Hello all. . . I was wondering, can anybody answer this question?

When rolling down a hill at 55+ mph with no foot on the throttle, why does the throaty sound of the diesel engine stop? Almost sounds like the engine shuts down, then when you slow to below 55mph, it comes right back. Has anybody ever noticed this? The reason I bring this up is that when my truck lacked power, it STOPPED doing this, it wouldn't seem to 'shut down', and to me that 'shutting down' is normal b/c it's what it did since I had the truck. Can anybody answer this question?

Thank you,

John

 

That's your injectors shutting off when fuel is not needed.

 

Oh, wow, thank you for that. So that diesel sound is the injectors, that's it?? I really appreciate you answering me, I have been wondering this for some time. I LOVE that sound! So why would they stop shutting off on me? I had no power and it stopped doing that. Do you think I have a fuel problem? It's intermittent. Sometimes the truck has power, other times it does not. And this only occurred after I did the EGR/Oil coolers. Thanks again for your help.

John

 

In laymen's terms...the truck computer (PCM) controls the injector opening/closing based on sensor values it receives. When you floor it, it tells the injectors to dump alot of fuel in, and tells the turbo to blow a bunch of air in, etc. When coasting down a hill, foot off throttle, the PCM may determine that no fuel or air is needed, so it "turns them off". Yes, that clanging sound you hear, is the injectors opening and closing.

I have no idea why they no longer turn off since replacing the EGR/OIL coolers....but apparently the PCM is seeing some reason to keep adding fuel. It could be something as simple as a brake caliper hanging up or low tire air pressure causing some drag.

Do you have any gauges to read live date yet? That could help diagnose it.

 

There would be a number of things for Muffled sound one that I learned was turbo veins closing with Egr Valve at closed position, once exhaust runs through ( pressure the valve is commanded open thus vein sweep )hearing the Glories of 6.0 Turbo

 

Is your tow haul on

 

I had a handheld code reader that had a button for "OBD Readiness Test", several things under the hood of a 6.0 powered truck would click and the last part was an eerily quiet idle for about 15 seconds. I don't think it was the turbo cycling because it really isn't doing much at idle in park. Maybe it was pulling open the EGR valve, bu whatever was happening kinda freaked me out the first couple of times I pressed that button.

Another thing to consider when driving is the transmission operation, if you lift the throttle at speed things get pretty quiet and you can see the tach drop. No engine braking. If you are in tow/haul mode the revs don't drop immediately but drop slowly with the speed and much more pronounced engine noise, in my truck anyway.

 

Very informative, thank you. I heard that before about the brakes or tire pressure. I'll have to check that. I have banks IQ. I always monitor everything, I'm very **** about the truck in general. I'm always making sure everything is right. I feel that I have a lack of power right now and I don't know why. I'm thinking fuel or exhaust clog.

And to everybody else, thank you for your responses, much appreciated.

John

 

The other way to put this is that when you are going down a hill you are coasting (no throttle), so the engine does not need fuel and the computer shuts down the injectors, then when road speed and engine speed come to a common point the computer starts the injectors back up and off you go (back on the throttle).

 

This is why if coasting down a hill and you look at realtime mpg it will be way high.
I saw 78mpg this weekend coasting down a hill lol.

 

Almost every modern fuel injected gas or diesel engine shuts the injectors off during coast.

Josh

 

Thank you for all of the helpful info guys. . . listen, I just bought the seal kit for the injectors (8) from xdp. They give you the top seal also! I am wondering if the seals being bad can cause lack of power?

Thanks again,

John

 

You really should get some readings before you
start to throw any parts at it. Doing repairs that way
tends to cost a lot more than it should.

In other words Shotgun repair is a bad idea.

Get something that can scan the Computer (PCM)
and also report live data. This way you can make
sure that what your doing will fix the problem and
not just cost money or make it worse.

Sean

 

I know you're right. . . it's just that I've been dealing with this for some time and on the forums for even longer and using AE for even longer than that, and I STILL have no power! I cannot find anything with AE, everything tests out right. It's now either take it to a mechanic, or fix what I think is wrong. Believe me, I HATE throwing money into it when it doesn't need it. I just don't know what else to do.

Thanks,

John

 

When was the last time the fuel filters were changed?
Might be a place to start that won't cost a lot.


Sean