N52 compression numbers: Help me decipher

r3vmatch · 05-21-2023, 07:02 PM

All,

I'm trying to troubleshoot a rough idle(+/- 10 RPM) low RPM performance loss on an N52/2006/70K miles. Symptoms include soot on tail pipe, so I thought replace DISAs, CCV and breather hoses (all look to be 2006 original). Decided to compression test before throwing a bunch of $$ at the car.

Are these numbers worrying? Specifically that the hot / cold PSI are close to each other? Edit: Re-ran on #5 & 6 cold and all the cold numbers are in line with each other.

Numbers hot[PSI]: 218.0, 221.0, 218.0, 219.5, 224.0, 218.5
Numbers cold[PSI]: 219.5, 225.5, 221.0, 223.0, 215.0, 211.5

Notes:

Idled car up for 15 mins, temp gauge in middle to do "warm" test. Steam came out of tail pipe even after 15 mins but NOT white smoke, no sweet smell. Car has not been driven very much in the past year. Car had electronic water pump+thermostat replaced by previous owner when they failed, not sure to be worried about warped head gasket or not
Cold test done with car sitting for 24-hours
All EFI fueses pulled and all spark plugs pulled (per other forum postings on how to compression test)
Using a brand new Mittyvac digital compression tester which automatically measures peak values
Throttle body completely removed for both tests

r3vmatch · 05-21-2023, 07:13 PM

Replying to my own thread:

Re-tested #5 & #6 cold and got 220.5 & 224.0 PSI . So all the cold numbers in theory agree with each other.

Saico · 05-22-2023, 04:56 AM

220 psi = ~15 bar. For my taste that's very high.

Tambohamilton · 05-22-2023, 08:10 AM

Have you checked for fault codes using INPA/ISTA? Have you checked smooth running test?

r3vmatch · 05-22-2023, 07:50 PM

Hi, thanks for the replies.

A) If 220 PSI is too high, what is that an indication of? Excessive carbon build up?

B) No codes in INPA or Rheingold. I did check the smoothess values but I didn't take a screen shot

. I started on pulling the intake + CCV so it'll be a few days before I can report back. I did find some oil on the 'inner' DISA connector (haven't gotten intake off yet) so I know this has to be dealt with anyway.

The tail pipe is sooty and when I pulled the large DISA I found several tablespoons of oil, so perhaps a failing CCV has been allowing too much oil into the pistons.

I did take pictures of the sparkplugs, I can post that.

05-21-2023, 07:02 PM	#1
r3vmatch New Member 4 Rep 21 Posts Drives: 3.0si Roadster Join Date: Apr 2022 Location: San Diego iTrader: (0)	N52 compression numbers: Help me decipher All, I'm trying to troubleshoot a rough idle(+/- 10 RPM) low RPM performance loss on an N52/2006/70K miles. Symptoms include soot on tail pipe, so I thought replace DISAs, CCV and breather hoses (all look to be 2006 original). Decided to compression test before throwing a bunch of $$ at the car. Are these numbers worrying? Specifically that the hot / cold PSI are close to each other? Edit: Re-ran on #5 & 6 cold and all the cold numbers are in line with each other. Numbers hot[PSI]: 218.0, 221.0, 218.0, 219.5, 224.0, 218.5 Numbers cold[PSI]: 219.5, 225.5, 221.0, 223.0, 215.0, 211.5 Notes: Idled car up for 15 mins, temp gauge in middle to do "warm" test. Steam came out of tail pipe even after 15 mins but NOT white smoke, no sweet smell. Car has not been driven very much in the past year. Car had electronic water pump+thermostat replaced by previous owner when they failed, not sure to be worried about warped head gasket or not Cold test done with car sitting for 24-hours All EFI fueses pulled and all spark plugs pulled (per other forum postings on how to compression test) Using a brand new Mittyvac digital compression tester which automatically measures peak values Throttle body completely removed for both tests Last edited by r3vmatch; 05-21-2023 at 07:21 PM..
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05-21-2023, 07:13 PM	#2
r3vmatch New Member 4 Rep 21 Posts Drives: 3.0si Roadster Join Date: Apr 2022 Location: San Diego iTrader: (0)	Replying to my own thread: Re-tested #5 & #6 cold and got 220.5 & 224.0 PSI . So all the cold numbers in theory agree with each other.
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05-22-2023, 04:56 AM	#3
Saico Private 31 Rep 90 Posts Drives: 330xi Join Date: May 2018 Location: PL iTrader: (0)	220 psi = ~15 bar. For my taste that's very high.
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05-22-2023, 08:10 AM	#4
Tambohamilton Brigadier General 3295 Rep 4,223 Posts Drives: E91 330d Join Date: Apr 2019 Location: Herefordshire iTrader: (0)	Have you checked for fault codes using INPA/ISTA? Have you checked smooth running test?
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05-22-2023, 07:50 PM	#5
r3vmatch New Member 4 Rep 21 Posts Drives: 3.0si Roadster Join Date: Apr 2022 Location: San Diego iTrader: (0)	Hi, thanks for the replies. A) If 220 PSI is too high, what is that an indication of? Excessive carbon build up? B) No codes in INPA or Rheingold. I did check the smoothess values but I didn't take a screen shot . I started on pulling the intake + CCV so it'll be a few days before I can report back. I did find some oil on the 'inner' DISA connector (haven't gotten intake off yet) so I know this has to be dealt with anyway. The tail pipe is sooty and when I pulled the large DISA I found several tablespoons of oil, so perhaps a failing CCV has been allowing too much oil into the pistons. I did take pictures of the sparkplugs, I can post that.
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