I have a 91 C4 coupe 6speed and It runs rough. What the car does is when I start it cold or warmed up the rpms sit at 300-500 and the car shakes and there is a clicking sound coming from under the hood the clicking sound eventually goes away after I drive it for about 2-3 miles and it only clicks at idle. The car gets crappy gas mileage and it has a huge amount of lack of power as you give it gas and once in a while the oil pressure gauge will start flickering ONLY AT IDLE the needle will be in the middle and then all of a sudden it will go passed the 80 mark on the gauge I also have taken it to 3 different corvette mechanics and they don't have a clue why it's running like that I have had it plugged into computers and they say everything is working the way it should but the car obviously isn't fine so I honestly don't know what to do from here so I WOULD LOVE TO HAVE HELP! And here's a list of what I have done to the car so far to try to make it run better...I replaced the egr valve, throttle position sensor, spark plugs and wires, distributor cap and coil, air filter, fuel pump, and the fuel filter. According to the mechanics I have taken it to they claimed that it has no vacuum leaks, they said the compression is good, the timing is good, the fuel injectors been flowed, all sensors have been checked and the exhaust has been checked for any blockage and everything seems to check out fine and the car is chipped and the mechanics said that's fine too so I honestly do not know what to do and like I said before I NEED HELP!!!! I'm 19 years old and I have a job that pays minimum and I'm tired of basically working for free cause all my money went into my car

 

..... Without watching a scanner its a guessing game ... but , based on the symptoms ... low idle ... crappy fuel mileage ... flat performance ... my best guess would be that your issue is timing related ... any codes at all ? ... the base timing may be set properly but what is the electronic spark control doing with spark advance ? ... if you don't have a scanner you can check spark advance with a timing light preferably one with the **** on the back ... put some white paint on the TDC mark of the harmonic balancer and verify that the actual SA is changing ... if it is , check the balancer to verify that the TDC mark is , in fact , Top Dead Center ... the outer inertia ring of the balancer may have moved/rotated out of its original position as a result of age and deterioration of the rubber that bonds it to the hub ........

 

This sounds like my L98 ZF last year. Took it to 5 mechanics who checked everything. OBD 1 doesnt tell you much. Turned out to be bad injectors which I found out in this forum is a very common problem with the old multec design especially if your burning ethenol which destroys the seals.

 

take it to chevy dealership

 

if you don't have big pockets and you go to Mr Goodwrench see if he'll give you a prognosis of whats wrong without fixing it. Talk to the Vette tech on the side and see if he works after hours. I mention this because the dealership is going to cost a bundle if its a major repair.

As an example, fuel injectors cost $150 each over the GM counter plus about $400 labor to put them in. Thats $1600 out the door. Buying injectors from FIC is about $200 rebuilt or $400 new plus about 4-6 hours of your time. Just a heads up

 

That is not a good Idea. Dealerships don't like to deal with old cars and will give it to a newb who wont know what to do with it. He is better off here with us or at a corvette specialty shop that knows C4s.

 

Many members have been turned away from dealerships including myself. They don't want to work on a car this old. I was told no they wouldn't work on it period. The guys here can help or you could find the nearest Corvette Club and get a recommendation from them.

 

One thing to check is the injectors.You say they have been flow tested but they would have to be removed from the car to do this.What you need to check is the impedence on the injectors. You can do this yourself if you have the knowledge, or have someone else do it for you.. You have to check the impedence on each of the 8 injectors with an ohm meter.. Set the meter to the ohm setting and pull the plastic caps off the injectors. Place one of the probes onto each of the 2 pins in the top of the injector, it doesn't matter which way you hook it up, either way will give a proper reading.. The reading should be 16 ohms for a injector in perfect condition with lower readings acceptable down to 12 ohms. Anything lower then 12 ohms is considered a bad injector and needs to be replaced.. If you have to take it to a shop to have them checked it shouldn't cost much and should only take 10 to 15 minites at most.. You should check them when cold , and again when up to running temperture. Injectors going bad because of deteriation from ethanol in the fuel are one of the major causes of poor idle and bad performance on these older cars.....WW

PS..Stay away from dealerships unless you have no other choice...

 

If they don't have a clue, they aren't "Corvette Mechanics". Probably janitors at high schools in San Bernadino. A 1991 Corvette is a simple OBD1 EFI system.

My real advice for a 19 year old making minimum wage is to sell the Corvette and buy a used econobox that runs correctly. When you've finished college, trade school, etc and have a decent paying job, then you can venture back into owning a sports car....but I digress. In the meantime....

1. Fuel pressure. Should be 38-44 psi at idle.
2. Base ignition timing. Set to 6 degrees BTDC.
3. Ensure plugs are fresh, gapped to .060. Cap, wires, rotor new.
4. Fuel filter new.
5. Check for vacuum leaks. You have EVERY symptom of a massive vacuum leak.
6. Noid light on all injectors to ensure they are firing

Start there, report back. Stop paying "mechanics" $100 an hour to guess at it and not fix it. Troubleshoot, don't guess.

They need three things, and three things only to run correctly:

1. Suitable compression.
2. Correct mixture of fuel and air.
3. Suitably strong spark delivered at the correct time.

That's it. If those three conditions are met, they run. If one or more is missing or deficient, they either don't run correctly or at all. Find what is deficient, correct the deficiency, and it will run.

I can't believe a "mechanic" can't diagnose 30 year old EFI technology....unless he's a stoned hippie janitor from Yucca Valley.

 

One more thing....take your ignition module to a parts store and have it tested. They will do it for free. If there's a hippie behind the counter, find another store.

 

Hang with this group, be patient.. work the problem.

 

Word.

Run tests, diagnose, process of elimination. You'll get it. And you won't pay someone $100 an hour to guess either.

 

To be honest, this is probably the best advice you could get.....WW

Your not a hippie are you???

 

Sounds like it's low on blinker fluid. Make sure you don't fill it with 2-cycle blinker fluid by mistake.

 

 

Thanks I will try everything you guys said And seriously THANK YOU!

 

Signing up to the corvette forums was definitely the best idea to figure out what's wrong with my car instead of taking it to dumb wanna be "mechanics" where I just waste my money and find out absolutely no information.

 

FTW

 

No way I coulda owned c4s without being glued to these forums youll need to do it or sell it

When I bought mine knew next to nothing about efi...after getting soaked for almost 3k and nothing fixed broke down bought a pc and hopped online.

Trust me..it will try your patience once you get a grip on it your views will change. Or youll burn it to the ground.



Hang tight learn how to do it yourself.

WHAT is your location maybe a member lives near you and can help out done all the time here.

Go to user CP in the upper left hand of the page and fill out your profile.

 

Rancho Cucamonga, California.