Set IJ timing

[byte]

Hello... I need some advice on setting IJ timing. GMTDScan shows the following readings at 185 degrees at idle

Desired Injection timing = 5.7
Actual Injection timing = 5.7
TDC Offset = -1.94 or -2.02

the truck seems to want to set TDCO to -2.02, but I can get it to lock in at -1.94...

<b>What should the Desired Injection timing be at idle, engine warm? </b>

at GMTDScan headquarters (the web page) they list these values under TDCO resetting instructions...
Take note of the current DES/ACT/TDCO values. OEM is +3.5°/+3.5°/-0.5°.

<b>Am I right that most set the TDCO to -1.5 to -1.9 range for extra performance?</B>

thanks for clearing this up for me!

[byte]

just 1 more question for now...

how much bounce will be seen in the actual injection timing number in GMTDScan? Is this normal or a sign of worn timing chain?

Thanks again...:D

[Robyn]

Timing chain can cause slight variations.
The -1.94 is the magic number but if your close and the little creature is happy with it I would leave good enough alone.

Jim or Greg could probably shed a little more light on what the window is on this as far as what is OK
GMCTD may chime in here too.

I am working on getting my scan software from GMTDscan.

If you are off too far the DTC 88 will set.
Dont want it to rattle like an unhappy Powerstroke. :eek:

Good luck

Robyn

[moondoggie]

Good Day!

TDCO (top dead center offset, or TDC offset) reflects what the actual injection timing is. I think the factory likes to see -0.5 TDCO. As you move towards -1.94 (pre-96) or -2.02 (96-on), you will see very slightly more hp, as proved by dyno runs by ronniejoe on John Kennedy's chassis dyno. I've been told they can get a little harder to start, but even if this is true, it doesn't seem to be much of an issue.

If memory serves (& it often doesn't), when we advance injection timing by advancing the IP, the TDCO goes more negative in the PCM's attempt to correct the difference between what it sees from the crank position sensor & the optical sensor inside the IP. I think TDCO was provided so timing changes / differences could be compensated for, like as your timing chain wears, TDCO would decrease, so your injection timing wouldn't drop off to the same degree as the timing chain wear would retard it. I thought this was in an approx. 5:1 ratio; if the TDCO was able to offset any timing changes, then it would fully compensate our advancing the IP, which it doesn't do.

Blessings!