MAP changes levels ?!?
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MBWorld Fanatic!
Joined: Jul 2005
Posts: 3,176
Likes: 19
From: London, UK
No longer stock '06 E55, A3 3.2 Quattro, GLE 400d, R107 280SL, Golf Polo
MAP changes levels ?!?
Weird MAP data behaviour - start car and range is from -11Psi to + 15
Refuel and the stream changes from -3 to +21 … the change happens when I open the fuel cap.
Possible the evap opens up reducing vacuum? But then why is boost so much higher? Running 180mm crank pulley.
charcoal canister checked out ok. In my model I dont have a canister check valve only the valve thats in the engine bay. Its the almost cylindrical canister not the odd shaped version.
Refuel and the stream changes from -3 to +21 … the change happens when I open the fuel cap.
Possible the evap opens up reducing vacuum? But then why is boost so much higher? Running 180mm crank pulley.
charcoal canister checked out ok. In my model I dont have a canister check valve only the valve thats in the engine bay. Its the almost cylindrical canister not the odd shaped version.
Last edited by stevebez; Dec 28, 2025 at 10:33 AM.
Member
Joined: Jul 2017
Posts: 126
Likes: 22
From: Dubai
2005 E55 AMG Wagon
Opening your fuel cap immediately changes your MAP readings confirms that your intake manifold is physically "linked" to the atmosphere via the fuel tank when it shouldn't be - it could be the purge valve that is stuck open. You have ruled out the charcoal canister which again points to the purge valve.
