Compression Test

SlowerThanU · 01-28-2012, 10:30 AM

Hey guys. Do you know which fuse is the fuel pump/relay so I cut fuel for a compression test.

Also, I need to have the throttle wide open...how does that work on our drive by wire cars. If I press the peddle down all the way when cranking, will the DME open the throttle?

Thanks

SlowerThanU · 01-29-2012, 08:38 AM

Bumpity

indy99gpgt · 01-30-2012, 12:43 AM

If you are looking for a bum cylinder, you dont necessarily need to have the car at WOT. Compression tests are more accurate with it open, but in my opinon, you really just want to make sure all the cylinders are in a similar compression range. Using this method, the bad cylinder will have a large gap between the compression of the other cylinders.

On the other hand, if you are not hunting for a bad cylinder then you will need it open for accurate readings. As for the fuel pump fuse, i cant help you there. Ive never had to look for it. You can always look in the throttle body to see if the throttle flap is open when the car is off and the pedal is down.

SlowerThanU · 01-30-2012, 06:04 PM

That is what I was thinking. I was getting roughly 115-120psi on all except for the one that was chewing up my plugs was at 110psi. I felt pretty good after that but really should be quite a bit higher than 200psi.

01-28-2012, 10:30 AM	#1
SlowerThanU Private 3 Rep 75 Posts Drives: 335i AT Join Date: Jun 2011 Location: San Jose CA iTrader: (0)	Compression Test - What fuel fuse and WOT? Hey guys. Do you know which fuse is the fuel pump/relay so I cut fuel for a compression test. Also, I need to have the throttle wide open...how does that work on our drive by wire cars. If I press the peddle down all the way when cranking, will the DME open the throttle? Thanks
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01-29-2012, 08:38 AM	#2
SlowerThanU Private 3 Rep 75 Posts Drives: 335i AT Join Date: Jun 2011 Location: San Jose CA iTrader: (0)	Bumpity
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01-30-2012, 12:43 AM	#3
indy99gpgt Private 13 Rep 98 Posts Drives: 2008 335i BSM coupe Join Date: Jan 2011 Location: Indianapolis iTrader: (0)	If you are looking for a bum cylinder, you dont necessarily need to have the car at WOT. Compression tests are more accurate with it open, but in my opinon, you really just want to make sure all the cylinders are in a similar compression range. Using this method, the bad cylinder will have a large gap between the compression of the other cylinders. On the other hand, if you are not hunting for a bad cylinder then you will need it open for accurate readings. As for the fuel pump fuse, i cant help you there. Ive never had to look for it. You can always look in the throttle body to see if the throttle flap is open when the car is off and the pedal is down. __________________ 2008 BSM 335i coupe- Sport.Premium.Dakota Sadel.jb4.dci.meth 1999 Pontiac Grand Prix-10.5 PSI.PRJ LL CAM.Supporting Mods
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01-30-2012, 06:04 PM	#4
SlowerThanU Private 3 Rep 75 Posts Drives: 335i AT Join Date: Jun 2011 Location: San Jose CA iTrader: (0)	That is what I was thinking. I was getting roughly 115-120psi on all except for the one that was chewing up my plugs was at 110psi. I felt pretty good after that but really should be quite a bit higher than 200psi.
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