Finally got around to having the timing set on my 97, thanks to Stamey for recommending Keith (Rammin On) at Forest City Diesel in St. James MO. Very nice guy, a wealth of experience and happy to share.

Keith said he measured the stock timing at 14 (factory) and recommended bumping it to 16.5 degrees. On the 140 mile trip up, I calculated the mileage at 18.3 mpg (my best since buying the truck last fall). The terrain is interstate with a mix of flat ground and some pretty good hills. I set the cruise on 72 and the rpm's were just over 2K.

On the return trip I stopped at a station near home and filled up to the bottom of the filler neck. The mileage calculated at 23mpg (twice). Since the ground around the pump I was using wasn't completely level I drove down the road to another station. This time I stomped as much fuel in as I could (about 1 inch below the top of the neck) and even then it calculated at 21.5 mpg.

I'll have to see how this holds up on longer trips but so far I'm very pleased.

 

what did he charge you?

 

I paid $125.

 

How long did it take, did you drive up wait and then drive home or leave it over night?

 

He wanted it overnight, I had two days work in his area so I took a rental home and returned it the next day.

 

My timing had slipped back to 9 degrees from the factory 12(early 93 P7100). I could not get over 12.5mpg on the highway. After bumping to 15.5 degrees I got 16.5mpg highway. However, I think if it was at factory timing it would not have been that noticeable.

 

Wow! Nice increase in mileage. I did not think it would make that much difference. I've been wasting time.

 

I've wanted to advance mine too, but haven't gotten around to it yet either. That's a good increase!

 

I'd love to get mine done if I could find anyone around here that can do it, right.

 

What did it do for power? How does the truck run?

 

I have to point out that average mileage only when up 1.5-2mpg. It was the highway mileage that really jumped. The truck has more mid to high end power with the timing advanced. I really did not notice much difference at all in the low end. Smoke is about the same as well from what I can tell.

 

Yes, its supposed to move power up the rpm range a bit.

Except for the short trip from the shop to the gas station, I didn't get on it as I was trying to see what it did for fuel economy. I can't really say I've really noticed a difference in driving performance at all so far. Keith said I might notice it idling a bit quieter (not sure why that is) and maybe it is just a bit quieter.

What I did notice on the return trip, was the boost gauge not climbing as high on the hills. I let the cruise handle the hills, and on the trip up the boost would go up to about 14 on the larger one's. On the way home it barely got above 10. I think the the advanced timing creates higher cylinder pressures, so less fuel is needed for the same work and this equates to less boost.

I have always felt this truck should do a bit better than 18mpg, but until my trip up to Keith's shop no combination of driving, speed or terrain ever exceeded 18mpg. I will need longer trips to know for sure what my new mileage will be but from my initial test its going to be significantly better than 18mpg!

I bought a set of Goodyear Wrangler Silent Armor's (245/75/R16) shortly after getting the truck, and they are a pretty aggressive tread pattern. When my mileage didn't quite meet my expectations I've wondered if less aggressive tires would help. I had been thinking my next set would be 265/75/R16's to get the rpm at highway speeds down a bit, but lately I've been thinking about 235/85/R16's instead since they wouldn't be wider than what I have now and would still be a bit taller.

Any opinions?

 

wider tires definately kill your mileage. i would go with the taller skinny tire as long as it is rated for your truck and whatever you tow.

 

another thing.... advancing your timing slows your spool up a little and reduces your egts so heres the answer. MORE FUEL!!!!

 

When you guys talk about timing you do mean the pump timing correct?