1st Tow and strange throttle oddity

[mdadgar]

So I did my first major tow with the DMax this week. I ran down to Los Angeles to pick up my new racecar trailer (365 miles each way). The temperatures varied from 95 degrees to 115 degrees both days, generally hovering right around 105. I had the cruise set at 70 mph and was towing a 3500 lb trailer (but it has a v-nose, which helps).

The truck ran like a champ. Neither of the temp guages moved, even at 115 degrees ambient, uphill, with the A/C on. Incredible.

One odd (read: irritating) thing I noticed about the electronic throttle: the gas pedal apparently takes precedence over the cruise contol. If I had the cruise set and then pressed the gas pedal to temporarily speed up to pass WITHOUT cancelling the cruise, I got some odd behaviour, Specifically, if I would press the gas pedal down LESS than I normally would need to maintain the speed that the cruise was set at, the truck would SLOW DOWN. This implies that the throttle signal overrides the cruise control signal, even though the cruise is still activated.

Irritating. This behaviour doesn't happen with regular cable-activated throttles.

All in all, though, an amazing truck. Case in point: I got stuck in some bumper-to-bumper traffic up the Newhall Grade on I-5 north of LA Tuesday evening (right at the 14 split, for the locals). There was a big grass fire on the shoulder and the right two lanes were closed. It was a total cluster. It took me an hour to go 3 miles. Anyway, I was towing that 3500 lb trailer and the truck was climbing the hill AT IDLE, and it's a very steep grade. Now THAT'S torque!

- Mark
'02 Sierra 2500HD CC SB 4x4 D/A

[Colorado Kid]

I never noticed what you've observed, but I guess I haven't spent much time pushing the pedal down a little bit while the cruise was engaged. The thing I noticed was that, when climbing and towing with the cruise on, sometimes when I mashed down on the pedal to accelerate there wasn't much left, but it did always seem to have some ability to accelerate, no matter how steep the hill. I seems like if I just backed out of the pedal a little (just enough to not maintain speed) the cruise would take over as it slowed through the set speed.

The "throttle" action with cruise on seems to me to be a bit too well damped...sometimes you are going 2-3 mpg under set speed and it is still coasting (when flattening out at the bottom of a hill) other times its 2-3 over the set speed and still pulling like crazy (cresting over the top). On long steep grades (I-70 west of Denver) it works fine, and I use it. On rolling terrain (US 34 east of Greeley) it swings across a range of more than 10 MPH again and again, making it useless. By controlling the throttle myself I could keep it dead on the speed, so it wasn't that the hills were too steep. Both of these examples were when towing the 5'er, but even empty this is noticeable.

[TBC]

Colorado Kid

Have you had the trans updates? I pulled my trailer through mountain and rolling hills for over 3400 miles and mine did nothing like you are describing. Before I had the updates done it did what you are describing.

[SledZep]

I think one of the electronic upgrades cures this. I remember reading a listing here on the forum of what the upgrades were for and one was for some thing like you are explaining. Evidently we get 0% throttle till we push it down far enough to equal the speed you are set at.... I have experienced what happened to you also. I have not done any upgrades yet...

[Vette Racer]

When using the cruise the truck will try and maintain the speed within 4 MPH. At this point it will downshift. If towing, this is a pain in the A##. Either you have to not use cruise, or get a box that will up the power so the truck will hold the speed. Bottom line, Chevy doesn't offer anything else! Upgrades or not.

[jw461]

My truck does the same thing. I use the cruise a lot and play with the throttle too, to add a little speed. If applied very slowly, the truck will start to slow down until I reach/pass the point where it would be anyway if it were a normal cable throttle. As far as I know I have all the updates. It doesn't slow down by much, but it's very noticible uphill.

[Colorado Kid]

I don't think there are any relevant updates for my trans, see signature.

Perhaps there is an updated ECM in which the cruise control is more agressive. For now I just don't use cruise under the offending conditions. Not a big deal.

[SoCalDieselNewbie]

StrangeEngine,

I do that grade quite often while towing... Some people call it the Newhall grade but it is best know as THE GRAPEVINE.

I have done the vine in my D-max towing a boat with the cruise control set at 80 in tow-haul mode. I never had to touch the gas or the brake.

You should have seen the look on people's faces, I mean tons of cars struggle on this thing, when I truck towing passes them as if they were standing still. smile.gif

It usually puts an "Oh My God" expression on face of the person riding shotgun, in my truck, as well. smile.gif

Geesh, I LOVE MY TRUCK! I might have to marry it once I get the performance mods (haven't yet because it is a CA truck).

[mdadgar]

SoCalDieselNewbie,

I always think of the Grapevine as the other end of that stretch of road - the end that ramps down (or up, depending on your perspective) into the Central Valley. Where the town of Grapevine is.

It's a bitch of a road, either way.

In any case, the D-Max handled it without even breaking a sweat. In 115 degree temps.

- Mark

[bora]

Hey Mark

Glad that your first tow went OK,
I noticed the same behavior on my 02 as well.

I also think the truck is slow to react to the gas pedal when cruise is engaged.

Regarding towing, my truck is able to pull an 8500 lb trailer on flat terrain at idle.

Bora