Charlie944

Hello all, I through a compression gauge on the Callaway 944 today after I suspected a bad cylinder and it bumped up to 3-4psi then down to zero. The engine was all up to temp. The other cylinders read as follows:
#3: 156psi
#2: 133psi
#1: 89psi
I ran up to Road America here a couple weekends ago for the BRIC and the car ran great on the highway. On the track I noticed it was lean due to some hesitation when putting on the power so I held off. On the way home, ran great! I did a datalog on the TEC2 and it showed I was lean when the boost came up. I then richened up the accleration parameters and went out for another test. First couple hard runs it pulled great. AFR's were 12.8-13.2 narrow band. EGT's were 1150F at cruise up to ~1400F max @ 0.8 BAR. I turned around and got on it again and I noticed a bunch of grey blackish smoke coming out the exhaust. I immediately let off, and it felt liked I fouled a plug. I through a another set of plugs in and started it today and it still sounded the same. Drove it for a bit, pulled 21.2in/Hg at idle warm more so when coasing down. All the temps were fine, and EGT were all in norm. That is when I put the compression tester on it. I will have to put some compresser air down the cylinder to hear where it is leaking from. No noises or other weird occurances other than the smoke occured and the hesitation on the track.

I am hoping it is just the head. The engine supposly has a tad over 2000 miles back in 1997, but not under my ownership.

Ian Carr

black grey smoke is normally oil. Oil means it is probably rings. It is possible that it might just be a head gasket but im not to positive on that. Also that vacuum at idle is allot stronger than my motor and most motors i have seen. Mine does about 15 when warm and 11-12 cold. I do get 20-21 in/hg when decelerating but not at idle. I hope you fund out what is wrong and hopefully it is nothing serious.

Charlie944

Thank you Ian, I will look into everything here shortly. I have to replace the lower radiator hose on my 84' then I will start to tackle the turbo. I stuck a long 1/4" extension down the spark plug hole onto the dish in the piston, and there was a oil lying in the dish....to be expected I guess.

Chris White

A couple of tid bits for your diagnosis –
Grey / black smoke – rich/misfire
Blue Smoke – Burning Oil
White Smoke/Steam – Coolant

‘Good’ vacuum – 15 to 20 at idle up to 25 during engine braking. (25 to 30 kpa @ idle and 10kpa during engine braking).

I would guess valve issues based on your initial description. Add some heavy oil into the cylinder (tablespoon) and see if the compression numbers change.

Chris White

reno808

What would this determine. Sorry dumb question.

Chris White

At cranking speed (low RPM) the viscosity of cold oil will help seal the rings and /or scored cylinders. The oil will do nothing for worn valves. So if the compression goes up look at the rings/cylinder walls if it does not then suspect the valves.

There aren’t many dumb questions but there are a lot of dumb answers/assumptions!!

Chris White

Charlie944

Thanks Chris, I will put a bit of oil down the cylinder and run the compression on it again. I am really hoping the block and lower end is alright! Is 20W-50 good enough or will I want heavier yet?

Porsche-O-Phile

Nooooooooooo! Say it ain't so!

Here's hoping it's just a fluke or at worst a head gasket. . .

Campeck

oh my. it doesnt look like its just your #4. all those cylinders look alittle tired...

Charlie944

I hope it ain't so either Jeff! I did pour a little 20w-50 down the #4 spark plug hole along with the #1 as well. This was on a cold engine due to I do not want to start it up and trash anything more than it already is.
#4's compression bumped up to 8psi
#1's compression bumped up to 131psi

I will run both cylinders down to BDC and pressurize the cylinder and find where I can hear the air coming from

Here are my compression results from 10-18-04:
Compression check when cold (Should have be warm, but I figured this would depict the worse of the 2 tests) was:
cyl 1: 162psi
cyl 2: 159spi
cyl 3: 151spi
cyl 4: 162psi

Keep in mind I have only put ~3,000 miles on the car since then.

Zero10

Wow.... I have no idea how you could get next to no compression on one cylinder. That would take one hell of a leak! It would take a jammed open valve or something like that. I don't want to say much more since all of my guesses are bad news.

Campeck

a leakdown test is done at TDC. not BDC

thats what you mean by pressurize right?

Charlie944

Ashton, I have heard it being done both ways. Granted at BDC the piston will for sure not move unlike if it is not quite at TDC and happens to move the piston. I do not see why their would be a huge difference in the outcome. Please enlighten me if there is a difference.
Thank you for your concern.

Zero10, I am suspecting a head related failure of some kind to have that big of a difference in those few miles. Either way I will probably be pulling the engine because I plan on upgrading the clutch at the same time.

Peckster

With a reading that low, all will be clear when you pull the head.

Gator_86_951

Pull the head and survey!