Hello,

I just got a 1991 C4 coup (80,000 miles). I am new to the party but I have watched a good amount of youtube videos/ reading around this forum. I am sure I will be asking a lot of questions in the future on here. When buying this car I prioritized Runs/Drives over cosmetics. The guy I bought it from I trust here is a list of what he did.

New parts:
Starter Battery Ground and power cables
Fuel pump Fuel filter
Stock injectors Spark plugs
Spark plug wires Distributor cap and rotor.
Struts not installed brand new in box

Here are a couple WTFs I have questions about.

On the inside by the cup holders. There are two switches that turn on radiator fans. The guy said the original owner put them in. Does this sound normal? I don't understand why you would need a manual switch for that.

The guy also told me the original owner installed some sort of alarm system that causes a parasitic drain on the battery.

The brakes were very weak. He showed me the vacuum line to the brake booster was crumbling apart.

Lastly the big one. While we were test driving. Everything felt good/ very responsive. When we jumped on the highway I tried to give it the beans a little. The car would not go fast. the RPMs started jumping like I was hitting redline. The car would kinda just pulse when I floored it. Only way to get it up to speed was me tapping the pedal slightly. The seller was super surprised. We got it back to his house popped the hood. He diagnosed it as one of the throttle cables being loose. I believe the one that goes to the gas pedal. And used his hand to open it up all the way. The car went vroom with no weird sounds.

What do you guys think? Anyone of those things sound common or like a huge issue that will be unfixable? Thanks!

 

Welcome to the forum! Over the years, I have seen people install switches for cooling fans because they think that controlling the cooling fan themselves is best for keeping coolant temps down. In reality, if you keep your cooling system clean and filled with a good coolant/water mix, it will be fully functional and is just fine for normal driving.

Weak brakes can be a number of things. If the vacuum lines were crumbling, the engine would run rough from the vacuum leak and the brake pedal would be hard to depress, as it woupd not have vacuum assist. The weak brakes should be addressed promptly.

i would install the throttle cable properly and drive the car again. It should accelerate without issues. If it's weak or misfiring, there are more issues that need to be sorted out. These are not normal issues.

As far as the aftermarket alarm system is concerned, yes they are common and yes they can cause a draw. I would remove it.

 

I'm one of the people that mazdaverx7 is referring to. The car was engineered to run at temps that would seem alarmingly hotter to most people growing up in the 60s and 70s. My C4s never overheated once, but sitting in traffic and watching the temp go higher and higher before the fans came on was very stress-inducing. So, I installed a switch to manually start the fans; the temps go down really quick. The proper way to do this is to change the temp sensors in the heads, but I took the easy way out.

C4s will take a battery down quickly. Yes, take the alarm off, and if you take it to shows and show the motor, disconnect the underhood lamps.

I think you should take it to your mechanic or someone who knows about these cars. As mazdaverx7 wrote, the brakes and running issues could be a number of things and they compromise your safety. The good news is that once sorted, these cars run a long, long time. 80K is nothing for a driver C4. Good luck!

 

On your brake issue, the rubber part of the line by the wheels can fail on the inside. A part of the rubber can separate and the fluid movement push it to block the line. This can reduce pressure to one or more of the wheels. Even just the possibility is a great excuse for a set of braided stainless steel lines.

 

Thanks for the responses! Also sorry for making two threads. I couldn't figure out how to take my other one down.

Very interesting about the fans. So they will come on by themselves still? Also the tip about the hood lights draining the battery. Looks like the last owner thought of that. He added a switch to turn them on and off!

The brakes will need some help/TLC,the brake fluid is black. The guy did show me the vacuum line that goes to the brake booster there is a whole piece of line missing. Is that bad or can it damage the brakes letting air in like that. The brakes do work I just have to push hard. Also Stainless steel lines sound fun. I have put them on a motorcycle before. I imagine in a car is a little more difficult. Great idea Dburgjohn.

The throttle cable seems to move freely. and the throttle snaps back good. I think it's the part that connects the cable to the pedal. The pedal feels loose. Any advice?

Is it normal for the tachometer to get off? Mine goes all over the place. is that a symptom of something more or just old gages? Also the last owner said the odometer is off. It shows 140,000 miles. He said something about a sensor on the body that went bad and tracked a bunch of extra miles. He told me it really has 80,000 miles. I know that could completely be BS. But the Carfax recently shows 80,000 miles and he had shop paperwork showing his last service not long ago it had 80,000 miles. Have you ever heard of that?

Just some random how expensive/ how hard is it to do. The windshield has some cracks. The cracks are not terrible or high priority more cosmetic but I would like to fix them. I found a guy on Facebook marketplace selling C4 parts. He said 100$ for C4 windshield. Is this a part that needs to be OEM if I went to a glass shop would they have an aftermarket one you think? Also the glass top, I think it's called target top? Its spiderwebbed cracked. It still comes on and off still but needs to be fixed. I found a junkyard selling them. Does it need to be the same year to fit or any C4 works?

 

On Fans - the fans are controlled by relays mounted up front by the radiator. Computer provides ground to activate according to temp reading. Many people want the fans on sooner. Only way is reprogram computer or add bypass switch. The bypass switch will set a code but don't think check engine light will come on.

On Brakes - if you are missing part of or have hole in the vacuum hose from engine to booster brakes will be hard. This could be dangerous. There should also be a check valve usually where the hose goes into the booster. Looks like a elbow but keeps vacuum in booster from leaking back.

can't suggest anything on cable or tach, someone else will I am sure

On windshield - unless you are good at this or have a friend who is I suggest getting a pro. One wrong twist and you have to purchase another window.

 

Does your insurance cover windshield replacement?

Id be carful about removing the alarm system. My experience with aftermarket alarm systems (and radios) is that the stock wiring really gets chopped up and is sometimes very challenging to sort out. Trickle charger for the parasitic drain for the time being?

 

Well I do not think insurance will cover the windshield because I bought the car like this. It did not happen while I was driving or moving it.


Definitely on a trickle charger right now.

 

You certainly want to remove the aftermarket alarm, and yes it will be a PITA. You'll need to splice factory wires that were cut, but just take your time. It helps to have the Factory Service Manual with the wiring diagrams as a guide.

There's no way I would attempt replacing a C4 windshield. Call around and find a windshield shop that has done C4s before. I called several Safelites and found one where they had done C4s and knew what to do.


Good luck getting your Vette in shape.

 

It's a "targa" top
The word targa first came into use from the 1965 Porsche 911 Targa,

 

The bad vacuum line is a leak and can cause the engine to run poorly. I would replace it right away.

I would also run some Chevron Techron Through the fuel tank.

 

Welcome to the forum and congratulations on the car.

I’d pull that alarm. A parasitic drain can be a nightmare.

The fan switches are slightly concerning to me. Were they on during the test drive? Hopefully the car isn’t overheating and that was the PO’s attempt at keeping things at bay.

Keep us posted on what you find.

 

Welcome to the forum and with your new car... I agree with FACEMAN89... electrical gremlins are the worst part of C4 Corvettes and costs!

 

Update

Because of this forum I have gotten her running cherry again. Thank you!

 

Congratulations, I'm glad you got her running well

 

Congratulations on getting the car running!!! Have you had a chance to drive the car and if so, how does it drive?