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TDCO and GMTDScan

A

Acesneights1

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Hope I'm not using up my full nickel but again was inNY working on a few 6.5s for a buddy. This is a differnt truck than I posted about. This beauty is also a 94 but c3500. He said truck got shut off and when his guys went to restart is it would not start. Nothing. He had a local guy look at it and diagnosos the IP dead. He changed the IP with a reman and still could not get fuel from Injectors. I checked for fuel from Lift pump. No problem right to IP inlet. I then decided to scan for stored codes before I went any further. Got an error message invalid something with PCM. I'm thinking OK this is not good. I checked my laptop on my own 95. No problem So long story short the fuse was blow for the PCM Put new fuse in and got fuel right away and truck started right up. I pulled up the TDCO with GMTDScan and it read -1.58. This to me seemed fine for a work truck so I said it's good to go. BUT my question is did I read the actual TDCO or was that stored TDCO and the pump was actually running something different ? Truck sounded real nice and seems to run fine other than slight stumble which I attributed to air since it had not been properly run out yet. Did I check the TDCO right or should I have done something differently ?
 
Also any ideas what might have blown the fuse for the PCM ? Fuses generally don't blow without a reason. The truck needed some marinara sauce for the spaghetti uner the hood. The truck wasn't charging either which was a bad terminal on the batt side of wire coming from Alt. Also one of the grounds to the batt was a stripped wire jammed under the terminal nut. I gave my freind a good lashing about grounds and terminals.
 
That is the last stored TDCO...since the IP install you need to run a TDCO learn.....

Fuses blow on a short circuit....clean up all grounds and power wires to and from the ECM (batteries, alt, starter, etc).

This is all stuff you already know....
 
Yeah I kinda figured that. The wire going from the batt to Alt was so hot couldn't even touch it because of resistance from "rusted" terminal. Supposedly he fixed it although truck was gone already next day. He has enough 6.5s that I told him to
1)Join here and do alot of reading
2)Get gmtdscan.
It will be awhile before I go back to NY. Unfortunatley I had no PC access while I was down there. Oh well. Hopefully TDCO was close. It sounded alright.
 
OBD1 will learn new TDCO over a period of starts (~50) for any IP drivetrain change: IP, drive\driven gears, timing chainset, timingtrain cover, CPS, etc - owner may never notice change unless those starts/time occur quickly, as in a commercial vehicle - if he was alert enuff to install the replacement in the exact position of the original, TDCO will be same, unchanging - if not (99.99% of mechanics are not) best to keep an ear on start\run rattle intensity as an indicator that TDCO\timing is changing

Much better driveability results would have been noticed if tired old worn sloppy floppy dilapidated stretched 1994 timing chainset had also been replaced.....................
 
gmctd said:
OBD1 will learn new TDCO over a period of starts (~50) for any IP drivetrain change:
Click to expand...

Not disagreeing....I've just never seen it on my OBD I trucks.....a TDCO relearn was always required to change TDCO.

If you consider that on a normal day I would start my truck about 3 or 4 times, it should take less than a month to see a TDCO change after an IP rotation....no dice for this guy....
 
TDCO is also intended as an automatic-learn process to keep IP timing in spec as the timing chainset wears - manually rotating the IP as mileage increases is unnecessary with Stanadyne DS4 EFI system, as compared with the earlier DB2 system - the DS4 is precisely machined, such that internal timing of any DS4 will be within an RCH of any other DS4 - thusly, if replacement DS4 is installed in the same position as the original, TDCO LEARN is not necessary if the timing chainset is not disturbed - at that point, PCM will have relearned as the oem timingset stretched, and timing will continue to deteriorate from there - new timing chainset will require TIMESET\TDCO re-Learn to bring the DS4\camshaft timing back to oem as-new spec - there is very little mechanical wear in the properly serviced\lubricated DS4 - the Fuel Solenoid valve is the major point of wear, which is why GM suggested IP removal for test and possible replacement at ~70kmi - since very few owners have put 100kmi on a truck after having the TDCO\TIMING reset, then had the timing rechecked, it would not be readily apparent that the process works as designed - GMTD Scan has improved that scenario, such that it is now affordable and easy to keep tabs on the OBD1 EFI 6.5 - 100kmi is a long time coming, however, as will be the reported results..........................
 
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I knew I was screwing up but I could not get to a PC. I'm 200 miles away now but i will tell him if the truck changes to findsomeone with a T2 and set it again. For what it is worth he says he put it back in exactly as it was. Shutoff sol was perfectly straight up and down so hopefully close not to do damage. Truck was running good except for some remaining air.
 
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