?

We should be able to help you get this sorted out, it just takes time and answers.

Best regards,
Chris

 

If you can get a fuel pressure gauge connect it to the Schrader valve on the right side of the fuel rail.
Turn the switch to On and see if pressure goes up and drops off quickly, indicating a fuel leak.
Then remove the vacuum hose from the fuel pressure regulator and sniff for the smell of fuel...there should be none.

If pressure is ok, connect a vacuum gauge into a vacuum line off the rear of the plenum and start the engine. Pressure should be in the "green" at idle.

 

Hi retarded ignition will make it use more fuel, you should get 550km a tank highway anf 350 around town depending on your right foot.
That is what my supercharged 383 gets with 3.07 rear gears, standard was 600km.
Trip computer may show 7L/100km to 9L/ 100 but actual use should be 12 to 14 L per 100 km on highway.
6 deg before top dead center is where it should be, TPS throttle position sensor 0.54volts dc.
Are all your cylinders firing? Whrn cold run engine a few secs and feel each plug is warm.
Good luck should be a simple issue

 

How is the Thirsty Corvette in Belgium Doing?

A good way to see if each cylinder is firing is using a non-contact thermometer and check at each outlet on the exhaust manifold. While at it check your pre-cats and the main cat for temperatures and look for consistency.

Some of us are curious how this story turns out. Like I said before, I have never had mileage like yours. I Just want to know how the L98 was able to use that much fuel.

You got our attention with those numbers....

 

I would clean the MAF sensor.