cold engine quiet

[skyhigh4by]

Maybe a silly question but I'm curious if anyone can explain to me why my 98 24v is much quieter at cold startup than when its warm? Theres barely any fuel knock at all and its really smooth sounding. Once it warms up and during the warmer months it just sounds like most other 24v. I run 2 stroke oil in my fuel. It would be great if I could figure out how to make it sound so smooth all the time. 

[AH64ID]

It probably has to do with the ignition dealay being longer with cold cylinders. 

[Mopar1973Man]

I've gotta ask if you checked IAT and ECT temp values. Typically in stock form the timing is cranked up somewhere around 19 to 20 degree on a cold startup. Fully warmed the timing is back to 12.86 degrees. 

 

If the ECT or IAT are misreporting it might change the timing. Like MPG switch regards timing in the realm of 3 to 4 degrees from stock value as it warming up.

[skyhigh4by]

Next time I have a scan tool handy all check it out. 

[Mopar1973Man]

Clue. When an engine gets quiet the timing is retarded. This tends to make me a bit worried and want to check for error codes like the P0216 code. even like my last VP44 when it failed it died with the P0216 code as well but it was stuck in full advancement it rattled and knocked badly. 

 

As timing retards engine gets quiet. This is because the fuel is actually igniting slower and later and actually doing it work after TDC. As timing advances the ignition of the fuel is happening before TDC so you start to hear the rattle as the fire starts the ignition BTDC and then pushes over the top and finishes with the power stroke.

 

You might look at other factors as well. Fuel and cetane amounts. Higher cetane fuels are lower BTU's but ignite much faster. Low cetane fuel will have more BTU's energy and burn slower and later.

Edited November 26, 2018 by Mopar1973Man

[AH64ID]

Which is why it can simply be the ignition delay from cold cylinders and fuel, the timing may be advanced but if the delay is longer the actual timing at which the ignition occurs might not be as advanced (the main reason timing advances on a cold motor). 

[pepsi71ocean]

I have the opposite issue. my motor is super quiet at idle when hot (coolant temp ~200F). Compared to when its cold its a snarling beast.

EDIT: although I should mention that for me the motor gets fairly quiet much above 195F of coolant temperatures.

Edited November 27, 2018 by pepsi71ocean