Torque Pro unit conversion for MAF?

TrogDorInjection

Well-known member
Joined
Jan 6, 2007
Location
Portland, OR
TDI
2001 Jetta ALH 5 speed 148,000 mi
2001 ALH with manual transmission, stock turbo, 170,000 mi

I'm logging IAT, MAP, coolant temp, and timing advance with Torque Pro, and the values and units all look fine, but the MAF reading does not.

At Idle I get ~11 g/s, and when I tried to floor it on the highway in 3rd gear I could only get it up 83 g/s. However, the reference value is something like 900 mg/hour.

When I do the math, 900 mg/hour becomes 0.00025 g/s, rather than 11g/s. Is this 11 g/s number typical output for Torque Pro?

And if 900 mg/hour is the normal idle value, should it max out at 6790 mg/hour?
 

Diesl

Veteran Member
Joined
Dec 3, 2012
Location
Chicago
TDI
'78 Golf Diesel (long gone); 2012 Jetta Sportwagen TDI w/ DSG
Where is that 'reference value' coming from? Tens of g/s sounds reasonable, 0.9 g/hr does not.
You can do a quick order of magnitude estimate based on your fuel use: assuming you use about 6 L/hr, which is about 5kg (give or take), and the fuel is mostly chains of CH2, you need three parts O2 for 2 parts CH2 (to get two parts CO2 and two parts H2O), so that makes 96 gram of O2 (molar weight 2*16) per 28 gram of fuel (CH2 molar weight 12+1+1). The O2 comes diluted in air (23.2% by mass) so you'd get 96/(28*0.236)=14.7 times as much air as fuel if the car ran with just enough air to burn the fuel. (You could also just google 'diesel stoichiometric ratio'...) Of course as a diesel it runs a lot more air. So 15*5=75 kg of air per hour is kind of the minimum you should read. 72,000 gram/3,600 seconds = 20 g/s.
 

TrogDorInjection

Well-known member
Joined
Jan 6, 2007
Location
Portland, OR
TDI
2001 Jetta ALH 5 speed 148,000 mi
Thanks Diesl for reminding me of my Chem labs! Haynes manual quotes 200mg/H at idle (I assume "H" means hour) going up to 800mg/H at 3000 rpm. I saw a screenshot of VCDS that indicated units of g/str (grams per stroke). Now I'm thinking 200kg/h is a more reasonable number. I'll ask Torque Pro Forums for an empirical value.
 

altz1

Veteran Member
Joined
Jan 15, 2015
Location
Estonia
TDI
A8 4H 4.2TDI, Cayenne 4.2TDI, 6.0TDI
Probably in manual 200 mg/hub (stroke) and its ok, if egr is active.
 

BobnOH

not-a-mechanic
Joined
May 29, 2004
Location
central Ohio
TDI
New Beetle 2003 manual
Yes, I would expect the values to be somewhat close to expected. Low or high won't be by a factor of 10 or more. Careful with that Haynes manual, the Bentley has enough errors, the Haynes will have more.
A4 TDI engine measuring blocks/groups
shows many of the ranges.
 
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