This Corvette engine NEEDS a Leak Down test done more than anything at this point. The leak down will show you where the oil is finding its way out. It is a simple tool available at Harbor Freight or Summit racing.

I learned about them from a aircraft power-plant mechanic as they were required every year at the Annual of the aircraft. The Leak Down test results will give you a very accurate "cause" of the oil leak.

Under no conditions try removing the valve retainers without something keeping the valve in place. The idea of using an air compressor with 35 psi makes great sense as long as the piston is at TDC on the cylinder you are testing. It does not take long but does require the tool and compressed air.

 

So did you end up changing the valve seals? If so, did the oil consumption go down?

I have an a stock 85 w 72,000 miles, which uses a quart every 500 miles. (PVC OK, spark plugs dry, no blue, black, or white smoke. I use 10W-30 Valvoline Dino Oil).

 

yes I replaced the valve seals and I fixed the seal on the back of the intake it no longer leaks or burns oil but when I was reinstalling the intake I smashed the pigtail for the IAC now it’s idles at 3,000 rpm I will get that fixed soon there are other great threads to check out about the intake leak I would start by looking at the back of the block and seeing what it looks like and also check the oil pressure sending unit that can develop a leak best wishes

 

I use the "ole indian rope trick" ; pull plugs, rotate engine so piston is down in bore and moving up on compression stroke. get a couple feet of soft dacron rope, feed it into cylinder, continue to rotate crank till piston compresses rope against valves. Its cheap, its easy, it works like a champ.

 

What if you didn't? Isn't the big fear that your piston falls into the cylinder? At TDC, where does it fall to, if it can? Probably hit the piston and stop. I get nervous about introducing things into the cylinder. People are afraid to use the air in the cylinder because the valve can fall into the cylinder but if the piston is at TDC, is there an issue?

 

I used compressed air and it worked flawlessly. The only issue I had was the spring compressor I was using was garbage. If you have tour piston at top dead center the valve will not fall in I just avoided doing this because mistakes are easily made and I didn’t feel like pulling heads off

 

It's just easier to fit the seals and refit the spring(s), retainer, and locks if the valve stem is all the way up and the valve is held inplace either by air, rope or whatever.

 

Fair enough. I did it with the air and dropped a valve. Fortunately it didn't drop far. Since then, I did it with the piston at TDC.

 

Glad you got your oil issue fixed. My 85 has a very small leak, doesn't smoke, clean (for 30K miles) plugs, good PVC... I'm really stumped where the oil is going.

I just went through some drama getting my 85 to idle. I cleaned the throttle body, replaced a bad IAC Valve and adjusted the TPS and couldn't get it to idle below 770-780 in Drive and 950-970 in Park. I tried to adjust to Min Idle using the procedure in the 1985 FSM page 6E3-91. Still couldn't get it to idle lower. I discovered a few things that helped me get it fixed.

1) You need to disconnect the EST connector when doing the Min Idle Adjustment (not mentioned in the FSM, but I read this in a procedure from Wilcox Corvette). While it's disconnected make sure your base timing is correct.
2) There is a 1985 only Bulletin to set the Min Idle at 500 RPM. (Instead of 400 RPM as stated in the 1985 FSM)
3) Connecting my Tech 1A Scanner caused the Idle to jump about 100 RPM. Odd, and I don't know if this a 1985 only issue since the ECMS were upgraded in 1986.
4) Setting the Min Idle to 500 RPM caused the car to idle too low in Drive (550-570) and it would die sometimes. So I reset the min idle to 570-580 and now the car idles perfectly. It idles at 600-620 in Drive and 680-710 in Park.

 

IDK about Wilcox but I make sure that the timing is spot on before I do adjusting the IAC. When you set the idle speed, what do you use for RPM readings?

 

AK:
My 85 is 100% stock, so I made sure the timing was 6 before I started.

I set base idle to 500 and I was using my Tech 1a to read RPM and IAC counts and I had the EST connected. I also used the Tech 1a to read the TPS voltage when setting it at 0.54 V. But I could not get the idle to go down below 770 RPM in drive w/ everything connected back up.

On a test drive with my Tech 1a connected, I happened to notice my idle jump up to almost 900 RPM (from 770) in drive and my MPG counter on the cluster was stuck on 12. I don't really care about the MPG counter, but thought this was odd. I then disconnected my Tech 1a and idle (in drive) went back to 770 and the MPG calculator worked again. I tried my other Tech 1a scanner and the same thing happened. I also have a stock 1988 Corvette and it does not behave this way with the Tech 1a connected. I don't know if the ECM upgrade in 86 fixed this, or the extra adapter the Tech 1a requires on my 88 is the fix.

So after all that, I decided to set the base idle with my wife watching the RPMs on the cluster. The nice thing abut 85's is the that RPMS have two digit precision below 1000 RPM (reads 590,600,610,620 etc), while my 88 does not (only reads 600,700, etc). I also disconnected the EST. (Also made sure all accessories were off and cooling fan was not running). I set the base idle to 500. I set TPS and connected everything back and found the Idle (in drive) was about 570 and this was too low and it would stall. So I reset the base idle again (w/ no Tech 1a and No EST) to 570 RPM. I also set the TPS to 0.55 V using a special connector from MAMW and a Fluke MM. Now it idles about 600-620 RPM in Drive and 680-710 in Park and does not stall. It runs great now.

After thinking about it, it makes sense the EST would affect the idle but I am baffled at the Tech 1a affecting the idle speed.

 

https://www.corvetteforum.com/forums...-a-1985-a.html

I think it puts you in a different mode with the scanner attached. I don't have that in my 91.

 

https://www.corvetteforum.com/forums...tic-modes.html

 

Thanks for the info/ thread links.

I took a closer read of my FSM and it does say it sets the RPM to approx. 1000 and advances the timing in ALCL mode... Makes it impossible to use the scan tool for some things (like adjusting the min idle using IAC counts).

 

IDK how to get around that. When I made the comment that I would never get an 85 because of that "feature", I was told that several people have attached scan tools and got "no problems", whatever that means. Hard to say. Maybe they found a work around.