[s-cars] unstable idle problem solved

[Trevor Frank]

Ah, brilliant question,...I have not seem much difference in clearing up
negative boost that would require a change in software, as far as the
maf is concerned.  Custom software would always be best though. 

1)     Larger maf and a hot plate, even more, means that you will no
longer have to worry about the hot wire ripping out.

2)     Less restriction in the intake means less work done to get a
given amount of boost.

3)     If you use a voltage mapper to emulate whatever voltage you
want...i.e. mimic an rs2 you can use rs2 software.

4)     The negative is if you use rs2 ish software then you will no
longer have the maf at high flow there to aid in determining load etc
for the ecu since audi did a very good job of getting the rs2 maf to
full scale i.e. 5v at full load on a low hp motor...what 320ish.

5)     If you use a voltage mapper you can use whatever maf, a very
large one, and with custom software you can map it so that the ecu at
idle will have what it wants as far as voltage goes...around 2v if I
remember right, the American ish maf's that I have  used are at around
1. If the voltage is out of scale from what the ecu expects at idle it
will not allow it regardless of mapping, from what I understand about
what I have seen.  Ok so idle works now you can back off on the voltage
offset and allow your now large maf to go to full scale matched to
whatever that is on your car.  That is if you can find a maf big enough,
if not at least it will be much closer to it than the anemic RS2.



So what does this mean...well to illustrate, you have a 500hp car, and
your maf will give you 5v at 550hp/full load on your car.  But at idle
it only ouputs 1v.  So you offset the idle voltage with a voltage mapper
to 2v, then back off the voltage offset till you get to your full load.
So you can get full scale on your maf and so you are showing full load
to the ecu you offset your 500hp let's say this is only 4.5v so you
offset it by adding .5v.  Now the ecu sees 5v at your max hp.  



RS2/resistor offset.  From what I have seen people take, let's say a 928
or what Camero bosch maf.  On the same motor it would give let's say 1v
at idle and let's just say it's also 5v at 550hp.  Then they do a simple
resistor offset to get it to idle, so now you have it at 2v at idle, but
you have also crippled it at higher loads and offset it by 1v, so
instead of having 5v at 550hp you have let's say 5v at 400hp.  Now the
ecu from 400 to 500hp doesn't have the maf to add to the scaling of fuel
ect.  It just knows that the maf is at max load.



Take my car, with my rs2 maf and taking data from the voltage output of
the maf at full throttle at around 3500rpm my maf was at full voltage.
So from then on the ecu used, what speed density to do the calcs, still
not bad but honestly I still think that if you are going to bother with
using the maf you might as well get the benefit of having it functional
thru the rpm range.  Otherwise let's all just go to stand alone speed
density, which isn't such a bad idea either.



As I have seen most people just re-use rs2 software/maf mapping
regardless of the maf, like the big 928's.  The guy's in germany that I
have talked to use a simple resister offset so that they don't have to
figure out something new as far as mapping goes.  I think that they are
missing the boat, it is better imho to have the larger maf allowed to
work so that you have it there for your load etc..calcs at higher than
RS2 relative loads.



-----Original Message-----
From: Robert Myers [mailto:Bob at chips-ur-s.com]
Sent: Friday, May 06, 2005 2:27 PM
To: Trevor Frank; Elijahallen92 at aol.com; es2 at audifans.com;
s-car-list at audifans.com
Subject: RE: [s-cars] unstable idle problem solved



At 05:20 PM 5/6/2005, Trevor Frank wrote:



Go to stand alone or...you can do what I did...about $600 total with a
4.5"inlet and 4"outlet, I will give you the voltage offset's you need so
that your software doesn't even know you changed the maf.


Now the next question: why do it if it makes no difference to the
software?  It's the software that controls fuel flow and timing, not the
MAF.





Bob
Http://Chips-Ur-S.com <http://chips-ur-s.com/> 



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