Diesel Compression Test - Mercedes-Benz Forum
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post #1 of 12 (permalink) Old 05-23-2006, 09:27 PM Thread Starter
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Question Diesel Compression Test

Doe any one have any good links on how to do a compression test? thanks
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post #2 of 12 (permalink) Old 05-23-2006, 10:17 PM
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What do you need to know?

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post #3 of 12 (permalink) Old 05-23-2006, 10:34 PM
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For all the OM 615/16/17 engines normal compression is 24 to 30 bar or 348 to 435 psi.
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post #4 of 12 (permalink) Old 05-24-2006, 09:49 AM Thread Starter
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What need to know is how and where to connect the compression test and what are acceptable reading?
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post #5 of 12 (permalink) Old 05-24-2006, 11:57 AM
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You need a special compression tester for diesel engines; standard gasoline engine testers don't go high enough. The proper tool should thread in place of the fuel injection nozzles and Jdc already stated the proper readings. However, any cylinder that reads more than 30-40 psi different from the rest has a problem. If you have low compression in any or all cylinders, you'll want to perform a leakdown test to determine the source of lost compression. What is the reason you want to check the compression: just for good measure, or do you suspect a problem?

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post #6 of 12 (permalink) Old 05-24-2006, 12:56 PM
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Harbor Freight sell diesel compression checkers for $20.

http://www.harborfreight.com/cpi/cta...emnumber=93644

Don't know anything about their accuracy or reliability, though.

Jamie

But then again, I could be wrong.........

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post #7 of 12 (permalink) Old 05-24-2006, 01:02 PM
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I was just looking at the compression testers when I was at the store this weekend, but I didn't see any for diesels. It's good to know they have one that's affordable.

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post #8 of 12 (permalink) Old 05-25-2006, 01:21 AM Thread Starter
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I'd like to test my car before I start puttting a lot of money into it, plus I have my eye on another one. I did see the copression testers at the store and hoped I could figure out how to use it.
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post #9 of 12 (permalink) Old 05-25-2006, 05:34 AM
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You can also test through the glow plug hole with the proper size adapter.
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post #10 of 12 (permalink) Old 05-25-2006, 06:57 PM
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Mercedes Source in Bellingham, WA has a compression tester with a bunch of fittings and a booklet on how to do a compression test for $72.00. www.mercedessource.com is their web url. I bought 1 but have not had the time to do the job yet. I should also have purchased their injection hose but I forgot to order it.

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