As a quick check of engine mechanical condition as well as Intake and exhaust system, one can evaluate how good of an air pump it is. This is known as VOLUMETRIC EFFICIENCY. I think that checking this could be used to easily rule out things like plugged exhaust / catalytic converters. I found a nice article here on what you can do with it https://ricksfreeautorepairadvice.co...ficiency-test/ and it included a link to a VE calculator on the OTC web site https://otctools.com/ve

I was going to try and spiff up the calculation, but ya know - it's plenty good enough for our purposes. All we really need to know is the MAF reading and Intake Air Temp at a specific RPM.

Here I chose 4000 rpm because it wasn't too severe and I could hold it at 4000 using the brakes in second gear. MAP readings are given to show no engine vacuum, throttle position shown to show it was floored. Note that my IAT converts to 100F. Result is a VE of 86%. This is for Les Myer's 2001 Blazer on 8/06/2025. 60K miles on rebuilt engine.

This is for the simple calc on the OTC site. I tried to fudge it up with temp correction, barometric pressure, data from Air Density Online, etc. Best I got on an extended calculation was a VE of 89. I say the OTC calc is good enough (at least in the Summertime). Feel free to add your data to this thread (simple MAF reading @ steady RPM is fine - but ensure WOThrottle) and if we get enough participation I will sticky it.

Les

 

Oooh! Fun! I love having data to analyze!

 

Yeah! You can get so much more than failure codes to replace a part!!! Of course you know this. Kick the calcs around and see what you think! I used some data from Air Density Online for Osceola Indiana race track. But it really doesn't fit very well for me VE%.

 

Yes I will, but onky after I get my front end back together. LOL

Do you live near Osceola? I lived in South Bend for a couple years in the mid-90s. It was quite the shock for me how flat it was having lived my whole life in WA and OR until then. LOL

 

I live in Granger, which is located in the strip of land between Osceola and the Michigan state line.

 

Les
Good stuff. I would be interested in the value that you get with the old standby 1-2 full throttle shift for comparison purposes. I know that you feel that the data may not be accurate due to the scanner update speed.

George

 

Hi George, I'll try to get that for you the next time I drive the Blazer. I just feel it is difficult to watch the rpms and the MAF at the same time when both are increasing rapidly, not to mention with the scanner scan rate delay. I suspect most people won't be logging - just watching the MAF alone on a scanner, while trying to watch RPMS on the vehicle tach.

 

Hi George, here's data from the 1-2 shift, twice. Looks like scan rate was around 0.1 seconds / 5 PIDs = 10 individual PIDs per second the way I have it set up.. My 13 year old BAFX Blouethooth OBD2 adapter is actually pretty fast on a 2001 Blazer. other vehicle are unknown. Way to check for slow obd2 adapters is if they give a stairstep when logging RPM. Or know that Torque Pro actually gives a scan rate for the connected vehicle (somewhere I found). Also attached is the air conditions for my location at the time of the test.

 

Les

Well, you were certainly right, the brake torque method generates essentialy the same VE result. Nice work.

George

 

thanks!! And now it would be nice to get your data. Just to a value at rpm is sufficient if you don't want to go through actually logging it. Would like a decent sampling of Blazers to know what MAF range is normal at full throttle 4000 rpm.