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TDCO

ak diesel driver

ak diesel driver

6.5 driver
Messages
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Location
alaska
So I was under the impression that once TDCO was set it would stay where you set it until you initiate a relearn. Doing some work on my truck today and decided to check it and it was -2.46:eek:
 
so your saying it can/will move to anyone of the 4 or 5 TDCO options that are available in a certain position?
 
THEFERMANATOR said:
Every 50 starts, the ECM will recheck the TDCO so it is correct and current.
Click to expand...

I thought that was obd1 and it was resistor values that were checked.

Les, did it code? once mine coded with the TDCOffset being wrong and that is when I got GMTDScantech.
 
ak diesel driver said:
so if that's the case why bother setting it at all it will set itself. I don't buy that
Click to expand...

You have to set it to start with so you know the pump is in the correct position for the ECM to be able to reach the full desired timing range. It rechecks the TDCO to account for timing chain stretch, and other wear facors and variables the engine goes through during it's life cycle.
 
I would think the ECM would maintain the TDCO setting initiated by original first relearn within its parameters and not wander of track if the chain wears a smidgen.
 
ak diesel driver said:
from -1.94 to -2.49 is quite a bit of chain strectch
Click to expand...

Not really. 1 MM of pump movement is 2 degrees. .55 degrees is roughly .25MM's of pump movement or chain stretch. Remember the pump runs at half the crank speed, so small changes make a big change at the pump. This is why the ECM rechecks TDCO every 50 starts so it can keep track of chain stretch since such a small change makes a big difference.
 
ak diesel driver said:
so if that's the case why bother setting it at all it will set itself. I don't buy that
Click to expand...

That was part of the question I was after when I asked about why to set the TDCO to anything other than OE in a OBD system.

I can understand advancing TDCO for a DB2 as it stays where we set it. The stumper was why do it on a DS4 when the computer 'corrects' what we do and throws a code if we advance / retard too much. So far it looks like the answer is that we can get a smidgen more into the advanced range, but only what the computer will work with anyway; hence we are not getting any more or less than what the computer allows / accepts.

And the TDCO topic is one of the reasons why I want to understand what the little computer box does (and why), but that is another set of questions in other threads . . .
 
Here's another reason I don't buy it. I remember TD saying he ran a full year with no resistor in an OBD2 truck. OBD1 different story
 
AFAIK the resistor is there to fine tune the amount of fuel per stroke to the injectors.. should have nothing to do with TDCO
Similar to the diff size shimms for a injector to get the right pop pressure.
 
If no resistor is present, the ECM defaults I think to a 2. So you can run without a resistor(it should set a code, but possibly not turn the light on).
 
what I remember was part of the steaksauce ordeal where he claimed to be able to vary the fuel with an adjustable resistor so to speak, and TD ran over a year without one at all to prove the PCM only sampled it during a TDCO set.
 
Been wondering if it wasn't a glitch/hiccup in my system. I couldn't get it (the TDCO) to move at all until I moved the pump. I ended up moving it back within an 1/8 of a MM of where it was and got a range of lowest of -1.67 to highest of -2.12 IIRC. You'd think it would be REALLY rattly at -2.49 and it wasn't at all. I have it at -1.67 now
 
You've already PROVEN the TDCO resets on it's own by your own findings of it changing. And teh arguement about steaksaucxe was that his device would change on the fly. A change from a 1 to a 9 only makes about a 10MM3 of fuel adjustement in total IIRC. The resistor was left out to prove that the ECM wouldn't just automatically readjust like steaky said it would. I wish I had some of teh old literature still from back in the day when I was poart of all of these findings, but that's been almost 10 years ago now and I haven't done any 6.5 stuff to speak of since about 08.
 
The first time I changed the pump in my truck I ran it for almost a year without doing a TDCO and what the PCM said was way off where the pump actually was when I finally got carcode and checked it.
 
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