PMAS vs Gen3 airbox

[WildHorse]

right, so, after a week or so .. with the screen it's removing more fuel than adding. LTFT went to 9%.

I download that VCM scanner so I can DATA log and one of you HPTuner guru's can take a look at the logs.

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[K4fxd]

This is on the stock airbox and tube, errr 18 up?

 

[GregO]

so, after a week or so .. with the screen it's removing more fuel than adding.

What does that tell you ?

 

[K4fxd]

What does that tell you ?

It tells me either it is flowing less air or the signal is better causing the meter to be more accurate.

I'm going with "B" More accurate.

 

[NightmareMoon]

+9% or -9%? -9 would be removing fuel.

If it were simply flowing less air and than it was (with an accurate signal before the screen mod and afterwards) then it wouldnt be trimming. It would see the correct air, see less of it, and supply correctly less fuel w/o trimming.

In closed loop operation, the trim happens when the tables which take mass air flow as an input now give different results in measured exhaust o2 for the same input airflow signal. I.e the car ‘sees’ more air, supplies more fuel and then goes ‘whoa that was too much’.

Negative LTT means it simply doesnt need the fuel to maintain its target fuel richness, that could be because the maf signal values are smaller now than the true air, or its just easier to stay above it’s target AFR marks because the values are cleaner.. the former isnt good or bad or even idicate flow increase or decrease, it just indicsts the computer inputs are different now versus reality (as indicated by the o2 sensors).

To draw a comclusion about actual volume of airflow while we’re messing with the very sensor, you’d need a third party opinion like a dyno. The MAF sensor doesnt meter air (it doesnt count every molecule or measure pressure in the intake manifold after the TB, it infers airflow by taking up a very small sample in the intake tube and inferring flow through the rest of the tube. If the air there is turbulent or asymmetrical, changes to that flow to even it out could cause the MAF signal to read higher, lower, it depends.

 

[K4fxd]

It's pulling fuel. The ECU thinks it's getting more air than it is. Hence pulling fuel. The engine is getting less air than what the sensor is telling it.

Which makes sense if the air is now laminar with it being turbulent before.
I would assume as engine speed increases the miss-match will get smaller.

 

[WildHorse]

I would assume as engine speed increases the miss-match will get smaller.

That's exactly what happens.

 

[K4fxd]

That's exactly what happens.

Do a log and in the areas where it is off make a half correction. In other words if say period 760 is 10% rich, lean it out by 5%

If you don't have tuning software 10% pulling fuel is perfectly safe. Personally I like them pulling fuel instead of adding.

 

[WildHorse]

Do a log

So I downloaded the VCM Suite onto my laptop. Also have a OBDLink EX dongle . Is the suite what I use to DATA log ?

 

[K4fxd]

VCM scanner to log, but I believe you need an MPVI dongle.

I think the EX works with Forscan.

 

[WildHorse]

VCM scanner to log, but I believe you need an MPVI dongle.

Soooooo you can't just go direct from the OBDII port straight to the laptop ?

 

[K4fxd]

Soooooo you can't just go direct from the OBDII port straight to the laptop ?

I've never tried it. I have a MPVI2. If the EX works let us know.

 

[NightmareMoon]

Soooooo you can't just go direct from the OBDII port straight to the laptop ?

Unfortunately VCM suite is an HP Tuners product and it only works with their ODBII devices. The ODBLink EX is not one of theirs.

 

[WildHorse]

Unfortunately VCM suite is an HP Tuners product and it only works with their ODBII devices. The ODBLink EX is not one of theirs.

Thanks for the heads-up.

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