does a governed truck lose torque?

Of course. ECM cuts fuel. Less fuel equals less torque. Otherwise it would continue to accelerate.

 

Depends on how governed it is. Some companies reduce power as well as limit speed. Funny thing about that? I didn't see an improvement in fuel economy. I also run legal. I don't go more than 70 in a 65

 

Not to be nit picky but limiting torque is exactly how a modern engine is governed. It works like this.... Say you're governed at 65mph accelerating on a flat road. As you get to 65 mph the ECM starts limiting fuel to slow your rate of acceleration. If the programming is perfect you would ease up to 65 and the truck would just stop accelerating. At that point the engine torque will exactly match what's needed to maintain 65mph. However, programming is never perfect and the variables of weight vs road grade are infinite.

Engine speed governor works the same way. ECM limits fuel to what's needed to maintain rpm.

 

The ECU can be set to control many parameters. Max pedal speed and max cruise set speed as well as torque have separate selections. I wouldn't think the company you drive for would want to lower torque, but they might. Some of the engines have split torque ratings automatically adjusted according to which gear you are in. Speed and the increased wind drag is the biggest factor that wastes fuel. Then terrain, weight, traffic, and tire resistance also affect it.

 

The answers so far are correct, but I get the felling that you're asking if it limits peak torque??? That depends, there are many parameters that can be set to limit the engine speed and torque. It will have rated power until it hits A governor. The governor is RPM, road speed and/or a few other optional settings (if used). If it's limited to say 1800 rpm and 60 mph and not other governors are set, and you're doing 30 mph at 1200 rpm, the engine will have all rated power available until you get to 1800 rpm or 65 MPH.

There is also a multi-torque setting that many companies use. This reduces torque to protect the drive line depending on what gear you are in. Our Detroit's for instance only have peak power in the top 2 gears. This helps on the highway hills, but limits abuse running up through the gears.

There are also progressive shifting parameters. These limit speed in each gear for the so called "optimum" shift points for economy. This is a tactic many big fleets use to keep drivers from revving out every gear and wasting fuel. Once it wont rev any higher, the only way to go faster is to shift, so it's supposed to get drivers used to shifting for better economy. In my experience, drivers hate it.

 

I don't have cruise control and I do a lot of hills. So I sometimes get to 67-70 mph and my gps dings so I roll it back to 65. My gps warns me at 5 mph over the posted limit.

 

Most engines that are governed to a certain speed will always be able to develop 100% hp and torque until the ECM sees the road speed reach it maximum allowable, then it will not allow the RPM to increase any more by cutting back power.

 

That's pretty close to how I was always told. The governor is a limiter, not a reducer.

Back in the days of mechanical governors, some made the mistake of simply setting the throttle throw stop back a little bit. This would reduce everything. Those that knew how things worked, had the pump settings changed internally to limit the rpm of the engine, and would have to build the truck with ratios to limit the ground speed. This would allow full engine development, but reduce the rpm. Ah, the good ol' days.