(02-02-2014, 10:29 PM)pro_steve Wrote: But the problem with masking the fault is the car will always be smoky/bad on fuel, when they ask who tuned it it comes back to you doesn't it. I've done it a few times when setting up a car with a bad MAF, but I do it so that once a working MAF is plugged in it over rides the setting, probably be easier if I kep a pile of MAFs in stock?
I agree Steve.
If you can't afford a MAF, or just go to a scrapper and pick up a few cheap and test them out (95% of the time MAF are fine over the hundreds of cars I've seen) you are not gonna be able to afford a MAP sensor and the time/effort to do that, AND then have the appropriate remapping changed which is a faff, to suit the mods.
MAF is only really present because of EGR, EGR needs to get AFR really accurate to keep emissions perfect.
So you could argue MAF is the best solution all round. The problem is sizing at big power. But the standard MAF in theory is calibrated (that means it meters pretty accurately) out to 180bhp... even with some non-perfect metering it'll be fine to 240bhp purely on the cross-sectional considerations of restriction.
I'm fairly certain there is a MAP in the ECU that is what is used when the MAF is un-plugged, that is basically a Look Up Table for MAF values when they are not provided. To run without a MAF is basically running off another MAP that guesses what MAF value will be present at certain RPM and throttle inputs.
Like Steve says, you are 100% better with the MAF present than not because it is measuring all sorts of variables and real air mass, vs guesses mapped into a LookUpTable (LUT).
As per boost adjustments impacting fuelling, you can do that too with MAF. More boost = more MAF flow = more allowed fuelling.
You can punt around with 0.9bar boost and about 130bhp, then as you turn the MBC up to 1.3bar you get about 155bhp. Weeee!
If the smoke map is populated properly with good values that is how it should work all the time surely!?
That is if you don't use the boost control on the ECU, which is as much a pain in the arse as anything.
Remember that it's values are hard-set (calibrated) to the smoke map, and advance maps and everything else. It's a circular tuning affair. Changing boost request low down will impact restriction on the turbine, lean out the AFR, change the ideal advance point in steady state etc etc...
I guess if you went really wrong you could end up with a smoke map set such that the requested boost might never be met, or not met so easily, because the AFR allowed via the smoke map isn't enough to get turbine energy up to achieve the required boost.
In the end I think unless you are gonna fit a 200bhp+ engine with a VNT turbo, then keeping everything standard HDi90 with a working MAF is perfectly tune-able and fast and good enough.
MAF-less is do-able but just unplugging it and tweaking the appropriate map is 'ok' if you are THAT tight for cash (for a £15 spare from a scrapper)
MAP seems a backwards step for me. It's slight advantages are outweighed by a complete faff of work. If you want mega power just use a bigger MAF. Iirc some C5's use a MAF that will meter accurately out to 240bhp or so of air, and they are a fair bit fatter too, probably 280bhp theoretical air flow limit.
Dave