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Could Use Some Help Setting TDCO on OBD I

Following these OBD I instructions from the technical reference here:

Standard procedure

When installing a replacement DS4**, or resetting timing, start with the Engine Shut Off solenoid in 90* vertical to horizontal plane across valve-covers - this should within a RCH of +3.5* Base timing

Start the engine, do an initial scan on engine parameters for 180*F ECT, idle speed 695~750rpm, ACTUAL IP timing +8.5*BTDC, DESIRED IP timing +8.5*BTDC, TDCO -0.5*

ECT must be at operating temperature ~180*F or timing procedures are invalid - I prefer 195*F

Scribe a line across the IP and timing cover flange

Scribe a second line across the timing cover flange, 2mm to the right of the first line - 1mm = 2.5*

Loosen the 3 12pt nuts on the IP flange, rotate the IP, aligning the IP flange line to the 2mm line for a +5* advance, secure the nuts

Start the engine, scan again verifying at least +180*F ECT, ACT\DES +8.5*, idle 695-750rpm

Command TIMESET, rpm will increase, engine will hesitate and stumble as PCM determines new IP position, wait ~5 seconds, exit TIMESET

Command TDCO LEARN, engine rpm will again increase, and hesitate\stumble, will self-exit when new value is learned

Scan again for +8.5*BTDC ACT\DES IP timing, TDCO at -1.5*

NOTE: engine stumble\hesitation is resulted during the period when PCM wratchets OS timing 22* between minimum and maximum limits to determine IP position

When we command TIMESET, nothing happens. RPMs do not increase. Engine does not hesitate or stumble. Then we command TDCO Learn and it simply defaults to -2.46.
 
jrsavoie said:
As we all know, new means nothing anymore.
Not that it ever did, but especially in the last 20 years, new has not been a guarantee of good.
Might be just my experiences
Click to expand...

Yeah I’ve heard this repeatedly, but before I throw baby out with the bath water I need to exhaust all options. This IP has been in briefly last fall and I do believe that we set the TDCO on it.
 
So from what I remember OBD1 can get stuck in that mode. What I would try is making sure the IP is plenty far to the left, get it up to operating temp, plug in the block heater to try and maintain engine temp, disconnect the batteries for about 10 minutes, then try doing timeset ASAP when you get the batteries reconnected
 
ak diesel driver said:
So from what I remember OBD1 can get stuck in that mode. What I would try is making sure the IP is plenty far to the left, get it up to operating temp, plug in the block heater to try and maintain engine temp, disconnect the batteries for about 10 minutes, then try doing timeset ASAP when you get the batteries reconnected
Click to expand...

Les your trouble shooting approach is much appreciated.
 
Last evening we tried as Les described.

ECT at operating temp of 190. Disconnect the batteries for 10 minutes. Reconnect batteries. Make sure codes are cleared but they immediately come back. Did this process 3x with the same results.

Truck runs fine.

Is there anyone out there with expertise on DS4 IPs in OBD I trucks?
 
So you should be able to verify that the stepper motor is working by watching the arm move while varying the RPM. If it does not move take a screwdriver and gently push on it and see if it will move a bit.
 
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