mk2 jetta gt trip computer problems

[jettagreny]

hi i have a jetta gt with a trip computer i recently had the engine out of it to clean it up and also fitted a stainless manifold and full system.  before i had the engine out the trip was reading an average mpg of around 30mpg but after i refitted the engine it doesn't get above 12mpg! i hope this is wrong! dose anyone have any ideas as to why it is doing this?

[gazareth]

sounds like the small vacuum line from the brake servo pipe to the back of dash clocks is not connected. if the clocks are not getting a vac reading of the engine they think the car is running flat out all the time.

[Screech16v]

Gaz how does the mk3 get it mpg reading?

[itavaltalainen]

from ecu

[gazareth]

glad someone stepped in there coz I have no idea . but I would think the ecu takes readings from engine speed/throttle position and air intake.