Leakdown test results

larry47us · 08-25-2003, 01:03 PM

I have purchased and read Wayne's book on restoring Porsches, and I am in the process of arranging to buy a 73 911E Targa that is being restored for me by a shop in CT. The car has 98K miles on it. The shop has just done a leakdown test and a compression test. Here are the results:

1: 140psi 19%
2: 140psi 18%
3: 145psi 18%
4: 145psi 9%
5: 152psi 10%
6: 140psi 10%

He said "I don't want to tell you what to make of these numbers. I think you should do some research to make your own decision. Personally I think they are good and would keep driving the car. It ran great last fall."

The car has been sitting idle for the last 6 months. He just replaced the injector pump because it wasn't running within specs, and said that before he ran the leakdown test, it was running rich, and the extra carbon probably affected the readings on cylinders 1-3.

From what I have read, it seems to me that the compression test went very well, all cylinders within 7% of each other. The leakdown test numbers seem inconsistent with the tightness of the engine I see in the compression test.

I am a total novice at this. Should I have him try to "burn off" the extra carbon and redo the leakdown test? Or, since the compression test is OK, should I consider the engine all right? He said he heard the hissing in cyl 1-3 out the exhaust.

I appreciate any comments you might throw my way. Thanks for helping.

larry

Wayne 962 · Wayne 962's Garage

Hi Larry. In general, leakdown numbers like those shown above are not ideal, and indicate something may be wrong with the engine. Re-read chapter 1 again, and do some of the other tests (if possible) on the engine.

These cars do not do well sitting around for long periods of time. Leakdown numbers are typically bad after sitting, and unexplicably, they start to leak if they aren't periodically run. The compression numbers here look good indeed, but I would run the car for 200 miles or so, and then repeat the leakdown tests. It may get better, or it may get worse.

-Wayne

dad911 · 08-25-2003, 01:21 PM

I'm confused. If the shop is working for the seller, (shop owner said it ran great last fall?) it would be in your best interest to find another shop for PPI. If the shop is working for you, you should be able to use these leakdown numbers to negotiate a better price.

larry47us · 08-25-2003, 01:21 PM

Wayne:

Thanks for the response. I will reread the chapter, and try to run the tests.

I plan on using this car during the summer only (a weekend, fair weather driver). Are you suggesting that I may do damage to my car over time by "storing it for the winter?" Or, do you just mean that I need to understand that after I take it out of storage, it won't run as smoothly until it has run that "200 miles".

larry

larry47us · 08-25-2003, 01:27 PM

dad911:

It is kind of a strange situation. I asked this shop to do a PPI for me on another car. The car was a BOMB. After we were done, I told him to keep his eyes open for me. He told me of this car, which he bought last year and had in "storage" and said he would restore it for me.

I have another long time early 911 user that is going to do a PPI for me before we finalize our deal. And we agreed that the shop should run compression and leakdown tests before we do that actual PPI.

The shop even told me to have someone else help me evaluate the results. I think the guy is being honest with me, I just don't know any of the answers yet. My hope is to make this learning experience a fun one that is not too painful!!

larry

Wayne 962 · Wayne 962's Garage

Quote:

Originally posted by larry47us
Wayne:

Thanks for the response. I will reread the chapter, and try to run the tests.

I plan on using this car during the summer only (a weekend, fair weather driver). Are you suggesting that I may do damage to my car over time by "storing it for the winter?" Or, do you just mean that I need to understand that after I take it out of storage, it won't run as smoothly until it has run that "200 miles".

larry

The latter - the car needs to be run-in for a while before all of the junk is cleared out...

-Wayne

larry47us · 08-26-2003, 03:29 AM

Quote:

Originally posted by Wayne at Pelican Parts
The compression numbers here look good indeed, but I would run the car for 200 miles or so, and then repeat the leakdown tests. It may get better, or it may get worse. -Wayne

Wayne - If you could just clarify a bit. If the compression numbers are good, then how can leakdown numbers be bad? Are we really measuring two different things, or is the leakdown test just a more sophisticated way of identifying why the engine is unable to hold (or build) pressure? If an engine is leaking badly, then wouldn't it be unable to build pressure to give good compression numbers?

larry