97 A4 B5 2.8 Intake Manifold Tuning Circuit Problems
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97 A4 B5 2.8 Intake Manifold Tuning Circuit Problems
I replaced the vacuum actuator for the intake manifold tuning system and can get it to move and hold vacuum now but it still doesn't seem to work. When I apply 12V to the plug on the solenoid valve it works perfectly but it does not function when I plug the connector in. I get 13.8 volts when I check the connector at idle which makes sence. It is my understanding that the valve is energized, allowing vacuum to reach the actuator, until the engine reaches 4,500 RMP.
My question is where does the electrical connector go from the IMT solenoid? Does it go directly to the ECM? I'm starting to worry that I might have to replace the ECM. Does the ECM control the positive or negative wire on the connector?
My question is where does the electrical connector go from the IMT solenoid? Does it go directly to the ECM? I'm starting to worry that I might have to replace the ECM. Does the ECM control the positive or negative wire on the connector?
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Joined: Jun 2008
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From: Fallbrook, CA
You're supposed to be able to rev to about 4500 and watch the actuator move, thought I've never tried it. The tuning actuator solenoid valve is named N156 on the schematic. It's powered throught the fuel pump relay, fuse S229, same as the O2 heaters. The yellow/white wire of the solenoid connector goes to the ECU, where it is grounded to turn the valve on. You should see the 13.8 volts at either wire of the valve until it turns on. If you have a licenced version of VAG-COM available, this solenoid valve will be cycled in one of the output tests.
AudiWorld Super User
Joined: Jun 2008
Posts: 2,284
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From: Fallbrook, CA
The intake manifold works at any speed, it's the tuned-length butterfly valves that are being discussed. The 2.8 manifold has very long port runners, so the resonance or bouncing of the air collumn will pump more air in at low speeds, improving torque. At high speeds the air collumn is too long, and the pressure pulse arrives out of sync, with the intake valve closed. The manifold's butterfly valves open to shortcut the paths, so the pressure waves will be in better sync again. If you look at the graph at 12V.org, you can see a chart showing how the (nearly) peak torque is maintained to a higher RPM.
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