My 1985 D100 with slant six 100% stock, is currently getting 11MPG 95% city driving, which isn't very good considering it is only a 6 cylinder.
Heck, even the 360 gas hog probably gets better MPG than my sl/6.
So far i have changed the air filter, crankcase oil, differential fluid, fuel filter and the PCV.
The exhaust has no leaks and engine runs really smooth and quiet.
I'm sort of leaning towards "don't touch it if it ain't broken" philosophy, which is based on my past bad experiences, but the bad mileage is hurting my wallet so i might have to re-think my position.
I need to know if there are some inexpensive ways to increase my mileage.
Would any of these help?
new distributor cap?
sparkplugs?
changing the tranny fluid?
Other suggestions....?
If yes for any of the above, what kind of difference can i expect in MPG?
Thank you in advance for any suggestions.

New cap/rotor, plugs and changing the tranny fluid might help a bit, depending on the condition of 'em. Also might want to check the points in your distributor (if it's not points style) and see how they're lookin.

I got a bit better mileage in my truck (about 1 mile per gallon) after I switched to full synthetic oil. Some people say they get big improvements with synthetic tranny fluid, but since I put in about 9 quarts on a change, I haven't tried the synthetic route yet. I probably will when I roll over 200K miles in a few months (190K and never needed a rebuild, ohhhhh yyyyyeah ).
Another thing would be to play around with your spark plug gap and find the optimal gap for a good spark. I've found it's usually good to up the gap about 0.002-0.003". Still gives a reliable spark, and adds a touch more mileage. No performance gain (or if there is any, it'd take a dyno to see it) there though.

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'74 Duster w/ HEI ignition, beat to snot suspension, A904, 8.25" 3.55 SG rear, still being tuned up and gets 17 MPG

Know how they always build a better idiot? That's me

i went from a 1bbl to a super six and increased to 19 hwy from 13.but that being said /6's are not know for their frugal mpg most do only get around 15

An exhaust system will help. Remove your cat, and replace the muffler to a performace one. If you don't want the performance sound, you could use two adapters (from 2" to 2 1/2") and weld them to a 2 1/2" muffler. That would decrease backpressure, and only give a slightly louder sound.

You could retard your timing and lean out the carb as well. But you will risk some damage if you lean out too much!

Also try to remove some weight. If you have a tool box, or sand bags remove them. Remove your tailgate and put a net one in place. You could replace your rear bumper with a fiberglass roll-pan.

Finally you could change your rear-end to a 2.7_ ratio.

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If it ain't broke, I haven't started "fixing" it yet.

My 87 did about the same, but with the cold weather up here my mpg got as bad as 7!!! Of all the mods i have made to my slant, the following gave me the most mileage gains:
1) Supersix & BBD...dont know why, but bigger carb jumped me right to 15 mpg city/hwy--doesnt matter which (IF you keep you lead foot out of it )
2) MSD 6A Ignition...major idle improvement, easier starts, and bumped me up 1-2 mpg
3) Removing the catalytic converters--mine were half plugged/broken to pieces. I noticed more of a performance gain (more "pep") than mileage, but i guestimate it helped about 0.5-1 mpg

Best my truck ever saw for mpg was 19 after i was stuck behind a mile of RV's going 45 mph for over 100 miles. Most of the time i get around 15 mpg with a 904 auto and 2.76 (yuck) gears. If my BBD'd throttle shaft didnt kick the bucket i think i would be getting aroun 17-18 mpg--we'll see when my offy intake and 390 holley get here

-Aaron

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The "Silver Bullet"
87 Ram D150

well, saying that you will have leanburn there isnt much you can do to get gasmilage, i converted back to the old setup and average around 23MPG with my shorbox (87) with a OD 4spd, supersix and just a light foot, if you got a timing light, bump it to 12degrees, if you can go higher than do it (mines at around 12.5-13) you really are limited when it comes to leanburn, you'll have the holley 2245 witch it a pain in the @$$ and is KILLER for milage and impossible to tune properly, you can do things like increase your spark gap alittle bit and a full tune-up, synthetic oils, just about anything can help. start off with doing the most basic things

Justin

Thanx for all the suggestions,i will start with the basics like going to synthetic in tranny, maybe a better quality dist.cap and i will increase the gap on the plugs.
As for removing the weight, i can't do it right now, because i need the extra traction in snow. I have a raised fibreglass cap, which i have no idea how much it weighs, but i learned that the back hinged glass door is pretty heavy as i had to put it back on, because someone broke it off.
I also have about 180 lbs in sandbags in the back to keep me on the road.
Could the added weight make that much difference?

Make sure your timing advance, which is controlled by the ESA computer, is correct. You should get 30 or so degrees advance at 2500 RPM and 16 inches vacuum on the manifold sensor. There won't be any advance at low temp, low vac, high vac, and whatever else the ESA feels like doing.

A good reason to go back to an old style distributer.

I get 14-15 MPG in the winter and 15-16 in the summer. This is a 1987 B150 wagon with 3.9 axle, 4 speed, and 200K miles, no mods.

Fred

Winter kills your mileage. The added weight will hurt, but only about 2mpg I would expect. The big thing is the temperature. Your engine is sucking in cold air, which it loves. Cold air is denser, and more compact, so you can fit way more in the engine than hot air. More air means more fuel, so less mileage.

If you have someplace warm to work, then change to a 2 barrel carb. It is a bigger job than many people say, don't bother working in the cold. You'll just get frustrated and cold.

You could put on larger tires. That would be like changing the rear end to a numerically lower ratio. Some 31.5" x 10"s would look good. You might need to raise the front end 2" though.

I have 280#s of sand in the back of my truck, and my milage is not too bad, maybe you need to have a tune up. Check your carbs specs, they may be out of wack.

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If it ain't broke, I haven't started "fixing" it yet.

Unless about 90% of your driving is on a highway, larger tires will hurt mileage bigtime. That much more rolling mass takes alot more to get moving until you reach your engine's power band.

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'74 Duster w/ HEI ignition, beat to snot suspension, A904, 8.25" 3.55 SG rear, still being tuned up and gets 17 MPG

Know how they always build a better idiot? That's me

I used to carry around 600# of sand bags in the back of my one-whell wonder AND had studded tires, still didnt help much on ice. I put in a limited slip and the difference was night and day--i didnt even bother with the sand anymore...didnt need it. Now the ol girl only gets summer duty (im sure she doesnt mind )and the 4x4 drives me thru the winter

What really kills winter mileage is all the extra warm up time. If you dont have a cold front get one (or a piece of cardboard). Your truck will warm up much faster (just make sure you leave enough of an opening for air to go thru so it doesnt overheat)

Some more options are narrower tires. Less ground contact area = less friction to overcome. Though it may seem backwards, wider tires actually have less traction on ice than narrow tires anyway.

-Aaron

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The "Silver Bullet"
87 Ram D150

I can attest to that. The weight of the vehicle is being distributed over a larger surface area, making it essentially "lighter". That plus you're already on a theoretically lubricated surface means major trouble.

Siping on larger tires helps a bit though. I finally caved and did mine (on my truck, not the Dart) and was fairly impressed with the difference.

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'74 Duster w/ HEI ignition, beat to snot suspension, A904, 8.25" 3.55 SG rear, still being tuned up and gets 17 MPG

Know how they always build a better idiot? That's me

Siping does make a night/day difference--as it gives you about 200% more "biting" edges. As an added bonus siping also makes the tread last longer..ill guestimate in the 10-15% more miles on the tires just for siping (as long as you dont travel gravel roads frequently--gravel will tear siped tires apart after a while)

-Aa

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The "Silver Bullet"
87 Ram D150

What is "siping" a tire?

Basically making slices in a tire's tread, stopping about a quarter of the tread's height above the tire's "base".

Wish I could be a bit more specific, but given that I agreed to drink a beer every time Miami got a TD today, I'm a little sauced
Granted it seems Oakland's defense is a little sauced too

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'74 Duster w/ HEI ignition, beat to snot suspension, A904, 8.25" 3.55 SG rear, still being tuned up and gets 17 MPG

Know how they always build a better idiot? That's me