Is the amount of air measured approx. linear to RPM when engine just free-reving. - Alfa Romeo Forum
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Is the amount of air measured approx. linear to RPM when engine just free-reving.

Is the amount of air measured approx. linear to RPM when engine just free-reving.

Ex. if 350 at idle, then at constant 1900 RPN, the amount should be 700 & 1400 at 3800. (Offcourse still without any load on engine)

It a 2.4 210..But should be pretty same for any engine i“d guess :-)
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The 2.4 is turbo charged so it will depend on the boost
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It makes no real boost when not loaded ;-)
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the amount is dependant on egr, boost and volumetric efficiency. but roughly 450-480mg per cylinder per rev without egr or boost.
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Originally Posted by Cuore_Sportivo_155 View Post
the amount is dependant on egr, boost and volumetric efficiency. but roughly 450-480mg per cylinder per rev without egr or boost.
I hardly get more than 600 mg at 3500 RPM free-reving..Turbo can build pressure above 2K RPM when driving, but totally dead below. At idle it measures whats requested....350ish

EGR blanked, so no influence from that.

I do get a quite a lot of black smoke when pushing hard above 2K though, wonder if my MAF should have killed itself when my timing-belt died without any other damage..Or the (bit) leaking swirlflaps makes the loop bad, so the turbo never gets enough gasses to be able to spool up before the 2K mark.

Funny thing, if MAF...Theres absolutely no difference whether disconnected or not. VGT has been "oven-cleaned" & vacum from solenoid is fluctuating when flooring it in short bursts (freereving), so that side should be ok.
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ECU controls torque so doubt free revving would be representative of loaded air volume
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as mentioned earlier above
the maf should be approx 485mg/i at idle and boost pressure should be around 1000mb (at sea level, change for your altitude above sea level, quick google your pressure at altitude)
at idle or free reving the ecu will not be requesting boost but the car will make some just from the speed your reving up at and the ability of the vnt to reduce the boost so you may see boost go to 1100mb or 1200mb or so.
this will automatically increase the maf value, so for example 485mg/i x 1.2(1200mb)=582mg/i
this is a graph of mine doing idle and free revving in steps as example
maf vs revs graph.png
also the above calculation works pretty well for diagnosing things of say you put new map sensor on and boost is 2300mbar take your boost divide by 1000/485=2 so 2300mb/2= 1150mg/i maf
now if your cars showing 1000mg/imaf you can pretty much guarantee somethings amis.
of course it could be maf issue or manifold blockage or swirl flap or split pipe after maf or many other things but the relationship of boost and maf should be fairly constant (will vary with air temp and humidity and intercooler temps etc)
my boost div maf.png
and lastly if your egr blanked and your only reading in the 300s maf you have an issue right there

ps heres hopefully your ve map if not yours should be close enough, revs left column fuel accross top ve % in the table see nowhere is 100% and variations accross the table with revs and fuel.
2.4jtdm ve map.png
so engine can only breathe this % of theoretical 100% so 1500revs better than 3000revs free reving for example by a few percent so at same boost pressure 1500revs would have slightly higher maf than 3000revs with same boost pressure but 4% would barely be provable due to all other variables.
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Last edited by sussexa; 23-08-16 at 10:39.
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(Post Link) post #8 of 11 Old 23-08-16 Thread Starter
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Thank you VERY much for your effort Sussexa.

I have a former graph from when driving attached..Start of recording is <80 C & end on other picture is >80 C. I simply dont understand why the request for air is so low? its like its calling for less, both pressure & air...When its already low...Would imagine that is leaking swirls, it would call for more air, if it dissapered through there...Or am i toally of in my understandig of it...Since when at high RPM/load theres a lack of air/pressure.
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File Type: jpg 2.jpg (148.3 KB, 10 views)
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ok, there's too much information there to see a clear picture, but it seems the measured air quantity is less than the desired?

I'd double check the plugged EGR, it's not uncommon for the blanking plate to develop a hole.

how is the car running otherwise?
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Quote:
Originally Posted by Cuore_Sportivo_155 View Post
ok, there's too much information there to see a clear picture, but it seems the measured air quantity is less than the desired?

I'd double check the plugged EGR, it's not uncommon for the blanking plate to develop a hole.

how is the car running otherwise?
opposite with air :-)

its a little bit rough perhaps, idle is steady 850 RPM, a bit down from approx 16 to 14,5 km/l average.

EGR was ok when i blanked it, so would imagine it just to react normal if there should be a hole in the plate (Not removed in s/w, i have a dongle)

You should be able to se trends at the more steady periods of (hard) acceleration and idle :-)
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(Post Link) post #11 of 11 Old 23-08-16 Thread Starter
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I have attached a more clean one, where only air mass is shown + RPMs.


At approx. 1:27 where he revs it. This is from a 1.9 i do know..But mine doesnt give this kind od pressure at all when free-reving...More like 11-1300 Mbar.

Mine from start...Fully floored right from start in what i remember as 4.th gear:


This is how she used to start:

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Last edited by Chipmik; 23-08-16 at 22:04.
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