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2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
XENTRY Compression Test
XENTRY allows you to perform a "compression test" which measures the speed of a cylinder during a fuel-less start cycle and compares the difference between the slowest and fastest cylinders. I performed this test on my two cars, a 2014 C350 (M276 3.5L NA engine) and a 2015 SL400 (M276 3.0L Bi-turbo engine). The comparative results show the engines to have good relative compression. Not sure what the threshold is between healthy and sick engines.
XENTRY allows you to perform a "compression test" which measures the speed of a cylinder during a fuel-less start cycle and compares the difference between the slowest and fastest cylinders. I performed this test on my two cars, a 2014 C350 (M276 3.5L NA engine) and a 2015 SL400 (M276 3.0L Bi-turbo engine). The comparative results show the engines to have good relative compression. Not sure what the threshold is between healthy and sick engines.
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
New Compression Test after changing my oil to Pennzoil Platinum Euro 5W-40. Interesting results. There is now about a 15% increase in rpm speed. I did capture oil, coolant, and transmission temps this time (see note in image). Ambient temperature is 78°F. Not sure how to interpret a faster spinning engine. Certainly there is less resistance to compression that the starter has to overcome. I know my battery voltage was 14.4V this time and with a battery charger attached. I do not know the voltage of the previous test, but I did have the battery charger attached then, as well. Master Investigator @S-Prihadi and Master Analyst @CaliBenzDriver , any ideas?
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
There could be multiple differences between the conditions the two were tested at. And initially and intuitively, we would say slower speed means better compression, but I'm not sure of that. Faster speed means less resistance, either due to friction or greater pressure (or both). I would like to think it is due to less friction. The Pennzoil Platinum Euro is more than just another 5W-40.
I have another oil change coming up for my C350, which had similar result to my earlier SL400 tests. I'm not sure now if I want to go with the Pennzoil or the Motul Molygen I was going to use. If I use the Pennzoil, I can then compare with the SL400 to see if there are similar results.
please can you tell me how to run the compression test on the xentry. Thank you
Originally Posted by JettaRed
XENTRY allows you to perform a "compression test" which measures the speed of a cylinder during a fuel-less start cycle and compares the difference between the slowest and fastest cylinders. I performed this test on my two cars, a 2014 C350 (M276 3.5L NA engine) and a 2015 SL400 (M276 3.0L Bi-turbo engine). The comparative results show the engines to have good relative compression. Not sure what the threshold is between healthy and sick engines.
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
Originally Posted by N33LTA
please can you tell me how to run the compression test on the xentry. Thank you
Go to the N3/10 Motor electronics module and select the Tests tab. Scroll down to Compression test. Select Continue and you will be walked through the process. Basically, you turn the ignition off and then on, but don't start the engine. You will then be told to hold down the brake (left foot) and the accelerator pedal to the floor (right foot) and then crank the engine until a message says the test is complete. It takes about 6-10 seconds. The engine won't start during this time. Again, just follow the instructions.
Last edited by JettaRed; Oct 28, 2024 at 12:54 PM.
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
Interesting. What year is your car?
I am not suggesting you try this, but I wonder if you manually select your car and uncheck the AMG box at the startup of XENTRY whether it would let you run the comparative compression test. Just curious. Again, I am not suggesting you do this as it may potentially eff things up.
Its a 2019 c63s, im not getting 100-200 timing ls as they should be, getting around 6.8 seconds when should be 5.2 seconds, trying to find out where im losing power. I would like to upload a video of my cylinder stats but dont think i can using this..
it was because I had just started the car so the revs were sitting around 1200, I was told to measure a misfire the car would have to be started on a cold start. It was monitoring as the compression test has been disabled on xentry
Originally Posted by JettaRed
Your engine speed in the first video is too high. It needs to be between 500 and 900 rpm; you were at 1200+ rpm.
Your engine speed was correct in the second video. Was that a test or just monitoring?
I am not suggesting you try this, but I wonder if you manually select your car and uncheck the AMG box at the startup of XENTRY whether it would let you run the comparative compression test. Just curious. Again, I am not suggesting you do this as it may potentially eff things up.
Xentry had removed this feature for amg cars since at least the 2020 software version. I cant remember but I think it disappeared in 18. Even though my car is a 13, I can not use my software that is from '20. If you uncheck the vehicle type, its still going to know the engine is an amg engine when it connects to the control module or does its cross referencing, similar to how it knows if you pick the wrong car. My thoughts when reading the test was removed way back when was that MB knew about scoring and did not want to rely on a digital readout vs a true compression and or leak down test for warranty diagnosis.
Im sure someone that knows developer well could figure it out, maybe.
Last edited by Baltistyle; Oct 29, 2024 at 11:43 PM.
im not getting 100-200 timing ls as they should be, getting around 6.8 seconds when should be 5.2 seconds, trying to find out where im losing power. I have done a lot of work to the car to make it run 800+ bhp, uprated turbos and fuel lines as well as uprated low and high pressure fuel pumps, bigger intercoolers, bigger air intakes, upgraded manifold..
Originally Posted by JettaRed
Thanks. But did you tell us why you are doing this? Is there a problem you are trying to fix?
- What meaning can we attach to this test of "smooth cylinder operation" ?
- What does this test mean? based on what data?
We see Cyl.1 is not doing so well at that test.
It would be very interesting to figure out WHY Cyl.1 is always the troublemaker where things go south. Seeing it happening is really interesting.
No1 gets short straw 1st:
I think there's something the ECU computes that cause No1 to often run the way it does.
-- Does smooth running has to do with... jittery timings??
Contributions don't look too even... is that from loosy compression seals?
-- I dunno for fact_
Consider also the data Xentry is sampling may be subject to CAN-Bus delay more so than ECU internal data.
I know ECU is sensitive to CAN-bus C delays caused by EPS and ISM. Does that affect all or simply No1.
> Settings I Know Impact Engine Timings:
CAN-Bus C solderless modules
drafty piston stuck rings
injection mode
weak chain tensioners
VVT solenoid low oil pressure
unfavorable frictions cyls + heads
poor timings cause ECU to lean LTFT
Work on these items! The better all these items are the stronger the ECU can tune the engine overall output with responsive controls.
Last edited by CaliBenzDriver; Oct 30, 2024 at 06:26 AM.
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
Originally Posted by N33LTA
im not getting 100-200 timing ls as they should be, getting around 6.8 seconds when should be 5.2 seconds, trying to find out where im losing power...
Sorry, I missed this before. If you think there is a compression problem, then a mechanical test is needed, compression and leak-down.
You are in theoretical territory with 800 bhp on a C-Class. Why do you believe your 100-200 kph times should be 5.2 seconds? What are you comparing with? Have you dyno'd your car or how do you know what your HP is? Dynos are done in nearly ideal conditions; real world conditions are seldom ideal.
Still, I can understand your frustration. That's why I manage my own expectations. I can outrun school buses and I'm happy.
It has been tuned by MSL and have dynoed to 730whp. I am comparing the timings with multiple other cars which have similar builds, tte910s, zac intakes, csf intercoolers, fx170 fuel pumps. I am posting a new video which after speaking to my mechanic he says cylinders 4,7,8 are not reading correct figures the figure should be below 0 so reading a minus figure, I am especially concerned about cylinder 8
Sorry, I missed this before. If you think there is a compression problem, then a mechanical test is needed, compression and leak-down.
You are in theoretical territory with 800 bhp on a C-Class. Why do you believe your 100-200 kph times should be 5.2 seconds? What are you comparing with? Have you dyno'd your car or how do you know what your HP is? Dynos are done in nearly ideal conditions; real world conditions are seldom ideal.
Still, I can understand your frustration. That's why I manage my own expectations. I can outrun school buses and I'm happy.
Anyone perform a manual compression test as mentioned herein? Would the brake/accel pedal technique work without a scanner connected?
I'm trying to see how to disable spark and fuel and be able to turn the engine over with a compression gauge fitted to the spark plug hole (ie manual/mechanical test).
Jay: You can find the fuel pump fuse and pull it. Not sure I would bother with the spark since you'll have the plugs and coils out. And it's best, test wise, if you have all the plugs out during the test because it cranks faster, and less power drain on the batt compared to one at a time.
Do yourself a favor and blow out the plug holes with compressed air because they can collect dirt and even little rocks. Then with the plug out that crap can end up in the cyl and you're Fkt, which is yet another reason to do plugs and this sort of work yourself because what are the odds the tech will?
I generally use shop air but sometimes use water or Carb cleaner first, depending on what kinda crap is in there.
Jay: You can find the fuel pump fuse and pull it. Not sure I would bother with the spark since you'll have the plugs and coils out. And it's best, test wise, if you have all the plugs out during the test because it cranks faster, and less power drain on the batt compared to one at a time.
Do yourself a favor and blow out the plug holes with compressed air because they can collect dirt and even little rocks. Then with the plug out that crap can end up in the cyl and you're Fkt, which is yet another reason to do plugs and this sort of work yourself because what are the odds the tech will?
I generally use shop air but sometimes use water or Carb cleaner first, depending on what kinda crap is in there.
Much appreciated!! Yep- had the same thought to remove all the plugs at once. And great advice on the shop air. Assume I may get a CEL for misfires? Or maybe not since the engine will never actually start and monitor...
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the figure should be below 0 so reading a minus figure, I am especially concerned about cylinder 8
