TDCO relearn questions

[DA BIG ONE]

When I had my IP changed out TDCO was set via device controller.

Question is, if TDCO is not set by adjusting pump location would the PCM set the proper TDCO value using the ign on/off throttle down/up relearn. or?

[joed]

I'm not sure if this is correct or not, but I think using the KOKO/throttle procedure will find the more 'natural' TDCO based on the IP position, while using a Tech 2 or other controller can 'force' the TDCO to a certain value as long as it falls within the range the IP stepper motor can adjust for.

So in theory both ways should end with a similar TDCO, although one time I had to bump the pump after doing the KOKO procedure to get it within range....

Joe.

[gmctd]

Correct - the OBD2 KOKO procedure determines the expected TDCO for any IP position - the scantool allows selecting a specific value within the +/- limits for that position - KOKO is best for initial determination in OBD2 systems to see where you are, then use the scantool for any desired 'enhancement' - this is usually done by increasing rpm off-idle, then nailing the desired number - PCM will DTC at something over 1700rpm, which will require clearing the DTC or further timing attempts will not work.

It works this way - injection timing must increase as rpm increases: PCM DESIRES advance, moving the advance piston as required, then reading the ACTUAL\MEASURED position from the OPTICAL SENSOR - in TIMESET and TDCO LEARN, PCM determines physical IP position in Degrees Before Top Dead Center by cycling the advance piston, with it's attached Optical Position Sensor, to each limit of advance\retard (+\-), noting and storing the +\- values in degrees in memory - PCM then retards the advance piston to full stop and locks it - TDCO LEARN then calculates TDCO on that fully retarded position - however, if engine rpm is manually increased, PCM still DESIRES advance, calling for advance piston to respond - even tho TIMESET\TDCO function has the piston locked full retard, the DESIRED number increases as required by the rpm increase - now, if TDCO LEARN is commanded with the scantool, PCM will calculate the new TDCO value based on the DESIRED advance number, rather than the ACTUAL number - you cannot see this in OBD2, as it was hidden so results would agree with FSM admonishment that any attempt at advancing injection timing would not result in any performance increase - the only TIMESET figure you will see will be +3.5*, no matter what position the DS4 has been adjusted to. (yeah, I know - bad grammar to end a sentence with a preposition - so, sue me, eh!)
Empirical data absolutely refutes that FSM blurb.

Ennyhoo - KOKO first, then piddle - try it, you'll like it.................

[gmctd]

One small item I fergot to mention: all bets are off if using other than Tech2 because T2 programming is specific to 6.5 PCM - aftermarket scantools were not required to support then-current emissions standards, and some do not totally follow GM protocol, far as displayed values and specific rules go - f'rinstance, some do TIMESET and TDCOLEARN soon as the button is pressed - T2, bound by GM protocol, will refuse the commands until ECT is above 172egF, where PCM is not demanding cold advance, so you get reliable TDCO numbers.

[Warren96]

f'rinstance? Is that French?

[gmctd]

Red-neck french.....................

[DA BIG ONE]

I just reset TDCO w/koko and it is giving me a reading of -2.02 it seems to run better than ever, starts better too. Timing is 10.5 w/desired 10.5 thinking this is the 2 deg built into the gear drive.

Is this reading too far off, or?

[gmctd]

That is a little high -

In winter time, you need to keep an eye on ECT and IAT - PCM still calls for advance if ECT is 180deg, but IAT is 50deg, verified by fast idle -

So, at 180deg operating temps, IAT above 85degF, -2.02 is a little high, indicating the IP is too far advanced - need to back it down a mm or so, crank it up, let ECT and IAT come up, do the ko ko thing again, look for -1.94

Or, if you want to leave it at -2.02 for awhile, depending on your lowest ambient temps, it will run but may be a little hard-starting with too much advance

Remember: when ECT and IAT and idle speed are normalized, then you will get correct TDCO with koko - go from there with your scantool

[Kennedy]

I've not had any cold starting issues running numerically large TDCO settings, but it can get to sounding a bit on the crisp side and also tends to be a little hard on glow plugs.

[DaveNY]

I am a Little deficient in Redneck and French (Born in Brooklyn). I have long thought that something not quite right with the timing on my truck? I seem to eat up glowplugs It sounds like marbles in a cuisinart when start up 40' and below.
If I uderstand this right although my AE says -1.81 it may not be where it should be?
Time set says 3.5, and desired and actual follow each other pretty close from 11.2 at idle and up. All this is questionable info??
Dave

[gmctd]

Good questions, Dave - oem factory timing is -0.5deg - high performance timing is generally accepted as -1.94deg max, which will really rattle - your -1.81deg TDCO setting, while not as agressive as some, is advanced over oem -0.5deg, so the engine will protest very loudly at all ambient temps, moreso as temps drop, which was one reason I reset mine from -1.94deg down to milder -1.54deg - even in deep-cold south-east Texas weather of 40deg the seeming mechanical agony was fairly scary - advancing the timing does result in higher performance, but rest assured, the clatter doesn't hurt a thing - me, I'm just a wuss.:o

Glow plugs are another animal, tho - what exact problems are you having?

FYI -
Long starts - I consider anything over one full turn of the crank to be long-starting - engine will take longer to crank as temps drop below 40deg due to reduced battery power, thicker oil, colder intake air (an intake-air heater ala Cummins would really help), colder fuel, colder combustion chamber\piston\cylinder walls, colder glow plugs, etc, all resulting in slower cranking speeds and reduced compression temperatures - high cranking rpm creates high compression temps making for easier starting.

Repeated glow cycles usually damages any but the G60's, which require longer glow cycles, and certain of the aftermarket quick-heat gp's - some vendors offer cheap quick-heats, which should be labeled as 'quickly-over heats' - good quality gp's are necessary for below-40deg starting, way moreso as temps head toward -40deg.

The oem 60G's do require some method of increasing glow-time over oem duration - usually in the form of an operator-controlled in-cab switch.

The condition of the gp-harness and connectors becomes highly critical in cold weather - frayed wiring at the connectors, burned heat-damaged wire-crimp connections resulting from loose-fitting connectors at the gp's, same-type damage at the glow controller, hi-mileage glow-controller, all contribute to long starting and glow plug failure.

[gmctd]

Here is the actual OBD2-only KoKo footsie\fingers thingy, for yer liesure enjoyment............

NOTE - do not attempt this at home without a scantool, kiddies
If scantool gives different TDCO than KOKO, the value obtained from KOKO procedure is correct relative to the actual position of the IP

If timing is to be adjusted, loosen the IP except for the easiest to reach nut - it will hold the Ip in position before and after any adjustment.

With engine at operating temperature, all DTC's cleared, observe as-found TDCO with a scantool to get your baseline reference - kill the engine, then:

Key On, depress accelerator pedal for not less than 45secs, then release - this gives PCM time do do some housekeeping for the coming event

Key Off for not less than 30secs - PCM powers down, allowing memory to clear, including, and this is important, any driveability parameters

Key On, START the engine - TDCO will reLEARN as soon as Engine Coolant Temp and Intake Air Temp come up to operating temps.
- you may feel the engine hesitate and hear some increased rattle as PCM hunts for Inj Position if timing is way off - may not be any symptom if timing is close

Connect Scantool and note TDCO value in degrees - noting that 1mm movement is about 2.5deg timing change, loosen the nut:

- if less than -0.5deg (more positive) rotate Inj Pump away from turbo-side to increase BTDC timing
- if greater than -1.94deg (more negative) rotate IP towards turbo-side to decrease BTDC timing

Lock the IP down with one nut, do the KoKo thing again - repeat as necessary to get TDCO between -1.54deg and -1.94deg
- you will want TDCO to read above -1.54deg - once it is in that vicinity, then you can adjust TDCO with the scantool by commanding TDCO LEARN, then slowly increase idle till you see the desired value, immediately exiting TDCO LEARN - then recheck TDCO in the monitor-only screen

NOTE: increasing idle above ~1700RPM will give TDCO DTC, which must then be cleared B4 proceeding - timing adjustments do not function unless all DTC's are cleared

Also NOTE - pay no attention to TIMESET or timing readings with OBD2 - if TDCO is correct, timing will read somewhere between +8.5deg and +10deg, which can also depend on ECT and IAT in wintertime - +8.5deg means timing is at low end of acceptable range, +10deg means timing is at high end of acceptable range, or PCM is still calling for advance, which you can see by checking IAT for over 85degF

Lock the Ip down with all three nuts.

Take a final as-left TDCO reading with the scantool for future reference - take the vehicle for several 15min easy start-off runs so PCM can relearn normal driveability parameters.

Any re-LEARN is permanent in that it will not change during normal operation - once PCM learns any TDCO value, takes the KOKO procedure or the scantool to change it

One final thing - do the procedure not more than twice, then drive the vehicle normally for ~15mins so PCM can adjust driveability parameters to the new timing value - some reports indicate that PCM refuses to cooperate if TDCO LEARN is attempted frequently at one sitting, without relearning the other operational parameters

[DA BIG ONE]

Thanks for the easy to understand instructions on TDCO. I now have a better understanding of the whole process, surely others do too!

I commend all of you on this page for the professionalism and easy to understand help that keeps our GM diesel products going, and going.

[DaveNY]

GMCTD
Thanks for the translation, will set timing today. As far as glow plugs seems a year ago last fall I needed to replace a few (5) plugs so put a set of QH's in and was dissapointed they didnt make the winter. Installed new controller and 60's mid winter. All was good. The truck as of late seems to be a little slow on startup and a little more than normal white smoke. I suspect GP's but have not checked them out as of yet. The engine is in fine shape 17-18 mpg Hwy,no oil consumption nor blow-by at filler.Boost and EGT fine no smoke beyond normal grey when hard acceleration.So the whole thing maybe a non-issue or just time for a set of injectors?
Dave

[gmctd]

"Little slow on startup" could be interpreted as low battery(s), oxidized\corroded cable(s), worn brushes\dragging armature in starter motor - this time of year most Diesels, and particularly those that are somewhat long of tooth, tend to blow white vapor on startup, as do gassers (patooie!) - which is also one sign of worn injectors - I'd check the electrical system first, then the starter motor, then on to the injectors - it still won't start easy with new injectors if the 'trons are sub-par.

[DaveNY]

Gmctd,
Wrong terminology,Instead of slow to start I ment maybe an extra revolution, Cranking speed is fine new batts and cables no problem there at all. Definetly alittle extra smoke not steam.Checked GPs today and all OK. I'm guessing Injectors a little sloppy.
Did do KOKO and came up with TDCO -1.85, At idle actual was 12.1 as was desired. Strange but when I went to time set it was moving between 3.4-4.1 (timing chain?)
Pulled TDCO back to -1.32 and actual and desired changed to 10.1 , and truck runs smoother or less crisp but good power. sort of like it!
Dave

[gmctd]

Yes - in TIMESET mode PCM cycles camring 11deg between fully retarded position and fully advanced position, comparing Optic Sensor limits to Crank Position Sensor to determine physical position of Inj Pump relative to crank TDC - Optic sensor is then locked at full retard and CPS is unmovable, so variations are due to timing chain slop and any drive\driven gear backlash.

PCM does same routine in TDCO LEARN, so, with OBD2-only KoKo function, TIMESET is not required in OBD2

Only functional test for G60 gp is to connect one directly to the battery via jumper cables - not a battery charger, but a 12.6v battery - the gp should glow center-to-tip within 5 seconds - if it glows center-only it is failed and won't supply sufficient heat for winter cool

Same for the Beru\Bosch quick-heats - glow center-only is failed

Also, if either type emits dark from center to tip it is failed...............

[DaveNY]

Ok now if understanding correctly, after KOKO and TDCO came up -1.85 Im just about where I should be with the pump position and that the only tinkering to do is tdco learn to my prefrence.
Only did testlight on GPs, But if I were to find some are deteriorating in less than a year (60gs) the problem may be timing related or ?
Thanks Dave

[gmctd]

Correct on the TDCO - or you could leave it there for a while, see how you like it halfway between harsh and even worse.

If you pull any gp's that are chewed up, that could be caused by timing, but most likely bad injector spray pattern - only electrical damage would be from repeated way-extended glow duration, and I've not heard of that with 60G's - those half-season quick-fails recently on the market were a Disneyland product with the oem label wirebrushed off - if you held them in the light at just the right angle you could just barely make the label out: mickey mouse enterprises - the BERU's are the good ones.

[DaveNY]

Well thanks, I like things simple and am glad I dont have to move the pump.
On the other subject I think Ill take a good look at the GPs while I have some mild weather this week!
Thanks Again for your input
A Lot of help Dave

[gmctd]

Well, I would wish you good luck, but luck has nothing to do with it, so good wrenching, eh..............

[DA BIG ONE]

I set TDCO to -1.50 less noise now and not much loss of power (Butt Dyno). Being that I have gear drive instead of chain the max recommended is -1.80 so thinking -1.50 w/KO KO method should be fine.

[gmctd]

Drive it a while, see how you like it - TDCO of -1.5deg is where mine has done well for many years (on DSG gears), and you know KoKo has it right.

[DaveNY]

Well not being one to leave well enough alone (Truck running great), But can't figure out what change took place? Before KOKO my TDCO was -1.81 adjusted by my AE, again my des and actual was 12.2, After KOKO my TDCO was -1.85 and des and actual dropped to 10.2
History is as follows: 40,000 mi ago took truck to dealer and was denied warranty (dirt in fuel), lost temper and told them to push it out side and I would come and get it.
Put in new filter and got it running (rattled like hell). When home found Crank pos. sensor unplugged.
Installed Heath remote, and truck ran, timing was to far advanced to set TDCO -2.48.
Lost temper again , took piece 4x4 and brass punch and whacked ear on pump towards the pass side twice. Bingo quit setting code and was able to set timing!
Ran OK, playing with AE and TDCO. But since KOKO it has been very noticable Improvement?
somethings been out of whack for 3yrs???????????
Much Mellower Dave

[DA BIG ONE]

Here is the actual OBD2-only KoKo footsie\fingers thingy, for yer liesure enjoyment............

NOTE - do not attempt this at home without a scantool, kiddies
If scantool gives different TDCO than KOKO, the value obtained from KOKO procedure is correct relative to the actual position of the IP

If timing is to be adjusted, loosen the IP except for the easiest to reach nut - it will hold the Ip in position before and after any adjustment.

With engine at operating temperature, all DTC's cleared, observe as-found TDCO with a scantool to get your baseline reference - kill the engine, then:

Key On, depress accelerator pedal for not less than 45secs, then release - this gives PCM time do do some housekeeping for the coming event

Key Off for not less than 30secs - PCM powers down, allowing memory to clear, including, and this is important, any driveability parameters

Key On, START the engine - TDCO will reLEARN as soon as Engine Coolant Temp and Intake Air Temp come up to operating temps.
- you may feel the engine hesitate and hear some increased rattle as PCM hunts for Inj Position if timing is way off - may not be any symptom if timing is close

Connect Scantool and note TDCO value in degrees - noting that 1mm movement is about 2.5deg timing change, loosen the nut:

- if less than -0.5deg (more positive) rotate Inj Pump away from turbo-side to increase BTDC timing
- if greater than -1.94deg (more negative) rotate IP towards turbo-side to decrease BTDC timing

Lock the IP down with one nut, do the KoKo thing again - repeat as necessary to get TDCO between -1.54deg and -1.94deg
- you will want TDCO to read above -1.54deg - once it is in that vicinity, then you can adjust TDCO with the scantool by commanding TDCO LEARN, then slowly increase idle till you see the desired value, immediately exiting TDCO LEARN - then recheck TDCO in the monitor-only screen

NOTE: increasing idle above ~1700RPM will give TDCO DTC, which must then be cleared B4 proceeding - timing adjustments do not function unless all DTC's are cleared

Also NOTE - pay no attention to TIMESET or timing readings with OBD2 - if TDCO is correct, timing will read somewhere between +8.5deg and +10deg, which can also depend on ECT and IAT in wintertime - +8.5deg means timing is at low end of acceptable range, +10deg means timing is at high end of acceptable range, or PCM is still calling for advance, which you can see by checking IAT for over 85degF

Lock the Ip down with all three nuts.

Take a final as-left TDCO reading with the scantool for future reference - take the vehicle for several 15min easy start-off runs so PCM can relearn normal driveability parameters.

Any re-LEARN is permanent in that it will not change during normal operation - once PCM learns any TDCO value, takes the KOKO procedure or the scantool to change it

One final thing - do the procedure not more than twice, then drive the vehicle normally for ~15mins so PCM can adjust driveability parameters to the new timing value - some reports indicate that PCM refuses to cooperate if TDCO LEARN is attempted frequently at one sitting, without relearning the other operational parameters

With engine at operating temp I clear the dtc 1656 (running mech boost controller) for boost control circuit then do the Ko Ko but when I restart the dtc comes back. This will not allow the TDCO to be set, or? I did go into ecm controller and set it manually and updated ecm but not sure this will work properly?

[gmctd]

DTC 1656 has nothing to do with the wastegate actuator at this point, as you're not blowing Boost at idle- that error indicates some problem with the MAP sensor: low output, hi output, no output, erratic output - you will need to address that B4 proceeding: frayed\broke wire(s), loose connector pins, unplugged connector, failing\failed MAP sensor, etc

It's just like being married: if Mother PCM ain't happy, yer day promises to go downhill from thereon, eh...........

[DA BIG ONE]

DTC 1656 has nothing to do with the wastegate actuator at this point, as you're not blowing Boost at idle- that error indicates some problem with the MAP sensor: low output, hi output, no output, erratic output - you will need to address that B4 proceeding: frayed\broke wire(s), loose connector pins, unplugged connector, failing\failed MAP sensor, etc

It's just like being married: if Mother PCM ain't happy, yer day promises to go downhill from thereon, eh...........

Even though there are no codes for map/boost sensor?

It's my understanding that the turbo boost control circuit consists of some type of variable relay within the ecm and 2 wires going to the wastegate control vacuum solenoid.

[JohnC]

If you disconnected or removed the wastegate solenoid, that's probably what it's complaining about. Put it back long enough to get the TDCO learn done.

[joed]

According to my alldata subscription, P1656 sets when:

* PCM requested Wastegate solenoid ON.
* Voltage on Wastegate solenoid control circuit high (near battery volts).
* 2 consecutive faults detected.
* Conditions met for 2 seconds.

or

* PCM requested Wastegate solenoid OFF.
* Voltage on Wastegate solenoid control circuit low (near 0 volts).
* 2 consecutive faults detected.
* Conditions met for 2 seconds.

Also, "'This diagnostic will set when control circuit does not follow the PCM command (when the solenoid is requested ON voltage will drop, when the solenoid is OFF ignition voltage will be present). Its possible DTC P0236 may set along with DTC P1656."

The troubleshooting chart discusses checking the connector at the PCM as well as at the Wastegate solenoid, and associated wiring. It does says it's possible to have a PCM control circuit problem, but "this is an extremely unlikely failure."

Supposedly freeze frame data should be stored - use Carcode to view this, probably under the enhanced freeze tab - this may or may not be useful.

Hope that helps.

Joe.

[JohnC]

Based on what Joed said, if the solenoid is not there it will definitely set that code. I've heard you can substitute a resistor for the solenoid. It needs to see a complete circuit from the power source through the solenoid to the PCM.

[DA BIG ONE]

Based on what Joed said, if the solenoid is not there it will definitely set that code. I've heard you can substitute a resistor for the solenoid. It needs to see a complete circuit from the power source through the solenoid to the PCM.

Installed resistor to no avail so will wire the solenoid back in place and see what happens

[DA BIG ONE]

According to my alldata subscription, P1656 sets when:

* PCM requested Wastegate solenoid ON.
* Voltage on Wastegate solenoid control circuit high (near battery volts).
* 2 consecutive faults detected.
* Conditions met for 2 seconds.

or

* PCM requested Wastegate solenoid OFF.
* Voltage on Wastegate solenoid control circuit low (near 0 volts).
* 2 consecutive faults detected.
* Conditions met for 2 seconds.

Also, "'This diagnostic will set when control circuit does not follow the PCM command (when the solenoid is requested ON voltage will drop, when the solenoid is OFF ignition voltage will be present). Its possible DTC P0236 may set along with DTC P1656."

The troubleshooting chart discusses checking the connector at the PCM as well as at the Wastegate solenoid, and associated wiring. It does says it's possible to have a PCM control circuit problem, but "this is an extremely unlikely failure."

Supposedly freeze frame data should be stored - use Carcode to view this, probably under the enhanced freeze tab - this may or may not be useful.

Hope that helps.

Joe.

No DTC 0236, but will place solenoid back into circuit after I remove the resistor that didn't work.

Thinking wires or pins to ecm maybe not connecting, had this before w/other issue. The harness in the footwell frt/pass side gets abused by feet especially when pass stretch out putting feet up into well and on harness stressing it.

[DA BIG ONE]

Replaced the boost control solenoid and did relearn to no avail, DTC 1656 only pops up after Ko Ko at restart. Truck is running great w/o any drive-ability issues.

I have ASE-8 module-16 for my model year 6.5td will have to dig deeper to find what is causing the code to set after 2 cycles of key.

[gmctd]

Maybe the solenoid really is bad now, or the connector pins, or the wires in the pins..........