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Hey people, I have been following the past couple of discussions on faulty APC valves.
I have a problem similar to others on this forum; being that my car fails to boost into the red section of the gauge. I did find and fix a leak in the hose that leads to gauge in the dash, though this doesn’t seem to have made much difference. Now, I don’t have much faith in the accuracy of factory boost gauge, so I will be fitting a ‘proper’ one next week in the hope of getting an accurate reading.
In the meantime, I have run a couple of tests on my APC valve. I have done the ohmmeter test; pins 1&2 and 2&3 both read 3.7.
I have tried pulling the plug from the unit and taking it for a drive. This made no difference.
I have also checked that the valve is clear. With the ignition off, I can blow down the top nozzle and the air comes out of the middle one. With the ignition on the opposite happens; I can blow into the bottom nozzle and air comes through the middle while the top is closed. Does this sound like the APC is behaving itself?
Also, where is the best place to plumb in the new boost gauge?

Thanks, Billy.
 

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I'm sure I remember reading cases where a faulty solenoid can burn out the drivers (probably MOSFETs or SCR's or whatever) in the APC. Also, there is a fuse which can go. You didn't say if you car is Trionic, or LH/DI/APC? Other things like selecting reverse pressing the brake will limit to base boost, so a fault in these circuits can cause you only to get base boost. I am not sure that the resistance test of the solenoid can be taken as 100% either. If it fails, then it's definitely shot, but I think it is possible for a bad one to pass that test. The only solid check is to use a known good one. Also, I believe that the APC sends pulses (probably PWM or something) to the solenoid, so I think connecting 12V across it to test it is a bad idea. I have a feeling that in normal operation it actually oscillates (hence the buzzing).
 
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