how much boost can stock CIS handle?

[Kaklikian, Gary]

I'm also using an Autometer A/F meter with a MC-2 engine. Since I misplaced
the spec sheet, I can't confirm its range (0-1V per Ameer) nor do I know the
range of the MC-2 oxygen sensor. But what I do see is:

-A single led lit in the Rich range when the engine is warming up and in
open loop mode.
-The leds cycling rapidly throughout the Stoich range and a bit into the
Lean and Rich areas when the engine is operating in closed loop mode, at
idle and part throttle/low boost levels.
-Several of the leds in the Rich range lit solid at higher boost levels, not
necessarily WOT.

I do have two additional (Motronic) injectors cycled separately by a  MF2
controller that supply fuel above ~9psi boost (or wherever I set the
threshold).   The MF2 allows me to adjust the injector duty cycle in 1000rpm
buckets.  From strictly seat-of-the-pants testing, I've gotten the best
results when ALL of the leds in the Rich range are lit (pegged) when
accelerating hard under boost (>3500rpm , >9psi).  

I'd be curious to know what the actual A/F ratio is in these conditions and
whether I'm exceeding the range of the O2 sensor and/or A/F meter. 
What is the A/F ratio during warmup when only a single led in the middle of
the Rich range is lit, and wouldn't an extremely rich mixture under load be
indicated similarly?

Unfortunately, I haven't had the opportunity to tune using an exhaust gas
analyzer or dyno. I haven't checked emissions either since I'm using a test
pipe. Nor am I willing to shut the engine abruptly at high rpm/boost to
check the plugs.

I do recall that before I added the extra injectors (and a second fuel
pump), I would see only 2-3 leds lit in the Range range under load. Above
about 9psi, the CIS was unable to supply enough fuel, and the A/F meter
would go Lean suddenly (lucky I still have an engine!)  This engine has many
mods, including a larger turbo and intercooler,  so with the stock
intercooler, K26, etc the CIS should be fine to at least 14psi.

Gary Kaklikian
86 4ktq
92 S4

 

> ----------
> From: 	Orin Eman[SMTP:orin at wolfenet.com]
> Sent: 	Friday, October 20, 2000 12:06 PM
> To: 	ameer at snet.net
> Cc: 	quattro at audifans.com
> Subject: 	Re: how much boost can stock CIS handle?
> 
> > >An AFR gauge attached to the O2 sensor will only read from
> > >'definitely lean' to 'maybe OK'... unless you get one of
> > >the really expensive wide range sensors and meters... which
> > >would cost way more than say IA's box.  I think even the
> > >meter (unofficially) using Honda's wide range sensor
> > >is (will be actually) over $400.  (Search the archives
> > >on diy-efi.org for 'EGOR'.)
> > 
> > actually the one I have by autometer is pretty nice. It uses 20 led's 
> > instead of others which use 8 or so, and msd's which only has 2! So 
> > resolution is pretty fine. I can even see on the afr gauge when the ecu
> is 
> > adjusting the mixture w/ the freq. valve when the led's start cycling.
> The 
> 
> I make them myself out of LM3914s...
> 20 LEDs doesn't tell you anything more than 10.
> 
> > range of the gauge is dependent on the o2 sensor, not the gauge, b/c the
> 
> > gauge reads from 0-1V which is the max output range of the sensor. So
> it's 
> > not like the gauge is cutting off the extreme lean or rich values. The
> only 
> 
> It is.  The O2 sensor works in a very narrow range.
> 
> > The main point though is if the engine was running anywhere out of range
> of 
> > the stock o2 sensor, running would be extremely rough, there could be 
> > detonation, and emissions would be through the roof. I don't see the
> need 
> 
> Not true at all.  WOT or under boost, the system goes open loop,
> well out of the range of the standard O2 sensor.  Maybe Mr Mockry has
> put his exhaust gas analyzer on an 10V... I recall the 20V
> runs around 12:1 air/fuel under boost, well out of the range of
> the stock O2 sensor.
> 
> Orin.
>