Hello,

My grandpa-in-law has an 1986 F250 6.9L diesel with a large 3500lb camper that he let us use last weekend. The truck had been sitting for 2-3 years. New tires and batteries, and off we went.

I may be buying the truck off him; excellent condition with 94k original miles, however I do have a few questions/concerns about it.

During pulling, especially with the first tank of gas (first tank of gas was good, put new gas in it before I left), it didn't want to get over 55mph. On the way home, I could just barely touch 70mph (WOT), but it was a struggle. So it seemed to get better the more we drove it. Now, I do NOT need to go that fast, I'm just generally concerned about performance. I only had 3 gears I noticed (automatic); is that normal; am I missing a gear or did these come with 3-speed automatics?

Also, I got about 8.5mpg on my trip (was a 4-hour trip each way on the highway). I know it had a 3500 camper on it, and the camper kills aerodynamics, but what can one normally expect out of these engines? Perhaps a tune-up would bring things up a bit?

Speaking of tune-ups, any recommendations? A general Diesel noob, but have been reading quite a bit. Truck is in great condition; headliner perfect, AC Ice cold, seats in great condition, carpet spotless, so if I can get this motor going well I think I'm set. Note: The engine actually ran great, was just a bit surprised by the lack in power, fuel economy and speed (and that's with some already low expectations). Just want to know if that's below par for the engine, or if I need to reset my expectations!


Thanks!

 

having owned more of them then I can count on my hands and my feet I will tell ya one thing, they are not fast. they get the job done and usually do a ok job of it.... the 7.3's had a little bit more power then the6.9's but not much, 8.5 seems a little low to me, I remember my 90 super duty with a 7.3 and 14' flat bed getting over 15 towing my boat at the time but it had 4.11 gears and a 5 speed and it did alright, I remember being on the freeway and giving it full flank and it toped out about 75ish and it kinda took its time getting there

I would change the fuel filter and when you do fill the fuel filter with transmission fluid, that should give the whole system a good douche.... the only auto offered behind the 6.9 was a C-6 3 speed, they are damn near bulletproof, I would almost gamble that the truck has 4.11 gears and with the C-6 it is just making the truck feel anemic, you might want to change your expectations a little bit cause even the stick shifts barely put 100 hp and 200 ft lbs to the ground and the automatic will just add more drag

 

my 6.9 is not as powerful as my newer truck. ck these things 1. air filter must be clean 2. fuel filter make sure you change it every 10,000 to 15,000 miles it is a 6 micron filter and will capture a lot. 3. run diesel clean every fillup it dose wonders to clean out your engine. 4. i also add 2 stroke oil to my fuel to help lube every thing i run it at about 200 to 1 ratio. hope this helps.

 

with 4.11 gears and the automatic, u wil,l have a top speed of around 65-70 mph.

 

Yes I agree top speed not much more than 65-70 but dosnt the 6.9 usualy get much more than 8.5 mpg even towing? there must be something going on here.

 

I would recommend turning up the pump a bit.. maybe 1-1/2 turns on the screw (sure you can find this in the 6.9 section)

when I first got mine, same truck you describe I couldn't get it to spin the tires if I tied it to a building, turned up the pump a bit and i could lay rubber all day long.

keep the air filter clean
unrestrict the exhaust

keep expectations lower.. it's not a powerhouse but it'll work all day!