RJB

I know that this is a very basic question - so please excuse my inexperience in this area.

Does anyone have a good procedure for performing a compression test of our cars? I have searched the forum and have found only limited information on this - most likely because it is so basic of a test. I want to do it right.

Thanks for your help.

944Targa-fan

Remove DME relay, fuse #34, spark plugs and move leads out of the way. Screw compression test meter in spark plug hole and crank the engine for 10 seconds. While cranking, fully depress the accelaror pedal. Now you can read the meter.

Don't forget to decompress the meter before removal.

Good luck.

billybones

It is important to note the compression gauge as the engine strokes.. Optimum is to have it near peak on the first stroke and make minimal movements upward the next three strokes. IF it continues to climb significantly after the first stroke. (ie. 90,105,120,150) There is problems. Watch and keep it recorded. After the initial test you need to put a teaspoon of oil into the cylinder and do the test again and note the results. If the end result is 10 psi higher then the dry run your rings are bad.. so sayeth the haynes... THe most important thing is continuity between the cylinders,, IT is better to have four cylinders at say 120 then three cylinders at 140 total and one at 90. Wore down is better then uneven.

EDIT: this is to be done on a warmed up engine.. Yes it makes a huge difference.. Rings do not seal till it is hot.. You run the risk of dammaging the threads on the plugs removing them warm. I crack them loose when cold. just a notch,

RJB

Thanks for your help with this very basic question! This group is the greatest!

Granite 944

Take a look at this link, it will give you a little more info to think about. Compression tests are a good start, leakdown test is the logical followup test if more info is needed. Link from 928 owners club.
http://www.928oc.org/tip/tip667.htm

Another informative link:
http://www.geocities.com/dsmgrrrl/FAQs/leakdown.htm

Another link (another not directly related to the 944) however informative.

http://www.geocities.com/dsmgrrrl/FAQs/compression.htm

I just went thru this with my car. I need rings real bad.

HTH