Computer & Physics Question: Timing the DS4 IP

[JayTheCPA]

Ok, I'm confused (and I'm sure that at least a few out there are already reading this and thinking: 'Like this is a surprise . . .?' ).

Here is what I know (based on what I have read):
> The ECM controls the DS4, including TDCO.
> After installing / rotating the DS4, the ECM needs to 're-learn' to establish some sort of baseline / offset.


Here is what I do not know:
The question I am trying to get my head around is why physically rotate the DS4 to an 'advanced' position when the ECM is also capable of electronically controlling the TDCO?

The only thing I understand at this point is that the ECM re-learns something (presumably where the IP is); what I do not know are the re-learn's effects on both the ECM's logic and the physical TDCO. After a re-learn, does the ECM now know where the DS4's physical location is and use this as the starting / reference point for the existing data curves, will it try to counter-act the location and electronically adjust back to a desired TDCO based on the logic, or . . .?

And from what I have read, it is possible to re-map the TDCO curves in the ECM, so this opens the question of why physically move the IP as opposed to just letting the ECM do all the TDCO work through logic. Is the answer that we really have not dug into the ECM's logic, or am I simply missing too many pieces to get the questions right?

 

[ak diesel driver]

the advance in the IP is controlled by the stepper motor. The stepper motor has a limited amount of travel. the ECM need to know where the pump is in order to control the stepper motor. When you command the ECM to learn it's physically determining where the IP is at. It will show approx. 4-5 offsets available, basically the range of the stepper motor.

 

[JayTheCPA]

Ok, this helps. Am still missing something in my puzzle . . .

ECM learns the IP position to apply an offset on the stepper motor's range and the stepper motor controls advance (TDCO); got-it. Then what?

Once the ECM learns which offset to use on the stepper motor, depending on the ECM's logic, this determination has the possibility to defeat the reason why people install the DS4 in an 'advanced' position . . . Does the ECM attempt to counter-act the actual IP position to keep TDCO where the ECM wants it?

Ultimately, what I am trying to get to is why mount the DS4 in any location other than OE if the ECM has the capability to control the timing? Natrually, the first goal is to understand how the ECM is working.

 

[ak diesel driver]

With the IP in the stock position the ECM is limited to how much advance it can command. By advancing the IP position your moving the range of advance that the ECM can control.

 

[ak diesel driver]

Perhaps a better analogy would be to compare the IP to a gasser distributor with mechanical fly weights. The flyweights will only move so far and in order to get more advance out of the distributor you need to move the distributor itself to achieve that. The stepper motor is our fly weights and in order to achieve more advance we need to rotate the IP. In a perfect world there would be more travel in the stepper motor (and related parts) and it could all be commanded by the ECM

 

[JayTheCPA]

Think I'm there . . .

By installing / rotating the DS4 in an 'advanced' position:
> the ECM gets a baseline of the actual IP position.
> under normal conditions, the ECM adjusts the stepper motor to desirable TDCO knowing that the IP's physical orientation is in an 'advanced' position.
> under conditions calling for max retardation, the ECM puts the stepper motor to the most retardation possible and recognizes that it cannot actually get there, but goes with what it can do.
> under conditions calling for max advancement, the ECM puts the stepper motor to full advanced knowing that it can get higher in the range.

Put another way, for the most part am sensing that we are not fooling the ECM by rotating the IP to 'advanced' as it sets TDCO (per the logic) to an optimal position anyway, but when it is time for max advance the ECM is able to get higher into the advanced range, and when it is time for max retardation the ECM knows it has a limit.

Does this recap the scenarios correctly, or do I still have it balled-up?

And presuming I actually have the relationships correct, last questions are:
> What are the effects of not allowing the stepper motor to get as far into the retardation range?
> What is the capability of the stepper motor in terms of the TDCO range? +/- 2, wider, narrower?
> Inferring what I have read so far, the ECM looks like it might have a software TDCO limit of:

} +/- 2
} +1.75 / -2.75 (OE range (-0.25 to -0.75) plus the allowable 'learn range limit' (+/- 2) when it will throw a code)
} or +3.75 ((-0.25 + 2) + 2) / -4.75 ((-0.75 + -2) + -2).

So, What is the max usable 'advance' TDCO setting where either the ECM will limit the stepper motor, or we are no longer getting the combustion pattern we are looking for?

 

[THEFERMANATOR]

I did a write up on this in the DIY tuning thread(so bear with me here as I try to recall of it, I'm sure I will get some of it wrong and some expert will be along shortly to correct the errors of my explanation). The ECM doesn't control TDC offset, TDC offset is the relation of the injection pump to actual engine timing with the pump at the fully retarded timing position. Basically the injection pump has to be installed and timed to a range that will allow the ECM to command minimum and maximum needed timing. The IP uses the stepper motor to control the timing of the pump, and has an 11 degree range of movement. At full retard of the pump, the ECM wants to see 3.5 degrees of timing(this is a -0.5 TDC offset). This setting allows the ECM to command the ECM's 25.5 degrees of max advance that it may call for(you have to double the 11 degrees of IP movement and you get crank advance which is 22, plus the 3.5 base setting and you have 25.5). If you were at say a 1.5 TDCO, then you would lose 3 degrees of total timing and only be able to reach 22.5 degrees of timing, but on the other hand you could go to a -1.94 and be able to reach over 29 degrees of timing at full advance. Due to the way the injection pump works, even though it is electronic in it's timing control, it still must be timed to get it to where the ECM can control it through the full range of advance the ECM could call for. The TDCO is to make sure you have the injection in the range setting for the ECM to control it.