ironlung

Hello, long time reader first time poster,thanks for taking my call. I asked a reputble dealer fro a PPI on a future purchase. He said that a compression test is done if the tech determines one is neccessary during the test drive. Is this a standard across the country? Can a problem be hidden during test drive that a compression test would uncover. Thanks in advance, you guys know your stuff.

Curt911

I would do the compression test, but I would do the rest of the PPI first in case something else rules out the car before I spent the $$$...

SRL

If someone tells you that they can detect one cylinder lower on compression than the other 5 by the seat of their pants, they are either a liar or have the world's most sensitive ***.

Put it this way, if you could tell the motor has poor health just by driving it, you'd pass on the car before it ever came time to PPI.

ironlung

thanks for the back up, if PPI turns up nothing serious I'll soon join the club of smiling Porsche owers. red/blk 88 coupe. One area of concern is the A/C has a leak. CO's mechanic says that it is a seal on the codenser, called my local guy who has not seen the car and he said it was more likely the hose. Any thoughts on this and is this common.

Peter Zimmermann

iron: No tech I've ever met could test drive a car and tell you if "a compression check might be necessary..." Sheeesh... Please read my thread that heads up this post - you certainly want a leakdown test. Also, I've outlined a sensible procedure to do the PPI...
Pete

imcarthur

As above, but . . .

I went thru 3 PPIs along the search path & learned that the mechanic should do the compression & leakdown first. To me if it fails here you walk. If you have him spend the first hour doing Peter's 1 - 24 (see sticky), then it fails, you've thrown away an hour of his time & your money to pay for it. So, I would say do the compression & leakdown first. That way you're only out $75 - $100 or so if you do leave empty-handed.

FWIW

Ian

Pete: Great PPI list.

Bill Gregory

If you haven't already, you may want to read the just posted PPI article at the top of the 911 forum. I like to have both a compression and leak down done. Relative compressions don't tell you much, but cylinder to cylinder is informative. Leak down, done by someone who knows what they are doing, can tell much about the inside of an engine.

Peter Zimmermann

Hi Ian: Like I said, what works for me won't be right for everybody. I've always placed accident damage (bent frame, etc.) that lives on after repairs were done more important than an engine problem. For me, to re-repair a 911 with frame damage not only is extremely costly, the availability of craftsmen that can carry out the procedure are far fewer than there are techs who can rebuild a 911 engine. I've done a number of serious accident repairs with Brace's Auto Body in Marina Del Rey. He is the finest craftsman that I've ever met, and his accident repairs equal that of original factory construction. While doing numerous cars with damage in the $20-30K range I learned about the dedication required to do what Brace does - it's truly extraordinary. I'm sure that many techs are out there that can put together a fairly nice 911 engine, but I'm not sure that many Braces exist! It is so wonderful to be able to put a just repaired 911 on the hoist, re-install its engine and trans and have the four mounting bolts just drop through their holes, which is something that I can't say about projects that I've done with an array of other body shops. That's my perspective... and it's probably founded in my fear of body work, where I have no fear of things mechanical. Ah, life's experiences...
Cheers!
Pete

imcarthur

As you say Pete, we all have differing perspectives. All the cars I looked at were 'accident free' per PO's & CarFax (I know, I know neither can really be trusted). So, that was lower on my radar & I trusted the wrench to assess. Not being a mechanic & faced with my determined self-wrenching attitude the state of the engine was more important.

The first 911 I almost bought, I saw for the first time at the mechanic in Houston. I had talked to the owner & a Pelican had kindly driven & inspected the car. It was great. So I flew in expecting to own it. The mechanic called after I had dropped the PO at work & said he had bad news. Leakdown & compression on 2 cylinders. 55%/110 & 50%/120 vs 0%/140-145. And getting back to the point of the thread - the mechanic drove it before his tests & said it was great. Just like the Pelican said. So much for driving determining whether it 'needs' a compression test.

Ian

Dan Cobb

I'd suggest that you consider the following approach:
I am assuming that you have already scrutinized the vehicles in question prior to even considering a PPI.
A shiny car that doesn't run is just a hunk of metal, but a solid mechanical car can look like anytihng less.
If there are no "warning signs" or "red flags" with respect to body/undercarriage/etc. damage & the interior and paint are at least 7 of 10, then pay him to do the engine checks first.
If you have ANY reasonable concern about hidden accident damage, have him look there first, then do the engine work.

This way you are covered best for both cases without sacrificing the other.
+++

BTW, EXCELLENT mechanic that can determine the need for a compression test without having done one first.

ironlung

Ok, great advice from the many who have been there and done that. I will proceed with caution and request both leakdown and compression along with the walk around. 400 spent here can avoid 4000 spent later. Thanks again and I'll keep ya'll posted.

Curt911

I guess what I was saying, and most places I have used, the compression test (with leak down of course) usually runs more than the PPI, so I would go with that first to spend less money if something other than engine compression was at issue that might make you not want the car. If your familiar with these cars and can get a good idea of it by doing your own walk-around, then yes, I may just do the compression test first if everything looked good to you. If a $5000 problem would keep you from doing the deal then the motor is not the only concern, trans, clutch, brakes, electical, hidden body damage could easily rack up big bucks, so if the PPI is less than the C/T...I'd rather spend the least amount first!

DustinTarditi

I've spoken to 4 shops (3 local to me, one out-of-state) and they all related a similar policy that the PPI service did not include compression/leakdown - this was extra.

A few of the techs I spoke with said that many times the PPI reveals something that is enough of a dealbreaker for the buyers in question than the engine test(s) were not needed. They also said that often (at the buyer's request) the additional tests are skipped if the buyer feels comfortable with the results of the PPI - quite a gamble I think. The cost of the test is only a couple fill-ups of gasoline in cost... could save on a costly repair.

I feel that if a PPI turned up good results it is still worth it to pony up the $75 or $100 for the engine test(s) to REALLY know what one is dealing with - cheap peace of mind, IMHO.

Grady Clay

You have some good advice here.

Many shops will look at a 911 first for no charge. Ten minutes can rule in or out a car. There is no substitute for some skilled and experienced eyes.

I agree with the above priorities for a comprehensive PPI:
1) Previous crash damage & repair.
2) Rust damage.
3) Overall condition from a visual perspective. Is everything there and in reasonably serviceable condition.
4) Mechanical inspection, certainly including cranking compression test and cylinder leak test.
5) What to expect? A good PPI will also give you a clue to the things that have to be attended to right now, things that will probably need service soon, and the “it would be nice” category. Of course there are all the up-date and performance mods that you want to know about in advance.

Any competent shop will stop spending your money if they find a deal breaker.

Best,
Grady

mobilewrks

on my ppi as a mobile mechanic,i always do a leak down...compression gives you a ball park,leak down lets you know how dirty they might be. if the guy selling it seems hesitated DONT BUY IT !!!!!