Compression Test question

[bmiszuk]

On gas engines I've always done a compression test with 4-5 puffs of the engine. Last night I started checking the 6.2 and I found that compression would continue to build up until 7, 8 or 9 puffs. Should I keep cranking until the guage doesn't go any higher or should I stop after a certain amount of puffs?

And how important is it that the engine be hot? Pulling glow plugs from a hot engine is no fun but if I have to, I have to.

So far, the driver's side compression were all 370-380 after 5-6 puffs, except #1 which I cranked longer and was able to get up to 450. Hopefully I check the passenger side this evening.

Thanks.

Bob

[Robyn]

Cold is fine
You need to do it about 5 puffs and look for similarity of pressure.
If you are getting 360-390 on all cylinders your fine. Its when you see a low one , say 290 in there that you need to worry. If they are all close and up in the mid to high 300's your good to go.
Robyn

[DmaxMaverick]

The official procedure....

Hot engine. At or near operating temp.

All glowplugs out.

6 puffs each.

Highest/lowest cylinders should be within 15%. If the spread is more, you'll have to look at the actual cylinder numbers and values. Any value over 300 will be a good cylinder, but too much of a spread will cause rough running, and accessory problems. Worst case could cause a broken crank and/or cracked main webs.

NEVER add oil to the cylinders, like you might with a gasser. Disaster will follow.

[bmiszuk]

Got compression test completed, from front to back I have:
driver's side: 400, 380, 385, 380
passenger side: 350, 385, 375, 350

Any problems there? The previous owner said he had to replace one cracked piston, and she smokes from the right side a little more than the left. But these are a lot better than I expected!

I think it's time to put a fresh set of injectors in like Robyn suggested and see if that perks things up a bit. Power is way down.

[DmaxMaverick]

Those numbers look OK. All but 2 are within 10%, and 2 are within 15%. Not out of the park, so to speak. I wouldn't be concerned about it, as your error range is also a factor. The differences you are seeing won't likely cause any noticeable running issues.