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Re: 4KTQ Conversion Questions
The early (1/85-7/85) '86 model year 5000TQ with the MC engine used a fuel
distributor with banjo type injector lines and according to the Bosch parts
catalog, the replacement (rebuilt) fuel distributor "FD70X" for this early
MC engine is also shown as the replacement part for the US 83-85 ur-quattro
with the 2.144cc WX Turbo engine.
This would seem to indicate the ur-quattro fuel distributor would work on
the MC engine.
The Bosch parts book does list a different air flow metering assembly for
these two vehicles, as well as different warm up regulators.
I have not compared the MC air flow meter assembly side by side with the
ur-quattro air flow meter, but when the MC part is compared to the CIS-E
air flow meter assembly (87 5000S, non turbo), the MC part has a
larger/wider opening near the top of the inlet funnel (4.70 in diameter
versus 4.47in dia.) which would indicate the CIS-E air flow meter would top
out earlier with less air flow than the MC air flow meter.
The control pressure on top of the fuel distributor plunger as set by the
warm up regulator will also dictate how far the air flow plate will be
pushed upward for a given air flow rate into the engine. The MC engine warm
up regulator incorporates some altitude correction mixture control.
The later dual knock sensor MC engine (89-90 200TQ) uses the same fuel
distributor as the earlier 86-88 5000TQ MC engine, but uses an externally
mounted system fuel pressure regulator instead of the one inside the fuel
distributor. The dual knock MC also uses a different air flow meter
assembly part number.
One nice feature found on the MC air flow meter, is the potentiometer
(variable resistor) mounted on the pivot shaft, which can give you a
relative indication of mass air flow into the engine, (i.e. how far up the
air flow plate is moving upward) under full throttle near engine redline.
You can connect a voltmeter on the 5kTQ potentiometer to measure this air
flow plate travel as the 5kTQ uses this varying voltage signal for the trip
computer MPG calculations.
If you use the MC air flow meter assembly on the 4KTQ project, a ohm meter
can be used to measure the travel to give you an idea if you are getting
close to topping out the air flow meter for a given boost level.
As mentioned by others, the MC Engine control unit diddles with the freq
valve duty cycle to change the differential pressure across the fuel
distributor plunger slit opening, as the manifold boost pressure rises to
richen up the mixture. Using the MC Engine/ECU/Fuel system components in
the 4KTQ project would be my recommendation for best drive ability and
operation at modest boost levels.
More ramblings on fuel distributors can be found at