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[T3] FI Wiring Harness and Lowered Compression


You have the question on your throttle switch 
connection ? Also you have a question on your 
compression lowering using EFI.

Do you have a four wire throttle valve switch ?
Is your harness plug a four wire one for this ?
Do you have a Bently Manual ? Turn to page 
17, 18 and 19 . this shows the connections to each 
component and their connection to the " brain ".
The connections will vary depending on the year. 

The switch on my car can be disconnected with little 
effect on the EFI system.

The eariest year (1968 to 1969) throttle valve is installed
to turn off fuel to the injectors or at least
minimize it to prevent backfiring when removing the
foot from the pedal or going down hill or in 
other words , high vacume conditions. The earliest has 
two wires (screwed in ) and they are pins 20 and pin 
17 on the throttle valve switch (they are casted
in the switch )to the same pins on the  
"brain" . The Brain is ver "A" or "B"
(Part # 311 906 021 A or B)

1970 to 1972
The next version of EFI system is shown on page 18 in the EFI
section. This version uses the brain known as the  
" C" brain (Part # 311 906 021 C ) and has the gas 
pedal pump feature incorporated that 
the last versions did not have. The throttle valve 
switch has four connections on it and has the 
pin numbers 9, 14, 17, and 20 casted on it and these
go to the same pins on the "brain". This switch has two
features now: the deceleration mixture control 
(prevents backring) and the pedal gas pump .
The addition of the gas pump feature provides
additional 25 injections per full throttle movements
when throttle is at rest. This provides more gas when 
starting car (pumping gas pedal when engine has not started)
and when accelerating faster when foot pedal is pressed 
in; just like a carburator acceleration pump feature.
If you open this Switch you can see about 25 little connections
that provide electromechanical control of the pump
feature as well as electromechanical control of the
antibackfire feature.

1973 (only one and last year)
The latest version I am not fully familiar with since 
I do not have this brain. It should be the "D" brain
(part number 311 906 021 D ) . I beleive this is 
an emission brain that has the exaust gas circulation
valve relay incorporated to it . The Throttle valve
switch has 5 connections ; 9, 14, 17, 20 and 47 which is
ground. All connections go to the brain of the pins of the same 
number except pin 47 which is ground. These pins are 
casted in the switch. The features of this version
are probably made for emissions control and may
provide electronic control of the features of the last
version instead of electromecanical.

After said all of this, you should match your brain with the 
switch, if your brain is an older one , you should use 
the two connection switch and so on.

It all depends on the brain style. The system will
work with a disabled switch , at least in my system.
My car is a 1969 and I set my car up with the 
throttle pump feature using a newer throttle valve switch
and a " C " brain . I just wired it up like it should.

If you need a different switch to match your brain 
and wiring just ask the list about one or you can buy
a new one or find one in the junk yard like I did.
You can find one in a pre 1975 luxery Mercedes
with V8 or 1973 volvo with D-jectronic or all
70's Volvo with straight 6 cylinders; they
have similar bosch switches to our cars. 
The wire connectors on these cars are similar
to ours. All these items are available new at their 
respective dealerships. If you cannot find the
plug or switch e-mail the list or me we can 
help you get one. you can get new connectors,
pins, and plug from the dealership.

I have gone thru this before. I hope I did not
give you any incorrect information, the guys on the
list should be able to straighten me out if my
data has flaws.

What version brain do you have ?

----Your compression question .

Lowering compression will not affect your EFI
operation at all in fact EFI can take compression
modifications bettter than carbs. The recommended 
modification (my recommendation, other people on 
the list may not see it the same way as I see it)
is to make your Pressure sensor adjustable to
adapt it to your driving conditions and engine 
requirements. More the compression less gas is needed
since you have more power with this engine setup.
This system will tolerate a leaner fuel mixture
since the fuel injected cools off the combustion
during entry and is more denser than a carburated 
setup. A carburated setup when leaned up will 
cause damaging pre ignition to your engine but 
the EFI will not be pre ignite as easily unless
the prewssure sensor is leaned excessively to
the point that the engine shakes in idle. Leaning
will give better gas mileage and run the engine 
a little warmer.


***When compression is lowered your EFI will
adapt to it, your engine will be cooler but you will
slightly lose power (just a little , sometimes you
will not notice it, depending on how low you get it)
I accidentally lowered it so much that I was running
a compression of 75 lbs per cylinder for one year and
to compensate to the lowered  power, I richened the mixture
by tweeking the adjustment on my modified pressure sensor.
I ran this for one year. The deck height on my pistons to
head clearance was over .01 in which was huge and worked 
perfectly. When I burned  my heads when my brother
disconnected the heaters from the fan shroud when he went
to Arizona (he did not know how to turn off my heater),
I lessened the deck hieght for more compression .008 in.

What I am saying here , there is no problem affecting the
EFI when nodifing the compression.

If you wish to tweak it better (more zoom or better gas mileage)
, you can make the pressure sensor adjustable. I can verse you on this,
just ask . If you want additional zoooom on your car, 
I can suggest all sorts of things, kick ass
gas mileage with pep. 

I hope I have helped you.

LEON MARTINEZ

1969 SQUAREBACK EFI/AUTO
SAN DIEGO AND TIJUANA













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