[s-cars] Overboosting..Revisited - and the culprit is...

[Tom Mullane]

Firmware (the chipset).

Before I explain, I owe a huge "thank you" to Adam Cramer and Marc Swanson.
Adam loaned his ECU to me for testing purposes, shipping it cross
country in exchange only for my promise to return it (we've never
met).  Marc loaned me just about everything else, allowing me to use
his car as a rolling parts bin, often in the middle of the night, as I
swapped and reswapped trying to exorcise my demons.
Thanks also to Mike Cialowicz and Bob Sass.  Mike let me borrow his
ECU and Bob pulled it out of the car for me.  And lastly, thanks to
fellow listers who emailed me over a dozen suggestions and ideas.

Anyway, it appears that my Chipset (and Marc's, which is cloned from
mine) is responsible for demanding the high levels of boost.  I'm
guessing that the MRC  chip may have had some sort of glitch (it's a
custom chip, not "off the shelf" so others need not worry) but that
still makes me wonder why it doesn't do the same thing in Marc's car. 
The only difference is that my turbo is an RS2, Marc's is a turbo from
Javad that is supposed to be similar.  Marc and I have swapped ECU's
several times; regardless of whose ECU is where, Marc runs 26 psi and
I run a million psi.  One thing I recall about the tuning session when
Mihnea worked on the car was that he told me to crank down on the
wastegate spring 6 turns before we hit the road.  After we returned
from the highway runs, he told me to back the WG spring screw out
three turns.  Odd.

Currently, I'm running RS2 turbo, MAF and injectors (the later two
purchased from what used to be Adam's avant) and the ECU is Adam's
with an IA chipset.  Boost peaks at about 25 psi.  I tried Adam's
chips in my ECU with near identical results, so I guess the VMAP is OK
(Adam runs the Bosch transducer).  The one thing I haven't tried is to
reinstall the MRC "plain Jane" chipset that I was running prior to
custom tuning.

I like the IA chip.  It's not as linear as the MRC chip, and the car
isn't quite as fast (25 psi versus 32 psi - go figure), but it is
smooth even under light or moderate throttle and the car is still
plenty quick.  It's tempting to buy the ECU from Adam, but I think the
current plan is to go back to the custom MRC chip and take it easy for
awhile.  We have a local tuner, experienced in the 1.8t and 2.7t, who
is going to be getting into the urS market shortly.  Perhaps I will
let him sort it out.  ...unless, of course Mihnea is around and wants
to take a look at it...?

Tom

On 9/2/05, Tom Mullane <tmullane at gmail.com> wrote:
>
> Folks,
>
> I have a strange problem with my 95.5, and I can't seem to get to the bottom of it.  The car will overboost to 30+ psi in fourth and fifth gears.  I assume it would do the same in the lower gears, but it accelerates fast enough so that pressure is unable to build to these levels.
>
> Some background:  The car has 82k on the clock, RS2 EM and turbo, Stromung, 34 lb/hr racetronics injectors, stock MAF, Hyperboost BPV, and Mihnea's custom tuning.  Wastegate spring is at the factory setting.  There are no boost leaks or ingition problems.  Since Marc S is running a nearly identical set-up (034efi turbo and stock exhaust are the only differences), I have been swapping parts back and forth between our two cars, attempting to isolate the issue.  Marc's car runs about 26 psi.
>
> So far I have:
> Reverted back to Minhea's "off the shelf" standard chipset for the RS2/34# combination
> Swapped ECU's
> Swapped the altitude sensor
> Installed a new WGFV
> Unplugged the electrical portion of the WGFV and observed 7 psi max boost
> Swapped the wastegate
>
> Since I just recently started running an installed boost gauge, I have no idea how long this problem has existed.  I suspect it was there even last year when Mihnea tuned the car.  Before we went out, he had he uncap and crank the WG down 3 turns, but after the tuning he told he to crank it back out 2 turns.
>
> I'm running out of ideas.  Anyone?
>
> TIA
>
> Tom