B204FT occasionally low boost....

Hello to all of you.

I`m the owner of Volvo 960, B204FT engine. I have a problem, and I dont know where to start looking for solution.

Occasionally it happen, that car have low boost, and my AC compressor go off. I also noticed, that when this is the case, my cooling vent is ON, and my idle is high (about 1100RPM) I check blink code, but there is nothing.

By looking wiring diagram, AC compressor, and boost valve are controlled by TCU unit.

Any tought where to start?

Thanks in advance,


Peter

What do you notice with "low boost" ?

I think the ECU receives information that the engine is too hot.

First check the actual temperature of the engine with an infrared thermometer.
Second check ect value.

Hello,

By low boost i mean 0.2-0.3 bar. This happens even in the morning, with cold engine after start.

Ok, I have to see what ECU see, all parameters about temperature. Do you know how to check EGT sensor?


Thank you,


Peter

This problem is possibly related to the TCU unit. That unit switches the AC blocking relais positioned at the left fender (see pict). The AC is temporarily switch off during full boost. Could be that the low borst situation is also TCU related. Check all plugs and vacuüm lines toward the TCU that is positioneel under the dash driver side (black box).

The AC blocking relais is positioned at 2/48

This problem is possibly related to the TCU unit. That unit switches the AC blocking relais positioned at the left fender (see pict position 2/48). The AC is temporarily switched off during full boost. Could be that the low boost situation is also TCU related. Check all plugs and vacuüm lines toward the TCU that is mounted under the dash driver side (black box with plug toward the ecu and vacuüm line toward the inlet manifold).
Good luck