Those that have tuned or programmed

4x4ord wrote:


I know the Cat in my 07 Peterbilt will defuel when it gets too hot on a long hard pull. I suspect my Ford will defuel if ever gets too hot and I hope the Cummins will as well. I see that as a good thing. When TFL pulled 30,000 lbs up to the Eisenhower tunnel I wouldn’t call that a short burst of HP.

As I said, all modern diesels will defuel. Some more than others especially of they have a lot of power. This is one reason why I never care about stock power numbers and those that gloat about them because they don't know any better. Just because a truck has x hp, doesn't mean you are getting that horsepower all the time especially under sustained conditions.

The other other thing is, people believe that a certain condition will force a diesel A to defuel X amount of horsepower, then the very same conditions will force diesel B to defuel the same X amount of horsepower. This is false and it depends on how "hot" the initial power level is.

For example, manufacturers of diesel A may want to post the highest power levels possible for marketing so they post 400 hp even though it cannot sustain that power for very long. So they tune their engine to make the most power possible, and then have the ECU back it off as needed. This is all perfectly legit using SAE standards. So under towing conditions, engine A may need to defuel to 350 hp depending on many variable such as barometric pressure, turbo speeds, trans temps, EGT's and so on. Hotter ambient temps such as 90F exacerbates this issue making it defuel even more than it would at lower temps.

Then you have the manufacturer of diesel B who may want to give their customer sustained numbers so they tune their engine to 350 hp even though can easily do the same power levels as engine A and back it down as needed. Since engine B is tuned for sustained power, it does not need to defuel and cut power in the same type of conditions. It may eventually need to defuel, but it will take a lot more to get it to that point of cutting power from the stock power levels since the stock tune was very conservative to begin with.

Generally, when someone says that a truck feels more labored with a load, then that is a clear sign that it is in the category of engine A. Adversely, when someone says that an engine does not feel that it has to work harder with more load or that higher loads do seem to effect it as much, then it is in category B.

I will also point out that what is happening in the engine A example is essentially how it is with my tunes except I back it down myself instead of the computer. Unloaded, I keep it on my highest power level. Towing, I will lower the power levels(defuel) on the fly depending the load and temps. Just because it is safe for me to tow 12k lbs in 40F at 500 hp at 50F, does not mean I can do the same at 95F.

There are many variables that come into play that you have to be mindful of. Hence the reason why I tell people that do not have gauges or want the computer to do all the work for them to just leave it in the lowest power level possible. Higher power levels are for those who have gauges, know what they are doing, and know what are the limits of the truck. There is a reason why heavy duty trucks had so many gauges and the professional drivers had to know what those gauges meant back in the day. Now, with computer controlled engines, it is not as important to have all the gauges since the computer will keep the truck within safe limits so the need for professional drivers is becoming a thing of the past and are being replaced by steering wheel holders.