update

pulled the bosch and no name o2 sensors, put in motorcraft. while I was putting in the right side I noticed I was missing the nut off 1 of the exhaust manifold studs and the others on the bottom looking ripe. It pi**es me off that their only 3 years old and rotting away. yes I live in taxachusetts and plow but I get to a car wash at least 3 times a season to rinse. time to research alternative studs. the end of the stud is only a little rusty so it hasn't been that long. see how this goes.

should I stay with studs or switch to bolts? stainless or grade 5? factory gaskets or aftermarket(who's)?? double them up or single? mayo or mustard? chicken or egg?

 

After changing to mc o2s and disconnecting the battery my last fillup is 9.5mpgs. On the on ramp got on just a little was surprised how much quicker it was. From the speed limit to almost triple digits at wot was quicker than it has ever been. Throttle response is much better. Hopefully double digit mpgs are back! Now have to fix the exhaust studs again.

 

So, the only change that you made this time was back to the MC O2's? And you noticed an immediate improvement? I am encouraged, as I am having similar issues to you, as you know. Just not sure if I can justify spending another $100 to replace 6 month old O2's.

 

I had a hard time swallowing it as I had replaced mine about 8 months ago. I also figured if it worked it would pay for itself in 500 miles. half way thru the 2nd tank since I changed the o2s it looks like around 10 mpgs. maybe after I fix the exhaust studs 12???

 

been thru a couple of tanks now. runs better power is still off to me, from a stop put the gas to the floor still won't break the tire loose. the best mpgs is just under 10 running the 5 star 93 hp tune.

 

changed caliper brackets, at least 1 slide each was frozen on the rearend. checked the fronts to make sure, they were fine. last 2 tanks after fixing them were 10.5 and 10.1 mpgs.

 

I want to thank you for continuing to update this thread. I am having similar issues with my 2001 6.8. Please continue to update this form time to time.

 

I still haven't figured out what's up. I don't think the manifolds studs are enough to mess it up ( missing 3 total). The power steering pump is making noises, doubt it's hurting me 2 mpg. Leads me to a sensor that's out enough to mess it up but not enough to trip a code.

 

I have found that the OBD-II on these trucks is not very communicative. All of the normal stuff is monitored, however alot of the parameters are not reported with a cel. For instance, my truck has a deffinate popping through the exhaust under no load, but sets no cel for misfire. However, monitoring the short fuel trims, one of the banks is quite a bit richer than the other bank, indicating a misfire (remember O2 sensor measures oxygen, not fuel, and a misfire will read lean to an O2 sensor).

I replaced my Bosch sensors with motorcraft as well, and my mpg was up a bit, but the truck does run better. I have either a bad plug, cop, boot or injector, just haven't had time to check anything yet. I am glad you are making headway, but it frustrating to not be making any significant progress I know.......

 

Just spent 8 hours changing to eBay headers and SS studs and nuts. Had 3 broken studs on each side, black markings on each gasket. Tells me I had a small exhaust leaks. Changing the brake pads, then finish putting it back together. Fingers are crossed, in my search for my missing mpgs.

 

Wtf. Another brake hanging up. Get off the highway and I can smell cooked pad. Getting REALLY tired of this truck.

 

filled up after ebay headers and retorque and making sure no leaks. towed a waste trailer(1200-1500 lbs)to the job empty40 milesish towed to empty with 3700 lbs in it 55 milesish. filled up 11.2 mpgs.

could it be that small of an exhaust leak has been killing me this whole time?

by the by both sets of exhaust studs and nuts all oem ford pieces were not stainless. they are now though :-}

trying mike's 93hp tune see what that nets me

 

Congrats! These ecm's are very sensitive it appears. I re gapped the plugs from 0.045 to 0.052" and have gotten 9.9 with all city miles, and 10.33 with a 40/60% city/freeway driving. I think part of my problem is the truck seems to want to run at 75mph.

 

whats the latest update?

 

still getting 10-11 mpg. still trying to figure out the vacuum leak sound around the throttlebody/manifold area. new pcv elbow/hose assembly. going to have it smoked on monday. the truck still feels underpowered. going to try some 27" tires to simulate a gear change to 4.56. see what that feels like.