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Gregarious · Joined: 13 Sep 2003 Posts: 86 Location: Los Angeles

I just had my 931 smogged at a CA Gold Shield shop. Two days later I took it to my regular mech and complained about the bad vacuum reading, poor power, and terrible milage. He did a compression test, removed the exhaust manifold, and gapped the valves. Also checked the plugs and injectors for vacuum leaks. He found the #1 cylinder is not firing, but no oil on the exhaust. No vacuum leaks. Valves correct. He said he thot it was the DITC, because it COULD NOT be the head gasket, as the vacuum was leaking into the crankcase. And a recent case he had of a broken ring showed alot of stuff inside the exhaust mani. So I promtly brought him a backup DITC. No change. So he changed his story, and it now WAS a broken ring, and I need to dish out 3 to 4K to rebuild engine and turbo. Alright, alright, I know. I need a new mech. Already figured that out. So, tomorrow, I am towing it, flatbed, to the guy who told the state it was passing the emmisions with only three cylinders. And I think I should have him remove the head and check the gasket. I run 100% 0-40 synthetic, and Water Wetter, so I know I have no lubrication or heat problems. That is why this is so baffeling. Am I correct in deducing that it MUST be the headgasket? I know this was one of the first cars with a DITC, and that vacuum problems create all kinds of mysterious challenges. It took me a year to figure out that the injector seats had melted, and I recently replaced them. So where is the vacuum leak in the cylinder? I figure rings, or gasket. And I do not believe it is logical to conclude rings under the circumstances. Any thoughts?
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Gregarious · Joined: 13 Sep 2003 Posts: 86 Location: Los Angeles

I realized I said some things that may not be understood. First, the #1 IS getting spark, just no compression or vacuum. The mech states he can hear it going into the crankcase. Second, he thot the screaming was the turbo, but I think it is the belt tensioner, so that would save rebuilding the turbo, BUT he says it is getting zero boost. Different problem tho. Working fine last week. And, I am not stupid for taking it back to the smog guy. If he passed it with 25% of the engine not working, he OWES me work to fix the prob. I found a fella that is pretty sharp on these,real close to me now, for next problem. I think that should make it easier.

Raceboy · Joined: 01 Mar 2004 Posts: 2327 Location: Estonia, Europe

It could also be a piston with a hole melted in it.
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Racing · Joined: 27 Apr 2004 Posts: 374

As raceboy says,it´s most likely that the slug in hole 1 has passed away.

Paul · Posted: Wed Aug 10, 2005 11:21 am Post subject:

Stop running the motor, holed pistons have a habit of breaking which may bend valves and will trash your turbo's exhaust vanes.

Gregarious · Joined: 13 Sep 2003 Posts: 86 Location: Los Angeles

That may already have happened. It won't start now, and the mech ran a pressure test. Found the leakage was into the crankcase. Which confirms either ring or piston. Unfortunately, I cannot rebuild it at my current location. Anyone want to buy a 1982 931 with; new windshield, new fuel pumps, almost new Pirelli's, new plugs, new wires, new flywheel sensor, new paint, new foam air filter, new gas filter, new shocks, 100% synthetic Motor and brake fluid, M471, new sunroof rubber, recently recharged A/C, and things I'm sure I forgot. I know pretty precisely what little it still needs. Oh, I love that car. CA will give me 1K to retire it after taking off what I want, and those things are worth at least two grand. Only dent in the body is a little one under the driver side rear brake light. Some college girl talking on her phone.

-nick · Joined: 16 Nov 2002 Posts: 2699 Location: Cambridge, MA

All the top compression rings came out in pieces when I opened my 931 engine up for the first time (~100k miles). However, it still ran surprisingly well. No misses, and still pulled decently under boost.

If yours doesn't even have enough compression to fire then something is seriously not good. A burned/bent valve is usually the reason for this, but if it's leaking into the crankcase then the piston is probably looking pretty nasty.

Did you notice hearing any "ting ting" detonation sounds under boost? That's the surest way to kill pistons.

Best of luck, but it doesn't sound very promising.
nick

Gregarious · Joined: 13 Sep 2003 Posts: 86 Location: Los Angeles

Thanx Nick, and no, never noticed the ping. I give up. I am just astounded that this could have happened. My cooling is excellent, and my lubrication is now far superior to standard. What needs to be done about turbo cool down after stopping? I know about occasionally opening up the waste gate with high rpms.
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