Knocking sound under load

[MaxRock]

I've noticed the last couple of days, while cruising down the highway, I get a knocking sound when a load is applied to the engine. This is happening when running solo, climbing a small hill. As soon as the turbo starts making boost, I get a knocking sound for a few seconds and then it will clear. I know that it is fuel related. I filled up last night and added a fuel additive, hoping this might help, no luck.

This morning when leaving home, the outside temp was around 58 deg F. The knock was prevalent for the first few minutes, then cleared. Any ideas?

Thanks,
MaxRock

[a64pilot]

Sticking/bad injector?

[NWDmax]

I get the same thing when the engine is not fully warmed up then it gradually goes away.Seems most prevalent under part throttle conditions and sounds like the pilot injection shutting off.
I do have the Hot Juice so its not an apples for apples.Btw this happens under 2200 rpms so I don't believe its related to the PI.Seems like a timing issue but these trucks are kind of quirky sometimes so I'm not worried about it.
Whats your rpm when you hear the knock/ping sound?

[MaxRock]

The knock is prevalent from around 1700 to 2000 RPMs. I'm not going to worry too much just yet. I will run a few tanks, hoping I got a bad load of fuel, to see if it clears. I'm pretty consistent in fueling at the same high volume truck stop.

My gut feeling is an injector. Like a64pilot stated, probably either a sticking or bad injector.


Thanks,
MaxRock

[akrockhound]

I don't have an answer for you but thought I'ld share my own "knock" and "tap" experiences so far with my '03 DMax.

I get periods (like a week-long) when the truck seems to have less power and makes more injector noise, especiall when I step on it. When it runs like this I feel sick and basically hate my truck.

Then I go a couple of weeks with it running quiet and it's fast, really peppy and quiet.

After watching the symptoms I am beginning to believe it's all related to the varying quality of the #2 fuel I am buying. Strange thing is that I buy just about every tank of gas from the same truck stop.

I will continue to watch it.

[george morrison]

Some other possibilities with the 'knock'. Low cetane fuel, slightly dirty injectors, combustion area. The regular use of a good quality fuel additive with cetane boost, detergency to keep the injectors, combustion area as new, etc very likely will eliminate the problems.
George Morrison

[MaxRock]

George,

I'm inclined to agree with you. This tank of fuel I've added a fuel additive. The knock is quieting down. In the past, I was adding the additive every other tank, but got away from that schedule. I will starting adding the additive every tank.

What is your opinion of the Rotella DFA?

Thanks,
MaxRock

[a bear]

I've always treated my fuel at the recommended dosage then give it a double dose at oil changes. The engine runs much smoother and quieter with the additives. ;)