Faulty ECU Pressure Sensor (MAP) on the 5KTQ '86

[Paul S.]

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Hello,
New to the list, I consulted your archives and was impressed.

Background, you may skip to questions:
On my 5KTQ with the MAC 11A ignition control box, the ECU pressure sensor w=
ent bad, as confirmed by the ECU fault code 2222 and a zero reading on the =
boost gage.
The excellent SJM Auto-Technik site shows how to test the sensor inside the=
 ECU:
At the atmospheric pressure, I get 5.05 V on the pin 2, 0 V on the pin 1 an=
d the ground voltage on the pin 19 (had to resolder) of the pressure sensor=
 daughterboard.
On the pressure sensor's pin 1: I get ground +0.2 V, on the pin 2 : +Vout, =
on the pin 3: Vcc=3D 4.85 V and on the pin 4: -Vout. When I apply pressure =
/ vacuum to the sensor, the  two output voltages do vary, but they are not =
equal and the voltage at the pin 1 of the daugterboard remains at zero. So,=
 maybe the daugterboard is at fault. I could not find any information on th=
at circuit or its Hitachi IC, but I think that it provides the temperature =
compensation function to the stock MAP sensor.

Questions:
There is no part number on the stock 2 bar sensor. Is the original replacem=
ent still available and where?
I found three Motorola temperature compensated MAP sensors which might be s=
uitable replacements: the MPX4200AP (2 bar) and the MPX4250AP-ND or MPXA425=
0AC6U-ND (2.5 bar). It appears that the first might be discontinued and har=
d to get. Do you know a good source for these?

Is the transfer function: Output Voltage vs Absolute pressure of the stock =
sensor published somewhere?
What needs to be done to the output of the Motorola 2 bar and 2.5 bar senso=
rs to avoid too high error in the engine management process? If I could not=
 get the 2 bar sensor, will I need to get the EPROM remapped to work with t=
he 2.5 bar sensor?  Can the output voltage just be shifted up by 25% and ho=
w?

I gathered that at some point the performance enhancers were shifting down =
the output from the stock sensors to increase the boost. In effect, the 2.5=
 bar sensor would do the same thing accross the full pressure spectrum. Wha=
t is the penalty?

Shall I connect the new sensor on the MAP daughterboard or bypass it altoge=
ther, since the Motorola absolute pressure sensors are temperature compensa=
ted?

Thanks and Best Wishes,
Paul Stefanik
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