Before computers were running cars, I had no problems with compression testing. Still have most of the equipment. My concern is the way the engine starts when the start button is pushed --- it cranks until it starts.
Does it have a timer, to quit cranking if it doesn't start?
Is there a special test fixture to plug into the starter?
Remove all plugs before testing?

I'm afraid to just connect the compression gauge and hit the starter, not knowing what will happen, and don't want to just start experimenting with different possibilities. Had a dealer test it for me a couple years ago - good results, but an hours worth of labor charges. No explanation on how they performed the test.

So much to learn about the '07 R56 ---

All helpful inputs / links appreciated!

 

It has a crank time inhibit function in the ECU so it will crank for X amount of time then time out. I would just disable the fuel supply however you choose and go about it normally. Hope you don't find out anything BAD with the test!

 

Good info --- thanx. I'll post my results and any other helpful hints discovered, hopefully today or tomorrow. Maybe even a ballpark value for "X"!

 

That didn't take long! Pulled plugs then the fuel pump fuse and cranked it for 10 - 15 seconds to clear fuel from the system. Found out that after the start button is pushed, it cranks for 17 secs before stopping by itself. Also discovered that while it's cranking, it can be stopped by pushing the button again. Seems obvious, but I was afraid to try it before prepping for this test. Still running the original battery - 62K miles and car was built in 9/07.

Compression gauge with spark plug adaptor is about 2' long. I believe this long length causes readings to be low - at least I hope so.
#1 = 105psi
#2 = 105psi
#3 = 115psi
#4 = 115psi
Dealer check 2 years ago was between 168 - 171psi. Not concerned about actuals, just variance. I'm happy with the results, but I'm also open for criticism ---

 

Now that is a damned helpful piece of experience - thank you VERY much for sharing. I might now have the courage to measure my own beast, and would have stumbled on the very questions you asked.

What sort of mileage is that engine returning I wonder?

Cheers,

Charlie

 

I'm happy someone else can use the info. This forum has been of great help to me, so I want to share my experiences, radical as they are, with the intent of helping others.

I'm getting between 35 - 40 MPG, as calculated by the gas pump and odometer. Lotsa hiway driving with cruise control, and very little "pedal-to-the-metal".

 

I don't understand how a turbocharged engine can be accurate because there's no boost when performing a compression test!? Cranking the engine over 4 cycles can't be the same as when there's boost being added during operation, your PSI reading will go up with more boost.

Also how do you get those coils off without damaging them?

 

Yep you are right, but folks running turbocharged/supercharged Minis expect a relatively modest compression number, and as the OP mentioned the consistency across the cylinders is perhaps the most important fact that comes from the measurement.

The blown cars also run a lower compression ratio than the NA cars, so a Justa will pump more than an R53 for example. Gollum I (R53) pumped around 150 psi as measured by Mini of Peabody at 60k miles. The same car at 119k miles pumped 160 for Turners, but MoP testing showed this:
1. 160
2. 130
3. 130
5. 160
... which is why I put a crate motor in it at that point...

The compression test does not measure power of course - just the mechanical health of the "air pump" which is the fundamental nature of the internal combustion engine. Most of the techs I know will prefer a leak-down test as an even more accurate indicator of ring seal and valve condition.

Hopefully the OP will elaborate on the coils - he's done it on the R56 and I have not!

Cheers,

Charlie

 

My intent for performing a compression test was to ensure the integrity of the combustion chambers --- rings, pistons, valve seats, and head gasket. Cracked block or cracked head would also show up as a variation in readings. The fact that it's turbo-charged has nothing to do with combustion chamber testing, other than the acceptable reading limits.

As for leak-down testing, I'll reserve that 'til after I obtain a shorter hose for my compression tester. Reason being, I'm still clueless on what this test is all about --- more studying req'd! Also, my concerns have been satisfied.

Coils are press-fit over the spark plugs - to ensure a good electrical connection, and provide a "water-tight" seal over the plug well. Removal amounts to removing the input connector (lift the coil "lid" and the connector will be partially ejected - its a cam action) then pull the coil straight up. A little wiggling helps - wiggle the coil, not yourself. Note that the coil is shaped to fit inside a pair of guides on the valve cover so it won't wiggle much. Then you need a 12 point spark plug socket if using OEM plugs. A deep-well socket will work, but removing / installing the plug is easier with a proper plug socket - one that grips the plug.

 

Thanks mate. I hate to use "OP" as a salutation but yer moniker is so tongue in cheek that I am hesitant to use that either.

The leak down is just what you think. It takes an external pressure source, provides an initial pressure to the combustion chamber, and then the decrease in pressure over time is recorded.

It gets around the whole cam timing question and aims directly at how good the valve/seat and ring/cylinder seals really are.

When I was trying to make a live/die decision on the R53 the leak down numbers were the most useful ones, and as in the case of the raw pressure measurements it is variation as much as absolute curve that tells the tale.

Thanks for the details on the electrical bits sir...

Cheers,

Charlie

 

A leakdown test only tells you about the sealing of the valves, and the rings at TDC. You set up the cylinder at TDC (and possibly lock it there) and pump air into it through the spark plug hole. Since the piston is only at TDC, you only are checking the seal of the rings at TDC. That, and the extra equipment and time involved, are why leak-downs are usually done as a secondary test after a compression test.

BTW, you can also listen for where air is escaping the combustion chamber. If you hear hissing at the intake snorkel, you have leaks at one or both intake valves. If you hear it at the tailpipe, it's the exhaust valve(s) that are leaking. If you hear it at the oil filler, it's rings or a bad piston.

 

Did a compression test today on mine (2007 R56, 55K miles). All cylinders were between 152 and 155 psi. The low variance is good but the overall readings are below the 168-171 you saw from your motor in its younger days.

Plug tips looked real consistent across all cylinders with a nice brown. Still, I will be changing out the plugs as soon as the new ones arrive.

 

FYI --- my dealers service report from the compression test included "All cylinders are within 5% of each other and between 160 - 180 PSI. Checked OK." Mileage was 36110.

New plugs at 55K should show a noticeable improvement. Enjoy!

 

Just for grins, I tried a variation on the compression test. i squirted a bit of oil in the cylinder, then did the test. Readings were about 10 - 15 PSI higher than without the oil, indicating that rings are the probable cause of the low readings --- oil on the top helps seal the chamber. Also used a new gauge. Resolution isn't as good, but close enough.

Engine has about 65K on it, but getting a remote AP map took a lot of data-logging. Must have put some serious wear-and-tear on it.

So now I gotta resign myself to the fact that the lower end of the engine is ready for upgrades. Gonna be awhile before that happens --- still running pretty good. Since changing the WMI threshold, I've been using a tank of 50 - 50 mix (maybe 3 gts) for every tank of gas. Hopefully cleaning up my OCC fiasco at the intake valves. Seems to be a bit "smoother" and more responsive while cruising.

 

I had the same problem as you a couple of weeks ago. I got a compression tester and used a really long extension pipe (about 12") to reach down to the spark plug hole in addition to the hose attached to the gage (probably about another 12"). Got 90 psi at first. I got a little scared at that point then though about how friggin long the tube was. When I took the extension off it was about 180psi across the board. Feeling much better now

 

Someday I'll probably change the hose on my tester to be as short as possible. I expect that's another possible cause for my low readings. Working with a set of hoses (different plug sizes) and one gauge with its own hose, results in one long piece of test equipment! I can still shorten it all up by almost another foot or so. But for the time being, I'm content with what I have.

 

Just FYI, here are the numbers from my fresh (20k miles) Cooper - which should pump more pressure than the turbocharged version.

---- Cyl1, Cyl2, Cyl3, Cyl4
Dry - 168, 171, 169, 171
Wet - 212, 216, 211, 212
-----------------------

Mini of Peabody made the measurements at my request, just so that I'd have something to compare to later in the car's life.

Cheers,

Charlie

 

That 180 psi sounds like a great number. I wish I was seeing that. I tested my engine again and got the same 150-155 range across all cylinders. I wonder if my low numbers are due to testing a cold engine in the am after all the oil has settled overnight. (Florida cold, that is.) Did you do your compression test on a warm engine or cold engine?

@ 'the busted breeze' about the hose length - it should not make that big a difference (if any at all). I bet your hose had a leak, was not fitting tightly, or you needed to crank over the engine for more revolutions. The longer the hose the more revolutions it will take to get the correct reading as the first compression strokes will not build max pressure since the air has to fill the long hose.

One more possibility is that the extension you used may not have a one way valve so no matter how many times you turn over the engine it will loose the air pumped in from the prior compression stroke - were you able to trap that air then the readings would eventually be accurate after a few revolutions. If this is the case, then you want to either eliminate the extension hose altogether as previous posters have done, or you can try switching around the hoses so that the hose originally attached to the gauge is closest to spark plug hole (chances are, that hose has a working one way valve so more of the air pumped during the compression stroke gets trapped, allowing for an accurate reading after a few revolutions).

 

Engine warm. 219 deg F.

I believe the length of hose has a direct influence on the results. The perfect test would be the dial gauge connected directly at the spark plug hole. That is the true reading of the compression in the cylinder. When a large volume of air is added between the cylinder and gage, in this case a long hose/extension, the air acts as a cushion of sorts to what pressures are occuring in the cylinder.

 

What would be the default psi readings of a compression test for a 2008 R56S? Does BMW documentate the default readings somewhere in the manual?

 

Did anyone mention being able to open the throttle body is rather important is getting readings?

 

I compression tested the cylinders in my engine this evening. I purchased "Sunny" new and have changed the oil every five to six thousand miles. I currently have app. 89k miles on the car. The results are below:

1 cyl. 2 cyl. 3 cyl. 4cyl.
162 lbs. 160 lbs. 158 lbs. 160 lbs.

I am very happy with the numbers and this was tested dry. I intended to also do the test wet, but decided that it wouldn't really prove anything with these numbers.

I replaced the spark plugs and they look very good. They only had about 22k miles on them.

The reason I did this is that I am getting some engine stumbling when pulling out from a start every once in a while. I have gotten the P2065 code a few times recently on the Torque app. The Bentley manual says "P2065: Fuel level Sensor "B" Circuit". Could this be the HPFP?

I walnut blasted the intake about 20K miles ago, so hopefully that's not the problem.

Thanks to "Oldbrokenwind" and everyone else who contributed to this thread. You really helped make this job very easy!

 

What was the temperature of your engine (cold, warm or hot) when performing the compression test? Those are great numbers, better than mine for consistency. How much oil does your engine consume? I'm going to perform another compression test 30 minutes after shutdown and see if the high readings drop down to number 2 and 3.

Here's mine:

1 cyl. 2 cyl. 3 cyl. 4cyl.
170 psi. 158 psi. 170 psi. 155 psi.

 

Systemlord, the engine was hot when I checked the engine compression. I left it cool down for about 15 minutes before pulling the spark plugs. The engine uses a quart of oil about every 1,500 miles. More than I like but less than what many report.

The engine seems to be smoother at low rpm's and better at starting from stop since installing new spark plugs.

I still have the original battery and the car is now six years old. Clock lost it's time yesterday and got an unexplained warning in the tach. I guess that's next on the list but I can't really complain at that.

 

I did my compression test the second I turned off the engine. I also burn about 1 quart every 1500-2000 miles, I also have the original factory battery. Mine is 7 years old and still going strong with no signs of strain. I would love to know where the psi readings should be on a new N14 engine, I'm going to guess 170 psi. I think 180 psi would be a little high for a turbocharged engine. All of my Nissan and Toyota non-turbo sport cars have been 180 psi.