This article describes the conversion of a carbed
1968 Volkswagen Type-3 Squareback to Megasquirt-II controlled Fuel Injection.
Starting point:
1968 Volkswagen Type-3 Squareback, 1776cc engine
with Engle-100 cam, "Berg Special" 42mm Weber DCNF carburetion,
1-1/2 quart Berg Sump, Full-Flow oil system with Setrab auxiliary oil cooler,
plain 009 distributor and a Bosch blue coil.
This car is my sometime daily-driver and
long-distance cruiser. On carburetors, it gets around 25 MPG. I was never able
to solve a serious lean transition issue with the Webers, resulting in
overheating problems. Getting jets for these out-of-production carbs was also
becoming a problem.
So the object of this conversion is to use most of
the stock type-3 intake system (manifolds, plenum, air-cleaner), modern
injectors and sensors and a Megasquirt-II ECU.
In this iteration, we will only be controlling
fuel. No boost either. Ignition control may come later.
Process
Since I didn't know anything about fuel injection
systems, I started with an internet search. What I found was a thread already
in place in which the original poster had started down the Megasquirt /
type-3 mind-meld, but then went in another direction.
Most of this build is chronicled in that thread.
http://www.shoptalkforums.com/viewtopic.php?f=23&t=132864
The inner workings of the MegaSquirt EFI solution
are described on the MegaManual web-site.
http://www.megamanual.com/
I learned that for fuel-only control, I needed a
Throttle Position Sensor (TPS) and two temperature sensors to measure Intake
Air Temp (IAT) and Coolant Temp (CLT). Megasquirt also requires Manifold
Absolute Pressure, but most of the MS boxes already have a built-in MAP
sensor to which one simply connects a vacuum line with the manifold at the
other end.
The TPS is used mainly to detect rapid throttle
movements in order to apply an accelerator enrichment. This is the FI
equivalent to the carburetor's accelerator pump.
The CLT measurement is used to drive an enrichment
function when the engine is cold. This is the FI equivalent to the choke on a carburetor.
The IAT measurement goes into the control
algorithm as part of the math involved in calculating the amount of air going
into the engine at any time. The ECU also needs to measure the Manifold
Absolute Pressure, another necessary parameter of the Ideal Gas Law. The math
behind the Megasquirt control algorithm is explained on the MegaManual web
site: http://www.megamanual.com/v22manual/mfuel.htm
Shopping List
ECU : Assembled
MS-II from DIYAutoTune
Wiring Harness :
12' MS1/MS2/MS3 harness from DIYAutoTune
TPS : Bosch
0 280 122 001
IAT / CLT Temperature Sensors : GM
Closed Element CLT / IAT Sensor with Connector from DIYAutoTune
Injectors : Spec for a 1997 Ford Escort 2.0 liter 110 hp from
autopartswarehouse
Fuel Pump :
Airtex
E2000
Fuel Pressure Regulator :
MSD
Boost Adjustable Fuel Pressure Regulators
The above adds up to a little under $1000. It
will only get you started. There will be plenty of incidentals to keep you from coming in under budget.
In order to establish the basic functionality of
the Megasquirt ECU in the comfort of your bench, build or buy the
MS-Stimulator. It plugs into the ECU where the wiring harness ordinarily
would be and 'simulates' the primary engine sensors and signals. I'm
color-blind so I just bought this :
MegaSquirt
Stimulator v2.2 - Assembled Unit from DIYAutoTune .
You will need a portable computer (laptop) to
interact with the Megasquirt ECU. I happen to have a little ASUS my kids got
me several years ago. Almost anything that will survive a ride in your car
should be sufficient.
I highly recommend use of a wideband O2 system
for tuning you new engine management system. The point of your new FI system
is to properly supply the correct amount of fuel to the engine under all
conditions. A wideband O2 system is how you will directly measure the
resulting Air Fuel Ratio (AFR) and determine how to adjust the Megasquirt's
various data tables. One popular WB O2 solution is the
LC-1 from Innovate Motorsports. This will run you about $200.
Construction
Injectors
Fuel Loop
Throttle Position Sensor
Coolant Temp Sensor
Intake Air
Temp Sensor
Wiring