91 C4 sitting 20 years need help
 

Hi everyone I am new to the forum and a new vette owner. I found a 91 C4 in a garage sitting with 46k miles on it. I bought it and continued to let it sit for a few more years until I had time to get it going. I have it running now but I am blowing white smoke and through the exhaust and it smells like it is running rich. here is what I have done prior to the initial starting:

Sent fuel injection in to be cleaned and tested through AFI
cleaned fuel tank and all fuel lines with carb chem then rinsed out carb chem and then flushed with clean fuel
I put a few drops of transmission fluid on the spark plug side and injector side of the cylinders prior to turning motor over
drained all fluids. Let the oil drain for a couple days and pored a few quarts of oil through and let it grab any gunk that may be of been sitting in the pan.
New plugs new wires new cap new rotor new ignition coil. all new plenum and throttle body gaskets
She fired up first try. I expected some smoke in the beginning considering tranny fluid in the heads and who knows what has been built up in the exhaust.
Its seems that the smoke is at idle or low RPM's when I drive her hard she runs great and I don't see any smoke once I stay under 35 it seems to come back worst is at idle.
I have only driven about 140 miles since I have gotten her running. I am scared to push it and destroy a great deal that I got you know. I don't see any moisture in oil and I don't seem to be losing any water anywhere. I only have water in at this point no coolant.
Any ideas on my next steps? Did I miss Something?

White smoke is always moisture, usually on start up. Same with blue smoke, but thats from oil in cycs. hopefully you dont have bad head gaskets but perfer that to a bad head. You have Alum heads on your car. I wil stop and let more knowledgeable folks chime in now. If you have coolant in you oit things will look muddy on your dipstick. Old shade tree is to drop a few drops of oil from a running, warm engine, onto a exhaust manifold.If it just smokes, good. If it sizzles and bubbles, bounceing around, water is mixed with it. Thats way old school tho. Best of luck and welcome to the forume. Whars worries me is that the white smoke returns after driving..you sure it isnt light blue?

Couple of things you can do that might help determine what's going on. One is to pressurize the cooling system and see if it holds or not. If not then suspect a bad head gasket. A car that has sat a long time could have stuck rings. I've heard of people using things like Mystery Oil and others to soak the cylinders and sometimes have the rings come loose.
You can do a compression test to see if there's a crack in the head etc, which typically show a low cylinder.

Good luck.

The oil looks clean.
I syphoned some fluid out of the over flow box and there is some brown stuff floating around. Looks like it could be oil. I have not seen oil get in the cooling system on a blown head gasket, I have only noticed it going the other way into the oil. That does not make sense to me. The pressure is building the opposite way how could oil go into cooling system on a blown head gasket?

Now I am definitely confused or over worried. Coolant pressure held at a solid 16 lbs for 10 minutes. Which indicates no coolant leaking anywhere. 2 minutes would of indicated this. it did drop 1/4 pound in 30 minutes. which I chopped up to it being the coolant system and of course it should drop some where at some point. Am I wrong on this?
The car smells rich but yet the exhaust is white. I have very rarely not been able to diagnose my own mechanical issues on any year vehicle. Anytime I have decided to spend the time to diagnose and completely fix the problem myself I have also succeeded. Im not the normal tear shit apart screw it up guy. I am very mechanically inclined without the professional training. I had 2 30 year mechanics at my house as I was putting it back together and they were impressed with where I was at with it. So I am pretty confident with everything being put back together correctly.
What else could be checked for white smoke?
I did run sea foam through the system as well and then followed by lucas octane boost. Could this be the problem that the sea foam put a coat on the converters and needs to be burnt off?

Seafoam would need to be burned off, yes, but that usually is gone pretty quick once you fire it up and it billows out of there immediately.

if there is a lot of white smoke, then there is water going somewhere. If the tuning is messed up because of a faulty O2, i could see there being a lot of smoke and it wouldnt necessarily be a black cloud. It could look white. I just dont know what youre seeing. Brown stuff in the coolant could be oil, could also just be gunk that built up from sitting. Did you flush out the whole system?

If oil pressure is good and coolant system pressure is good and a compression test is good, then the motor should be fine. I might push it to see if it burns off with hard running.

lets see a video of the white smoke. iphones can work well then upload to youtube and post link.

X2. At this point, you've done good PM and checking of things.... I'd go BTF out of it for a while....see if it goes away or reveals an actual issue.

Pull the vacuum line to your fuel pressure regulator and check for wet fuel in there. If so the FPR is bad.

https://cimg8.ibsrv.net/gimg/www.cor...1fd3a47ef0.jpg
BAD FPR

One more possible thing is the valve stem seals. Big thing there is it typically will occur on restart after sitting a while. Being the cooling system is holding pressure, I'd be more inclined to think it's actually oil related. A compression test of the cylinders may help narrow it down. Big thing though is I don't know if it would show a stuck oil wiper ring in a cylinder. As noted, if there's a stuck ring oil could be getting into a cylinder and that's the smoke you're seeing. Although not as likely is if all the end gaps on the various rings are aligned in a cylinder, it's an easy way for oil to get into the cylinder. Checking the plugs might give an indication if they are getting contaminated with oil.
Typically I work on small engines and I've had more than one that sat for years that had one or more stuck rings in them.

If the water jacket on the throttle body has corroded through, it might be extracting a small amount of water through there.
If you live where it doesn't freeze, your engine should run ok without heating the inlet.
If it is corroded through, go to autozone and get caps to cap off the water fittings on throttle body.

This was my first guess. Usually worse at low speed as described.

oil doesn't make white smoke does it???? also pretty easy to smell an oil burner car, drive it... use it...

"White smoke" could be steam (from water/coolant) or it could be oil. What does it smell like? If it happens at idle but not under hard throttle/load, then it could be the valve seats. Have you taken oil filler cap or PCV off of the valve covers and let it idle... is a lot of smoke/pressure coming up through the openings (would indicate blowby through rings). Video the engine running, video the smoke coming out of the exhaust, video the opening in the valve covers to give us more info.

On an engine that has sat for a couple of decades, stuck rings are common. I'd pull the plugs, put some Seafoam or Marvel Mystery Oil into each cylinder, and let it sit for a day. Then I'd run it. I'd expect some smoke at first but it should go away quickly... this should help unstick the rings. You must have gotten a bargain, but expect to spend something on it getting it to work well. Otherwise it wouldn't have been a bargain.

Thank you for all the replies. This where I'm at now. I ran it fairly hard through the hills (about 70 miles). when I got up there I parked it for the day. No smoke after I got out of town and was able to open it up. Went to start it and it acted like the battery was dead. Jumped it motor turned over then a hard stop. Let it sit charging and fired right up. Brand new Battery and alternator is working. Seemed like something was stuck. Smoked and smelled like fuel really bad. Checked the oil and looked very light. Drained the oil and definitely had fuel in the oil. I researched fuel in the oil on the forum and found that fuel pressure regulator could be the cause. That is the one part I did not change or check. I parked the car for a couple weeks up there. Purchased a fuel pressure regulator and replaced it. Did a oil change and drove it home. I expected the there to be some stuff to burn off so was not to concerned that there was still white smoke. The smoke was not as heavy at that point as well. I drove it 70 miles back home. It seemed to run a little smoother. Let it cool down and when I started it up same issue with white smoke and very rich fuel smell. I checked the oil and the level looked the same as when I filled it and couldn't smell gas. From reading here with fuel in the oil after FPR is changed next step would be to change injection, my concern with that is I had my stock injectors professionally cleaned and tested. So would the injection be eliminated or could it be and original injector problem that this year was prone to. Someone had mentioned to me that the injectors were a problem on this year, not sure about the truth on that just what I heard. I have not checked the vacuum at the FPR. Makes me feel like a dummy that I didn't even think of that.


Here is my plan hopefully this weekend if I have the time any input would be greatly appreciated:

Check vacuum on FPR


Pull spark plugs and look to see if they are burning correctly


Compression test

Should I do the o2 sensors first?

I will post videos and pic this weekend. Just been so Busy barely have time to get anything done.

Taking a different approach, when someone parks a car for years, many times it's because the car has a problem that the owner can't afford to fix. Can the previous owner shed any light on the problem you are having?

This may sound stupid but did you replace the 02 sensors yet? They are only good for 50 k miles or a few years and then you replace them. If your car's still using the old 02 sensors it could be messing up your air/fuel ratio. 02 sensors age badly and will start to lag behind and cause all sorts of trouble. The Fuel pressure regulator is rubber and likely damaged by the ethanol in the fuel and should be replaced with a newer material modern one.

Getting your rings to free up and seat properly is probably why you had the smoke, after a few miles they tend to loosen up and start to seal. I use snake oils in my oil and there are many products out there to help loosen things up a bit. Marvel Mystery oil works well.

I let my C4 sit for a few years and my fuel supply line corroded shut. Check your battery voltage at the battery and then check it inside the car. You should not see a big difference between the two readings, if you do then you should follow the battery positive to a post near the battery where the fusible links that supply power to 99% of the car get their power. If there is corrosion on this post it will wreak havoc in your Corvette.

A "Leak Down Test" is the best test for determining if there is a problem on the top of the engine. It is not hard to do but is time consuming and you need a good source of compressed air and the special tool which is readily available. They use Leak Down testing on piston aircraft to determine the engines overall health.

Good Luck and Have a great time getting that Corvette where it belongs, Back on the road again!
Chris

The person I bought the car from was a hoarder. She moved out of the home and left it full of crap. There was a 97 camaro convertible next to the vette. I also purchased that one as well and had it on the road in a couple days. It had been sitting same amount of time and had 36k miles. The neighbor that tried to purchase the vette from here multiple times told me that she would buy a car and park it when she was tired of it then buy a new car. I am fairly confident that the problems are from sitting.