I had my first towing experience this past weekend in my 2004 lb7. Keep in mind regarding this post that I am running 315's. I towed my ski boat, which is a 20.5ft with a EFI 5.7 engine so I am guessing 4-5K lbs, to the lake. My trip to the lake includes some flat land and hilly country.


I was pleased at the ease of the flat land pulling and taking off. I was more than disappointed at pulling up the hills http://www.dieselplace.com/forum/smileys/Confused.gif. It seemed that I kept my foot to the floor most of the time trying to maintain 50-60 mph (which is probably faster considering tire size). What is wrong? I hope this is not what I should normally expect. Is it my tire size... but I ran the same tires on my 1500 5.3 which had no problems running 70 with the same boat on the same road. Let me know if you need any more information.


Please HELP

How many miles on the truck? I ask because most people have noticed a significant increase in power as the engine breaks in. If you have less than 10K your probably not getting everything.


The 315's are kinda tall for a towing application, not that your boat is all that heavy. All duramax trucks have a 3.73 rear, combine that with the 315's and your looking at a 2 something final drive, even with 520 lbs of torque thats not a good towing setup.


Finally if you have lots of miles on the truck you might be looking at a fuel restriction in your filter, most of us change them every 5k or so. Thats a long shot but it has happened.


Other than that, I would say get some juice in that bad boy and you won't even notice the boat, you'll have a tough time staying below 70 uphill!

I have 15K miles on my truck. I am sure that I need a fuel filter change. I bought the truck when it had 13K on it. I don't know if the filter has ever been changed. That is on my agenda for this week. I realize the 315's are not a good idea for towing. My boat is the only thing I ever tow and that is only every now and then in the summer. Plus the 315's were on it when I bought it and they look good http://www.dieselplace.com/forum/smileys/Approve.gif. Oh, my 6-gun will be in today so maybe I can get some help from that. Looking for exhuast now... but still I was hoping for better stock performance.

I pulled a tandem axel dovetail trailer with an 89 4x4 chevy on it for a friend for about 20 miles with no problems. He said he had to downshift to keep up with me in his 97 350. PM me and I will meet you somewhere to show you my exhaust setup and what I am running.

You using tow/haul and O/D lockout? When I first started pulling my fifth wheel I thought power wasn't that good either. I didn't know about the O/D lockout switch and when I would hit pretty steep grades if I just mashed the go pedal it would drop down to 3rd gear and run near red line. With the O/D lockout switch it only droped to 4th gear and I could use the torque better and run higher speeds. Of course then I got the juice and on level 2 (90 HP box) I rarely get out of 5th gear on grades and have met nothing I can't pull at 65 or better in 4th. My 5er weighs about 9,000lbs.

The majority of your power loss is from the change in tire size. You have 2 choices, go back to stock size tire (not) or do what you did. Order add on power package to bring back what you lost in tire change. I noticed the same thing when I went from stock to 285's. Juice took care of my problems. Let us know how the 6-Gun works on your truck!





Bill

I am appreciating your suggestions on this. Hopefully with a little more experience with my DMAX I will learn the rpms and speeds it likes the best in combination with the tow haul / OD off options. My first trip was too short to find out what worked the best . I still plan on changing my fuel filter soon and going to either a 305 or 295 tire next time around as well. Any more suggestions are welcome!

what RPM did the 5.3 turn @ 70MPH going up the hill?


BTW, I would not use more than an extra 40 or 60 HP for pulling. And yes, get a pyro guage!


Ski boat of 20,5 ft..... Moomba, Master, Supream, Natique or what? I think most of these boats weigh 3,500 to maybe 4,500 lbs, probably about 4,000.





Burner-------------->http://www.dieselplace.com/forum/smileys/Big Smile.gif

Burner,


My 5.3 Z71 ran flowmaster exhuast, complete K&N intake, helix, and a hypertech III to top it off. I don't really remember what rpms it ran at 70 mph up hill, but only remember that it would do it. For some reason, it was impressively fast \ powerful.


My boat is a crownline 202 LPX. The Crownline specs claim dry wait of 3400-3600 lbs which is without fuel, gear, trailer and 2 coolers http://www.dieselplace.com/forum/smileys/Big Smile.gif . I am unsure how much the trailer it self weighs; I am sure it is not much.

The tire size is not your problem. I am pulling a ****** load more than that with 365/65-16 and just zipping along. Sure sounds like fuel filter, but I would think it would set a code.

BigdaddyG............are you saying that you tow with the O/D locked out and in tow mode?


I'm looking forward to my first heavy tow, but wasn't sure where to set that control; I thought you could tow in O/D. My truck is still stock; does that mean that I should keep O/D locked out at all times while towing? I guess I need help with info. Thanks

Yes, basically it is due to tire size.
The computer makes an assumption about the relationship between rpm and speed, it is only valid for the stock tire size(s) and causes more trouble the farther your rolling circumference gets from standard. There is only one rear axle ratio available for the 6.6 D-Max, but a couple of standard tire sizes, single and dual rears.

What ArrBee said. GM warns Dmax owners about increasing tire sizes for this very reason. Larger tires throw off the Allison's shift points and as the engine RPM and the transmission are out of sync. The good news is there is an easy fix. http://www.dieselplace.com/forum/smileys/Big Smile.gif

A programmer won't fix that? you know, something that adjusts your speedo?

Black Max,


I only tow with O/D locked out on steep grades. If I let the trans pick it will jump down to 3rd from fifth and rev higher. If I lock out O/D I can use lower RPM where the most torque is. Other wise I am running in fifth at 75MPH and it pulls most grades.

My truck stock felt like it struggled to tow our 10k 5er. Was unimpressed that I had to put my foot to the floor for extended periods to try to keep speed, or constantly downshifting to speed up. The juice on level 1 really helps the truck tow the weight. Makes towing the 5er almost effortless. It is amazing what 40hp and timing changes can do to this thing for towing. Very happy with how it tows now. Sure you don't have to be the first one up the hill, but you shouldn't be holding up traffic either....

A programmer won't fix that? you know, something that adjusts your speedo?

Adjusting the speedo - adjusts the speedo.
The speedo is just an analogue representation for the driver's eye.

If you decide to get a turbo and pyro gauge, 4X4 mud connection in Little Rock installed mine and they did a good job.

I would agree the large tires are affecting your power a little but you should still have no problems pulling a small load like that. Expanded metal will actually create more drag than a solid sheet when pulled thru the air at high speeds. If you notice when you see semis hauling loads of pipe and such they cover the front of the pipe because the air moving thru the pipe will create a lot of drag. They are not exactly same case but they have similar results. Just my .02-