BMW M5 Forum and M6 Forums banner

1 - 14 of 14 Posts

·
Registered
Joined
·
63 Posts
Discussion Starter #1 (Edited)
I performed a compression check, and then a leak-down test on my 2003 with 20k miles. I figured some folks out there may be interested in seeing the data. The motivation for doing this was 2% fuel dilution in the last oil analysis, and I wanted to see if I had a mechanical issue in any of the cylinders. The results are shown in the table below.


<TABLE dir=ltr height=200 cellSpacing=0 cellPadding=0 width=275><TBODY><TR><TD style="BORDER-RIGHT: black 1px solid; BORDER-TOP: black 2px solid; VERTICAL-ALIGN: top; BORDER-LEFT: black 2px solid; BORDER-BOTTOM: black 1px solid" width=80 height=23>
Cylinder​
</TD><TD style="BORDER-RIGHT: black 1px solid; BORDER-TOP: black 2px solid; VERTICAL-ALIGN: top; BORDER-LEFT: black 1px solid; BORDER-BOTTOM: black 1px solid" width=109 height=23>
Pressure (psig)​
</TD><TD style="BORDER-RIGHT: black 2px solid; BORDER-TOP: black 2px solid; VERTICAL-ALIGN: top; BORDER-LEFT: black 1px solid; BORDER-BOTTOM: black 1px solid" width=88 height=23>
Leakage @ TDC​
</TD></TR><TR><TD style="BORDER-RIGHT: black 1px solid; BORDER-TOP: black 1px solid; VERTICAL-ALIGN: top; BORDER-LEFT: black 2px solid; BORDER-BOTTOM: black 1px solid" width=80 height=23>
1​
</TD><TD style="BORDER-RIGHT: black 1px solid; BORDER-TOP: black 1px solid; VERTICAL-ALIGN: top; BORDER-LEFT: black 1px solid; BORDER-BOTTOM: black 1px solid" width=109 height=23>
189​
</TD><TD style="BORDER-RIGHT: black 2px solid; BORDER-TOP: black 1px solid; VERTICAL-ALIGN: top; BORDER-LEFT: black 1px solid; BORDER-BOTTOM: black 1px solid" width=88 height=23>
2%​
</TD></TR><TR><TD style="BORDER-RIGHT: black 1px solid; BORDER-TOP: black 1px solid; VERTICAL-ALIGN: top; BORDER-LEFT: black 2px solid; BORDER-BOTTOM: black 1px solid" width=80 height=23>
2​
</TD><TD style="BORDER-RIGHT: black 1px solid; BORDER-TOP: black 1px solid; VERTICAL-ALIGN: top; BORDER-LEFT: black 1px solid; BORDER-BOTTOM: black 1px solid" width=109 height=23>
195​
</TD><TD style="BORDER-RIGHT: black 2px solid; BORDER-TOP: black 1px solid; VERTICAL-ALIGN: top; BORDER-LEFT: black 1px solid; BORDER-BOTTOM: black 1px solid" width=88 height=23>
1%​
</TD></TR><TR><TD style="BORDER-RIGHT: black 1px solid; BORDER-TOP: black 1px solid; VERTICAL-ALIGN: top; BORDER-LEFT: black 2px solid; BORDER-BOTTOM: black 1px solid" width=80 height=23>
3​
</TD><TD style="BORDER-RIGHT: black 1px solid; BORDER-TOP: black 1px solid; VERTICAL-ALIGN: top; BORDER-LEFT: black 1px solid; BORDER-BOTTOM: black 1px solid" width=109 height=23>
196​
</TD><TD style="BORDER-RIGHT: black 2px solid; BORDER-TOP: black 1px solid; VERTICAL-ALIGN: top; BORDER-LEFT: black 1px solid; BORDER-BOTTOM: black 1px solid" width=88 height=23>
1%​
</TD></TR><TR><TD style="BORDER-RIGHT: black 1px solid; BORDER-TOP: black 1px solid; VERTICAL-ALIGN: top; BORDER-LEFT: black 2px solid; BORDER-BOTTOM: black 1px solid" width=80 height=23>
4​
</TD><TD style="BORDER-RIGHT: black 1px solid; BORDER-TOP: black 1px solid; VERTICAL-ALIGN: top; BORDER-LEFT: black 1px solid; BORDER-BOTTOM: black 1px solid" width=109 height=23>
195​
</TD><TD style="BORDER-RIGHT: black 2px solid; BORDER-TOP: black 1px solid; VERTICAL-ALIGN: top; BORDER-LEFT: black 1px solid; BORDER-BOTTOM: black 1px solid" width=88 height=23>
1%​
</TD></TR><TR><TD style="BORDER-RIGHT: black 1px solid; BORDER-TOP: black 1px solid; VERTICAL-ALIGN: top; BORDER-LEFT: black 2px solid; BORDER-BOTTOM: black 1px solid" width=80 height=23>
5​
</TD><TD style="BORDER-RIGHT: black 1px solid; BORDER-TOP: black 1px solid; VERTICAL-ALIGN: top; BORDER-LEFT: black 1px solid; BORDER-BOTTOM: black 1px solid" width=109 height=23>
192​
</TD><TD style="BORDER-RIGHT: black 2px solid; BORDER-TOP: black 1px solid; VERTICAL-ALIGN: top; BORDER-LEFT: black 1px solid; BORDER-BOTTOM: black 1px solid" width=88 height=23>
2%​
</TD></TR><TR><TD style="BORDER-RIGHT: black 1px solid; BORDER-TOP: black 1px solid; VERTICAL-ALIGN: top; BORDER-LEFT: black 2px solid; BORDER-BOTTOM: black 1px solid" width=80 height=23>
6​
</TD><TD style="BORDER-RIGHT: black 1px solid; BORDER-TOP: black 1px solid; VERTICAL-ALIGN: top; BORDER-LEFT: black 1px solid; BORDER-BOTTOM: black 1px solid" width=109 height=23>
195​
</TD><TD style="BORDER-RIGHT: black 2px solid; BORDER-TOP: black 1px solid; VERTICAL-ALIGN: top; BORDER-LEFT: black 1px solid; BORDER-BOTTOM: black 1px solid" width=88 height=23>
2%​
</TD></TR><TR><TD style="BORDER-RIGHT: black 1px solid; BORDER-TOP: black 1px solid; VERTICAL-ALIGN: top; BORDER-LEFT: black 2px solid; BORDER-BOTTOM: black 1px solid" width=80 height=23>
7​
</TD><TD style="BORDER-RIGHT: black 1px solid; BORDER-TOP: black 1px solid; VERTICAL-ALIGN: top; BORDER-LEFT: black 1px solid; BORDER-BOTTOM: black 1px solid" width=109 height=23>
192​
</TD><TD style="BORDER-RIGHT: black 2px solid; BORDER-TOP: black 1px solid; VERTICAL-ALIGN: top; BORDER-LEFT: black 1px solid; BORDER-BOTTOM: black 1px solid" width=88 height=23>
2%​
</TD></TR><TR><TD style="BORDER-RIGHT: black 1px solid; BORDER-TOP: black 1px solid; VERTICAL-ALIGN: top; BORDER-LEFT: black 2px solid; BORDER-BOTTOM: black 2px solid" width=80 height=23>
8​
</TD><TD style="BORDER-RIGHT: black 1px solid; BORDER-TOP: black 1px solid; VERTICAL-ALIGN: top; BORDER-LEFT: black 1px solid; BORDER-BOTTOM: black 2px solid" width=109 height=23>
194​
</TD><TD style="BORDER-RIGHT: black 2px solid; BORDER-TOP: black 1px solid; VERTICAL-ALIGN: top; BORDER-LEFT: black 1px solid; BORDER-BOTTOM: black 2px solid" width=88 height=23>
2%​
</TD></TR></TBODY></TABLE>

Note that cylinder #1 is a bit low. I did the leak-down test at various crankshaft positions and found that part-way up the cylinder, the leak rate was 5%, then as I rotated the crank toward TDC, it dropped to 4%, then 3%, and then 2% by the time I got to TDC. I suspect there may be some scoring in the cylinder. As a double check, I did the same thing on cylinder #5 (also most forward cylinder in the bank) and found that the max was 3% when part way up to TDC, but then quickly went back to 2% as I approached TDC. Since #5 had more average compression pressure and its leak rate stayed close to 2%, I figure it is close to nominal. Thus, this is why I'm thinking there could be some scoring in #1.

All of the above tests were done at 100 psi. Note that you need a pretty hefty breaker bar (see third photo below) to resist the torque. I used a 4 foot bar. My calculations showed that at 100psi, the max torque would be close to 160 ft-lb.

Some photos of the test are shown below.

When doing the compression test I found the same thing that was discussed in http://www.m5board.com/vbulletin/showthread.php?t=69610&highlight=compression+test+fuse
I pulled the fuel pump fuse, then started the engine until it died. I figured I had all the fuel out, but that was not correct. On the first cylinder I got 246 psi and on the next it dropped significantly. As soon as I saw that I realized I still had fuel in the system. I just kept performing the test until I got a consistent reading. I did this in a closed garage, and afterwards I really noticed an odd smell. Most likely, the fuel was burning in the catalytic converter. Hopefully I didn't damage it?!?

If you haven't fallen asleep by this point and are still interested, I put photos of the plugs on another thread at http://www.m5board.com/vbulletin/showthread.php?p=1190522#post1190522

Thanks for any comments.
 

Attachments

·
Moderator
Joined
·
10,451 Posts
i think all of those numbers are pretty darn good!

fwiw, many of us are having this fuel dilution issue on UOA.
 

·
Registered
Joined
·
683 Posts
+1 on the fuel dilution. 2% at 3,000 miles of oil use (I use M1 0W-40). Beast is a 2003 with 37K miles. I though it was because I was running rich; I recently replaced the MAFs and the car runs stronger and I hope that will improve the fuel dilution issue.
 

·
Registered
Joined
·
110 Posts
Those are great numbers.

I wouldnt worry about #1 being a little low...as long as they are within 10% of each other its all good.

Thats a very small difference you have there anyway and could be accounted by a number of things....i'd be very please with those results.
 

·
Registered
Joined
·
526 Posts
John, your car does pretty low mileage.
Is this because its trips are typically short in length and duration. This could be a reason for the fuel dilution. Motor not getting to operating temp, fuel in oil not vapourising at proper operating temps > 80 deg C+
 

·
Registered
Joined
·
63 Posts
Discussion Starter #9
Thanks folks for your replies. Glad to hear the numbers are pretty good.

My driving style has been to and from work, which is 32 miles of almost entirely highway driving. Mostly at 60 to 65 mph. At Terry Dyson's recommendation I've been using FP-60 fuel additive. I'll be putting in new plugs just to be sure that isn't the issue. I'm running the BMW 5W-30 oil, changing it every 3000 miles.

I just replaced the air filters and hopefully the next oil analysis will show less fuel dilution.
 

·
Premium Member
E60 M5 and building engines
Joined
·
121 Posts
Has anyone done a relative compression test on the S85? I am in process of purchasing vehicle, but test could not be completed as engine will "fire" and disengage starter before test can be completed.

Please advise,

Mr. P
 

·
Premium Member
E60 M5 and building engines
Joined
·
121 Posts
Hello xrviz,

New Q: Has anyone performed a relative compression test on the S62? I had issue on my unnamed engine from same manufacturer and was hoping for cross-platform info.

Mr. P

PS: I will provide any/all knowledge I have to support all forums. Go for //M
 

·
Registered
Joined
·
861 Posts
Hello xrviz,

New Q: Has anyone performed a relative compression test on the S62? I had issue on my unnamed engine from same manufacturer and was hoping for cross-platform info.

Mr. P

PS: I will provide any/all knowledge I have to support all forums. Go for //M
Mr.P, do yourself a favor and learn how to search this forum (read the FAQ and other stickies). You’ll find this forum way more useful.
Go to Google and type-

site:m5board.com e39 compression test results

It’s ok to ask questions of course, but the car is over 20 years old, so most likely your question has been asked and answered multiple times.
 
1 - 14 of 14 Posts
Top