Engine Noise at high speed

[Ranger354]

Anyone notice a different pitch in the engine at or about 85mph? I noticed the other day at 85 to 87 mph the pitch on the engine would change. Sometimes only for a second. The RPMs did not change so it was not shifting to another gear when this happened.

[Bobcat698]

What RPM were you running at?

Sounds like the pilot injection was just shutting off, going to direct injection.

[Trippin]

I notice mine changes pitch sometimes under part throttle right at the top of a gear, either second or third. It's real intermittent though.

[dieselburb]

Yes, it's that pesky pilot injection shutting down. If you feel for the change in power, it's almost like having a gasser with the A/C compressor shutting on and off. Don't worry, everybody's engine does it.

[Ranger354]

I would say it was around 2500 rpms. I wasn't paying much attention to rpms though. Thanks for the info guys.

[Oongawah]

My AC kicks on and off if I have it set for inside cab only(recirculating). As soon as I put it on outside air(even when set for heat) it stops. I think it's that way to dehumidify the cab. Notice it's like that for most vehicles when you use the defroster. Is this what you all are talking about? Chuck.

[MountainMax]

If I recall correctly, the pilot jet shuts off at 2700 rpm. Run it up onto a freeway under hard throttle and you will hear your engine get louder in various gears when it reaches this rpm. When running down the road, at some point (speed) the engine rpms will exceed 2700 and the engine gets louder. It is easy to hit if your running 85 and give it a little gas. The pilot jet is one of the things that made the Dmax a quieter engine. At 2700 it shuts off and goes to good old fashion straight injection and what you hear is how our engines would sound using old technology. In other words, like a diesel.