changing the governor (speed limit) on a 03 diesel truck

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Mwahahahahaaahaa - 19 Oct 2006 00:30 GMT

hello all... I was wondering the process of upping the speed of a truck
that has a governor cap or speed restriction on it.. It is a 03 diesel
truck made by GMC. I believe it is a w-series.. a box truck. Are they
usually mechanical or computer? Thanks!

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mandtprice@gmail.com - 19 Oct 2006 17:05 GMT

> hello all... I was wondering the process of upping the speed of a truck
> that has a governor cap or speed restriction on it.. It is a 03 diesel
> truck made by GMC. I believe it is a w-series.. a box truck. Are they
> usually mechanical or computer? Thanks!

I'd be surprised if it wasn't built into the ECU. Are you talking
about the factory limit or something much lower that your boss is
imposing on the fleet? To get past it you will need to get an
aftermarket ROM from some tuner supply house. There's a lot of that
kind of gear available for the PowerStrokes, so I am sure you will find
what you want for the Chevy.

If you are talking about bypassing the factory limit, why would you
want to? I can understand why you would want more power or torque to
get to max speed quicker, but changing what that top speed is is asking
for trouble. There is a reason why you don't see pickups out at
Bonneville breaking land speed records. Even on quarter mile strip I
doubt this truck could get to whatever the governed speed is. Either
you are trolling or crazy.

Just for kicks, what is it the governor set at?

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Mwahahahahaaahaa - 20 Oct 2006 04:33 GMT

The governor is factory set and is set at 70mph. On normal roads that
is way more than adequate, although we do a lot of interstate driving
where the speed limit is 70mph or above.. and it gets bothersome to
only go to 70 on straight land, but on uphill slows down to 60 etc. I
would like to be able to have the governor set at 80 that way I could
more easily pass someone if they are going 65 or be able to stay with
the speed limit uphill more easily. Now would I change a ROM, or is
this something I could get a ECU programmer and edit some commands?
Thanks for any help/suggestions!!

> > hello all... I was wondering the process of upping the speed of a truck
> > that has a governor cap or speed restriction on it.. It is a 03 diesel
[quoted text clipped - 17 lines]
>
> Just for kicks, what is it the governor set at?

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mandtprice@gmail.com - 20 Oct 2006 14:28 GMT

> The governor is factory set and is set at 70mph. On normal roads that
> is way more than adequate, although we do a lot of interstate driving
[quoted text clipped - 5 lines]
> this something I could get a ECU programmer and edit some commands?
> Thanks for any help/suggestions!!

The ROM is were the parameters and lookup tables for the ECU are
stored. A programmer would talk to an aftermarket ROM - not really a
ROM in the literal sense at that point - to update those parameters,
either while it is plugged into the vehicle or plugged into the
programmer. Shop around to see what the aftermarket shops are
offering.

The modern computer controlled diesels are grossly detuned on purpose
to maintain efficiency emissions. Besides getting past the speed
governor, you'll probably also be able to play with the available power
output. Don't expect Chevy to extend warranty coverage to any mods,
though.

You'll need to get in touch with the tuner shops to see what exactly
each offers.

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Steve W. - 20 Oct 2006 15:38 GMT

> The governor is factory set and is set at 70mph. On normal roads that
> is way more than adequate, although we do a lot of interstate driving
[quoted text clipped - 26 lines]
>>
>> Just for kicks, what is it the governor set at?

Adjusting the top speed will make NO difference in the pulling power of
the engine. It is a setting in the ECU that looks at the speed sensor
and the rpm of the vehicle and cuts fuel flow to keep the vehicle from
exceeding 70. It is not the reason why it will only climb hills at 60,
that is because it only has enough power to climb that hill at 60, if it
had enough power to climb it at 70 then it would still run 70 until it
hit the governed speed.

As for changing the top speed, that can be done by a dealer BUT they
probably will want you to sign a waiver to cover them in the event the
higher speed causes a problem. You might want to look at the tires on
that vehicle as well, they may not be rated to handle higher speeds.

Signature

Steve W.
Near Cooperstown, New York

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mandtprice@gmail.com - 20 Oct 2006 16:11 GMT

> Adjusting the top speed will make NO difference in the pulling power of
> the engine. It is a setting in the ECU that looks at the speed sensor
[quoted text clipped - 3 lines]
> had enough power to climb it at 70 then it would still run 70 until it
> hit the governed speed.

I did not say that the two were related, just that the two were both
equally tunable. The ECU controls all those things, so I mentioned
that changing out the stock parts could have many more benefits than
just changing the top speed. Changing the ECU programming will be able
to address both issues. Adjusting fuel timing and volume are just as
much a function of the ECU as rev and speed limiting.

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Steve - 20 Oct 2006 15:50 GMT

> The governor is factory set and is set at 70mph. On normal roads that
> is way more than adequate, although we do a lot of interstate driving
[quoted text clipped - 3 lines]
> more easily pass someone if they are going 65 or be able to stay with
> the speed limit uphill more easily.

Not to mention that driving on highways with an 80 MPH speed limit in
traffic with trucks that are arbitrarily limited to 70 is frightening
and dangerous, both for the truck driver and for the rest of us.... Been
there/done that!

That said, setting the governor at 80 will NOT improve the uphill speed
of the truck at all. That is a simple power/weight+drag ratio problem.
The truck is underpowered, and even if the governor is set at 80 it will
still drop back to the same speed on an uphill grade that it will with
the governor set at 70.

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