Engine/Transmission (1998.5 - 2002) Diesel clatter is missing!!

[Hohn]

This is weird.



I've noticed that when I rev the engine up, the engine's sound changes DRAMATICALLY once the tach passes 2100rpm. It's like the timing is radically retarded at that point or something.



I've noticed the following:



1) It only happens when the engine is fully warmed up in warmer weather.

2) It only seems to do it in the first three gears of the six speed.



So that leads me to another question: does the ECM know which gear the truck is in when you have the six speed? I was wondering if maybe the ECM putzed with the timing in the first three gears to reduce torque output.



The other thing I noticed is that it didn't seem to do this with the EZ. But I haven't driven the truck with the EZ in warm weather in a while. My EZ is gone (sold it), so it's just running on the DD2s. WG is blocked.



Finally, I don't think anything at all is wrong. The engine runs better than it ever has, as far as smoothness goes. Power is always there, and it always starts right up with no problems (unlike last year!).



I believe it to be normal, but I'd still like to know what's going on that causes this normal behavior. It's like a switch is turned off right at 2100 rpm!! The engine totally changes sound, going from a diesel sound to just a whirring sound.



Any ideas? Marco?



Justin

 

[RustyJC]

Justin,



If you're like me, you've had the EZ so long that you've probably forgotten the HO "2100 RPM surge". The emissions control settings in the ECM are such that, to avoid smoke, the engine seems to add fuel very slowly up to 2100 RPM, then suddenly cuts loose from that point on up. This may not be as pronounced with the DD2s, but I'm wondering if that's what you're seeing/hearing?



Rusty

 

[nps]

Since installing my EZ and the boost elbow, I noticed that above the 2000 mark with a heavy throttle I hear a low freq/low pitch humming-like sound that I attribute to the higher boost pressure. It tends to drown out other noises, but all gears will do it.



There are no wires from the 5600 to the ECM to tell it what gear is selected.



Try unblocking your waste gate and see if the sound changes.

 

[Hohn]

Justin,



If you're like me, you've had the EZ so long that you've probably forgotten the HO "2100 RPM surge". The emissions control settings in the ECM are such that, to avoid smoke, the engine seems to add fuel very slowly up to 2100 RPM, then suddenly cuts loose from that point on up. This may not be as pronounced with the DD2s, but I'm wondering if that's what you're seeing/hearing?



Rusty

This is news to me. I had never heard of such a surge, but it doesn't surprise me.



I wish I better understood EXACTLY what the ECM was doing that caused this sound change. If it's letting in more fuel after 2100 rpm, wouldn't the clatter still be there? Maybe even stronger?



I never remember this being there when the truck was stock. Of course, that was eons ago it seems. Also, the truck was still breaking in, so that may explain some of it. Yes, I bombed my truck at 13K. It never felt fully broken in until LaserBob's dyno put the hurt to it. It was like magic, the transformation.



Anyone know if Marco's ECM eliminates this "surge"?



jlh