I have a diesel engine comp tester with 2 options, taking a test through the glow plug hole or the injector hole. My question is which is better or is there any difference/benefit to either from others experience.

big discussion on this


I would go through the glow plug hole because you do not have to remove the injectors and then replace the heat shields. Even though with the glow plug removed you have a different volume than before, its a negligible volume.

Th is kinda what I thought and this makes sense to me! Thanks.

Or take the opportunity to replace the shields, check the injector pop and pattern, and use the injector holes.

I found it easier to just go in from above, rather than fighting to get the glow plugs out of the side of the head, but that was just my take on it.

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-Josh
Testing the cheap Mercedes axiom, one bolt at a time...

Wll, I ended up doing both! I took the glow plugs out and damn, the comp test guage adapter wont fit into it! However, one of my glow plugs died and I found that out after I jumped all of them one at a time to the battery so this was worth it. Feeling like it was hard to start and ran unevenly for the first few seconds was why I was doing a compression check in the first place!

But through the injector holes I'm getting between 218 PSI to 225 PSI which is fairly even and consistent. I'm just planning to get a good engine and rebuild it and have it ready when this one gets really tired. Right now it runs great!

do a valve adjustment and then retake the compression test. Maybe even a valve stem job as well

If those are cold numbers, I think that's actually pretty good, and like you said, consistent. So, happy motoring!

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1998 E300D, 287k, barely broken in.