"Bernd D. Ratsch" wrote:
> I'll email you all the specs from my work but here's the basics. (Sitting
> at home right now)
Thanks!
> MAP Signal (Normally Aspirated)
> Idle = 12-13"hg
> Part Throttle = 8-10"hg
> 3/4 Throttle = 5-7"hg
> WOT = 1-2"hg
> ** These readings were taken from a bone stock 1998 V6 **
I've had similiar results. Basically I'm guessing the MAP has the ability to
read in a range of approx 1"hg to approx 30"hg. But as you mentioned the PCM
takes a snapshot of the MAP at engine start time to get a baseline or "ambient"
pressure. It then uses this baseline in determining load. I've found that
based on what the outside or "ambient" pressure is, I'm reading ranges of either
1-9"hg or 8-30"hg from my scan tool. Maybe on days where ambient is already
kinda high it uses the higher scale (or vice-versa). It might be a method of
dealing with only 1Bar of resolution (response characteristics) on the MAP
sensor itself. I ran into this issue several months ago when trying to
determine if a MAP sensor was bad. I went into my directory of saved scans
covering about 2 years and discovered 2 different sets of values coming out. I
can only assume this is because of the changing outside or ambient pressure.
Whaddya think?
> MAP Signal (Supercharged)
> Idle = 12-13'hg
> Part Throttle w/mild boost (2-3#) = 14-18"hg (without check valve) - LEAN
> Part Throttle w/mild boost (2-3#) = 10-12"hg (with check valve)
> 3/4 Throttle w/boost (3-4#) = 16-20" (without check valve)
> 3/4 Throttle w/boost (3-4#) = 15-17" (with check valve)
> WOT w/boost (5-6#) = 28-30.8" (without check valve)
> WOT w/boost (5-6#) = 24-28.8" (with check valve)
> ** These readings were taken from my truck and a '99 R/T with a Powerdyne.
> **
These are pretty interesting also - from this data its easy to see why turbos
and huffers use 2 and 3-Bar MAP sensors - for the greater resolution on the top
end. Do you think it would help your situation?
> Keep in mind that the readings taken were on flat roads without too many
> uphill or downhill grades. Uphill will give a lower MAP reading (more load)
> and downhill will give a higher reading (less load).
>
> The voltage on the MAP runs from 1.7 - 4.3v (from what i've seen) with the
> higher voltage being lower vacuum signals. The 1.7-2.0v being at idle
> (factory specs as well) and 3.8+v being WOT/high load).
>
> Now at 28-30.8"hg under boost conditions, that leans the engine enough to
> "ping" unless the BTM is set at 1 on the START range (box) and at 3+ on the
> selector (dial inside the cab). What I do is monitor the TPS signal
> (4.2-4.4v being Wide Open on the blades) and then check it with the signal
> from the MAP. If the MAP is at 1.5v or lower, it bypasses the signal and
> replaces it with a preset voltage signal (3.3v - 4.5v). Once the TPS is
> below it's set monitoring range (3.3v-4.5v) it resumes the MAP's standard
> signal.
That makes sense - when you say "leans the engine enough to ping" - are you
seeing this also in you A/F gauge?
> I'm wondering about the VEC1 and what else it has inside its box. It's not
> a simple "Dual POT" system...i've tried (and built) that already. This way
> also runs about $25 at Radio Shack vs. $300+ from what most other companies
> are charging for a similar solution. Some fake the O2 signal, others fake
> the MAP signal...it all depends on how you want to do it. Personally, I
> found that the MAP signal is easiest to change and it resets itself
> everytime you start the engine anyway...no chance for "relearning".
I think that faking the O2 signal could provide good results if you could
somehow make it hover around 12.5 to 1 instead of 14.7 - I'm sure this would
eat cats but I wonder how much power it could unleash. Unfortunately the
electronics aren't trivial due to the frequency response and sensitivity of
those sensors. You would even need an expensive Wide-Band O2 sensor to dial it
in initially - not to mention dyno time. May as well go to an aftermarket EFI
at that point.
This is cool stuff for sure!
Latr,
Shane
-- '96 IndyRam-HisIndy-MPI/TB/Pulleys/AccelCoil/HookerSuperComp/CompTAs '96 IndyRam-HerIndy-numbered(#142)"Track Truck" '74 Triple-Black Dodge Challenger Rallye 360 home-brew EFI R&D vehicle '68 Black Corvette Convertible 427 (For Sale)
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