valve adjustment and now poor mpg?
 

Hi,
yestrday I wrote about the valve adjustment I did... seemed to go well, but some of the values were quite a bit off. Today I drove out the rest of my tank of fuel, and only got 26 mpg, not my usual 29-30. Also, I noticed from my turbo gauge that cruising at 70mph, I was at full (8psi) boost constantly, whereas I kind of remember (maybe Im wrong), that before my boost would be 5-6-7 psi at 70-75 when cruising, but go up to full when I accelerated.

Could an incorrectly done valve adjustment cause me to drop MPG a LOT, yet still have the car start great cold, and run very smoothly?
Could it cause me to in some way either require heavier throttle to keep a certain speed (which I didnt particularly notice), or require more boost (which I suppose is directly proportional to throttle position) when moving?

I just am not very confident in my work, and want to be sure that it is right, so Id appreciate info on this for reassurance or so I can get it fixed before I do damage and get really poor MPG...

Thanks

JMH

Snapshot
 

First of all, you really need to run at least complete two tanks of fuel for any assessment of mpg.

Second, check to see if the overboost/ALDA line has become disconnected somewhere.

I keep a running tab of MPG, every tank... And always get it from the same place (flying j truckstop). But I agree, and Ill wait a tank or two to see.

JMH

I always have 7-8psi @ 65mph and 10psi+ at any higher speed.

I've always noticed a small decrease in fuel mileage when I get my first tankful of winter formulation fuel and , of course, it does not increase until summer formulation of fuel is back. I have never had as big a drop as you have described (usually I notice about 1 mile to the gallon decrease). Just a thought.

Its been very, very windy in the Delaware/New Jersey area for the last couple of days. Your higher turbo boost is consistent with an engine that is producing more power to fight a headwind. Any chance you were driving into the wind for a significant part of your last tank?

Winter grade diesel fuels will also cause lower mileage.

Tim

Probably just winter fuel. It will be hard to tell unless you have MPG data from last winter. You may need to wait until spring to know for sure! ;)

last winter:27.36-30.68mpg
switched to my d1 mix part way through the winter...

jmh