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How much does a vacuum leak affect fuel consumption? Just filled mine and it dropped almost to half after driving to work (bout 25km, mostly highway). I was squeezing near 600/tank. I've swapped the fuel pump assembly, done the plugs and coils. Moneys a bit tight atm, so trying to trouble shoot on a budgetI'd imagine there could be a bunch of reasons.
If it were mine, I'd be spending the day doing a thorough service schedule on it.
Vacuum leaks would be a good place to start. Have someone smoke test the top end. Where the smoke comes out is where your leaks are. Replace the relative hose or gasket. Vacuum leak will create a whole bunch of issues, including high idle and high fuel use as everything is trying to compensate for the unmeasured air entering the intake system.
You could have leaky injectors. If they didn't swap your old injectors over, then that could be something.
The Crewman will eat fuel anyway though. If you got 400k's from a tank in the city, it would be good.