I've got a 2001 6.8 Excursion that's only a couple months old to me. I purchased it about the first of the year. Long story short I feel like I'm missing some power somewhere and I'm seeking advise. I had a conversation with a fellow 6.8 owner today in a store who commented on my X and talked about how he can pull a 30' travel trailer up I-70 to the Eisenhower Tunnel (west of Denver) with no trouble and hold 60 mph the whole way. I've taken mine one up that way several times in the last couple of months and on the long mountain climbs I'm losing speed sometimes down to less than 50 mph and its downshifting into second gear with the engine screaming at 4000+ RPM's! And all of this with just a few passengers, snowboards and duffel bags. Nothing at all like a 12,000# trailer. Why does this thing seem so gutless? It has a K&N intake from the previous owner. Other than that it was stock upon purchase. Here is what I've done to it in the 45 days or so that I have owned it.

Oil (and filter), trans fluid (and filter), T case and diff fluids changed
New spark plugs and boots
Exhaust manifolds removed, extracted all broken studs, manifolds machined and re-installed with flange head bolts and new Fel-Pro gaskets
5 star tuner, 87, 91 and 93 octane performance and towing tunes (none of which made any difference at all in performance)
SPD y-pipe (also from 5 star which caused the symptom outlined below)

After having installed the new y-pipe I've found that the truck vibrates and shakes at 1000-2000 RPM's when under load. It doesn't matter if it's mild acceleration or stomping on it, the thing shakes so badly that you can't focus on anything in the rear view mirrors, the door panels rattle like crazy, its terribly unpleasant to drive or ride in. It sounds like a helicopter! It feels like a cylinder or two or three are missing, but it smooths out above 2,100 RPM's or so. It idles smoothly, revs smoothly up to and beyond 5000 RPM's so I don't feel like it's starving for fuel or missing one or more cylinders at the top end. It simply thumps and vibrates in the 1000-2000 RPM range with the exhaust modification and has no power under about 3000 RPM's. It simply can't get out of its own way driving uphill, even a mild grade. I'm assuming that I would have a check engine light or some codes if there was a misfire?? I've checked it with 3 different code readers, no codes present.

Any and all suggestions welcome before I starting to shop for a 6BT to swap in...

 

How many miles on the engine? I test drove an Excursion that had no power at all, then I test drove a couple others than mine. Mine is a beast with 150K miles I can easily pull my 20 foot trailer with my classic car on it and the truck does fine. When I change oil I also use the Engine Restore in the silver can. I have always used that stuff on engines with high mileage and it helps.

 

146K at time of purchase, 147,500 or so now. I drive a 2000 7.3 pickup with 275,000 miles for work on a daily basis. I run a 80 HP tune and a billet wheel in the turbo but nothing too crazy. That thing will run up any hill I ask it to (trailer or no) and not shift out of overdrive unless I do it manually when the EGT gets up to 1200+

 

Yeah thats not alot of mileage... you can always run compression test on the cylinders and see where they are at. That will give you an idea of where the engine is at. I did that on a classic car we bought and found out 4 cylinders were dead low at like 60psi and 4 were decent.... so the engine was shot in that car.

 

Im tired and not wearing my glasses. Did you list your rear end ratio? Mine has the 4.30 gears and about 188,000 miles on it. No issues at all pulling my 32' that ranges between 8,000-9,000.

 

3.73's, running a 285 75 R16 BFG KO2 tire. I could see the gear ratio being an issue when towing but driving with just passengers? Being passed by 4 cyl VW's and Mazdas with basically the same cargo??

 

Something is up IMO. Are you sure your brake calipers aren't dragging or whatnot?

As far as 285s go, my truck is a 2002 with 3.73's, and after I went up to a 285 it became a bit less snappy, due to the overall tire weight I'm assuming so you may be experiencing some of that as well.

Also its ok to rev a mod motor out to 4k, it makes most of its power up there unlike an oil burner. Just food for thought.

 

 

was the other person running the same combo? or stock sized and 4.30 or lower gears?? that would make quite a large difference since your effective ratio is higher than 3.73 with the taller than stock tires.

 

Possibly a partially plugged fuel filter or catalytic converter? Double check that a caliper piston isn’t sticking.

Other than that a 3.73 equipped V-10 X even with 285 tires should be able to hold speed up a grade. And yes the V-10 loves to rev. Mine routinely sees 4K rpm going up the big mountains towing my 9200lb trailer.

 

My "guess" one of two things or both.

1. Clogged cat. Happens a LOT. In my last 10 vehicles 3 times.

2. 02 sensors. Change them all ! Its an electronic tune up...

 

The shaking you mention says misfire to me. It should run very smoothly at all RPMs. I would suspect a bad coil.

As to the friend holding 60 with a trailer up I70, I'd believe it when I saw it.

 

I know the Eisenhower grade is pretty substantial. But I’ve done some pretty good grades in CO and WY off the major highways where Super C’s can’t hild 50 but im moving right along at 55-60. So it is possible.

 

On the clogged cat deal, would one see substantially less exhaust coming out of the tailpipe?

 

He didn't happen to mention that he was also getting 18 MPG while doing the Ike Gauntlet did he? Between that looong steep grade and the high elevation (which robs NA engine power) I seriously doubt that claim as being totally accurate. Of course, there is no mention of what this 30' trailer weight was either, but I would think the claim may be a bit "optimistic". I've never towed that far West, but from my understanding, that grade is a well known test for towing abilities. And I'm pretty sure if his story is accurate that he isn't running the same tire size and gear ratio as you are, deeper gears make these V-10s completely different animals. And 4K in a mod motor is not "screaming", it's designed to rev up there where the best power lives, different flavor from the PSD for sure.


What kind of shape is that K&N filter in? They need proper cleaning care and oiling to be as efficient as they can, which in my opinion isn't as efficient as a street driven air filter should be. K&Ns are fine for track cars, but I wouldn't run one on the street, they pass too many particles in my opinion. If oiled too heavily the K&N can foul the MAF sensor and cause some performance issues, a good MAF cleaning is quick and easy. Is the "Cold Air Intake" properly installed with no air leaks and is it drawing hot under hood air vs the stock air box's cold air? Hot intake air is better for efficiency but bad for power output.


Go over everything under the hood again to check for any possible vacuum leaks.
In my experience the custom tunes really don't make a very big improvement in engine output BUT, they DO make some very nice improvements in the trans shift strategy which makes the seat of the pants feel much better. The application of the available power is handles better with the better shift points and pressures. This is more evident with higher loads on the drivetrain, like heavy towing where there are pretty significant gains.

That shaking sure does sound like a miss to me, and a miss (maybe a part time one) would explain the power being down a good bit too. Maybe pick up a new Denso COP and start trying it on different cylinders to see if the shaking goes away. And new O2 sensors (2 for most rigs, 3 for Cali spec) are pretty cheap and easy to do.