kennyPride

Is a Porsche Indy blowing smoke? I'm searching for an Indy to perform a PPI on a 996. This is the second shop telling/advising that a leak down test is not necessary as a diagnostic / adaptation screening will tell them how solid the engine is (ie valves, rings, head gasket). Is there any truth to this? How does the adaptation screening work and is it reliable into as to the health of the engine?

EastBay

In general automotive terms, it is a pretty marginal practice on water cooled motors unless the motor exhibits elusive symptoms.

kennyPride

I just don't understand why an Indy would recommend not doing more work ($$$)?

fpena944

Might be trying to build your trust. So when you do come back with a big job there won't be any questions asked on your part when he gives you the quote.

Macster

First a leak down test is generally reserved for use when a compression has revealed a compression problem, a low compression reading in one or more cylinders. A leak down test is then used to help identify the possible cause of the compression reading.

A compression test is used to at least verify the engine can generate/build compression in all cylinders equally to within some number. I don't recall now what the number is -- it varies from engine to engine -- but the compression wants to be above a certain threshold and all cylinders want to be within some percentage or PSI of each other.

I've asked some senior Porsche techs about the use of compression testing as part of a PPI and have been told compression testing is not necessary.

The engine controller constantly monitors the output of each cylinder every power stroke by measuring the acceleration imparted to the flywheel from each cylinder's power stroke.

If the output varies by too much -- too little (weak cylinder) or too much (strong(er) than normal cylinder) -- the engine controller will set a misfire error code (or codes) and turn on the check engine light, maybe even flash it.

What you want to do is when you view a car to ensure the check engine light bulb comes on when you turn the key to the on position and that it goes out when the engine starts. The CEL and all other warning lights.

Then you let the engine warm up at idle while you give a listen and just walk around the car.

After the engine has idled a bit and the cold idle speed has dropped and the engine is idling near normal and there were no untoward behavior during this time, go for a test ride. Yes, ride.

Insist the ride cover around 15 miles and cover a variety of driving scenarios from city/stop/go driving to high way driving. Have the driver demo the car's ability to accelerate smoothly from near idle to near red line in several gears. No need to have the driver beat on the car or the engine or risk life/limb but you want to concentrate on how the engine runs.

Keep chitchat to a minimum. Listen to the engine. Concentrate on the engine's sound, how it feels. Close your eyes to bring more focus to bear. You're not out to see the sights or enjoy what the driver has to say (unless you can get him to brag about his track exploits in this car...).

When you return to the starting point, continue to let the engine idle and check for fluid leaks, smell for anti-freeze, and make sure entgine is still quiet.

Next you take car for a test drive and follow the same route. Drive the car in much the same way as the driver before you. If car equipped with an oil pressure gage pay attention to its reading at idle and through the rpms. With engine hot the reading wants to be 1bar or higher -- 1.5bar to nearly 2.0bar (depends somewhat on what the ambient tempreature is) -- at hot idle and 4.5 bar or higher at 3K rpms and higher once engine fully warmed up.

You want to give the engine controller time detect any misfires or other problems and set the check engine light on.

You can have a compression test done: Your money; but you still want to do the above to make sure the engine's ok, as best you can given the access you have to the car and the engine.

In short the engine's natural state is to run. Run it and run it long enough to if there are any engine problems currently present -- and this includes cylinders weak enough to trip misfire error codes -- the engine controller can detect these and notify you of their presence.

Plus you get to feel how the engine runs, listen to it, after it is nice and warm.

Sincerely,

Macster.

ivangene

Nicely said

I will add that I did not do leakdown on the 996 and normaly my shop says not needed unless there is a reason (ie a computer fault code)
second when refering to the "smell for anti-freeze" comment, be aware that Porsche's smell when driven (esp with spirit) That is mostly cosmoline and the "regular" motor smell is something it takes a few times to become aquainted with (at which point you will miss it/want it/need it) but dont be missled by a "funny smell" - antifreeze is sweet and you can almost taste it when you smell it

kennyPride

A PPI is always recommended, but if no CEL, then aside from checking the tires/brakes/unibody damage/switches/gauges/why have it done? Are stage I and stage II revs all that is important if I don't have a durametric reader? Am I reading a move towards putting a critical eye and ear to the car and a thorough check of the service records can accomplish what a Indy would do?

stuckinkuwait

KennyPride, I just purchased a 996 2 months ago and I had a PPI performed by a Porsche dealer. He also told me that they do not do a leak down test on Porsches. the dealer also said that if there was a problem, you would know right away since the car would run like crap. I asked the question of the dealer because when I bought my Ferrari 4 years ago, a leak down/compression test was performed. On a Ferrari, if you have issues with your heads, it could be a $10-$15K repair bill. Hope this helps.

stuckinkuwait

Forgot to add - the dealer used a checklist to do their PPI and it cost about $150 vs $600 for the Ferrari.

nick49

I agree a leakdown test is not necessary but it's your dime. I'd imagine it would be fairly expensive to do on a 996. On a race motorif a problem occured, it could help to pinpoint a problem before a teardown, but with modern electronics a weak cylinder can be found in other ways.

Re a PPI, those that work on cars for a living see beyond the shiny paint and all the add-on crap that cause prospective buyers to go into an emotional frenzy. They will not be in denial regarding simple mechanical, visual and other issues often overlooked.

Macster

Well, there are PPIs and there are PPIs. Recently one Boxster shopper had a candidate car PPId and his mechanic removed the oil filter housing and spotted some signs of metal in the oil. The oil was fresh too whch means the metal appeared since the last oil change.

The shopper wisely chose to give this car a miss. Car was on a dealer's lot too, IIRC.

If one is very very confident in his ability to evaluate a used car and in particular the model he's considering, and is willing and able to go to the lengths necessary to learn about car, information about the car's condition that a PPI would also provide then a PPI not necessary, at least not by another person. A readout of the overrev counts very critical though and one must either be able to do this or have it done as close to when he buys the car as possible.

Also, the absence of CEL is not 100% proof there is no problem. The CEL can have been cleared on purpose with a code reader or by accident in the seller replacing a weak battery. A test drive is required and of sufficient duraton and content to give the engine controller every chance to set the CEL.

But a PPI, a thorough PPI, whether done by the potentional buyer or done at his request by a professional, is a very good idea. Some (more than a few) have managed to buy good cars absent a PPI but not everyone is capable or has the time to do a good PPI on is own. And frankly not everyone has the same luck.

A PPI should only be done once though. And this should be the car one ends up buying. If one is having cars PPI'd only to have them rejected or being unable to work out a purchase then this person needs to work on his used car evaluation and used car buying skills.

Service records can only tell you so much. If the car has had one owner, or 2 or even many, if all the records are present and show the car received regular services, show other things taken care of, little things, then this strongly suggests the owner(s) loved the car and took reasonably good care of it.

But you still want to verify the car's current condition as best and thoroughly as you can.

And if the records are not all available, that the car received good care early on and but 3, 4, 5 or more years later, this counts for less than what the car's current condition is.

Sincerely,

Macster.

Barry Lenoble

Hello,

One more comment on this.

If I were selling a car, and you wanted to have a shop perform an inspection, I would ask what tests you planned on having the shop do. If you told me leak down and / or compression test I would not let you do it. What happens if the shop screws something up and damages MY car? They need to remove coil packs, spark plugs, etc. do perform the test. Who is going to pay if they break a coil, cross thread a plug, or do some other damage?

I would allow a shop to run diagnostic tests, examine brake pad and rotor thickness, check for oil leaks, and that sort of stuff. But when it comes to unbolting things (more complicated than a wheel, anyway,) I draw the line.

Same thing with test drives. I drive, you sit and pay attention. If you like the car and we make a deal, I get a deposit BEFORE you get to drive the car. You don't like it after the test drive? I give you back the deposit. You damage the car? I keep the deposit.

Barry

jrgordonsenior

Leak testing a 996 is actually quite simple if you remove the mufflers and shields...

A friend almost bought a really nice 3.4 car last week that ran well a month previous in a TT event. He had it leaked and it had a 90% leakdown in one cyclinder. They tried it hot, cold, and drove it around a bit but it still has a bad hole. I didn't ask if it threw any codes....

Macster

You raise good point about the extent you'd allow things to be unbolted from your car. I'd be a bit leery of just any old shop doing a PPI. And a compression test? Even leerier. In fact I would probably say no to a compression test. Within reason I would allow a thorough test drive. No way would I permit the test drive to violate traffic laws nor subject the car to harsher driving. For instance if a test driver thinks he's going to "test" my Turbo's awd system by smoking the rear tires he's got another think coming. Nor is he going to get a chance to "verify" the 0-60mph 4.2 second time either.

As for the deposit thing: If you can get a used car shopper to agree to a deal *before* he test drives your car and on top of this you can convince him to hand you a deposit -- even if you state it is refundable -- more power to you.

I'm afraid though you'd not get a "deal" from me before I test drove the car and you would certainly not get a deposit.

You could ask for a valid driver's license, proof of car insurance. I'd ask the same of you, at least proof of insurance. No way would I want to be the only deep pocket with car insurance in the car should something go wrong.

The test drive I was referring to would happen with the owner in the passenger seat. And the test ride sets the route and while I didn't say it the way the car is driven by the owner on the 1st pass over the test route sets the tone of the test drive. Frankly regardless how the owner drove the car I'd be pretty gentle with the car cause I wouldn't want to put the owner, me or the car at risk. It is during part throttle higher load conditions the misfire monitor would be more likely to be invoked anyway. Pedal to the metal mode lets the engine controller go open loop and enrichen the mixture and this can tend to mask problems.

Sincerely,

Macster.

johnsjmc

I agree the engine should throw a CEL if one cyl is weak. We used to call this a cylinder balance test and we did it by disconnecting one spark at a time and looking at rpm drop. Problem is it doesn,t indicate an evenly worn engine with all cylinders down.A condition sometimes found on high mile engines, a compression and leakdown would do that. I would not bother with a leakdown if the engine has under 75000 mi and no CEL.