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Discussion Starter #1
I just upgraded from GMTDScan Basic to GMTDScan Tech. I'm diligently following the Time Set/TDCO learn instructions from Buddy's Mnx&Mods info_2.8.pdf and other FAQ links.

With Time Set OFF, I see:
Des=+8.5, Act=+8.5 (bouncing as low as 6.6 and as high as 9.9), TDC=-0.62
When I click Time Set ON, I get:
Des=0, Act=+6 (+/- ~0.5), TDC=-0.62

I did not proceed to TDCO LEARN, since I'm supposed to get Act=+3.5 with Time Set ON. My understanding is that I need to rotate the pump to make that happen, but before doing that, I'd like to know how it got so far off.

The IP was replaced by the previous owner at a Chevy dealer at 101k miles. The receipt says that timing was set, but didn't provide details. Assuming it was at +3.5 at that time, how did it get to +6, and should I be worrying about that?

Other than fish bites and gutless mountain climbing, which have been there since I bought the truck four years ago at 108k miles, it continues to run great...easy starts, never smokes, little oil usage/loss, 13-14mpg. The only other oddity I see is a 600rpm warm idle fuel rate of 11.25mm3.
 

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Discussion Starter #2
At the risk of high jacking my own thread, check out what I discovered while waiting to see what to do about the +6 deg ACT during TIME SET.

Looks like I've got bigger fish to fry.

Left: AC Delco 110k miles and 15 years
Right: ATP 43k miles in 4 years

I took off the original harmonic balancer and pulley as a preventive measure prior to driving to the tip of South America. Now, I'm wondering if I should've left it alone. Is this a testament to AC Delco over ATP, or a case study on the effects of deserts and salt air on rubber?

Back to the +6 deg ACT during TIME SET, given that the truck is running fine, I'm going to leave it alone unless someone tells me I'm causing damage.
 

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Discussion Starter #4
Pulley and HB definitely need to be replaced.
New pulley and HB should arrive tomorrow--also a new belt tensioner. How about the +6 deg ACT during TIME SET? I'll be in Denver later this week...
 

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My $0.02.......The tip I got was to ignore the time set and just set TDCO. So that is what I did when I set mine. What I was told is the the DES and ACT need to be equal. Since your TDCO is within factory spec, and the DES and ACT track the same, I would leave the IP alone.
 

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Discussion Starter #6
Since your TDCO is within factory spec, and the DES and ACT track the same, I would leave the IP alone.
Excellent! Do nothing is always a preferred option. Thanks.
 
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