Got the results of of the PPI today and it seems good <img src="graemlins/jumper.gif" border="0" alt="[jumper]" /> but I want confirmation from knowledgable Rennlisters since I know nothing about what makes these cars go. <img src="graemlins/burnout.gif" border="0" alt="[burnout]" />

Leak down results as follows:

Clyinder 1 2%
Cylinder 6 2%
Cylinder 2 2%
Cylinder 4 1%
Cylinder 3 3%
Cylinder 5 2%

DME Actual Values
Range 1 Cylinder 1-3(TRA) -0.17
Range 1 Cylinder 4-6(TRA2) -0.09
Range 2 Cylinder 1-3(FRA) 1.02
Range 2 Cylinder 4-6(FRA2) 1.01
Oxygen sensing (FR) 0.98
Oxgen sensing (FR2) 0.99
Hot film MAF 0.74 V
Ambient Pressure 930 hPa


CAN SOMEONE PLEASE TELL ME WHAT ALL OF THIS MEANS BEFORE I TALK TO THE TECHNICIAN?

Thanks!

 

Everyone says "make sure you get a leak down" Now I got one and I don't know what it means? HELP PLEASE! <img src="confused.gif" border="0">

 

Forgot to mention: '97 993 57,000 miles.

 

Your leakdown is fne, excellent in fact. A healthy 911 engine should be no more than 4-6 percent leakage.

However, Bruce Anderson, a noted 911 guru, doesn't believe leakdown tests are terribly valid, especially on the 3.6 liter 911 engines, because they only test for leakage at the top of the cylinder and because, he says, the later engines are prone to cylinder distortion. He puts much more stock in a compression test.

But with numbers like those, I don't think you have much to worry about as long as the car runs strongly. Others will chime in, I'm sure.

I don't have a clue about the DME stuff, sorry.

Vic
95 C4

 

Thanks for your quick response - Rennlisters seem to be ardent belivers in the Leak Down test - the P-Car dealer that did the test even tried to talk me out of it and suggested the given his impression of the car neither Leak Down or Compression were necessary but of course he would take my money if I insisted. He did talk me out of the compression test though suggesting that it was somewhat redundent considering the info that the Leak Down would provide.

Others thoughts are much appreciated!

 

If I were going to do only one of the two tests, I would have picked the compression test. But since you've already done the leakdown, and I agree you got good results, I'm not sure I would pop for a compression test if the PPI checks out everywhere else, especially if it runs smooth, and feels strong (compared to the other 993s you've driven, of course). But if you really want peace of mind, a compression test might make you sleep better. Perhaps it depends on how much you really want THIS car? Weigh in the color,options,etc...

Edward

 

[quote]Originally posted by fbfisher:
<strong>Thanks for your quick response - Rennlisters seem to be ardent belivers in the Leak Down test - the P-Car dealer that did the test even tried to talk me out of it and suggested the given his impression of the car neither Leak Down or Compression were necessary but of course he would take my money if I insisted. He did talk me out of the compression test though suggesting that it was somewhat redundent considering the info that the Leak Down would provide.

Others thoughts are much appreciated!</strong><hr></blockquote>

FBfisher:

Everyone has an opinion on this subject and I'll just toss mine in, too...

When evaluating the condition of a used engine and trying to acertain how much life is left in the engine, (or if there are any undiscovered problems), two of the best diagnostic tests are the cold & hot compression tests and a leakdown test. Short of a teardown, these are really the only way to get a snapshot of what shape the motor is in.

IMHO, each test is complimentary with each other and one should not preclude the other. One needs to perform both as they provide different data and together, are very informative and NOT redundent.

I do not mean to suggest that these tests are perfect, but they are the easiest and most practical methods to evaluate an engine. Neither one tells you anything about valve guide wear or even if there are broken rings (from detonation), however its easier and less expensive than disassembling the engine.

Now,.....the leakdown figures you posted look good to me as this indicates good valve & ring sealing. I would be inclined to perform a hot compression test, and simply make sure that each cylinder's pressure is within 15 psi of each other.

I hope this helps answer your question and clarifies issues about which diagostic test is better than the other, or whether both should be done.

 

Thanks for your excellent responses. Any clue about the meaning of the "DME Actual Values"?

 

TRA1 & TRA 2 is air/fuel mixtures and is more of a
"live action" mesurement while the car is running. It hard to tell with one value. Though
the "picture" is within specs. I would say everything that I seee looks to be from a car that is running properly. As the other gent stated, your leak down is good. This is evidence
you don't have any major valve or ring issues, such as a valve that taped a piston due to a misshift or major oil starvation. Looks good from what I see.

 

Just wanted to point out a complimentary story with an aviation engine. A friend of mine is a pilot who purchased a Sukoi (sp?) aerobatic trainer this last winter. I have flown with him from time to time. The plane has a radial engine configuration and had a leak down and compression test prior to his purchase. Those tests were done competantly in Arizona and were found to be within normal limits. On his initial 20 hours with the plane, the control tower calls him on the radio and says he is dropping puffs of smoke on take off and landing. He has the mechanic tear down the motor, and finds several cylinders with rings that are severely damaged and required complete engine rebuild. His explanation is that pistons with multiple rings can have the top ring intact, show little change on testing, but in fact have lower rings damaged without much other indication. This is fairly well known, I suppose, and all engines have their problems. From what I have read on 993 motors, you might be more inclined to have valve guide wear at this mileage than in a car with lesser miles. Basically, this is a used car and while you are trying to rule out major problems with your inspection, lesser or more chronic issues may not be real obvious until after a month or two as you familiarize yourself with the mechanics and performance. Good luck.

 

Go to

<a href="http://www.pumaracing.co.uk/comp.htm" target="_blank">compression & leak down test info</a>

for a good article on these tests.