I know this is not necessarily an EFI Live or tuning question but i thought that with your guys smarts on how these engines work you would be able to help me out.

ok, so here it is, a few months back i replaced my injectors (The infamous LB7s). while i was in there i decided to adjust the valve lash, based on some other forums recommendations as it would help quiet down the engine and make it smoother running. well it did, but i now it seems that i get worse mileage. (i know, internet mechanics)

the valve was already close to stock (.012~.013) and seemed fine but i was curious how much quieter the engine would run with them tightened up. well i adjusted them down to .010 as this was the max recommended and said to make the smoothest, quietest engine.

anyways, after installing the new injectors and making the valve adjustment the engine runs great. balance rates all below 1, spools great (maybe too well. will explain later). the only issue is that it seems that my MPGs took a dump. i used to get between 430 to 450 miles to a tank taking the same rout to & from work every day for almost every fill up for over a year. now for the last few month since the adjustment i have a hard time breaking 320 miles to a tank. that is a drop from about 16~17 MPGs down to about 12 MPGs. highway MPGs are also not much better

my theory is that the exhaust valve is now opening up earlier and letting the exhaust gases out sooner. this would lessen the amount of time the combustion pressure would be able to work on the piston. this seems to be backed up by the fact that i can now hear the turbo running, small amount of turbo whistle, all of the time ever so slightly when cruising around 60-65. i never was able to hear it before unless i pressed the accelerator down more, supplying it with more fuel to speed up. it also seems to spool faster then before and smoke a little bit more too. all while seeming to make slightly less HP on my butt dyno.

things i have done to try and remedy it:
-raise timing in the cruise area. probably went dangerously high on the test as i slowly worked my way up to about 9 degrees at 20 mm3 and 2200 rpm (about 500 pw at 115 Mpa). didn't seem to help much so returned it to the previously good values.
-raised and lowered fuel Mpa. got as high as cruising around at 150 Mpa. now running at 65 Mpa. thought that i might be able to get the fuel to finish burning by the time the valve has opened up.
-currently playing with pilot injection. running with the events closer together right now. not impressed yet but still too early to tell.

any ideas guys? do you think the valves are too tight? should i dig back into it and readjust the valves or just wait until the injectors go bad again. almost 100 miles less per a tank could add up to quite a large number $$$ by that time.

my next step will be logging boost during steady cruise to see if it is higher then my logs before the change

anyways, i am open to suggestions to tuning ideas that may get me by until i can restore the valves to stock.

thanks for any help and sorry for the long read

Jason

PS: this may make a good discussion on valve lash and MPGs. why some engine get good mileage while other don't, etc.