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TDCO magic number

625fireman

625fireman

I have injecter-itis
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Location
NE Ohio
Pending arrival of the cable, I will timing my 94 K3500 soon. I know there is a lot of talk about the right number. What do you think is the magic number to be at or is it different for each truck????

Thanks yall.
 
-1.94 is what I always see thrown around. I have yet to pursue it, as I have been doing other things before getting the scanner. I wish someone around me had one, but no luck yet.

Soon...
 
If you get to -1.50, or abouts.....Drive it and see what you think, AK is right -1.94 is clackity clack........Many have gotten to -1.50 or close, and seem to be just as happy as the -1.94 crew.

JMO
 
I'm at -1.50 and it's plenty clattery for me especially in the cold.
 
Have not looked at the link posted yet, but what would be a good timing for max MPGs?
 
rattle...rattle...rattle...

Running both of mine at -1.7~-1.8ish throttle response performance & mpg is much improved from the stock numbers IME.

Yup mine clatter more especially in the winter & even more so after I changed the injectors on my truck set em at 2300psi, still convincing myself the rattle is NOT doing any harm long / short term...:skep:

I do love that diesel rattle though :hihi:
 
If someone such as myself didnt care about power increases (would prefer to not decrease) but was was soley going for mpgs and being easy on the pump and the motor, basically trying to increase durability, reliability, and MPGs, what number would be the best?

I dont care about emissions or power, all I am concerned with is that I want the ol sow to last forever and get 20 plus mpg! :)
 
GM Guy said:
If someone such as myself didnt care about power increases (would prefer to not decrease) but was was soley going for mpgs and being easy on the pump and the motor, basically trying to increase durability, reliability, and MPGs, what number would be the best?

I dont care about emissions or power, all I am concerned with is that I want the ol sow to last forever and get 20 plus mpg! :)
Click to expand...

Get a 6.2 plenty of slow roll & mpg without the turbo :) other than that x2 to the -.75 to -1.1 TDCO doesn't really mess with mpg too much from what I've seen more to do with the right foot than as much as anything else,
 
Thanks for all replies. I will quest for some where between -1.5 and-1.94 as I am in NE Ohio and this is a plow truck. Thanks again y'all.
 
I backed off -1.94 simply because of cold start noise.

You're talking somewhere around 2-5 hp, tops, in the difference in the tdco adjustment range.

I gladly gave it up for a more "liveable" truck in the day to day grind.

get it on the negative side, but I wouldn't worry about it much more than that.

Unless you're looking to squeeze every last bit out of the old girl.....
 
The crazy thing is that going from about -0.5 to -1.94 TDCO is only about 0.5 cam degree change. 3.5 degrees to 4 degrees, which means a 1 degree change in crank angle, from 7 degrees to 8 degrees. So the change in response and noise hardly seems attributable to such a small difference. Especially when the PCM advances it much further even at idle, and way more with cold advance. Hard to say what the change in noise is all about, has to be pressure differences somewhere. Perhaps its that the IP pressure is able to build faster once the injection event begins and it does pop the injector like 1.94ms earlier than no offset, vice 0.5ms earlier, which could be extrapolated to some crank or cam angle, but GM didnt feel the need to. Because to them the beginning of the injection event likely means the beginning of the rise on the pulse width command from the PCM to the PMD which then switches on the Fuel Solenoid to close it to allow pressure to the injector to build. That and it would be an ever changing angle with RPM if the TDCO was a time thing. Still a mystery.

The timing sticky should also be updated to correct the info it has about that, where it says you go from 3.5 to 8.5 degrees advance. That is kind of a mix of cam and crank angles. Unless there is other evidence of actual injection timing happening differently than Scanners show Time Set as. It also says crank angles are half that of cam, but its the opposite where the crank is spinning twice as fast so it is always leading or lagging (depending on your reference point) by a factor of 2. So when we are showing desired idle injection timing of 11 degrees, thats 22 degrees of crank advance.
 
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