Per Mai from Scantune in Denmark has
mastered the PRS unit and here are a few
installation tips from him:
“The first thing is to plan the
conversion properly, to get the theory
right from the start. It is important to
understand the way PRS works and,
equally important, how the OEM engine
management works. Draw a diagram and
think every single function through. The
success of a project depends on the
knowledge when entering. So gathering
information is the key.
Access to a scope and a digital
multimeter is important too. In most
cases, I fit the PRS as a wire-in. It is
by far the easiest way and gives the
opportunity to do it step by step.
Another advantage is the OEM wiring is
often of a far better quality, than what
you can make up yourself. Noise and
other problems can be avoided. Functions
like idle and tacho can be taken care of
by the ECU and will not occupy any PRS
outputs.
Input
Signals that can be shared with the OEM
ECU:
1. CAS Crank Angle Sensor (in most
cases)
2. AMP or MAF
3. TPS
Signals that can't be shared:
1. WTS
2. ATS
1. CAS: You can decide if you want to
use the OEM pickup or want to build in
an external pickup(s). Pickups on the
crank provides the best signal due to a
higher speed and amplitude. Magnetic
pickups placed in the distributor
provide a very weak signal and should be
avoided. Problems occur when
cold-starting the engine. Another way is
to look for a signal from the OEM ECU
that can be used, like tacho. If the PRS
is to be used as fuel-only this option
is perfect.
2. AMP: An important thing to notice is
that the acceleration enrichment is
calculated from this input. In some
cases it is necessary to swap AMP with
TPS. This gives a far better throttle
response but makes tuning more
difficult.
3. MAF: Never done it.
WTS: PRS2/4. I replace the 2k2 resistor
with a 10k miniature pot meter. Without
that calibrating is a struggle.
ATS + WTS: PRS8 Use an inline 10k
miniature pot meter.......
Output
The resistance on every single output
has to be measured with a multimeter
before connecting, to avoid overloading
the drivers. If The OEM ECU is left
active to serve other functions, it is
best to solder in "Dummy resistors" to
the disabled outputs from the ECU.
Before fitting the PRS, it is a good
idea to measure the injector's operation
time in specific situations, this makes
tuning a lot easier later.
Like:
1. Cold / warm cranking
2. Cold / warm idle
3. Cruise, 5 specific rpm
4. Full load. 5 specific rpm
The more data the better.
A set of sparkplugs 1-2 groups warmer
than standard will be a help. It makes
it easier to recover flooding (this will
happen).
Any settings that will influence fuel or
ignition should be disabled.
Deflection: lowest rpm point should be
no more than 300rpm; this gives the
opportunity to specify a cranking
injection time.
Tuning fuel.
Described OK in the manual. A zero in
the lower right corner will create a
clear-flood area.
Tuning ignition.
I start with a base map with a linear
rpm advance form 10º at idle to 32º at
6000rpm in all columns.
AMP advance is set to 0º at 0.2bar to
12º at 0.6bar then 0º at 1bar then
linear upwards crossing 2bar with -10º
My tools are:
Two dual channel pc scopes
A single channel handheld
A multimeter
A signal generator/editor
WBO2
4gas
An eddy current dyno w/data logger
A stone age-knock-alarm (a set of
hearing protection with a 4mm plastic
hose to a small tube bolted to the
engine)
Have a look at
www.velleman.be
