Number54

I was told by the dealer that leak down and compression testing aren't really worth it.

This clashes a bit with advice from rennlisters saying it should be done.

The dealer said that if something isn't right, they can tell from the diagnostics, and only maybe then would you want a comrpession/leak down test.

Is this true or not?

The PPI is around $350. Adding compression/leak down makes it about $1000.

Advice?

Thanks.

Mr Michael B

Whoa! $1000 for a PPI with leak test? Cripes, stealerships are not a great option.

mooty

a Bauer in oakland
pacific power in walnut creek

Macster

On a good day a leak down test can deliver untrustworthy results.

A compression test is old school.

I checked with a Porsche tech cause my old school experience was a compression test.

Tech pointed out each cylinder's performance -- its contribution to the total engine's output -- is tested every firing cycle by the Ecu measuring the acceleration or lack of it at the flywheel imparted by the cylinder which is current on its power stroke.

If the Ecu finds a cylinder performing out of spec, it registers one or more misfire error codes and sets the check engine light.

What you have to do is 1) Ensure the check engine light (and all other warnin lights) comes on when the key turned to on (to ensure the bulb's working and present); 2) Verify the check engine light goes out at engine start (along with all other warning lights); 3) Drive the car sufficiently from fully cold to fully up to temperature under a variety of operating conditions. Nothing extreme but without abusing the car and with the engine up to temperature verify it pulls strongly and smoothly all the way through the RPM range.

In fact, I have the owner drive the car and let him (or her) demo the engine and its acceleration just being sure various throttle levels used, the engine's subjected to various loads and near max. rpms are obtained.

At a PPI what you want besides the overrev counters retrieved is other OBD related info is the number of engine warmup since DTCs cleared. If this number very low perhaps the DTCs erased to try to "hide" a problem.

Then you want the distance traveled since DTCs cleared.

In fact there is I believe an OBD regulation that requires the reporting of the number of misfires detected during the current driving cycle and the average number of misfires detected during the last 10 driving cycles for each cylinder.

There is a specific ISO test ID number for this.

This test and the info stored can help a tech id which cylinders are currently misfiring and which cylinders have been consistently misfiring in the past.

If the number of misfires reaches some threshold then this is a warning flag that something's not right.

With a shop that has the proper diagnostic equipment and a tech that can use it all the info can be obtained to let you know the engine is not misfiring excessively, that misfires are very low, and all cylnders similar in this regard, that the check engine light has not been cleared recently and the engine's in fine health.

Sincerely,

Macster.

Porshapwr

^^Excellent info. Thank you.

Backmarker

Hey awesome data Mactser

I paid for a full leakdown/compression test when I bought my car. And even taking into account the great info posted above I would do it again.

Why?

Well with a $40k motor I want the most scrutiny possible. I felt a whole lot more comfortable justifying the purchase at home with the data in hand. Also I feel it set a baseline for me to compare to over the years.

Macster

A compression test is ok of course if one willing to go the expense.

My info is a leak down test really only used if compression test shows one or more cylinders down on compression. The leak down test is more a way of trying to ID the cause of the low compression to avoid full engine teardown if possible.

A problem is a leak down test can deliver a false postive or a false negative. Thus a bad engine could "pass" with flying colors or a good engine could "fail".

Bad enough to reject an otherwise perfectly fine car/engine if a leak down test incorrectly "fails" this engine but really bad to buy a good car with a sick engine cause a leak down test failed to flag the engine as sick.

A compression test is if one wants to have it done best. Leak down test pretty much a waste of money but if you feel it justified who am I to disagree.

Sincerely,

Macster.

Ahmet

I generally don't do a test beyond reading the ECU when buying a car. If the money/effort spent is trivial, or you think it buys you a piece of mind, there's nothing wrong with doing compression/leak down tests.

However, one's unlikely to find something clearly outside of spec, without accompanying run-ability issues/ECU codes.

AllanJ

Just curious, but do you have any examples of a leakdown test giving inaccurate results? At TDC if the valves are supposed to be closed, there really shouldn't be much leakage.

I can see how there could be a case where mostly leak-free static test at TDC could leave out other key info (false positive).

Didn't know that about the extensive ECU info. Thanks.

Just trying to learn....

Cheers,

Number54

You guys are killing me, I still don't know what to do...

For starters, I asked Stevens Creek Porsche to do a PPI. But I'm still considering taking the car to Jerry Woods for another check. If only I could get somebody on the phone - two days of trying and still haven't spoken to anyone beyond the receptionist

I'm still struggling to determine whether there's any point going to Jerry Woods. From this thread, a compression test may or may not be useful. And a leak down seems less important than a compression test.

@Macster: I asked the dealer about detecting when ECU errors were last cleared (engine starts, miles, time, whatever). They said there is no recording of that information...

996FLT6

22k mile motor? Owner says no tracktime? If ecu shows no type 2's- I don't believe u need to do all that stuff-compression/leakdown. Only thing is peace of mind. Is the problem that owner will pay for repair have ne link to motor itself or just anciliary? Because defective motor-$$$. Mike

SH || NC

^^^ I would tend to agree with Mike. With the reliability of these engines, I'd focus more on the Service History, and only pursue the more in depth tests if you suspect heavy track usage. GL

Number54

Yup, 22K mile motor, 2 owners. The seller says zero track time. He also presumes the previous owner was unlikely to have tracked the car. But that presumption was purely based on the "type of guy" he was.

Okay, I just received a call about the PPI as I way typing my response above...

The car was chipped. They don't know what kind of chip, and it seems the owner didn't know about it. The car was CPO'd from Carlsen Porsche, which doesn't seem possible without a grossly negligent inspection.

The downside is that the chip does all the engine management, but doesn't allow reporting diagnostics. So no type 1/2 info is available. Apparently it will cost around $2K to get the original "DME" put back. Only after that could they do the diagnostics.

This is getting me depressed, at this point I'm going to walk away unless the owner foots the bill for the DME replacement and follow-up diagnostics. Sounds fair right? I mean, it's Carlsen Porsche that should really pay the $2K since they CPO'd a chipped car.

Thanks.

SH || NC

It all sounds a little fishy to me. For a Porsche dealer to sell a CPO car with a chip, assuming it had the chip when they sold it, which would be difficult to prove. Also, this PPI dealer could also be looking to make a buck with the ‘chip’ story. Too many bad vibes for me. I’d keep looking.

Macster

ISO documents it. Document 15031, near or at page 147, Mode 1, Pid (Parameter ID) 21 (Hex), Distance Traveled While MIL is Activated. 2 byte value. 0km to 65535km. Reset to 0 when MIL state changes from deactivated to activated by this Ecu.

Then there is PID 30 (Hex). Number of Warmups since diagnostic trouble codes cleared. One byte value. 0 to 255. 1 warmup per count. Does not wrap.

Pid 31 (Hex). Distance since diagnostic trouble codes cleared. 2 byte value. 0km to 65535km. 1km per count. Does not wrap.

Porsche may have chosen not to implement it as per ISO spec. But I bet the info is in the Ecu probably behind some proprietary communication protocol (maybe not OBDII compliant) and some goofy messaging scheme. Next time I'm at my local Porsche I'll speak with the senior tech and see if can get any insight on this.

If data not available to you then you have to give the car a thorough going over and an extensive test ride and test drive, ideally back to back, to give the engine controller time to recognize any misfires. You should have an OBD code reader/data viewer with you that you can check and verify there are no active or pending DTCs. Also, you want to see all readiness monitors set to complete.

Sincerely,

Macster.