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Discussion Starter · #1 ·
had some poor mileage problem

DS4 IP seem to works but...
when check out with Tech 1:
no DTC
TDCO learned -1.5 (fine) ...relearn at same value
DES/ACT timing 4.9 (very low timing value vs TDC )
fuel mm 12 (too high at idle).

about 230.000 km on it.

think is an IP problem but ask to some Guru if is time to change IP or there is something to check before buy a new one.
 

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Discussion Starter · #3 ·
yes, about 183 F over the mimimun temperature request for TDCO procedure
 

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Discussion Starter · #5 ·
no current and history DTC
 

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Discussion Starter · #7 ·
new injectors.... about 20.000 km ago
 

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Discussion Starter · #9 ·
"A stretched/worn timing chain can cause issues"
True... but i think if the timing chain is stretched/worn, you can see also difference from DES and ACT timing. if the value is very close and no degree delta average between the 2, i will suppose timing chain is OK, or i am thinking bad?
 

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Discussion Starter · #10 ·
the question is what can cause a so low timing advance with a TDCO set to -1.50?
usually i seen 8-8.5 DES/ACT timing with TDCO set at -1.50
and a value of 4.9 i have now is out of spec, or what i had before
maybe a bad stepper motor ? (but i have not a code 34 or other code related)
bad OPT sensor?
or something else?
the only issue happen before was a shorted cable to ground to IP Shutoff Solenoid that cause engine shutoff (isolated/repaired the cable it returned to works).
 

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Discussion Starter · #11 ·
it was long time never check with Tech 1A the timing....
and a Fass lift pump set to 14 psi was installed, ... more then needed to IP? ...too much pressure can take effect on timing?
when installed Fass LP seen what pressure is raccomented, and 14 psi was in spec, or not so bad for a DS4 IP...seen others forumist setting more pressure, but i don't know if their IP timing changed.
for what i know DS4 is not influenced by inlet pressure...or not?
 

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Discussion Starter · #14 ·
What scanner or software are you using to see that info?
I need to test it too
economic way:
you need a pressure gauge for it
you can measure at T valve from fuel filter, if the tap is in good condition and does not leak from the orings when opened
otherwise you have a false measurement (something less...depend from leaks).

more expensive way:
for a more precise and constant measurement you could buy an electronic pressure gauge with the pressure sensor positioned on the fuel hose that goes from the fuel filter to the IP, and gauge inside the cab.

that's all
 
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Discussion Starter · #18 · (Edited)
Thank You Very Much for your reply DieselPro
1) installed Bosch new injectors body made in India with new nozzle made in Brazil, pop pressure tested by myself at 2200 psi.
2) revert back to a stock eprom now is like impossible due to EGR delete, modified air intake, no vacum pump, etc...was an "S" intake. but all EGR sensors are pluged....
However I had already tried, ... made and tested an eprom with all stock table, timing table, fuel table, back to stock and had no effect, the eprom tested was same of original, retain data for "EGR delete" only, all DTC's code are set active, and had no code stored, actual or history.
No effetc, nothing change.

i will change timing kit chain in spring asap, bad news .... cloyer complete kit stored has not key included, where find the keys for make the job complete?

* for high fuel rate at idle: ... might the high fuel inlet pressure have anything to do? .... is it necessary to try to lower the pressure? ... or would it be a useless waste of time?

what i find very strange is why my timing is not going up to desired.
TDCO vs ACT/DES is not on spec.
.. something is not working as it should ... but what?
 

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Discussion Starter · #20 ·
this is also true ...
considering that a factory new IP is no longer available but you can only find it remanufactured (depends on who and how ... and how long it lasts)

my mileage before was from something more 19 MPG never under 18 MPG
and now something less 16 MPG to 17 MPG maximum, about 2 MPG drop

think i will consider buying one only after changing timing chain
 

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