Helping your MPG

[RussellK]

My MPG seems to be getting worse lately. First thing I'm going to do is check my odometer to see if it is actually working correctly. What steps do you take to improve mileage?

[sped372]

Slow down. :)

[JLT]

Do a tune-up: adjust valves, timing, carb settings. In other words, do Chapter 10 of the Idiot Book.

Check your tire pressures, and correct as necessary.

Have you added a roof rack? if so, that may be the cause.

[tristessa]

In addition to JLT's suggestions, take any un-needed "junk" out of the Bus. It's surprising how much camping gear weighs when you put it all together...

[RussellK]

No Roof Rack but plenty of camping gear that I hadn't given much thought. What about any adjustment to the AFM?

[Bleyseng]

What's your mpg now?

[drober23]

Russ,

I may be a pretty close comparable. I have a '75 Westfalia (with a 2.0 L motor). It has a bunch of stuff in it, and I like to drive it 70 mph.

That said, I have been playing with my AFR because my spark plugs looked like I was running a bit lean. (The AFM experimentation came AFTER an exiguous search for vacuum leaks, and a re-verification of spark, advance, and dwell).

My initial settings had me just under 17 MPG (16. average over several thousand miles. AFM cruising at 70 after warmup was around 13.9.

Dropping to a very rich 11.5 left me at 14.7 mpg (only a 200 mile sample).

Correcting closer to 13.0 at at 70 mph netted me 16.5 mpg over my last 300 miles. Haven't checked my plugs yet to see how "lean" they look.

That said, Colin had a very good post on that other site where he did lots of experimentation. http://www.thesamba.com/vw/forum/viewto ... hlight=afr

That said. If your spark plugs look the right color, I would be hesitant to mess with the AFR. Leaning your mixture will increase cylinder head temps, and shorten the life of your heads.

[RussellK]

I dropped from 16 mpg to 7. I hadn't done anything to the engine or changed driving habits. It's kept in a locked garage so its not theft.

[bretski]

Start with a basic tune up, as mentioned above by JTL. Can you smell gas in your exhaust fumes or see soot buildup on your tailpipe? 16 to 7 is quite a drop. Is this over one tank or several?

[Bleyseng]

Check that the CHT is in spec (it fails to going too rich) and that the cold start valve isn't stuck open or that anyother injectors aren't stuck or clogged open. Sitting does this.

[RussellK]

This is over 3 tanks. I'm going to pull the plugs and see what color I have and start checking everything else.

[TrollFromDownBelow]

check your temp sensor II for correct resistance as well as that it is fully seated in the head....mine gave me FITS for over a year, and one of symptoms was awful mpg .... 12-13 mpg hwy @ ~ 55-60 mph.

With no vac leaks, a good temp sensor II, and cruising around 62-65 actual mph (GPS confirmed v. 65-70 on the speedo) I get ~ 17-19 mpg

[JLT]

I dropped from 16 mpg to 7. I hadn't done anything to the engine or changed driving habits. It's kept in a locked garage so its not theft.

Yow! With that steep a drop-off, there's something else to consider: Is the fuel system leaking? It may not show up when parked with the engine off, but look at the fuel lines, pump, etc. very carefully when there's pressure in the system.

This is especially important. You don't want your bus to end up toast, in the most literal sense of the term.

[RussellK]

No fuel leaks I checked for that one already. I really appreciate all the suggestions.

[Gypsie]

locking gas cap?

Any changes in performance? Sluggish? That big of a drop should come with some sort of notable change.

I like the stuck injector theory as well as the nasty little TEMP II sensor possibility.

Over 3 tanks, like

"16mpg, fill, 14mpg, fill, 10mpg, fill, 7mpg..."
or
"One day I noticed that I was getting poor mpg and the next two tanks confirmed it"

do the 'pull one plug wire at a time elimination test' to see if all cylinders are in the game.

establish what the AFM is telling you about what your engine wants (more fuel, less fuel, just right...)

Curiouser and curiouser....