rattlsnak

I called two places today (dealer and independant) to get a leak down done for a PPI on my car I'm selling and both places denied me and told me its a waste of money. "The car is OBDII, if there was something wrong, the check engine light would be on." I guess I never thought of it that way, but they are right to a point. Im sure a cylinder could be getting close to high leak down percentages and still not have a CEL on. What do you guys think?

Robin 993DX

Well.. A compression test is what you should request for.

Leak down test is mainly for finding exactly where the problem is when you find a cylinder with low compression.

rattlsnak

I agree, but this is the request of the buyer. In reading my PMs and emails and a lot of threads, it seems that a leak down test is the preferred test among buyers, I just never thought about it much from an OBDII perspective. Of couse if I mention it, it will loook like I'm just hiding something, or not wanting to get it done.

Geoffrey

You want a leakdown test, not a compression test. The leakdown test will give you an idea of the health of an engine. This is particularly important on the 993 where the exhaust valves pit easily and lose their seat concentricity and begin to leak. OBD2 will not tell you mechanically that anything is wrong, it will only look at the symptom of a problem. ie CEL for SAI port BECAUSE the valve guides are worn and leaking, plugging the ports.

amfp

Unless you knew the previous owner and car from new, I would get a leakdown and compression test. It is cheap insurance especially if did not know how car was driven and maintained in the past.

J.PELLEGRINO

A leak down test is far more informative than compression test. I strongly recommend having one done by any perspective 911 buyer. Its a bit time consuming on a 993, so that may explain the service facility's
reluctance to do it. I would fine someone that will.

Good luck, Jerry

viperbob

Yeah, what he said... Nice to see you posting Jerry. Also good to talk with you this week. Hopefully I will see you at least at the Glen in June or July....

rattlsnak

So which one would occur first on a OBDII car? A CEL or bad leak down readings? In otherwords could a bad leak down catch a potetntial problem that OBDII hasnt recognized yet? I know OBDII is highly sensative. I think that is their point. I completely agree with pre OBDII cars.

And what is considered good/ bad readings?

J.PELLEGRINO

A good leak down done correctly will expose engine issues before the same engine begins to misfire. It is the presence of misfires that will usually trigger the dreaded CEL. As for what is a good vs bad leakdown result can vary depending on many factors. We generally want to see leak down numbers under 10% but more importantly, the results should be fairly consistent from one cylinder to the next.

Happy motoring, Jerry

H2NO

The shop that did the PPI on my 3.2 said the leakdown was a waste. I deferred to Peter Zimmerman and demanded it.