I've had my 6.5 for a few months now and have been very happy with it. One thing I have noticd is that fuel economy has not been as good as I had expected, I've been getting ~15.5MPG diving the speed limit (55 2lane, 65hwy)with a very light foot. Anyhow about 3 weeks ago the SES light came on so I took it back to the dealer, and according to him the mass airflow sensor was dirty and covered with "oily grime", his solution was to simply clean the sensor. Anyhow Immediatly after I began hearing turbo boost all the time and i got my best tank of fuel since I bought it (18.5MPG) Unfortunatly, lately I have quit hearing boost again, and it appears that my fuel economy has gone donw to the old 15.5MPG. If it keeps up I may take it to a better diesl shop, but i was wondering if anybody here any insight as to what may be the problem.

Replace the MAF. If cleaning it made it work, then a new one should too.

The question I got is where did dirty oily grime come from? What kind of air filter you run there?

Stock air filter; that was my question too, it seemed like the mechanic may have been looking to cure the symptoms rather than finding the actuall problem

Stock air filter; that was my question too, it seemed like the mechanic may have been looking to cure the symptoms rather than finding the actuall problem

You're going to find alot of guess-o-matic mechanics at the dealers when it comes to the 6.5 diesel, and most of their guessing is going to be on your dime.:mad:

I've heard the only thing the MAF sensor does on the 6.5 is work with the CAT's/O2sensor to control the EGR. So you might be able to bypass/disable it and go on about your buisness without spending any green. Disable the EGR while your at it! The EGR and/or CAT's will lead to the early demise of your truck.

Mines a '95 OBD1 no MAF, so I could be wrong about some of the function of the MAF, but I used to have an EGR and after seeing inside my intake manifold with EGR, I'm convinced removing the EGR was one of the best things I've done for my engine.

not all dirt comes from the air filter. I had my upper intake off over the weekend and was surprised by the amount of grime inside the intake. The air filter was clean around the edges, no evidence of dirt bypassing the filter. What I did notice was that where the crankcase breather tube enters the pre-turbo rubber intake boot, there was excessive play. This is where I the grime trail began. I took it apart and added some rtv and put it back together. This should give me an air tight seal from the turbo to the air filter.
Check all your connections between the turbo and air filter box. If you have a stock air filter box, make sure the air filter is not upside down! It will not make a tight seal if it is installed incorrectly. Also, I found out when ordering my K&N filter that there are 2 nearly identical air filter sizes for the stock air box . Make sure yours is right for your application.

That's because our airbox sucks for ease of maintenance (if you have the panel filter like me). I'm gonna get the 97 and up airbox from a boneyard ):h

Here's another question, is it possible for a relative novice to clean the MAF sensor himself, and if so how dificult would it be/ how would i go about doing it?, i'd kind of like to do it myself to see if it is indeed the problem and to check see if it again resores performance.

I'd imagine so. The MAF is in the rubber boot before the turbo.

one more question, which direcction should the arrow on the maf face (toward radiator or airbox) and what would be the best solvent to clean it with, I've heard everything form brakecleaner to electrical contact cleaner.

brake cleaner and electrical contact cleaner are quite similar (sometimes even labeled as brake and electrical motor cleaner). Carb cleaner should be safe, too. I'd recommend taking it out to clean it. You don't want to spray any solvents into the intake.