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timing

C

carguy13

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So I have the car code scanner and today i tried to do the TDCO learn. The best i could get was -0.53 with it sitting between -0.35 and -0.09 most of the time. i sat out there for a while trying to get it but gave up and decided to post on here. Could the timing chain be worn out and that cause this or do i just have to sit there even longer and just wait?
 
Okay from my experience 3 weeks ago with one of these, vs. my MT2500 you have hit the "window" of adjustment where the IP is currently positioned, so you'll need to move the IP now to get more "window" that will take you to the -1.5/-1.95 range we like for performance setting on the 6.5.

IP needs to be rotated to drivers side, do you have IP turning tools ? Worn timing chain should show up as large difference between actual and desired timing when accelerating, or decelerating, but I see from sig @ 275K if you have original chain there will be some stretch in there so it's a possibility there is some impact there.

But I'd try rotating IP 1st
 
You really should not be able to get values in a large range. You need to move the IP to actually advance it. Some people found some glitch in carcode that might make it say its offset is greater, but that is artificial, just as revving the engine would make it artificially set while doing the TDCO relearn.

It would be interesting to know if GM took into account RPM values when setting TDCO. I think in OBDII the relearn procedure sets an RPM, and there is a known mapped internal IP differential pressure that will affect advance function. Changing RPMs messes with that. In OBD1 it just idles at whatever RPM it was at the time, so some trucks you set it while its at 562rpm and others 600rpm and some others 700rpm.

Same IP position would result in different TDCO values in OBD1, so I guess GM wised up for OBDII and had the relearn procedure set a constant RPM
 
Buddy GMCTD & I got same "window" on mine using a GM T2 when comparing GMs readings to the MT2500, also same info from Kennedy when discussing TDCO with him, I'm not sure of the mechanics of it vs logic in the different scan tools, Kennedy didn't like MT2500 as it did not have ability to engine rev & set as his tech 2 tools allows.

I have no choice with MT2500 TDCO with it s strictly an "as moved/found" setting with ko/ko & APP to floor learn activation.
 
I was not denying that you get a "window", Im talking about the carcode guys that have a range of 0 to -2 of TDCO values without moving the IP. It should be a "window" of about +/- .15 if not messing with the fuel pedal.
 
Of course if you start messing with the pedal you could double that window, but I dont think thats a good way of doing it, unless its to bring you down into an acceptable number. When you are OBDI idling at 562rpm in the relearn, revving it makes the TDCO go down, so when I am getting -2.02 I rev and might get -1.94 or -1.85. In OBDII and your idle is set to high idle of 1050rpm I think during relearn, then revving seems to make TDCO values go the opposite way. But I suspect the PCM is not monitoring RPM, but the procedure is assuming the IP is at a differential pressure that was mapped at 1050rpm.
 
buddy said:
I was not denying that you get a "window", Im talking about the carcode guys that have a range of 0 to -2 of TDCO values without moving the IP. It should be a "window" of about +/- .15 if not messing with the fuel pedal.
Click to expand...

my window wasn't anywhere near that big
 
Check out the OBDII thread with the guys going from -0.5 TDCO to -1.94 by just staring down the computer and not even popping the hood. Interesting and informative read about how to use Carcode.

TDCO relearn times out in GMTDScanTech and maybe scanners, but Carcode must not have put a timer on it because they watch it for like 10 minutes.
 
so I reread the thread I started on obd2 and I didn't see anyone going from 0 to -2 but I did see -.88 to -1.94. and that was with rpms which I don't think is a proper way to do it.
 
The idle up is something that gmctd claimed in his timing thread. I noted it doesnt do that in OBDI, or at least with GMTDScanTech, but I have never worked with an OBDII truck or another scanner.
 
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