Need Definitive OM617 Compression Test Procedure - PeachParts Mercedes-Benz Forum

warmblood58 · #1 03-05-2010, 12:49 PM

Just purchased the Harbor Freight kit and wish to test compression and will use GP holes but need a good procedure from one who has done this the right way. Valves were just adjusted -anyone? Thanks!

toomany MBZ · #2 03-05-2010, 01:04 PM

This is from a different compression test kit.

lietuviai · #3 03-05-2010, 01:08 PM

It needs to be done on a fully warmed up engine.

Biodiesel300TD · #4 03-05-2010, 01:28 PM

Your harbor frieght compression tester is meant to be used through the injectors holes on the 617 engines. Not sure there is an adapter in the kit that will allow you to go through the GP hole. I have the same kit.

There is some arguement wether it's better to test compression on a cold or hot engine. To me the compression on a cold engine is far more important than that of a hot engine. A hot diesel is much easier to start, even with pretty poor compression. A cold engine with poor compression is much harder to start or won't start. A hot reading will give you a more acurate reading of what the compression is when the car is warm and running, but the cold compression will tell you what you are dealing with when you go to start the car in the morning.

As for doing the test. You screw the adapter in. Plug in the gauge, and crank the engine and watch the gauge go up until it stops going up. And thats your compression. If you do go through the GP holes you'll need to remove the injector lines or wire the stop lever down, to keep the engine from starting. Also if you take all the GPs out you'll reduce the draw on the battery and starter, because it won't be fighting the compression of the other cylinders to turn over.

tr1cky · #5 03-05-2010, 01:42 PM

Quote:

Originally Posted by toomany MBZ

This is from a different compression test kit.

I think HF needs some help with their technical writing and editing.

"compression text"

whunter · #6 03-05-2010, 01:47 PM

Quote:

Originally Posted by warmblood58

Just purchased the Harbor Freight kit and wish to test compression and will use GP holes but need a good procedure from one who has done this the right way. Valves were just adjusted -anyone? Thanks!

PROCEDURES FOR: COMPRESSION AND LEAKAGE TESTING
http://cust.educ.ubc.ca/wstudents/tsed/Students06/cdemers/PROCEDURE%20FOR%20COMPRESSION%20TESTING.doc

andrewjtx · #7 03-05-2010, 01:50 PM

Quote:

Originally Posted by tr1cky

I think HF needs some help with their technical writing and editing.

"compression text"

That's what happens when you have 8yr olds in China writing the documentation to go with the part that his 9yr old brother built...

warmblood58 · #8 03-05-2010, 01:53 PM

Quote:

Originally Posted by whunter

PROCEDURES FOR: COMPRESSION AND LEAKAGE TESTING
http://cust.educ.ubc.ca/wstudents/tsed/Students06/cdemers/PROCEDURE%20FOR%20COMPRESSION%20TESTING.doc

Good information, thanks but seems specific to gassers. I was hoping that someone had the actual FSM for the OM617 motor -thanks!

Biodiesel300TD · #9 03-05-2010, 02:13 PM

It's not a difficult task. Its going to be the same for any vehicle wether its gas or diesel. Disconnect the fuel supply. Remove the spark plug, glow plug, or injector(depending on you the fitting you have). Plug in your gauge, and crank the engine over several times until the gauge stops going up. Mark down the value and move to the next cylinder.

lietuviai · #10 03-05-2010, 02:24 PM

The FSM suggests doing it on a fully warmed up engine. That info is straight from the people that designed the engine. Doing a test on a cold engine will not accurately diagnose any engine problems. An engine is only cold for a short period of time. Most of the driving is done with the engine at full operating temperature. Does it make any sense to run tests on a cold engine if most issues occur when the engine is fully warmed up?
BTW, I wouldn't trust any tool from HF to accurately test anything. I'd bet their gauge would be off +/- at higher readings compared to a true professional gauge.

Biodiesel300TD · #11 03-05-2010, 02:46 PM

Quote:

Originally Posted by lietuviai

The FSM suggests doing it on a fully warmed up engine. That info is straight from the people that designed the engine. Doing a test on a cold engine will not accurately diagnose any engine problems. An engine is only cold for a short period of time. Most of the driving is done with the engine at full operating temperature. Does it make any sense to run tests on a cold engine if most issues occur when the engine is fully warmed up?
BTW, I wouldn't trust any tool from HF to accurately test anything. I'd bet their gauge would be off +/- at higher readings compared to a true professional gauge.

DJ, I'm not picking on you bro, just the concept.

I know thats what is suggested, it's because everything warms up expands, and seals up, which will give you higher compression, and a better picture of what's going on with a running issue. Which is important.

But I ask why then, when we all go look at a potential purchase of our beloved diesel cars, do we want to start it cold. Beacuse it tells you how good the compression is. If it fires right off on a blustery cold day, you know you've got a tight engine, if it takes some doing to get is started you know the engine is getting a little tired. And why is is getting tired, amongst other things, compression.

I guess it comes down to what you're trying to diagnose. Cold starting and cold running issues, then I'd suggest a cold compression test. Warm running issues, then a warm compression test.

toomany MBZ · #12 03-05-2010, 02:49 PM

Quote:

Originally Posted by tr1cky

I think HF needs some help with their technical writing and editing.

"compression text"

Maybe, that is a U.S. General tester, made in China, of course.

rrgrassi · #13 03-05-2010, 06:08 PM

Remove all the GP's or injectors to do the test, that way the is no pressure build up on the other cylinders. It also prevents a "cross reading" from a bad head gasket. Our shop teacher in HS preached that on every compression test we did.

lietuviai · #14 03-05-2010, 07:59 PM

Quote:

Originally Posted by Biodiesel300TD

DJ, I'm not picking on you bro, just the concept.

Sorry Andrew, I didn't realize it was your post. Didn't mean to bust your cajones on the subject. You bring up a valid point.

vstech · #15 03-05-2010, 10:36 PM

the HF kit I got did indeed come with fittings for the glow plugs on my car... of course it was the large body glow plugs I was testing...

and the 617 procedure I used was:
1 remove all glow plugs, injector lines, and accelerator linkage.
2 wire the IP in the full STOP position.
3 connect the fitting to the glow plug hole and connect the tester.
4 Crank the engine until the pressure stops rising.
5 bleed off the pressure, and remove tester and fittings, move to the next hole.
repeat.

I found it impossible to get the fitting on with the injector lines in place.
my car kept squirting fuel out the IP, so I put the lines back on the IP, and swung them out of my way. prepare for a mess of diesel fuel. the stop lever must prevent pressure build up, but I still got a fair amount of fuel squirting.