Originally Posted by ah-kay (Post 3613962)

Doing a compression test on a gas car is more straight forward then a diesel. No heat shield to replace ( unless it is done from the GP hole ), no injector line to remove etc. it is a 15 minutes job compared to a 1+ hr job. Some V6 front wheel drive may take longer. if I were the seller, I would decline. If I were the buyer then I will look for tell tale signs and take my chances.

Originally Posted by leathermang (Post 3614026)

So you are measuring the load on the starter ?

Originally Posted by 97 SL320 (Post 3614075)

Measuring load of starter on battery. Can pick large pos or neg wire near battery for easy access, no need to get near starter. The key is to record data in strip chart form so it can be viewed.

Originally Posted by 97 SL320 (Post 3613985)

To expand on the low end buyer. If someone comes to me says the right things and has the proper attitude, I'll make sure the down on their luck person gets the best value.

It's the "I gots no money because I have poor planning skills" person I avoid. Typical signs are lotto scratchers in the car , smokes / chews , has anything more than a basic cell phone, the "I should not have to work for anything because the world owes me" attitude.

There is a way to do a non invasive compression balance test. Place a clamp on amp meter attached to a recording oscilloscope on the battery cable and crank the engine. You should see a current spike for each compression stroke. On a 5 cyl if you see a low spike every 5th place, there is a cylinder with lower compression than the other ones. This won't tell you how low however.

Originally Posted by funola (Post 3614105)

That is a cool trick! Where did you hear about it and do you have a pic of a storage scope waveform you can show us? I picked up a storage scope recently and will give it a try sometime.

Originally Posted by ah-kay (Post 3614130)

It is a trick to check for consistency ONLY. It does not tell you much. It does not tell you which cylinder unless you rotate the engine to compress at a pre-defined cyl, say #1. It does not tell you compression numbers, if low, how low or how high? The equipment is expensive. The low compression could be due to valve adjustment so there are still a lot of unknowns. Just fire up the engine and do the simple checks.

Originally Posted by ah-kay (Post 3614130)

It is a trick to check for consistency ONLY. It does not tell you much. It does not tell you which cylinder unless you rotate the engine to compress at a pre-defined cyl, say #1. It does not tell you compression numbers, if low, how low or how high? The equipment is expensive. The low compression could be due to valve adjustment so there are still a lot of unknowns. Just fire up the engine and do the simple checks.

Originally Posted by funola (Post 3614144)

If the engine starts within a quarter rev of the starter and not having to crank it for 30 sec, you can assume it has good compression. If the test can accurately discern uneven compression in cylinders, that is a goldmine of information for a in the field non invasive test that is quick and easy. It would determine for me a buy or no buy.

Originally Posted by ah-kay (Post 3614130)

It is a trick to check for consistency ONLY. It does not tell you much. It does not tell you which cylinder unless you rotate the engine to compress at a pre-defined cyl, say #1. It does not tell you compression numbers, if low, how low or how high? The equipment is expensive. The low compression could be due to valve adjustment so there are still a lot of unknowns. Just fire up the engine and do the simple checks.

Originally Posted by funola (Post 3614105)

That is a cool trick! Where did you hear about it and do you have a pic of a storage scope waveform you can show us? I picked up a storage scope recently and will give it a try sometime.