Re: TQC boost problem?

[harrison@indigo.ie (George Harrison)]

At 09:18 30/03/96 -0700, Dave Lawson wrote:
>
>George,
>
>>My theory is the brain thinks I'm overboosting and is retarding the timing.
>>How can there be overboost even when the engine is not running????
>>Any help appreciated.
>
>On this euro 85, I am assuming that the ECU has a boost pressure
>display signal comming from it. Could be wrong. Or does the dash
>display still have its own pressure gauge, just digital in this instance?
>
>I would start by looking through the check valves in the vacum line
>system going to the ECU. Not sure of a failure mode of these, but
>maybe it has trapped boost pressure in the line feeding the ECU
>pressure sensor. After this I would test the pressure sensor, pull the
>hose from it, and see if it reads 0 bar, then maybe attach a piece of vac
>line on it and slightly blow on it to see if the display changes. If it
>doesn't read 0 or change with different pressures, something is wrong
>with the ECU and/or pressure sensor.
>
>Good luck and report back the findings.
> -
>Dave Lawson  dlawson@ball.com  
>
>
>

Dave,
As you correctly said, the boost gauge on the dash takes it's signal from
the ECU. I tried your suggestions re trapped boost but having removed the
hose from the pressure sensor the gauge still reads overboost i.e last three
segments of display light up. One thing I did try was to plug the hose and
start the motor.
Result....no difference: still reads overboost and still running VERY lumpy.
Next step was surgery. I opened the brain and disconnected the three pin
connector from the pressure sensor, started the motor and HEY PRESTO now got
a smooth idle and seems to rev normally! Reconnect sensor...back to old problem.
It appears as though the sensor has failed in the overboost position.
Out with multi-meter. No continuity between centre pin and either left or
right pin while applying pressure OR vacuum to sensor. Continuity between
left and right pin while applying both pressure and vacuum. I don't know
what reading I should be getting but I would have thought the resistance
would vary.
I've been told the sensor cannot be bought....you must buy the complete brain?
Starting to panick at this stage...I believe brains are REAL expensive!
I drove the car gently this afternoon with the sensor disconnected but its
not performing very well probably as the brain connot now vary the timing
depending on pressure or vacuum. However at least it is running and useable.
The sensor is marked   HITACHI PS2-02 Pressure sensor. The brain is MAC-01
Where to from here????????

George.