There are a few ways to see if they leak w/the engine off...
- One is to put a pressure gauge on the line. There should be 30PSI (give or take) at the rails overnight. Hell, I think mine probably still has 30PSI at the rails, and it's been at least a month since I fired it.
- One is to pull the injectors out of the heads (while still on the rails) and put a newspaper below them. If the paper gets wet, they leak.

Oh, and I forgot to ask: How did your mech adjust the mixture? Did he use a CO meter? He NEEDS to. Use a CO gauge to set running mixture (med revs under load meaning engine revving with tranny in drive). 0.5-2%. Then after running mixture is set, set the idle mixture to the same % using the idle mix screw on the ECU.

If neither of these were done correctly, you'll still be too rich.

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Back in the saddle - 1972 280SE 4.5