1987 Carrera Failed Compression Test

[DSM]

I own a 1987 911 Carrera 3.2 with 86,000 miles. It runs great with plenty of power. No strange valve noise or engine noise. I recently had a compression test. Test showed 2 cylinders to be at 6% capacity when compared to the others. Could this be carbon build up on the valves? Is there a good fuel additive for this?
The car isn't run much. In 2 years clocked on 6,000 miles. Does it need a valve job? Can any damage be done by driving it the way it is? Any help or advise would be greatly appreciated!!
Thanks All

[Wil Ferch]

Sometimes carbon can get lodged in strange places....under valve pocket for instance.

If the car runs great...add ( multiple times, even) Techron ...and run the car!. Do an Italian tune-up !!

Then check again for added peace of mind....you'll likely find you're OK.

Wil

[javadog]

I am not sure I understand what you mean by 2 cylinders being measured at 6% capacity. Did you mean the two cylinders had a compression number 6% less than the others? Can you explain it in other words and perhaps include the compression numbers of each cylinder?

JR

[DSM]

I totally screwed up. Sorry for the wrong explanation. The test that was performed was a leak down test. These are the results below. Can these tests be flawed?

6% 80% 10% 6% 42% 10%

LEAK DOWN TEST

[NoLift911]

I don't think your car would be running "great with plenty of power. No strange valve noise or engine noise" with those kinds of numbers...

Maybe the test was flawed - ? How many times was the test done and by whom?

-Jeff

[javadog]

If those are leakdown numbers, whoever did your test wasted both your money and your time. There is no way that an engine could be described as running great, with plenty of power, and have leakdown numbers like those.

It's possible to foul up a leakdown test, by getting a piece of carbon stuck under a valve when unscrewing the plugs, but I'd have to say you need to find a new shop.

JR

[DSM]

It was done 1 time at a local European car shop.

I'm going to try the Techron. Thanks Wil !

Any advise it much appreciated.

[Rot 911]

Originally posted by nolift911
I don't think your car would be running "great with plenty of power. No strange valve noise or engine noise" with those kinds of numbers...
Maybe the test was flawed - ? How many times was the test done and by whom?
-Jeff

My real world experience. My '86 3.2 had 130,000 miles used about 1 quart every 400 miles but really ran strong. The week before I had just driven to Indiana and back to Missouri, drove it hard and it was running great.

I had just purchased a leakdown tester and discovered one cylinder had a leakdown of 80%!!!!! When I tore the engine down this is what I found:

[afterburn 549]

leak dwn test should be reserved for real race engines, freight trains and UFOs. a comp test will yeild real dynamic results, A leak dwn will yield the operator a work order. A side pt- a comp test will go sour if batt cond, temp, and throttle no monitored .

[BK911]

Kurt:

WOW! I can't believe that valve was burnt like that, especially how well the car ran. Did you notice a huge difference after the rebuild? Did you rebuild back to stock specs?

[porschenut]

Techron isn't going to help if those numbers are real. Up to 10% leakdown is generally considered acceptable, but #2 and #5 are in big trouble. If I were you, I'd go to another shop and have them do the same test. Don't tell them about the first test. If the numbers come out similar, then your "strong" running engine is not running like it should. Do a compression test as well.

Also, a leakdown test is useless unless they tell you WHERE the leaks are occurring.

[Rot 911]

Originally posted by BK911
Kurt:

WOW! I can't believe that valve was burnt like that, especially how well the car ran. Did you notice a huge difference after the rebuild? Did you rebuild back to stock specs?

Brian, did the rebuild myself, pretty much back to stock specs, but went with SSI's and a Steve W chip. I was like you, couldn't believe how well it was running with that burnt valve. Idled just fine, ran like a bat out of hell. Those 3.2 engines are tough!

[jkarolyi]

FYI...the higher the percentage of leakdown, the worse the engine is...the problem cylinders are the ones with the 80% and 42% readings. And I've driven 911s with two low cylinders that ran great and pulled decently. See Kurt's post....Porsche engines are smooth and tough!

Could be carbon buildup on valves. Get another leakdown done, this time have the mech listen to where the air is leaking out of. Crankcase = piston ring problems, exhast pipe = valve problems.

Do a search...there's a method of filling/soaking the compression chamber of the low cylinders with Berryman's Fuel System Cleaner that dissolves the carbon buildup. I'd give that a try before breaking the engine down.

[masraum]

Originally posted by jkarolyi
Do a search...there's a method of filling/soaking the compression chamber of the low cylinders with Berryman's Fuel System Cleaner that dissolves the carbon buildup. I'd give that a try before breaking the engine down.

Or Brake fluid or running water through the engine.