problems with EFI car idle and pressure sensors

[dave.johnson at gb.abb.com]

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You could use a logarithmic TPS sensor....


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Please respond to diy_efi at diy-efi.org
Sent by:  owner-diy_efi at diy-efi.org


To:   <diy_efi at diy-efi.org>
cc:
Subject:  Re: problems with EFI car idle and pressure sensors

Security Level:?         Internal



TPS & RPM systems are TOUCHY. The trouble is  that at low RPM, the
slightest hint of a throttle
opening needs to cause a big change in injector  pulse length.

Ditch the TPS, and run a MAP sensor instead. Grab a  MAP sensor from a
80's=A04AGE toyota  corolla,
three wires: 5V, Gnd, and output (0-5V -=A0 4V  ~=3D~ 101.3 KPa).

TPS/RPM is not for beginners. Or anyone who cares  about idle.
----- Original Message -----
From:  David Sackett
To: diy-efi
Sent: Thursday, September 20, 2001 11:30  AM
Subject: problems with EFI car idle and  pressure sensors

hi, i'm developing a simple EFI=A0computer  based on a Atmel AVR
microcontroller running at 8Mhz for a Uni project. I have  installed it=
 on
my old 1977 Saab 99 and merged it with a Bosch D-Jetronics  fuel inject=
ion
system. the car originally had carbies and i have only used the  inlet
manifold, injectors and fuel system from the bosch system.

just to get started I decided to only use  throttle position and rpm as=

inputs to the computer. a lookup table is used to  determine the correc=
t
injector open time from these two inputs. we have  successfully perform=
ed
test runs in the car and it accellerates fairly  well.

the problem we are having is that we cannot get  the car to idle smooth=
ly.
the car refuses to run on all cylinders until it is  above about 2000rp=
m.
the car runs VERY rich and the plugs have to be cleaned  every 1/2 hour=
 or
so of running. if we reduce the mixture at idle it just  stalls. also t=
he
system fires all injectors at once every revolution of the  crankshaft.=
 i
have replaced much of the ignition system and am fairly sure it  is wor=
king
correctly.

does anyone have any ideas as to how to fix the  idle?

also i've read about the Megasquirt system that  uses an MPX4100 MAP
sensor, and as a general improvement to my system i wish  to add a simi=
lar
circuit board mounted sensor. I live in Melbourne Australia  and cannot=

find any distributors who will sell me less than 20 with a lead  time o=
f 12
weeks. does anyone know where i may be able to get just one sensor  or =
if
there are any other suitable alternatives?

thanks

David


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