Smooth running values and chassis numbers
As many of you know I do not work on Euro vehicles if I can help it. I just have never had the training on them or the car count to make it worth my while.
For those of us that do not work on euro cars can someone explain how to use smooth running values effectively?
Also is there a way to easily find the chassis numbers?
thank you for the help!
What Brand are you having a hard time finding Chassis numbers for? BMW, Mercedes, VW/Audi?
Hi Aaron, thank you for replying. For me it’s normally Mercedes and the earlier ones seem to be hardest for me. I can use my launch and enter the vin and get them that way normally though.
I was trying to be general across the board as I know this is something a lot of us struggle with that don’t work on euro cars as often.
The most accurate way for me is to enter the VIN into whichever VIN decoder you like. Alldata does a really good job when you enter the VIN. It will show the chassis number and engine number in the vehicle description.
Of course, the factory scan tools will show this as well when you enter the VIN.
I'm sure there are other ways, but I usually need to enter the VIN in Alldata or the scan tool anyway, so since that does the job, I haven't had the need to do it any other way.
Hope that helps. Have a good one.
If you need deeper decoding to find vehicle option codes and such, there are some free BMW and Mercedes decoder websites that I will provide links to. I've used them a few times and they work very well for this, but as with any website, use at your own risk. I assume they are safe since I've used them without problems before.
Here's a decent up-to-date list bimmerworld.com/About-Us/BMW-C…
Smooth running measures and compares cylinder rotational speed. With smooth, i.e., uniform combustion, you are looking for values at or near zero. It's a great diagnostic tool, but you are on your own after you find the problem cylinder(s), unless of course you have misfire or other related DTCs. It's good at finding small issues before they become a problem. I believe it was developed way back in the 90s for warranty claims on the Nikasil V8 blocks that were eating themselves.
Here's a tech document explaining smooth running in factory speak,
The smooth-running values of the individual cylinders are indicated for troubleshooting purposes. The engine must run at idle speed for at least 3 minutes to ensure that the correct values are set. Smooth idle speed can only be evaluated with the engine running at idle speed (cold or hot). An indication of the combustion quality of individual cylinders can be obtained by evaluating the crankshaft acceleration, measured at the crankshaft position/rpm sensor. An individual cylinder with poor combustion can be detected very well in this way. Random fluctuations of the individual cylinders can only be detected by close observation of the value. The values over all cylinders are zero in the engine with theoretically uniform combustion. An increase in the smooth-running values may be caused by various factors (e.g. misfiring, secondary air, mixture deviations, faults in fuel supply, low compression). For this reason, exact intervention limits cannot be specified. The rotational speed (engine speed) of the engine is measured at the incremental wheel with the aid of a hall-effect sensor. Moreover, the smooth running of the engine is also monitored (misfire detection) as a measure of the engine speed. To detect misfiring, the increment gear is divided (by the control unit) into 3 segments corresponding to the ignition interval, i.e. 3 sparks per crankshaft turn on a 6-cylinder engine and 2 sparks in 2 segments on the 4-cylinder engine. Within the control unit, the periodic duration of the individual increment gear segments is measured and statistically evaluated. For each point on the characteristic map, the maximum permissible rough running values are stored as a function of engine speed, load and engine temperature. If these values are exceeded within a certain number of combustion cycles, the cylinders detected as faulty are stored in the fault code memory.
Thank you Mr Burke! BMW data is fine, I thought this would be a good topic for all to learn from since Euro manufacturers use this instead of cylinder misfire counters. Any input for any manufacturer is good info!
You can use the operational smoothness to locate an issue that is affecting a cylinder, but not bad enough for it to cause a light. It's a nice feature to use.
The best way to use smooth running values or true running values for diagnosis is to graph the data, and also to set the scale for the graphs so that they are all at the same scale.
The snap on scan tool is great for graphing these, but as you know, snap on automatically scales the graphs which isn't good for this test because you are trying to find a very slight rough idle usually, and the numbers are moving too fast. That's ok, you can just manually set the scale for each graph to be the same. I think you have to do it in ShopStream though.
What you want to do is just find the odd cylinder(s) that have more "noise" or values that are off from other cylinders, whether it's positive values or negative, you just look for the odd pattern, as seen in this screenshot
That’s a great way to look at them, makes it easy to see. Thank you for the advice!
If you use Alldata they give you the Chassis number on BMW and Mercedes when you enter the vehicle info in at the top of the page. There is also real OEM which will give you the info for BMW with the last 7 digits of the VIN. There are other decoders through the factory sites if you need more detailed info but these are quick and free if you already use alldata.