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Old 01-06-2010, 06:05 PM   #1
yonmoor
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Smile I need compression figures.

Does anybody know of any published numbers we should be shooting for when compression testing an M54 330i?

Also, assuming that such numbers exist, how would they take into account the fact that different length hose extensions can produce vastly different compression numbers?
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Old 01-06-2010, 08:30 PM   #2
badboye46
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I've never heard of published numbers in those terms, I think there could be to many variables, I've always understood that your looking for numbers to be within a certain percentage or window between all of cylinders.
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Old 01-06-2010, 08:43 PM   #3
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I've never heard of published numbers in those terms, I think there could be to many variables, I've always understood that your looking for numbers to be within a certain percentage or window between all of cylinders.
There's a bunch of random **** out there, but the most common I've heard is no more than 10% variation between cylinders. Kind of vague, because if you take 10% of the lowest reading, it'll obviously be a tighter tolerance than 10% of the highest. Shouldn't be by much though.

Still, I've heard that there are "service limits" to these things, and some professional sources have cited that there should be published figures somewhere. If I can't find it though, oh well. Relative measurements should do OK.
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Old 01-06-2010, 08:46 PM   #4
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142 to 156 psi, 7 psi max deviation cyl to cyl. Bentley manuals are only $70 on Amazon. You can cook the ECM if you do it wrong, so get the Bentley and ! New ECM or Bentley......I think you would rather buy the latter!
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Old 01-06-2010, 08:55 PM   #5
Rob43
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Just did mine 2 weeks ago, first you'll be using a gauge with only "one" length
of hose for all cylinders, don't add or shorten as you go. More compression is
always better than less, having said that, what your looking for is consistency
between all cylinders. If your within 5% for all 6 your doing very good, if your
within 10%, thats still considered OK.

A) Good- 180-179-182-181-178-180

B) Bad- 180 179-94-181-179-180

If you have engine "A" your engine is in great condition.
If you have engine "B" you have a real problem.

Rob
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Old 01-06-2010, 09:01 PM   #6
yonmoor
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Originally Posted by 330I6SPD View Post
142 to 156 psi, 7 psi max deviation cyl to cyl. Bentley manuals are only $70 on Amazon. You can cook the ECM if you do it wrong, so get the Bentley and ! New ECM or Bentley......I think you would rather buy the latter!
I refuse to spend money. I already bought the compression test kit.

Quote:
Originally Posted by Rob43 View Post
Just did mine 2 weeks ago, first you'll be using a gauge with only "one" length
of hose for all cylinders, don't add or shorten as you go. More compression is
always better than less, having said that, what your looking for is consistency
between all cylinders. If your within 5% for all 6 your doing very good, if your
within 10%, thats still considered OK.

A) Good- 180-179-182-181-178-180

B) Bad- 180 179-94-181-179-180

If you have engine "A" your engine is in great condition.
If you have engine "B" you have a real problem.

Rob
Yup, that I understand. How exactly did you go about doing it?

Also, how'd you hold the throttle plate open? I'm still unsure as to whether or not holding the gas pedal to the floor would open the throttle on a DBW car (like ours) when the engine isn't operational.
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Old 01-06-2010, 09:08 PM   #7
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Originally Posted by yonmoor View Post
I refuse to spend money. I already bought the compression test kit.
The devil is in the details...if you proceed and cause severe damage to your BMW due to mis-information or incomplete data provided on the internet, you will understand.
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Old 01-06-2010, 09:11 PM   #8
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Originally Posted by yonmoor View Post
Yup, that I understand. How exactly did you go about doing it?
Also, how'd you hold the throttle plate open? I'm still unsure as to whether or not holding the gas pedal to the floor would open the throttle on a DBW car (like ours) when the engine isn't operational.
I was the number "2" man in the operation, so i don't want to give you bad info.
I'll make a call tomorrow, find out exactly, and get back to you.


Rob
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Old 01-06-2010, 09:30 PM   #9
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The devil is in the details...if you proceed and cause severe damage to your BMW due to mis-information or incomplete data provided on the internet, you will understand.
This shouldn't be as complex as to require shelling out $70 on a Bentley Manual. Compression tests are relatively simple, and given that several members on here have successfully performed one, it shouldn't be a big deal. How would it be possible to "cook the ECM?" Out of all the research I've done, you're the first to mention frying anything.

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Originally Posted by Rob43 View Post
I was the number "2" man in the operation, so i don't want to give you bad info.
I'll make a call tomorrow, find out exactly, and get back to you.


Rob
That'd be awesome, thanks. I'm considering doing a DIY as soon as I gather all the available info. Considering.
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Old 01-06-2010, 09:55 PM   #10
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Originally Posted by yonmoor View Post
This shouldn't be as complex as to require shelling out $70 on a Bentley Manual. Compression tests are relatively simple, and given that several members on here have successfully performed one, it shouldn't be a big deal. How would it be possible to "cook the ECM?" Out of all the research I've done, you're the first to mention frying anything.
Well, this being the first you are hearing about this should tell you that you are researching in the wrong place.
Bentley has 3 pages covering compression/leakdown testing on the 330i. One of the Cautions reads "Failure to remove the DME main relay or attempting to disable the ignition system by other methods may result in damage to the engine control module" from 113-31 in the Bentley. Some here may have run a compression test without removing the DME main relay and done it with no ill effects, but is there any solace in that fact for you to follow their lead and cook your ECM????
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Old 01-06-2010, 10:10 PM   #11
yonmoor
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Originally Posted by 330I6SPD View Post
Well, this being the first you are hearing about this should tell you that you are researching in the wrong place.
Bentley has 3 pages covering compression/leakdown testing on the 330i. One of the Cautions reads "Failure to remove the DME main relay or attempting to disable the ignition system by other methods may result in damage to the engine control module" from 113-31 in the Bentley. Some here may have run a compression test without removing the DME main relay and done it with no ill effects, but is there any solace in that fact for you to follow their lead and cook your ECM????
You just told me everything I needed to know. Thanks.

I read in several places that I should remove the DME main relay, but none cited why. See? Multiple sources will eventually lead to an extremely accurate conclusion. Wikipowar. Until I start doing more serious business, I don't want to buy a Bentley Manual.
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Old 01-07-2010, 08:53 PM   #12
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OK here it is, first it's a 2 man job. Pull out all coil packs, remove all
plugs. Remove the DME main relay. Have helper crank motor with throttle
wide open, about ten revolutions per test. Your looking for the average number
per test, so if the needle on your gauge is going between 170 & 180, that
cylinder is 175. Move to next cylinder until your done. Ideally you want all
cylinders as close as possible, within 10% is OK but 5% or less would be better.

Rob
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Old 01-08-2010, 05:29 PM   #13
yonmoor
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Originally Posted by Rob43 View Post
OK here it is, first it's a 2 man job. Pull out all coil packs, remove all
plugs. Remove the DME main relay. Have helper crank motor with throttle
wide open, about ten revolutions per test. Your looking for the average number
per test, so if the needle on your gauge is going between 170 & 180, that
cylinder is 175. Move to next cylinder until your done. Ideally you want all
cylinders as close as possible, within 10% is OK but 5% or less would be better.

Rob
Thanks. Do you know how I go about identifying which switch is the DME main relay (or the fuel pump relay, I plan on pulling that one too)? From all the photos I've seen they're all just little colored cubes. Not sure if they're labeled or not.

Also, this is something nobody's been able to answer. Can the throttle plate even open when the gas pedal is to the floor? These cars are Drive-by-Wire, so I'm wondering how to keep the damn thing open to allow the max. amount of air.
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Old 01-08-2010, 06:50 PM   #14
Rob43
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Quote:
Originally Posted by yonmoor View Post
Thanks. Do you know how I go about identifying which switch is the DME main relay (or the fuel pump relay, I plan on pulling that one too)? From all the photos I've seen they're all just little colored cubes. Not sure if they're labeled or not.

Also, this is something nobody's been able to answer. Can the throttle plate even open when the gas pedal is to the floor? These cars are Drive-by-Wire, so I'm wondering how to keep the damn thing open to allow the max. amount of air.
Sorry, i think the best thing would be to look up a online pic of the DME main
relay/location.
Next, remember your cranking the car, it's electrically on, so the drive by wire throttle is obeying your commands.

Rob
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Old 01-08-2010, 07:27 PM   #15
yonmoor
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Sorry, i think the best thing would be to look up a online pic of the DME main
relay/location.
Next, remember your cranking the car, it's electrically on, so the drive by wire throttle is obeying your commands.

Rob
That's what I thought, only difference between contact and "full operation" is the fact that the engine's spinning. I wasn't sure though because when I get in, put it on contact, and tap the throttle, I hear nothing from the engine... Probably just can't hear the plate though.
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