TDCO?

[98K2500]

Ok I'm a little confused here. I've read the FAQ and many other threads but I'm still not sure on this one. If I do a TDCO learn can that value change without physically moving the pump. TIA

 

[Brooklyn Tow]

To a certain point....Then you need to move the IP by hand.

 

[NVW]

It's a value the ecm see's and can change a certain amount.

 

[ak diesel driver]

The tdco has a range and if you need to go past the range to get the tdco your striving for you have to physically move the ip. To the drivers side increases the advance (will have a larger -#) conversly to the pass side retards timing (will decrease the -# or even start to show a +#)

 

[98K2500]

Well the reason I ask is I checked my timing today. It was 12.5 with a TDCO of 1.0. So would doing the relearn change it at all. I also just installed the GL4 and tried to the KOKO learn. Didn't get a stumble or anything but found out today that there was a boost solenoid code so figured thats why it didn't change.

 

[Turbine Doc]

What you are doing is setting a "window" of top dead center offset (advance or retard timing). depending which method/tool you use will determine your ease of setting exactly.

If you have a GM T2 tool or clone with same capability you possibly may be able to advance the or retard TDCO just by revving the engine and commanding learn, if there is sufficient "window" learn can capture a advanced position from factory, how much advance is determined by physical positon of the IP with relation to cam/crank/IP/timing chain slop to each other.

Those of us with "cave man" scanners, can only read current TDCO shut down and move IP advance/retard timing lock down command learn with ko/ko & APP to floor (OBD-II trucks only) then see what the resulting move did to change TDCO.

Remember TDCO is not base timing which can also be impacted by moving the IP, to set base timing like after a IP swap start truck, get up to operating temp and go to time set command, desired timing display will go to 0 degrees, and actual per factory spec should be 3.5 degs on average.

What I have found that if I set for 3.6-3.8 avg depending on vehicle when coming out of time set, that avg gets you TDCO pretty close to -1.5 TDCO more/less, and then only have to tweak just a little to set the desired TDCO you want.

Remember when in normal timing what you see displayed by timing actual/desired is wholly controlled by PCM/IP when engine is cold you will get higher timing as cold advance comes in via timer stepper motor advances, as engine warms up TSM backs out.

This is why engine has to be fully warmed up before making timing adjustments, or possible as son as it warms and influence of the TSM backs out you normal operating timing goes out of whack and you get odd idling or hesistaiton/stumble on acceleration or in reverse.

TDCO is a timing bias on top of the commanded time set by PCM, factory is (-.25 to -.75) better performance can be had with -1.5 to -1.94 wholly separate from time set, though physical movement of IP impacts both setpoints.

With a unknown vehicle I do time set 1st, establish the 3.5/3.6 avg lock down top IP lock nut, shut down, command via ko/ko APP to floor command, then restart and see where I am, if I'm happy with TDCO snug down bottom 2 lock nuts, if not rotate IP to direction I want TDCO to be. I only do time set 1 time to establish base time, after that I just tweak the IP to meet desired TDCO after that.

Does that clear it up more better ?

 

[Turbine Doc]

Well the reason I ask is I checked my timing today. It was 12.5 with a TDCO of 1.0. So would doing the relearn change it at all. I also just installed the GL4 and tried to the KOKO learn. Didn't get a stumble or anything but found out today that there was a boost solenoid code so figured thats why it didn't change.

What kind of scan tool you using to read,

12.5 timing with fully warmed engine ?

TDCO a + 1.0 ? that is retarded timing should be a (-) value for advanced TDCO unless using a snap on MT2500 scanner that depending on which yr cartridge you have in it gives some oddball TDCO values.

I have (2) different cartridges for mine neither agree with each other snap on could not tell me why,

so I verified mine against a GM T2 tool to know what value was equivalent to the GM tool at -1.5 & -1.94 .

IIRC +1.0 on one of my cartridges was = to factory TDCO -.6

But since I never set it at factory TDCO anymore I just have -5.4 & -.9 depending on cartridge I have plugged into the scanner as the TDCO I want to run it with/set IP with.

 

[98K2500]

Engine was up to temp and I originally checked with a solus and I remembered reading that snap on scanner readings were skewed so I disregarded the readings but today went to see my buddy who works at GM and checked with tech 2. Those are the readings I got. He didn't have alot of time so I left it at that. So I think anyways I've got this figured out now. Do the timing learn. If not at 3.6-3.8 adjust IP accordingly and redo learn until those numbers are reached. -1.50 is the TDCO I was shooting for. Truck seems to run pretty good the way it is though but I assume being retarded (not me the timing) would affect cold starts.

 

[buddy]

Very True. Another thing to realize is it may change if it was never done on last IP change.

Engine was up to temp and you had 12.5 desired and measured timing??? Were you at high idle? If idling 600-700RPM the timing should be around 8-9 degrees, unless Heath has decided to do something extreme with the tuning. I personally like lower timing like the N/A diesels had, so I programmed mine for 6.4 degrees at idle, even tried down to 4.5.

And you must realize these are cam timings, and crank timing would be twice as much. That is stated backwards in the timing sticky, because it says 22 degress stepper motor cam timing change would be 11 crank advance, and its really 44 degrees crank advnace variability.

 

[98K2500]

Yeah the actual was 12.5 and desired was 12.6. Idling at around 650. I don't know if the pump was ever changed. It doesn't have a tag on it.

 

[buddy]

Interesting tune then. I have found that you do save a little fuel with advancing it and even slightly higher smoother idle, but Im talking only like 1mm3 at idle. More advance would also help avoid black smoke at takeoff.

 

[Big T]

What you are doing is setting a "window" of top dead center offset (advance or retard timing). depending which method/tool you use will determine your ease of setting exactly.

If you have a GM T2 tool or clone with same capability you possibly may be able to advance the or retard TDCO just by revving the engine and commanding learn, if there is sufficient "window" learn can capture a advanced position from factory, how much advance is determined by physical positon of the IP with relation to cam/crank/IP/timing chain slop to each other.

Those of us with "cave man" scanners, can only read current TDCO shut down and move IP advance/retard timing lock down command learn with ko/ko & APP to floor (OBD-II trucks only) then see what the resulting move did to change TDCO.

Remember TDCO is not base timing which can also be impacted by moving the IP, to set base timing like after a IP swap start truck, get up to operating temp and go to time set command, desired timing display will go to 0 degrees, and actual per factory spec should be 3.5 degs on average.

What I have found that if I set for 3.6-3.8 avg depending on vehicle when coming out of time set, that avg gets you TDCO pretty close to -1.5 TDCO more/less, and then only have to tweak just a little to set the desired TDCO you want.

Remember when in normal timing what you see displayed by timing actual/desired is wholly controlled by PCM/IP when engine is cold you will get higher timing as cold advance comes in via timer stepper motor advances, as engine warms up TSM backs out.

This is why engine has to be fully warmed up before making timing adjustments, or possible as son as it warms and influence of the TSM backs out you normal operating timing goes out of whack and you get odd idling or hesistaiton/stumble on acceleration or in reverse.

TDCO is a timing bias on top of the commanded time set by PCM, factory is (-.25 to -.75) better performance can be had with -1.5 to -1.94 wholly separate from time set, though physical movement of IP impacts both setpoints.

With a unknown vehicle I do time set 1st, establish the 3.5/3.6 avg lock down top IP lock nut, shut down, command via ko/ko APP to floor command, then restart and see where I am, if I'm happy with TDCO snug down bottom 2 lock nuts, if not rotate IP to direction I want TDCO to be. I only do time set 1 time to establish base time, after that I just tweak the IP to meet desired TDCO after that.

Does that clear it up more better ?

Uhhhh, what he said. I had to get the timing set to around 3.5 average. That would get me -1.84 TDCO, but with a rev of the engine I was able to capture and lock in -1.94. But first I had to flip the CPS 180.:mad2:h:thumbsup:

P.S. My idle is at 564.