Already printed out the procedure. Gonna do it at the dealership once the tires are on.

 

And the 31's are on. They are MUCH better. I have my turning radius back and it feels much better on the highway cruising. Doesn't lug as much.

33's for the last time:


and now the 31's:

 

Very good sign and good to know for sure that that little bit to much is to much, might be end of problem of your injector sticking, less pressure to work against.

Well maybe not on the sticking part, I used 100psi+ cleaning mine they had no trouble opening at that kinda pressure and while using a 9 volt transistor battery power cycling em to do it.

 

Hey Evan, I posted this in the "show off your ... " thread but wanted to put it here also since you have this thread dedicated to your efforts. Thanks for posting, I got a lot out of the contributions in this thread. And thanks to everyone that contributed.

That just reinforces my choice to keep stock suspension on my '91 with 30x9.50's. I have the same drivetrain you do. Thanks for sharing!

 

Well I am sad to say not much of an improvement has been made. Drove 78.9 miles over the last 2 days and used 7.264 gallons. That works out to 10.86 MPG. That was about a 60/40 split of city to highway driving. I drove very conservatively. Speed limit on side roads, 55 in the highway and no hard accelerating. That is up from the ~9.5 I would normally get, but I feel there is still an issue somewhere that is causing the low MPG.

I think part of my problem right now might be my commute. It is about 7 miles each way, but it is literally a strait shot down the freeway. I have a sneaking suspicion that the truck simply is running in open loop for a majority of my commute warming up causing low MPG. I think I might fill the tank, take it on a highway loop when it is fully warmed up and then fill it again to see what the highway MPG is over a decent distance.

 

What temperature thermostat do you have in the truck?

 

Stock spec, 195*. It is however a parts house brand, not Motorcraft. I think I might get a Motorcraft one and put it in just in case. I also put my grill screens back in to help it warm up quicker.

On another note, if my highway mileage warmed up turns out to be good, what are your guys' opinions on a block heater to reduce warm up time in the morning?

 

What is your base timing set at? you might try another degree or two. I read your supermotors page, and you say you did the sixlitre tune up, but maybe the balancer is off just a little. Also check the tire pressure. Max it out to decrease rolling resistance and see if that makes a difference.

If your thermostat is good, it should be up to temp in a couple miles. I don't think the added expense of a heater will be worth it.

 

60/40 split city/highway and I would probably only get 11 or 12mpg with my truck (MAF OBDII with little 235/75R15 tires). City kills mpg in these heavy trucks. I get about 10mpg if I only drive in a city/town. If you can reach 15-16 mpg on the highway cruising steady at 65mph I think you'll be at about the max. May be able to eek an mpg or two more on a perfect day but 15-16 is more realistic. I'd test honest highway mpg before spending another dime on parts that you may or may not need.

 

Only other thing I can think of to check is driveline drag. Dry U-joints can have increased friction before making noise enough to notice. Invest in an infrared temperature reader. You can use it to check temps of bearings, brakes, etc. after a highway run to make sure things are staying cool.

Being a 4wd, make sure that the front driveline is not still engaged when you are in 2wd.

Just some stuff I think you want to verify even if you know its good.

 

Base timing has been brought back to 10 degrees with plugs gapped at .044". I have found the truck idles and runs smoother with the stock gap and timing.

I am going to do a fully warmed highway run here in the next couple days. I'll post up the results. As for the driveline, everything that can be greased, gets greased every oil change. Rear diff fluid has 10k on it. Trans has about 6k on its fluid. Front driveline is fully unlocked as well.

 

Well I decided to check the MPG tonight when it was cool and the roads were empty. With the windows up, A/C off and the cruise at 55mph I went 32.1 miles on 2.265 gallons. That works out to 14.17 MPG. The route I took required me to turn around 3 times to stay in the low population area and had 3 decent hills each way. So with 4 accelerations onto the freeway and 9 hill climbs I got 14.17 MPG. I feel if I was going constant I could likely get 14.5-15 MPG out of the truck. I think this means the end to my quest for MPG as that is right where I expected for my truck. Heck the 14.17 is the BEST I have ever gotten out of it and isn't bad for a 202k mile truck with a 351W, 4" lift and 31x10.5 aggressive all terrains. Thank you all for the help, I greatly appreciate it.

 

I think you got this one whipped. Your relatively short road trip yielded some real world MPGs for you.

 

Yep. At this point it is just going to come down to how I drive it. I have already made a decent change to my driving style of the truck. A big part of that comes from having the small tires. I don't have to work the thing nearly as hard with smaller ones on there to get around.