Got the PPI done, what do the numbers mean?

willtel · 04-02-2008, 10:43 AM

I have just read over the results of a PPI on an '87 930 I am considering and I have a few questions about the leakdown numbers I received. The car has acceptable compression on all cylinders but the leakdown on the #6 cylinder came back at 17% while the rest of the cylinders show a 4% leakdown.

I know these numbers tell of impending issues and will require at least a top end rebuild to correct (the shop says it appears to be leaking from the rings) but is there any way to guess how much time\mileage will pass before the engine has to be dropped? I don't own a Porsche yet so my experience with these cars is limited to my research, any opinions from the experts? Thanks.

jwernquist · 04-02-2008, 10:58 AM

Well the shop is probably right, the car may run fine but it is probably burning some oil, etc. If the price is right it gives you a good negotiating point, however it could require a top-end rebuild and a re-ring in the near future. That could run you between 4-6 grand! No real way to guess. It could run fine and not burn too much oil for many years or it may need attention right away.

Tell the owner to knock 5 grand off the asking price due to the issue put the money in a bank account and drive it until you need to tear it down!

How did the rest of the PPI come out?

willtel · 04-02-2008, 11:19 AM

The tech had similar things to say. "Some go years with these numbers and some will start eating oil and running poorly weeks after diagnosis."

These are the notes from the PPI. Most of these items seem acceptable for a 21 year old sports car that is driven on occasion. I'm not looking to buy a concours winner and I plan to make the car a driver.

Prepurchase Inspection- Leakdown on all cylinders 4% except #6 which is @ 17%.

Body- Small paint repair front bumper, missing rubber cover for door ground switches, door seals have small tears, front hood struts bad, trunk & engine compartment light not working, Rocker panel has slight damage on left side, hard oil line partially crushed at jack point. Air pump missing for spare tire, needs front wiper blades replaced.

Engine runs strong, air pump gear missing teeth, could use air pump belt, oil cooler line starting to leak at front oil cooler.

Suspension- has vibration in steering wheel at speed, front tires wearing inside edge- suggest getting alignment checked.

jwernquist · 04-02-2008, 11:25 AM

Well with their Engine runs strong comment is a good sign, lots of little things that can either be right up your ally or a nightmare. It sounds like a decent grounds for a good project. If the price is right buy it fix the little items and enjoy it until you need to do some engine work. My SC has a slight vibration as well, and it turned out to be the alignment and a poorly balanced tire, both fixed for 60 bucks.

Oil line can be fixed as long as its not restricting to much flow isnt really a big deal . Everything sounds fairly minor outside the leakdown.

If the price is right and you have enough left over in case that rebuild comes sooner than later, your getting a pretty standard as you said 21 year old car.

Give him 15k for it

then run as quick as possible. You have a good negotiating point call a couple shops get an estimate for the top-end rebuild and re-ring, and make him an offer that works. WHo knows mabey you will get a bunch of trouble free years out of it!

JW

tonythetarga · 04-02-2008, 12:28 PM

I'd be inclined to retest that cylinder to veryify it is, in fact 17%. Make sure the leak down is done on a warm engine.

Thack · Thack's Garage

Could be sticky rings. Put some Marvel Mystery oil in the cylinder and let it soak all night after you buy it.

cgarr · cgarr's Garage

You should be able to hear where the air is leaking from, intake, exhaust or rings, If its the rings you can rock the engine back and forth just a bit with a big bar during the test and you may see the numbers change.

equality72521 · 04-02-2008, 01:20 PM

How much difference in numbers can one expect when doing a leak down on a cold engine?

coollx · 04-02-2008, 06:02 PM

I agree with tonythetarga that you should have the low cylinder checked again.

Based on my limited experience, if the compression test is good and shows all cylinders pretty even, the leakdown should also show all cylinders pretty even.

In fact, a lot of good shops I spoke with about doing a leakdown test during the PPI of my car said it only makes sense to spend the extra time and money to do a leakdown if the compression test shows low cylinders.

Additionally, I don't think 17% in one cylinder is horrible and will require immediate attention.

muis · 04:11 AM

Do have the cylinder checked again.
I just bought my '89 after the PPI showed a leakdown of 50% (!) on cylinder 1, while the other cylinders were well under 10%. The seller was surprised by the bad cylinder, as he thought his baby was perfect at 73k miles. But he agreed to split the cost of a rebuilt by taking money of the asking price. Once the car was back at my mechanic, I had another leakdown test done. Everything came up smelling like roses; cylinder 1 is just fine.

Ditto on the 17%. Not good if it's true, but it doesn't require immediate action.

Also, read this: http://www.pelicanparts.com/techarticles/mult_Engine_Rebuild/mult_engine_rebuild-2.htm