# VE calculation

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Hello,

I'm a little confused about the fuel calculation in "Modelled" mode.

I have the settings according to the attached screenshots and I get 78% Injector Duty Cycle at 6000rpm (TPS=100%) with a value of 12% in the fuel table.

According to the documentation this value stands for the volumetric efficiency VE, which seems pretty low.

All corrections are switched off, injector deadtime is ~1ms, Short Pulse Width Adder is all 0.

Engine is 4 cylinder, 2l, on ITBs.

Why is this value so low or is there anything I missed?

Regards, Fant

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The most likely is either your fuel press is higher or your injectors are bigger than you think.  You can use the injector test function and a measuring cup to roughly confirm flow rate.

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Injector flow rate is checked (and in spec) and also fuel pressure. The VE should be around 9 times the current value.

Edited by Fant

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Ok, could you post a map and log so I can check the calcs.

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Thanks Adam. What values do you need in the log? Maybe you could give me a hint what to look for so I can figure out the problem by myself.

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Ok, I just took a closer look and it does seem something is amiss(maybe a bug) in Links calculation.  Going off the runtimes posted above here's is how I would do a quick reality check.  Since baro etc is missing I will just assume standard air density which will introduce some error but should at least be close enough to give us a ballpark number...

Fuel density 0.74Kg/litre

Air density (std) 0.00122g/cc

Injector flow 264cc/min.  Injector mass flow = 264 x 0.74 = 195.4g/min or 0.00326g/ms

Fuel mass per cycle = inj Eff PW (x2 for group fire mode) x injector mass flow = 6.576 x 2 x 0.00326 = 0.0429g/cycle

Air mass per cycle = fuel mass x (target) AFR = 0.0429 x 14.7 = 0.630g/cycle

Air Vol = Air mass/density = 0.630/0.00122 = 516cc

VE = Air vol/cyl capacity = 516/499.5 = 1.03 = 103%

So as I say although there are plenty of sources of error in my calcs above, 103% VE seems in the ball park Vs the ECU's calc at 12% seems wrong from the info you have posted.  It will need the link techs to take a closer look.

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Hello,

I'm a little confused about the fuel calculation in "Modelled" mode.

I have the settings according to the attached screenshots and I get 78% Injector Duty Cycle at 6000rpm (TPS=100%) with a value of 12% in the fuel table.

According to the documentation this value stands for the volumetric efficiency VE, which seems pretty low.

All corrections are switched off, injector deadtime is ~1ms, Short Pulse Width Adder is all 0.

Engine is 4 cylinder, 2l, on ITBs.

Why is this value so low or is there anything I missed?

Regards, Fant

Two things stand out as out of the norm for a modelled mode set up.

One is the fuel system type being set to none.

And the injection rate being set as 1/2 cycle. (1/2 cycle is normally only used for single point injected applications)

For us to check the set up fully if you can email the full PCL file to us

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I would 100% agree with Simon here. The ECU needs to the fuel system type to determine the differential fuel pressure. The fuel pressure must move around at some point in the RPM range of this particular setup. With NO FP calculation the injector rate is used with no compensation to pressure. I would assume that the pressure is increasing to a point where it is actually making a difference and the ECU can not calculate this. Try switching to traditional and see if it changes. I have been meaning to bring up that the modeled fuel equation mode lately has been acting up for me. It would not even run the car the other day. My base was on a similar vehicle I had tuned like 3 months ago and the car would not even run until I switched back to traditional.

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I would 100% agree with Simon here. The ECU needs to the fuel system type to determine the differential fuel pressure. The fuel pressure must move around at some point in the RPM range of this particular setup. With NO FP calculation the injector rate is used with no compensation to pressure. I would assume that the pressure is increasing to a point where it is actually making a difference and the ECU can not calculate this. Try switching to traditional and see if it changes. I have been meaning to bring up that the modeled fuel equation mode lately has been acting up for me. It would not even run the car the other day. My base was on a similar vehicle I had tuned like 3 months ago and the car would not even run until I switched back to traditional.

I disagree...  This is a NA ITB engine.  FRP would not normally be MAP referenced in this case, fuel pressure would just be static.  Yes, diff fuel pressure will vary a bit over the engines operating range but not enough to make crazy VE numbers like Fant is observing.

I agree that Fant's settings are a little odd (For NA with ITB's I normally still have a MAP sensor and FPR connected to airbox to compensate for aerodynamic effects), but what he has set should still work and give believable numbers.  Since it doesn't my feeling is something is wrong in the modelled fuel equation - probably only apparent due to his choice of load =BAP, F system type = none and inj rate = 1/2 but still these are valid choices for his setup and should work

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I disagree...  This is a NA ITB engine.  FRP would not normally be MAP referenced in this case, fuel pressure would just be static.  Yes, diff fuel pressure will vary a bit over the engines operating range but not enough to make crazy VE numbers like Fant is observing.

I agree that Fant's settings are a little odd (For NA with ITB's I normally still have a MAP sensor and FPR connected to airbox to compensate for aerodynamic effects), but what he has set should still work and give believable numbers.  Since it doesn't my feeling is something is wrong in the modelled fuel equation - probably only apparent due to his choice of load =BAP, F system type = none and inj rate = 1/2 but still these are valid choices for his setup and should work

The reason for saying this is just that. Maybe the ecu does not know anything, in the case of it should, but does not is where I was trying to get at. I do believe that there is something wrong with the modeled fuel equation right now as it has been acting up for me. But typically he should shoot for Alpha N tuning on this and the numbers will most likely be a lot better. I have not looked at the base file. Seems as you have inspected it. But I agree to disagree on this issue. I would bet on the fact it is a bit of both issues. Have you seen logs? I don't disagree with your math. But something is definitely funky here. Single point injection was my main agreeing upon. In this mode 1 or 2 injectors is used to supply the whole engine with fuel. In the case it's usually before the throttle body. So it all is not making much sense if you can see where I am coming from? I have tuned a handful of ITB engines. This is not the way I would approach the base map setup.

Cheers,

Rich RDE

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This setup was created as a 1:1 replacement for an outdated, old and locked aftermarket ECU to be able to do tuning in the future when the engine gets new cams, etc. All the existing sensors were used and the behaviour of ignition and fuel injection was replicated and verified on a test bench. And yes, the engine runs.

Is there a way to see any internally calculated values which could lead to the right path?

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Hi Fant,

The best way to go forward on this is for you to provide a PCLog of the engine running in steady state at a few different points of the fuel table, and also the base-map used to create the log. You can either post them here (depending on size of log file), or email to tech@linkecu.com

Scott

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Hi Fant,

The best way to go forward on this is for you to provide a PCLog of the engine running in steady state at a few different points of the fuel table, and also the base-map used to create the log. You can either post them here (depending on size of log file), or email to tech@linkecu.com

Scott

Ok, Scott, I will email the files within the next days.

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Hi Guys

I was running the above setup about 6 months ago, Had the same problem the VE fuel tables values were very small. So compared air per cyl values and found by reducing the engine capacity from 1752 to 250 cc was able to have VE table around 70% WOT.

What setting makes this happen is "Equation Load Source:  Load = BAP"

Have since changed to Load = MAP  and all is good.

Solution for you is wait for correction from Link, or change your engine capacity value,  or if possible switch to "Load = MAP".

Hope this helps and best of luck.

Cheers

Andy

Hi Andy,

Cheers, Fant

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Hi Guys

I was running the above setup about 6 months ago, Had the same problem the VE fuel tables values were very small. So compared air per cyl values and found by reducing the engine capacity from 1752 to 250 cc was able to have VE table around 70% WOT.

What setting makes this happen is "Equation Load Source:  Load = BAP"

Have since changed to Load = MAP  and all is good.

Solution for you is wait for correction from Link, or change your engine capacity value,  or if possible switch to "Load = MAP".

Hope this helps and best of luck.

Cheers

Andy

This is very good information. Great to know. Thanks Andy!

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Hi Fant and Simon

Reading another post, Fant you do not have a MAP sensor so you need to change your engine capacity by dividing it by 10.

Simon

With Load = BAP there is decimal place correction required.

Cheers

Andy

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Andy, yes I think you are right with a factor of 10 being at play in the mix somewhere...

Fant, another work-around you could use to get you running with realistic numbers and settings would be to switch your equation load source to MAP. Then just set up one of the analog inputs as a MAP (but you don't need to have a MAP sensor connected), just set up the error value to 100Kpa so the ecu sees a MAP of 100 all the time.

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Engineering have taken a look and have found a issue that will cause the errors to vary from a small difference to a very big one.

At this point DO NOT use BAP for the load.

One option is as Adam mentions above to try.

Edited by Simon

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Engineering have taken a look and have found a issue that will cause the errors to vary from a small difference to a very big one.

At this point DO NOT use BAP for the load.

One option is as Adam mentions above to try.

Hello Simon, is there a date when this will be fixed?

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Andy, yes I think you are right with a factor of 10 being at play in the mix somewhere...

Fant, another work-around you could use to get you running with realistic numbers and settings would be to switch your equation load source to MAP. Then just set up one of the analog inputs as a MAP (but you don't need to have a MAP sensor connected), just set up the error value to 100Kpa so the ecu sees a MAP of 100 all the time.

Thanks Adam. But wouldn't I loose barometric fuel correction with this workaround?

I guess I will wait for a new firmware from Link.

One alternative would be to install a MAP sensor - seems this ECU was neither designed nor tested for pure Alpha/N.

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Hi Fant

You could still get baro correction by adding a overlay table spanned of BAP and then apply the correction this way.

If you were to run traditional mode it would also be fine.

I can say it certainly wasn't designed for Alpha/N but was intended to be suitable for this mode of tuning.

The Modelled fuel mode is a recent addition which has introduced this issue.

The fix shouldn't take too long but we want to do some testing as it is a bug that could have an impact on a number of areas so the time delay will be around testing.

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Hello Simon, is there a date when this will be fixed?

Hi Fant, the engineers have identified the cause of the problem. They are currently working on a solution, and once we have that we will need to do some pre-release testing. We will have it available as soon as we can.

Scott

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Hi Simon and Scott, ok, I will wait for the new release, thanks.

Fant

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Hi Fant, the engineers have identified the cause of the problem. They are currently working on a solution, and once we have that we will need to do some pre-release testing. We will have it available as soon as we can.

Scott

Hi Scott,

is it possible to say when the new release will be available?

Fant

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