Cold fuel knock

[stevens cummins]

OK guys I may just paranoid but I seem to have a excessive fuel knock until at operating temp, I know its gonna be noisy when cold its a Cummins with 197k on it but this knock seems to come in recently, could this be dirty injectors or just over thinking it

[Mopar1973Man]

First I would check the IAT temperature with a live data tool. See if the IAT data. At key on the IAT and ECT sensors should match.

[stevens cummins]

OK I I will as soon as I can odd part is the knock goes away at about 150 degrees

[Mopar1973Man]

1 hour ago, stevens cummins said:

odd part is the knock goes away at about 150 degrees

I gather coolant? I still need to know the IAT temperature. IAT as it get colder the timing gets more advanced. Typically the advancement get so steep it sounds like a mechanic trying to beat his way out of the engine with a 6 pound sledge.

[stevens cummins]

OK I will get you that reading asap but I'm out of town till tomorrow and my scan tool is at home

[Mopar1973Man]

This why the MPG fooler was built was the problem of the IAT temps diving off too deep on the cold side the ECM cranks up the timing advancement even harder making the engine knock. So this is why I'm asking about the IAT temps. Because just by flipping a switch between MPG mode to OFF you can here the VP44 advance heavy and start knocking when turned to OFF. Then turn the MPG fooler back on then the knock nearly disappears.  

So back to checking the IAT temp and where you stand in the morning. ECT and IAT temperatures should match exactly. 

Like here is a screen shot of my OBDLink LX on a first key on.

[stevens cummins]

I hadn't thought about the VP being able to take timing that far

[Mopar1973Man]

Simple really. Being the intake air (sensed) is super cold the ECM commands the timing to be advanced heavily to give more time for the compression of the piston to convert the fuel from a liquid mist to vapor to go BANG! So now lets say the IAT is misreporting the value and ECM is calling for advancement because of bad data. Now the air temperature is actually high than sensed so now the fuel converts from liquid mist to vapor faster and the piston is still travelling up when it goes BANG and you get you knock because the explosion happened early on before side of TDC.

I've been told by Quadzilla stock VP44 and ECM can make full advancement in stock form. It just when does it occur. IAT temperature are a key factor.

Edited February 26, 2016 by Mopar1973Man

[stevens cummins]

OK I under the impression the VP was limited by the ecm endless tapped guess that's what I get for over thinking it?

[Mopar1973Man]

Wire tap just modifies fuel pulse length and possibly modifies when it occurs by adding pulse before time. Most modules use a high priority bit to override the ECM stock tune. Most all timing is handled over the CANBus connector typically.

[stevens cummins]

? I learn sumn new everyday 

[Mopar1973Man]

So now that where the concept of the MPG fooler came from because up in the nrothern states the IAT temp can be as cold as the outside air on start up. So after starting the IAT data would cause a VP44 to be highly advanced in timing till the IAT temps fell again. This may or may not happen depending on several things like winter front usage, coolant temperature, cold air intakes, speed of travel, etc. So aggressive timing would produce a heavy knock on the engine. Neat trick is toggling that switch back and forth and listening to the sound of timing and how it affect the engine. Then while doing that watch a live data tool like Scan Gauge II as you toggled between OFF and MPG mode. What you'll see is in OFF (using the actual IAT temp) the timing was heavily advanced. lots of rattling/knock, but MPG typically are about 1-3 MPG lower. Flip to MPG mode which just fools the IAT to believing its summer time and MPG will rise instantly as the knock/rattle leaves. So aggressive timing advancement isn't always a good thing!

So now as for the fuel temperature that also plays a role here too. If your missing your fuel heater then colder fuel sensed by the VP44 will also create heavy advancement of timing too. Ask yourself how many times have you see some report a error code P0168 for overheated fuel?

Remember the whole design of diesel engines is to create enough heat in the compression stroke to convert the fuel from liquid to vapor to make it go BANG. So the VP44 was the first electronic system to attempt at sensing all these different things and adjust timing anf fuel amount electronically. Not to mention our engines happen to be the lowest compression ratio engine out of the entire series at 16.3:1 (SO) or 17.0:1 (HO) where all other generations are higher. So this why we have a heart passage in the intake manifold to help heat the air entering the cylinder.

 

Edited February 27, 2016 by Mopar1973Man

[stevens cummins]

After reading that it makes me wonder could my fass cause this I'm running the stock filter housing with the heater but could the extra flow push more fuel than the heater can heat when cold and the VP sense colder than normal fuel a advance the timing to far

[Buzzinhalfdozen]

I had quite a few filters gel up just sitting there idling when I had the stock lift pump and filter housing. So yes I don't think the factory heater can keep up once the engine is running. 

Unfortunately it's hard to say what's excessive noise without hearing it. Like Mike said these engines get pretty angry when they're cold.  

[Mopar1973Man]

Stock fuel housing does pull heat from the coolant passage in the take manifold once the coolant is warmed up. As for the fuel heater I can't say one way or another if it's capable of heating or not. I just know at least with all my minus temps I've never gelled once. 

[stevens cummins]

Humm looks like I need to get to testing some things. I'll get those iat and ect reading soon and need to test my stock fuel heater and check my grid heaters

[stevens cummins]

Sorry it took so long to get back. I checked the iat and ect sensors they are reading the same after setting for the night  so I don't see this being the issue