valve adjustment and now poor mpg? - PeachParts Mercedes-Benz Forum

JHZR2 · #1 12-07-2003, 12:22 PM

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

R Leo · #2 12-07-2003, 12:30 PM

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.

JHZR2 · #3 12-07-2003, 12:34 PM

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

#4 12-07-2003, 05:08 PM

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

Mike123 · #5 12-07-2003, 07:50 PM

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.

TimFreeh · #6 12-08-2003, 09:37 AM

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

gsxr · #7 12-08-2003, 03:58 PM

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!

JHZR2 · #8 12-08-2003, 04:11 PM

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

jmh