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AFAIK TDCO is never reset unless commanded. the resistor value on OBD1 is checked every 50 starts, on OBD2 not so
 

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Discussion Starter #23 (Edited)
I just completed the following:

-ran clear hose from T-Valve. Fuel ran into container with no air bubbles present. I closed the valve and opened the air valve on top of the filter and fuel spurted out.
-changed PMD with my spare. #5 resistor is in place.
-searched for optical filter and I do not see one.


Drove it a short distance and ran fine. I am going to hold off on changing the new Rock Auto HB and pulley I received until I make sure this code is not coming back. I will drive it for a few days and see if code returns.
 

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I just completed the following:

-ran clear hose from T-Valve. Fuel ran into container with no air bubbles present. I closed the valve and opened the air valve on top of the filter and fuel spurted out.
-changed PMD with my spare. #5 resistor is in place.
-searched for optical filter and I do not see one.


Drove it a short distance and ran fine. I am going to hold off on changing the new Rock Auto HB and pulley I received until I make sure this code is not coming back. I will drive it for a few days and see if code returns.
The clear fuel line needs to be installed on the return side of the IP to properly find air in fuel, as shown in this link:
https://www.dieselplace.com/forum/63-gm-diesel-engines/21-6-5l-diesel-engine/736442-1999-gmc-bluebird-6-5l-td-pmd-resistor-settings.html#post7305306
 

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Discussion Starter #25

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Discussion Starter #27
update:
One week of driving and no code. I am hoping it was the PMD. The PMD I put in was the one I used for years with the old pump. After I replaced the pump in December I used the PMD that came with the rebuilt pump. The engine seems to run quieter and smoother. Crossing fingers







I'd be doing the tests for the CPS and OPS

CPS replaced in December by shop as they could not get it timed after I replaced the pump until they changed it out. I will replace OPS if i get code again, thanks.
 

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As a test, you can put the PMD that caused the DTC and see if that is still causing the DTC.

On the other hand, you may not want to disturb anything except probably get a new PMD for spare.
Now, make sure you test it in the truck driving for a few weeks before retiring it as a WORKING spare.
 

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Discussion Starter #29
just to finish this thread off for someone who may have may same issues..


Codes kept coming back. I finally replaced the encoder/optical sensor on the pump back in September and no more problems. The rebuilt pump I purchased obviously had a bad optical sensor and this was the source of all my problems.
 

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thanks for coming back and posting what your fix was.
 
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