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feed back TDCO from -0.18 to -1.94

In OBD-I it is supposed to be "warm-up" events transitions from cold to above 170F H20, not ko/ko of 50 cycles, or at least that is my interpretation of the logic, I don't own a OBD-I or have one nearby to confirm that is how it works.

For those un-initiated to what is being discussed ko/ko is key on key off, if done on OBD-II in addition to ko/ko you also have to have the APP to floor >1 minute with ko then ko for > minute to command the learn to be active at next start up, also there can be no codes stored in the PCM, and coolant temp has to be > 170F or learn will not activate.

Again as Buddy pointed out this is a OBD-II capability only, OBD-I guys have to use a bi-directional scan tool or a bi-D program to make this work.

As Kenny points out this may be a self learn for you OBD-I guys, Buddy since you own a OBD-I can you confirm or dispel the 50 cycle self learn function please?

Tim
 
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I think AK was just being facetious

However, there is no 50 cycle TDCO relearn on OBD1, but it learns the resistor value every 50th cycle.

If there was a 50 cycle TDCO learn there would never be an OBD1 guy with a TDCO value different than when they do the relearn before moving the IP. And definately have seen that more than once. And Ive done it myself. I set the TDCO to -.85, then tightened up the IP. Well I went and redid it several months later it was still reading -.85, but before moving IP I did relearn and was at -1.45. So thats why since then I always set it then tighten and then relearn again to make sure the act of tighening the nuts down doesnt move it at all. Its not changed once on its own, and since following the tighten all then relearn its always been right there with similar numbers before moving IP.

It would hardly ever end up on the same value as well, since it jumps about 0.25 up and down during the relearn. People would have TDCO values varying over time, and I dont think anyone notices their -1.5 changing to -1.35 a few months later.

And it doesnt make sense that it would attempt dropping the timing as low as possible while driving or operating it in general.
 
In a way it was published by GM that you can advance it more. Since the manual states that the TDCO values can be -2.02 to +2.02. The factory timing procedure is just that though, how they set it. Its published in both the area of the manual that provides typical values for each scanner item and in the DTC88 information. However if they had timing checks for these vehicles like they do on gassers during smog certifications then we would have to be -.25 to -.75. It amazed me that the smog certificaion actually required the technician to get a timing light and he failed my buddy's 86 mustang because it had a cam in it that wouldnt run unless it was at 14 degrees, and stock was 12, or something along those lines.
 
buddy said:
In a way it was published by GM that you can advance it more. Since the manual states that the TDCO values can be -2.02 to +2.02. The factory timing procedure is just that though, how they set it. Its published in both the area of the manual that provides typical values for each scanner item and in the DTC88 information. However if they had timing checks for these vehicles like they do on gassers during smog certifications then we would have to be -.25 to -.75. It amazed me that the smog certificaion actually required the technician to get a timing light and he failed my buddy's 86 mustang because it had a cam in it that wouldnt run unless it was at 14 degrees, and stock was 12, or something along those lines.
Click to expand...

Bend timing tab 2 degrees... ):h
 
i have a few questions on this. according to my tech 2 my 94 6.5 TD is now set at -2.02 and was set there by the relearn on the tech 2 itself. now my question is which way does the pump need to be turned to advance and retard the timing? i also have a TDCO code that will pop up after going about an 1/8th mile down the road. its strange to me because no matter the tempuratue of the truck it will blow white smoke at idle and lower rpms, but it will stop instanly after the SES light comes on untill it is shut off and restarted! its confuesing the hell out of me. thanks for any help guys!
 
Your IP is way too far advanced, which causes white smoke. You need to retard it toward the passenger side. Just try to get the edge of the IP flange close to in line with the timing wedge on the timing cover. Like below where the red line edge of flange needs to move closer to the black line. Get temp up, clear the DTCs and then do timeset and relearn TDCO. Start from there as a baseline.
BigT Timing2.jpeg
 
Just to add to what Buddy said, I suggest you scripe a line in IP flange before attempting to move it, mine had a factory mark I found after I cleaned the top flange...you will only need to move it a RCH hair...a little goes a long way IME.
 
When it reads -1.94 TDCO its at about 4 degrees cam timing, which is 8 degrees crank timing. And it will read -2.02 at anything more than that. It could be sitting a mm beyond, or an inch beyond and it will still read -2.02.

You can get an idea of how far off you are now by looking at the desired and measured injection timing. If desired at warm idle is 9 degrees, but measured is 12 degrees that tells you your base timing is 12 degrees when it should be no more than 4. So you would need to retard it 8 degrees which is about 1mm per cam degree.
 
oh ok that clear it up a bit for me thank you! i will give it a try this weekend. now what performance changes do you think i will see? its running pretty awesome IMO right now as it is. i belive i read somewhere in the tech 2 my desired timing was 4.04 something, now i dont remeber if it was negative or positive or if i just read something that doesnt matter. thanks again guys!
 
dangerousdave said:
With over 200K miles on my 94, would a TDC bump be good or bad for the remaining longevity?
Click to expand...

Would probably restore timing close to when she was showroom clean, and tight engine tolerances... timing chain specifically... I'm sure the 200k has retarded things over the long miles. IP Wear, etc.

Mods don't kill trucks. Mods increase longevity at all ages.

Your very own right foot on the other hand....:nono:
 
so i got my ip changed 600 miles ago because it was dying. well the dealership who did it seemed like they retarded the timing a lot because when i got it back it had lost a lot of power. now suddenly month later my power is back. think that has anything to do with the 50 key starts or with tdco?
 
the dealership did everything. my dad doesnt trust with me with working on my truck that much and he took it to the dealership without me knowing. also i got ssds hot air intake and before the ip change with a a new vaccum pump i could hear the turbo whistle very well. then after the ip change i could not hear it hardly at all. now i can hear it and power has improved a lot.
 
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