Understanding TDCO Learn/setting timing

[knkreb]

One of my greatest weakness is understanding the timing of the 6.5.

Years I've read about TDCO, advance, retard timing and I've never focused on it.

So, in another thread in asking for help with starting, someone brought up timing. I read posts and threads about koko, time set, etc, etc.

If I understanding this correctly, KOKO (key on, key off) is pressing the accelerator pedal to the floor (with the engine off of course) for 60 seconds and start the engine. I didn't find the most concise write up on as it seems like it's just kinda either yours truly was too lazy in his search or it's just part of the secret inner circle knowledge of the 6.5 crowd. Since I've long since lost my secret decoder ring, I'm coming hat in hand to make sure I've got it right.

When you do koko, does the engine change rpm, speed, idle or anything to indicate that it's "learning" or does it learn as YOU change the rpm of the engine.

I'm thinking I must have done something here, because my ScanGauge II is giving me better looking numbers. I keep it on the average MPG and real time MPG to see what's going on. After this little exercise the other day, I'm finding my MPG numbers are much higher. I don't know if it's the placebo effect or what, but even my GPH reading at idle is much, much lower. I haven't filled my tank to verify anything either, nor have I ran my ScanGauge through another fuel recalibration (at each tank fill up) to make sure it's reading accurately with what may have been me really doing a TDCO learn.

 

[THEFERMANATOR]

I've tried the KOKO method on a 2000 3500 truck before, and it did NOT work. Even after he had it flashed to the latest from GM it still wouldn't work. So I wouldn't count on it working for your 01 van.

 

[jmiller]

I too have not concentrated on the 6.5 timing guts.

But I can take knowledge of electronic timing of other engines or computer controlled machines and some specifics of the 6.5 setup and make some guesses. ( I hope are educated )
The closest gas engine example I can think of would be 3rd and 4th gen small blocks with distributorless ignition's.

Without spending time to read out the PCM code and deconstruct it and understand it, a few principles of machine / computer interaction are kind of understood.

The computer is controlling the injection of fuel at a specific time in the engines rotation or the angle of the crank. So the computer must know where the piston and other mechanical's are in their cycle.

Mechanically, the relationship to the crank position / Piston position / crank to cam position and cam to IP drive shaft is fixed with the error introduced by mechanical slop. (timing chain / gears) The position of the IP can be changed mechanically with the pump mounting bolts. (mechanical base timing adjustment)

The Crank position sensor reluctor ring has 4 dogs to give rough position of the crank. The PCM will keep count of these pulses from the CPS for many things, but for this discussion its one of four positions of the crank in relation to other things, like the injection pump.

The injection pump (DS4) has the optical sensor. This sensor gives a very fine resolution of the IP's position. (I may be out of school here) IIRC there is also a rough position and or a home or base position.

A procedure to establish the relationship between the CPS and IP's optical sensor must be made. I will discuss my best guess that this is the purpose of KOKO.

Through experience we know that the PCM get "lost" after the battery is disconnected too long, because it takes two cranks before it starts. (also produces no glow cycle until after first crank, I'll bet no fuel either)
This first crank is to find the home pulse so the PCM knows were the engine is in its rotation. This "position" is stored in ram, or volatile memory. This makes sure the fuel get injected into the correct cylinder.

But how does the PCM know the relationship between the crank / cam / IP / the output discharge of the IP? It needs an offset count of high res optical sensor pulses from the home pulse to a crank pulse. With that count, the computer can calculate the position of the piston is its cycle and when to inject fuel from a base timing event. It could be just the home pulse to the CPS, just don't know the specifics.

For reasons I can think of for storing this position offset in non volatile memory make some sense. It should not change unless the mechanical's are disturbed or wear.

For these reasons I believe that KOKO establishes this base timing offset in the PCM.


Then we have to think about the timing offset procedure. This is a dynamic compensation, since this is done while running. Something needs to make the fine adjustments of where exactly the CPS is in relation to TDC / crank reluctor ring. Also optical sensor to the IP housing / fuel distributor output. This could be used to make fine timing changes required for efficient operation of the 6.5.

I would expect KOKO to be the base time. So if the timing chain has stretched, maybe the timing is off enough to impact mileage.

I would always perform timing offset after perform KOKO, because of what I believe the interaction / relationship is between them. It would fine tune the timing performance of the PCM.


With all of this BS written, how much is accurate?
I DO NOT KNOW!
It is just my best guess. Besides what I know about the electronic timing of some gas engines, I also look at some of the OBDII error codes, the sensors on the 6.5, the data I've seen from my car code live data screen, along with dealing with computer controlled assembly machines and the need for their timing of electrical mechanical interactions. This gives me an indication to what I would think about needing if I had written the PCM code.


The few people that may know for sure will not tell because it is not in their financial interest to discuss it.

I'd love to look at it, because software is my thing. But tools are expensive or non existent for me to putts around in the PCM code. I would hope that one of these knowledgeable ones might share, one way or another, but I do not have any hope of that.

 

[jmiller]

PS,

I've tied KOKO once, it seemed to do something when I replace my engine.

But I used the timing offset procedure through the car code sw to set final timing and tweak the pump position.

 

[ak diesel driver]

IIRC it's key on for 1 minute with the throttle pedal held all the way down and then key off with the throttle all the way down and then start it. if you have a scanner that will read but not set you can set TDCO with this method albeit alot of trial and error

 

[nobby]

KOKO Routine as follows:
engine above 170 DEG F
Clear all DTC's
Turn Ignition On with engine OFF
Hold Down Throttle for minimum 45 Secs
Turn OFF Ignition for a minimum 30 Secs
Start engine when temp gets above 170 DEG F and RPM below 1500 a new TDCO will be learnt. You can tell TDCO is relearning as the timing figures will momentarily drop and the engine will momentarily lug.

Cheers
Nobby

 

[Big T]

Tried KOKO when I installed a reflashed PCM from Heath. It did work, but it was also supposed to remove the "security" light and never did. Now that my ABS problem seems to have been resolved, the "security" light is the only one lit on my dash.

 

[knkreb]

Ok, thats one thing i wanted to know was "does the engine react by changes in rpm etc as it "learns"
I didnt do the key off for 30 seconds, but something changed. Still have very favrorable MPG numbers. We'll see at the pump if it holds true.c

 

[Turbine Doc]

Yo Kev "pick up da phone man" reach out & touch someone did ya lose the #

KO/KO is as per Nobby's explanation, I'll add my experience also the hotter the better on coolant, I found out hard way if temp drops below 170F as seen by PCM/ECT not what your dash indicates there are (2) sensors dash & PCM use independently your KO/KO can be disabled.

Timing the 6.5 is not as complex as procedure would have you believe.

I'll try the KISS explanation PCM controls the timing events based on various engine speed & temperature inputs though engine sensors and sensors in the IP, then take the inputs process them to tell the timer stepper motor what to do with timing for a given engine condition/load demand. For this KISS discussion I'll continue, plenty of threads in the TRL that discuss the specifics of engine governing system.

So from a timing perspective we know the PCM sets timing required via the timer stepper motor but that range of TSM movement is limited and gives us a "window" of full open & full closed movement authority, hence the code we recieve from the PCM with too much retard or advance, there is only X amount of movmenet capable in the TSM to advance or retard the timing to get more "window" you have to move the IP advance or retarded. In theory and per GM manual changing a PCM should not require a TDCO relearn, relearn is only required if timing has been effected by a mechanical piece part hass been changes ie IP swap or timing gears, because when a new PCM is installed that has been set to VIN specific tune there should be adequate "window" to allow TDCO to meet the GM timing spec for TDCO.

Enter in now a reflashed PCM with a different than factory "window", or a IP that has been moved off of factory setpoint for a little more grunt then it is advised to do a TDCO relearn so that "window" center of open/closed is restored, vs offset too far to open or closed of the window.

Way to do it from my experience very simple, loosen to just a little snug the bottom IP mounting nuts with engine cold so you don't burn your fingers in between adjustments, you will use the top locknut to hold the IP while making adjustments; start the vehicle and get to 175F or so ECT, clear any codes and take reading of current TDCO, then command time set with the bi-directional scan tool.

What happens then if the engine is close to being on "base timing" the display for time desired will go to 0 and the average should be close to factory 3.5 deg if time displayed is more like 2.6-3.0 on avg you need to move the IP. If you are way out of time the truck may shut down on it's own or "lope idle" as soon as you enter into time set, in time set you should be able to sustain idle without the PCM input. This is somewhat similar to what you do when timing a old gasser with electronic spark control, to unplug the puter so your ignition is firing on base postioning of the the distributors timing mechanical setting.

Shut down the truck (assuming it still stayed running in time set) & depending on the avg you observed; move IP to driver side advancing the IP if avg was low, if your avg is too far advanced say +3.8deg you need to retard timing by moving IP toward passenger side direction, lock IP down with just the top lIP mount.

Now if wanting to retain factory timing and TDCO window set for 3.5 deg avg.

I prefer myself a timing average of 3.6/3.7 degrees average which will put the window for the TDCO to be at a performance setting (-1.5 to -1.95) vs factory set for emissions/economy in stock setup (-.25 to -.75) don't get wrapped up in that number it is basically a reference point for setting TDCO as once the PCM is in control again it sets the actualy timing, TDCO is a reference for us to establish the "window" of authority we allow the PCM to tell the TSM where to go.

Once you have the base-time set by moving the IP and locking down the top IP mount nut, then restart, check coolant temp, clear codes, shutdown then do the ko/ko to command the learn, then start you may feel a momantary stumble to the idle and new TDCO value shoud be in the PCM & will remain there until a TDCO releanr is recommanded. repeat & adjust as necessary. OBD-I guys don't have this capability, and can only do it with a Tech 1 or laptop tool.

As far as a PCM going "dumb" by not being powerd, in OBD-II PCMs from what I have seen that does not happen, I at one time had several that I would swap out while looking for a tune that works best with ATT, they keep the last settings programmed to them including TDCO and theft learn codes if you have that system, at least up to a year I had them powerde down or beyond ???? I don't know as I've gotten junkyard PCMs that allowed my vehicle to start/run and Lord only knows how long those were not powered up.

In summary PCM controlls all timing via the TSM, & PCM has to be out of control when setting base timing, "window" for best movement is determined by TDCO setting, TDCO is a stored value and has to be "taught" to the PCM via ko/ko or scan tool not a requirement but for best operation my personal view any time IP is moved or a performance PCM is put into operation needs to have a TDCO learn completed.

Yes more details to it than what I just posted but just trying to make it simple & understandable and not a "black boxy mystery"

 

[Turbine Doc]

Tried KOKO when I installed a reflashed PCM from Heath. It did work, but it was also supposed to remove the "security" light and never did. Now that my ABS problem seems to have been resolved, the "security" light is the only one lit on my dash.

ko/ko for timing set is not same as ko/ko for theft learn timing is a minute or so, theft learn without scan tool takes about 45 minutes to complete and is a PITA