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Discussion Starter #1
Has anyone seen a positive TDCO value from carcode?

My values are reported as follows:

IPT: 9.0
IPTD: 9.0
TDCO: 1.85

When I do the timeset command, IPTD goes to zero and my IPT hovers around 3.8-4.0 which is well within spec.

I was thinking of advancing the pump further to lower the TDCO, but want to be sure the value I am seeing is actually positive 1.85 and not -1.85. The truck runs and starts fine with no excessive smoke or problems.

I have emailed carcode support, but thought members here may have an answer.

Thanks in advance.
 

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Mine is currently at .7 with carcode,it started at 1.5 so I intend to adjust my pump to get back to the - side.
I havent tried timeset with carcode yet.
The posts I have read about carcode have shown when set properly,a negative # will be present.
Since I am in the same boat as you I hope others will respond.
With my snap on MT2500 tdco always read 0.0 but during timeset I had 3.5 avg. so from what I have gathered carcode is the more accurate tool.
 

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Discussion Starter #3
I just read a few threads where "gmctd" says not to use timeset on a OBD2 system and adjust pump based on TDCO values only using the relearn between adjustments.

I am perplexed as I also read the truck should be running like crap with an offset of +1.85. It runs pretty good and starts fine. Mind you, I am used to driving a CUCV with a 6.2l for the last couple years.
 

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Mine runs decent but its always been this way since I have owned it,I dont know any different yet.
I just got carcode going a couple of nights ago to check it.
I didnt trust the readings from my snap on scanner.
The truck I have is a bit hard starting but I have to replace some known bad glow plugs.
If time permits I will be advancing my IP and rechecking with carcode this weekend.
Sure would be nice to get the magic -1.5 to -1.94 and find out what this thing should run like!
The main thing from my research on tdco is to note if the desired timing and actual timing are the same,the ecm can compensate some if the timing is off.
tdco has an effect on the fuel curve as well as starting from what I understand.
 

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Discussion Starter #5
I readjusted my pump this afternoon by about 4mm (in total) towards the driver side.

During my scans, I completely ignored the IPT and IPTD values as they were both almost identical which should rule out any component failure ( i think ). They also didn't change from one scan to another more than +- .5 or so.

I initiated the relearn via carcode using the '02 L65 profile. First time with a 1mm adjustment the TDCO went to .65. I bumped the pump another 2-3mm and now my TDCO reads -1.67!

I am stopping there for now. I will lock it all down in a bit and rescan.

Carcode support did reply that the program will show +- for TDCO which as I found today IS the case with a properly adjusted pump.

Kudos to member GMCTD, his posts on the subject pointed me down the right path. To paraphrase his posts from different threads. For OBD2 systems, ignore the TIMESET and IPT/IPTD values for timing. Time off TDCO using the relearn between adjustments.

Excerpt:
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If initial scanned TDCO value is elevated to some level greater than -0.5*, this may indicate BASE timing is not +3.5*BTDC

In this case command TDCO LEARN or KOKO, then rescan TDCO - if same elevated value, or any value other than -0.5*, you will have to punt: either

- move IP to exacty vertical and do the standard setup

- or move IP 1mm to right, do TDCO LEARN or KOKO, scan for new value
repeat at smaller increments until desired TDCO value is attained - PCM will DTC for TDCO over-range at some value over -2.20* in OBD2

*Again, aftermarket tunes seldom comply, but TDCO values at idle always represent Base timing, if you interpolate after the initial scan:

-0.5* = +3.5*

-1.5* = +8.5*
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Supporting threads:

http://www.dieselplace.com/forum/showthread.php?t=64710

http://www.dieselplace.com/forum/showthread.php?t=218725

http://www.dieselplace.com/forum/showthread.php?t=227239

http://www.thetruckstop.us/forum/showthread.php?11754-FYI-TDCO-Timing-the-DS4-Injection-Pump
 

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great news!
I hope to follow in your foot steps when time permits and get as good as a result hopefully.
Do you notice a difference with starting and performance since you got the timing right when you road tested.
(keyboards on the fritz so I cant puncuate correctly)
 

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Discussion Starter #7
Got it all tightened down and did the relearn via carcode.

TDCO went to -2.2

I then did the KOKO and now my TDCO reads -1.94

Interestingly enough, the carcode programmer said the offset learn was not added to the OBD2 spec until model year 1998. Which is why to use the function you need to tell carcode your vehicle is a 02 L65. Perhaps this is part of the issue causing a difference between KOKO and carcode set values after a "learn".

Another point to note is that my rpms did not noticeably increase during either procedure. I was under the assumption that a learn would increase rpms to find the right value.

I am going to run it for a week or two and recheck. I'll have to rescan for codes as my SES light was either disabled at some point or has a burnt bulb.
 

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Discussion Starter #8
Found this tidbit from GMCTD and it makes sense from what I've seen:

FYI - KOKO does TIME SET automatically, so there's no need of doing it with the scanner - where the scanner is a problem is that KOKO will only do it when conditions are permissive: 180deg ECT, 80deg IAT, no cold-advance, but the scanner can ignore that restriction, adding any cold-advance offset into the mix - PCM then may LEARN erronious value for TDCO - could even die and not restart, if the number is way outside probability - KOKO should always be used for OBD2 timing procedure in order to establish the baseline

http://www.dieselplace.com/forum/showpost.php?p=2484692&postcount=23
 
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Well I took some time this afternoon and adjusted my pump.
I figured I need about 3 degrees advance so I moved the pump about 2mm and ended up with -2.45(I know everyone says it can't read beyond -2.2).
I moved the pump back about 1 mm towards passenger side and did the relearn and had -1.85 and I locked it down.
I reset carcode and tried the relearn again to verify results and it jumped around between -0.9 and -1.26.I exited carcode and restarted the program and without doing the relearn a second time checked tdco and found it to read -1.94.
I shut down carcode and restarted it and it repeated the -1.94 tdco
reading so I figure its set now.
I then went and connected my snap on mt2500 and it now reads -0.1 with both of the cartridges that cover my model year.
I figure it was too far out of parameters for the snap on scanner to read when it was originaly at +1.5 tdco?
so in conclusion:
actual timing at idle is 9.3,desired timing at idle 9.3 and tdco -1.94.
I have driven the truck very little since the change but it does seem to start better hot and is more responsive with much less smoke.I hope it has a posative effect on mileage too.

The knowledge and resources at this forum are indispensable and I sure am greatfull for this community.
 

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Hi Guys, My timing is set to -1.58 TDCO is this ok ?
I think book spec's call for -1.25 TDCO most shops set them at -1.50 TDCO so -1.58 should be ok ?
 

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Just for reference a lot of what has been said about TDCO in the past was incorrect. Making the machines work right is mostly correct, but the concepts were off.

-.5 TDCO = 3.5 cam degrees base timing, but it means that the IP is sitting at about 27 degrees crank timing in its nominal position and the lowest it could go is 7 degrees crank advance. because 3.5 cam referenced degrees is 7 crank reference degrees.

-1.94 TDCO = ~4 cam degrees base timing, which when changed to crank reference is 8 degrees.

The pump wants to sit nominally at 25.7 degrees advance. The TDCO is how far off from that it is in crank degrees.

OBD2 systems do not code for TDCO fault until 2.46.

-0.5 = 7 degrees crank advance
-1.94 = 8 degrees crank advance

But the PCM will advance the timing at idle to at least 9 crank degees in the lowest of GM calibrations, and more like 17-22 crank degrees in the majority of 6.5s

Timeset works fine, ive used it with success a couple times, and had negative TDCO values. But IPTD is determined by the PCM program, so normally it will always be the same regardless of what your TDCO is. The PCM advances it to a set value taking into account the TDCO value. During time set, the desired goes to 0 so the PCM can see how low the stepper motor can get the timing, or your "base" (which should be shown in IPT), to determine how far the pump is from 25.7 crank degrees advance.

a 96 OBD2 truck I worked on for some reason would have a 1 degree timing offset when the TDCO value was not accurate, like pump had moved without running TDCO, or put a different PCM in without running TDCO. Although I dont know if it was accurate or PCM just confused.

If for some reason the TDCO values dont make sense, with reported values in timeset, its possible the CPS is not installed correctly, because if its rotated out of the correct position it will send the wrong data back to the PCM and confuse the heck out of it. Although it might not understand something is wrong and wont throw a code, just muck up your timing and TDCO process.

Most "F" OBD1 trucks had a timing of 8.5 degrees cam reference at warm idle. But with later OBD2, GM started giving 11 and even 12 degrees advnace at warm idle. If your IPTD and IPT are for some reason oddly low it may also be a sign of CPS installation issue. Some special 94 truck with the HO DS4-5068 and the "S" trucks had lower timing around 5 degrees, so it would be normal on them, although it makes for poor throttle response.
 

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What is the IPTD and IPT ? The numbers I get off them is 9.4 to 10.2 < almost the same numbers, dose this sound right ? did not check if these were - or + I was really just looking at the TDCO -1.58
 

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That is injection pump timing and injection pump timing desired, they are positive values, the number of degrees advance referenced at the camshaft. They should be the same value or very close. This is the timing that the PCM is commanding according to the timing curve programmed for the given RPM and fuel rate.
 
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