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Limp Mode: 7/07


DTC Codes from the engine

Traveling out for lunch the car experienced a sudden loss of boost. After a little experimenting, the car would hold 10psi just fine until 3000 rpm. The boost would dump after that to vacuum level. The car was laid up and every hose was gone over. Several Vacuum hoses were found to be cracked and frayed so all of them were replaced with new braided hose from the dealer ($10 / 3 ft.).

Additionally, the N75 was tested by measuring the resistance between terminals. Spec is 25-35 ohms and the measured value was 30.2 ohms. The N75 is an electronic solenoid valve that is used to regulate the boost pressure via the ECU.

The N249 valve was removed and cleaned. This is a mechanical valve that connects to the case breathing system and could also have been a source of errant boost loss. There is no established test for this mechanical valve.

Finally, the Forge 007 Diverter Valve was completely disassembled and cleaned. Moly grease was used on the o-rings during reassembly. Currently, the Forge has a red spring plus one spacer installed. Thought was given to reducing that to a blue spring which is more suited to the 15-21 psi loads under the second program stored in the ECU.

Valve Spring Color Coding
Green5-15 PSI
Yellow15-23 PSI
Blue23-30 PSI
Red30 + PSI

After all this work a test drive yielded no improvement. A Ross-Tech VAGCOM tool was attached to the car and the DTC codes were read from the ECU. Codes were reset and blocks X & Y were viewed. A test drive revealed that boost had returned. A post DTC reset code reading revealed a persistent code of P0103 16487 - Mass Air Flow Sensor (G70): Signal too High. This is something to watch as it may indicate a failing MAF sensor.


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