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>>>* for high fuel rate at idle: ... might the high fuel inlet pressure have anything to do? ...
Pressure has nothing to do with it.. What is happening is the computer is trying to maintain a certain speed and to do so is calling on the IP to inject more fuel. A bad chain could retard engine as well as IP timing. Timing that is off will require more fuel.
 

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I think if I ever need a DS4 pump for some reason I might go through rockauto and pick up one of their acdelco reman units.
 

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IIRC, I believe Kennedy Diesel and Badger Diesel also advertise a new pump as well
They could I just remembered for sure that Leroy did. I'm hoping I'm not going to be in need of one for a very long time
 
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Discussion Starter · #26 · (Edited)
I did not miss the opportunity to buy a NEW IP last stanadyne production
 

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Discussion Starter · #27 · (Edited)
I haven't started the timing cover dismantling work yet
... I'm waiting for some pieces😔 ... was looking at what to do to get ready

... for Camshatf gear bolt torque to 125 ft / lb I would be a little doubtful
before 1996 was 65 ft / lb ... find also 75 ft / lb torque for this bolt... but after 1996 GM changed the values to 125/126 ft / lb

GM changed because they found that this bolt tended to loosen as DieselPro already mentioned .... OK

but did GM also change the bolt grade to 12.9 to withstand the increased torque?
 

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Discussion Starter · #28 ·
Timing Chain, Cam and Crank Sprocket replaced
changed woodruff key, ....
BUT.......PROBLEM NOT SOLVED
desired timing average is always low compared to TDCO

now I have TDCO -1.58 and desired timing of 4.8/4.9

change the chain produced no effect

my old chain was sloppy near to 0.7" deflection
 

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TDCO -1.58 is good enough, I think?
How is the truck running?
 

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Discussion Starter · #30 ·
truck runs as before ...nothing changed

always a DES/ACT timing 4.9 (very low timing value vs TDC )
fuel mm 12 (too high at idle).

low performance compared to when was DES/ACT timing to 8.5/9.0
and low mileage compared to was before the problem happen
 

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Discussion Starter · #31 ·
think i must test Crank Position Sensor
i have no error code stored
but there is something doesn't work as intented
 

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Discussion Starter · #32 · (Edited)
some update

tried to test CPS and it is working.
I also tested Opctic Sensor by disconnecting it and alternately disconnecting OS and CPS. some hesitation but then the engine starts. so they are both working.
when disconnected you have the codes DTC 17 OS related, DTC 18 OS related, and DTC 19 CPS related. clean DTC and with both sensors plug-in, no code is present.
I also replaced the CPS just in case....
TDCO procedures
the strange thing is that even if the TDCO value changes from -1.50 / -1.58 / -1.94 the DES / ACT timing always remains at 4.9 as if it was the maximum allowed value.
 

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Discussion Starter · #34 ·
I must say it works
have not DTC 34 - Injection Timing Stepper Motor Fault. when engine is cold i can see DES / ACT timing to 7.3 then as the engine approaches the operating temperature it changes until it reaches 4.9
however ACT timing value always very close to the Desired ECM timing value. so I would say it works
 

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Discussion Starter · #35 · (Edited)
Update

checked the CPS
engine off, turn key to run, at CPS connector, pin C Gray wire (reference signal 5V) value 5.04V, pin B Black wire (ground) 12,48V.
then start the engine and backprobe pin A Yellow wire (return signal) value 4.48V

check the return signal wire from CPS connector to ECM (pink 32 connector - pin D13) = 0 ohm.

it is not a problem from CPS signal, CPS are working.
But the DES Timing value is always to low (4.9) compared to TDCO value (-1.94 / - 2.02).
 

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Discussion Starter · #36 ·
I don't know what else to check

ECM takes the value from the CPS to determine the Crankshaft position, and then set Base Timing and DESIRED TIMING.


something else that escapes me????
 

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I don't know what else to check

ECM takes the value from the CPS to determine the Crankshaft position, and then set Base Timing and DESIRED TIMING.


something else that escapes me????
ECM also takes values from the Optical Sensor and utilizes both CPS and OS for timing
 

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One thing you mignt try.
The optical sensor electrical filter may be bad and sending corrupted data to the PCM. If you still have one you can remove it and plug the OS wiring direct minus the filter.
 

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Discussion Starter · #39 ·
already tried with or without optical sensor electrical filter...nothing change
 

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Discussion Starter · #40 ·
checked OS sensor
all wires are good
all values checked are inline
the only one i cannot check is the 60 hertz on PD15 PCM terminal (Pump Cam Reference Pulse)
i have not a tool for it

no DTC is present, but maybe this value needed for know what happen.
 
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