Why such strange Leakdown Results?
 

My car (Kermit) has had its final leakdown test, as part of a final PPI. I am picking him up tomorrow in CT, and will be taking a long drive back to Chicago. Here are the leakdown results:

Leakdown measurements

1 -- 8%
2 -- 22%
3 -- 5%
4 -- 4%
5 -- 1%
6 -- 20%

Four of the cylinders really are tight. Two are really, really loose. What does this mean? Is it possible that there is carbon in those two cylinders? The shop said "don't plan on carbon, it's just bad valves - you will need a top end job real soon."

But it is obvious that the engine has had a top end job recently, since the numbers on 3, 4, and 5 are so good. What could cause these terribly bad numbers on 2 and 6, and is there anything that I can do? Is it possible that someone just misadjusted the valves and that caused it to burn them? How likely is that?

Now the Newbie question, If it is carbon, what is the best way of "burning it off?" If I try that, and it really is an engine problem, do I stand the risk of being stranded someplace by the side of the road?

larry

Re: Why such strange Leakdown Results?
 

I don't think you can conclude it is "obvious" it had a top end rebuilt just because some of the numbers are good.

I'd be figuring the "worst case" senario and go with what the shop says -- "don't plan on [just] carbon..."

OK, I understand, but if you see numbers like this, do you "automatically" go to get the top end done, or do you wait till the performance of the engine is significantly affected? And it would be a shame to take apart the engine and find "oh, look at the carbon buildup on that one side of those valves."

Under most circumstances, people don't do leakdown tests annually to assure that the engine is tight, or do they?

larry

Don't know about leakdown, but my car was serviced by Andial for almost it's entire life (100,000 miles).

I noticed in the service records that they did a compression test every time they did a valve adjust, and noted it on the records.

(It registered 150 on each cylinder from the first to the last test!)

So, at least some do that kind of testing regularly.

Did you have a compression test? What were the results? (Just curious).

Also, if your car recently had a top end, carbon doesn't seem likely.

No and no. When doing the PPI on my track car we got very similar results - 2 cylinders with pretty high leakdown and the rest were fine. Compression was almost perfectly even and the car runs great. It had a recent ring and valve job as well. So after talking to several experts, including Jerry Woods Enterprises (who did one of the PPIs for me) it was decided to run the car as is. There is no obvious problem with it - we ran 1,000 miles of track time before we even had to add oil. If you read Wayne's tech article about leak down tests, he also mentiosn that on occassion cars run great that get dtrange number. If I were you I would drive the car and look for signs of problems - such as high oil consumption, excessive oil smoke on start up, or smoke when shifting. As for carbon build up, run some Techron thorugh it and change the oil.

This is a car that I bought last year, and the body restoration was just completed. I had the PPI done just to verify that everything was done as expected prior to my picking the car up. There has been no mechanical work done on it during the restore.

The thing about the carbon is that the MFI pump was running really rich, and two of the injectors were malfunctioning. Those have been replaced, and the MFI pump was replaced as well. Hmm, I wonder if the two cylinders that had the bad injectors are the ones that have the high leakdown numbers?

I am unsure of when the top-end may have been done, but it wasn't that recent. The compression numbers (when this test was done last fall) were in the 146 - 150 range, if I remember correctly, nothing unusual there.

I have been told that the car idles and runs smoothly and quietly. That it pulls well. I will find out for myself, when I get there tomorrow.

Thanks for the info.

larry

If a car had a couple of slightly bent valves, would it get normal compression readings?

Larry,

I would almost never recommend a top end without confirming data. Your equal compression test results makes me suspect the leak test. I would do some spirited highway driving and re-test (both cylinder leak and cranking compression asap – before your trip.

Has the oil been changed a couple of times in the past week? MFI 911s that sit in body shops are notorious for diluting the oil with gasoline. You don’t want to get out on the highway and find your gas-oil mixture evaporated and no lubricant. Check the oil level at every opportunity until you see the pattern of use. (I assume you know it must be hot and at idle for correct measurement.)

Another common issue is rust in the fuel tank. The symptoms here are the engine feels like it runs out of gas on the highway but runs OK after sitting for a while.

You are going to want to use the highest octane fuel you can find for a while. Until everything settles in, the extra oil consumption will reduce the octane of the mixture.

Remember, you will be essentially breaking in a new engine. You don't want to get stranded on I-80 in central Pennsylvania.

Best,
Grady

Larry,

FWIW, I don't think you can make any assumptions about your engine condition at this time ... as Grady has said! The verbage from the shop sounds like their attempt to empty your wallet rapidly!

A tech performing a proper leakdown test will find out where the leakage is happening as a diagnostic procedure ... not just write down the numbers and tell you what the 'bad news' is ...

Cylinders with high leakage can be left locked at TDC with the compressed air 'on' for several minutes while the tech listens at the air snorkel intake ... the exhaust tip ... the oil tank with cap off ... under the engine beneath the heat exchangers and individual cylinders, etc. in an attempt to locate the leak source. If this was not done ... the tech and shop don't have your best interest at heart and the veracity of their 'bad news' is in question! Procedural errors are possible during leakdown tests if the tech isn't careful and methodical ... and results obtained are completely untrustwothy!!!

<b>You don't even need a leakdown tester to investigate this reported problem yourself ... just an air compressor and air chuck adapter to spark plug threads ... the removeable hose on a compression gauge can be adapted and used. Turn the engine to TDC firing location on cylinders #2 and #6 and lock the emergency brake with transaxle in 5th gear and crank up the air compressor to a series of steps ... 25 - 30 psi. 50 psi, 75 psi and 100 psi ... and listen at all of the above locations for hissing leaks. </b>

Larry,

Hopefully you have a laptop with you. If you have questions, feel free to post them here or e-mail me directly at gradyclay@hotmail.com.

This Forum will keep you pointed in the right direction.

What is your planned route? There are fellow Pelicans in lots of places.

Best,
Grady

Back Home
 

I have gotten home with little problems - except for my lost alternator - Thanks to Rob Gordon for getting me back on the road.

Ref the Leakdown tests and how the car drives.

1. The cylinders with high leakdown numbers are different than the cylinders that Mike measured last fall. That makes either or both of the tests suspect.

2. Mike ran the car 50 miles or so and has changed the oil twice before giving me the car.

3. The car popped and backfired a bit when at idle, while I initially drove it. Under load, when warm, it ran like a champ. Gas mileage was about 12 - 13 mpg. Less than I expected.

4. After three tanks of gas on the highway, gas mileage suddenly was 15+ mpg - for 3 straight tankfuls. My guess is that something happened in the engine that was good.

5. At Tom Bridger's (Sithot) suggestion, I bought a bottle of some "Top end Lube and cleaner." He recommended a T-44 poduct, but I couldn't find it. Bought a product called Upper Cylinder Lubricant from Lucas Oil. After that tank, the car no longer backfired, only pops a bit now and then, and idles much much smoother.

6. I have now put 1,800 miles on the car in the past week. I plan on getting a valve adjustment, the MFI adjusted, and the timing verified. Then another leakdown test to set a standard for what it is running now.

Thanks for the advice. I am a very happy camper.

larry

Welcome home Larry! Glad you made it with minimal drama...now we want a full write up and showing!

Techron and drive the snot out of it.

Nice to hear you are home Larry, when can we see her in person!

Larry glad to hear you made it :cool:

Now we need a picture of you setting in the car with a recognizable landmark in the background and today’s news paper. ;)

Re: Back Home
 

Larry,

Sounds alot like what I see after I drive my car in "anger". It runs much better. They are like thorobreds. You need to let them run sometimes.

I hope I am able to get some road trips (sans the alternator problems :D) under my belt sometime in my future.

Be sure to try out some of the drivng events like Autocross or DE to get a better picture on what your car can truly do. You will be amazed.

Larry, you need to find an MFI expert near you, or become one yourself. It's not too hard to do, just spend a lot of time reading Check Measure and Adjust, the other MFI resources on PPBBS, and post lots of questions here. If you live close to Souk, make fun of him for being too much of a weenie to learn about the joys of MFI, and maybe he'll learn enough about it to help you out. :p

I know what you mean, when I was with Souk and Chris a couple of weeks ago, I asked them about MFI, and their response was . . . . .

Carbs are easier to adjust.

So much for help in that arena. :rolleyes: I do wish they lived closer, though. Naperville seems about as far as Nashville sometimes with rush hour traffic!!!

larry

Hey! Jim, I could learn MFI faster than you can do one lap at Road America! When you come, I'll crack the manual open as you pit, by the type you come around once, I'll be able to ajust that MFI (mo-fo-idiot :) ) for you. OK? :D

I never had an occasion to play with MFI, and there was always other projects to deal withy...maybe I should just go buy an MFI car and learn...

Larry, I work Saturdays too!

Larry,

Jim is right on, you become a MFI “expert” in your own self defense. The more you know about how the system works, how to check components, how to measure the parameters, and how to adjust the system or communicate to a mechanic; the better for you and your 911.

I recommend you start your own personal, car specific, combination workshop manual, parts manual, MFI instructions, service info, clips from relevant posts, and photocopies of relevant parts of commercial books. It should be in digital form with a current paper printout. You can also include photos, invoices, etc. to have a scrapbook.

A good place to start is with the Porsche MFI CMA booklet:
“Check Measure Adjust” (CMA)
http://www.scatliff.mb.ca/pelican/MFI_Check_Measure_Adjust.pdf

It is worthwhile to go through all these threads and then clip or summarize for your 911.

“MFI thermostat spacers”
p. 1 end has CMA extension, p. 3 has nozzle, fuel flow, and fuel pressure.
http://forums.pelicanparts.com/porsche-911-technical-forum/169445-mfi-thermostat-spacers.html

“More Fun with MFI and LM1”
How to use protractors for correlation.
http://forums.pelicanparts.com/porsche-911-technical-forum/179707-more-fun-mfi-lm-1-a.html

“MFI Problems”
http://forums.pelicanparts.com/porsche-911-technical-forum/173700-mfi-problems.html
“MFI Speed Switch”
http://forums.pelicanparts.com/porsche-911-technical-forum/160057-mfi-fuel-shut-off-solenoid-questions.html
MFI tools
http://forums.pelicanparts.com/porsche-911-technical-forum/170242-mfi-tools-diyer.html

“Mechanical Fuel Injection” site with OK stuff:
http://www.my930.com/MFI/TipMFI.htm


I’m glad you got home OK. I’m always cautious and apply the “An ounce of prevention is worth ….” philosophy.

Best,
Grady