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Old 06-27-2004, 12:50 PM   #1 (permalink)
Texas Diesel Guy
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I just thought I would start a new thread to in case anyone wanted to know a little more about what really makes these pump tick, and eliminate a lot of the misnomers and myths associated with this system. So first, lets start off with the basic.


DS4 831-5XXX


(D)istrubuter Style, (S)olenoid Operated, (4) Plunger, (8) cylinder (31)mm plunger pump


Basicly its a rotary pump with a fuel solenoid in the rear of the pump that when energized, pushes the poppet valve closed to start injection, and opens to end the injection.


Optic Sensor: is locked to the cam ring and advances/retards with it. reads 2 tracks inside the pump that rotate with the drive shaft.


Lo Res track sends a cam pulse to the computer, that sends voltage to the PMD to close the Fuel Solenoid. It is also used by the PCM to measure timing relative the the Crank Pusle so the stepper motor can be adjusted to provide the desired advance.


Hi Res track is nothing but a counter. The computer takes several inputs (throttle postition, engine speed/temp etc. and resistor value) and converts that to a number of hi res counts for the fuel solenoid to stay energized to give the desired fuel delivery (Pulse Width).


[] Lo Res / Cam Pulse.... []


|||||||||||||||||||||||||||||||||||||||||||||||||| ||||||||||||||||| Hi Res Track


(1 )(2 )(3 )


( Pulse Width )


_________/lobe begins....peaks....and ends\____________________/


Hard to draw a cam profile with ASCII, but just imagine a cam lobe over the words there.


1) Cam Pulse sent to PCM, which signals the PMD and energizes the Fuel Solenoid, which starts to close. Duration here is approximated and will vary with engine speed (longer distance at higher speeds) and Closure Time (amount of lag between this signal and the fuel solenoid actually pulling closed). The computer also starts counting hi res pulses here until it reaches the desired count to end injection (Pulse Width).


2) Fuel solenoid is closed, but injection has not begun, Rollers still ride on flat between the cam ring lobes. Duration again is approximated. This gap is needed to ensure that variations in CT do not cause uneven start of injection events.


3) Start of Pumping: Rollers begin traveling up cam ramp, plungers are forced together and fuel is sent to one injection port. now this Duration is determined by basicly 3 things, calculated by the computer: throttle pos+other PCM inputs (temps etc)+resistor value. Now, Resistor value works like this. The PCM reads its value on startup and treats the 1-9 resistors as if they were -4..0..+4. That tells the computer that it needs to add or subtract X hi res pulses for the pump to deliver the appropriate amount of fuel which is what the pump is calibrated to.


thats the basics, now for the theory.


if you move the optic sensor slightly towards the oncoming ramp of the cam ring and lower the resistor value, you will get the same (1) it does not affect closure time, a shorter (2) and the pumping range (3) will only be slightly longer, and the total PW will be shorter. but now the pumping event will start slightly earlier (advancing timing ever so slightly) and providing more effective pumping time from the same pulse width, which is why the dropped resistor is needed, to compensate partially for the added fuel delivery by shortening the duration. Assuming the optic sensor is moved far enough to gain more fuel

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Old 06-27-2004, 12:54 PM   #2 (permalink)
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TDG,
Welcome!
I'm really greatful that you've arrived at the diesel place.
Your advice and experience is sought after here.


I received the code for pulse bandwidth too short duration before I made the Optic change.
I have a #7 resistor plus 42" fsd extension and connections, maybe a 9 total resistance.
also my APP gives a volt spike on #1 and #2 resistors.
Also I have a 25 ohm switch on the MAP signal. I run it at about 1.12 volts, down from 1.45 volts.
Where do I need correction to give a long enough duration.
I saw this code after the change too.
Edited by: quantum mechanic

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Old 06-27-2004, 01:37 PM   #3 (permalink)
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Interesting, I'm assuming your working on the 96 model truck then, surely only the OBDII computer would be able to assess such a condition. I'm going to have to say it has something to do with the 42" of extension, which is effectively 7' since the signal has to travel to and from the PMD. My electronics experience is not good enough to really estimate the effects of that much resistance, but I know that Solenoid operation and CT are both measured based on changes in voltage when the solenoid is opened and closed and this could possible throw the readings out a bit...do you know if your CT changed when you relocated the PMD?? I'll have to do a bit of research on that one, but thats my guess. Edited by: Texas Diesel Guy
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Old 06-27-2004, 03:18 PM   #4 (permalink)
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It's the '94.
and yes the fuel delivery and idle seemed to change when I put in the extension.
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Old 06-27-2004, 04:02 PM   #5 (permalink)
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well I think we need go no further then right? got to change your FSD cooler arrangement, or live with the code.....
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Old 06-27-2004, 04:20 PM   #6 (permalink)
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It only flashes this code when under full load and above 2700 rpm.
other than that, I might rewire the extension with 20 awg intead of the 18awg I used.
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Old 06-27-2004, 08:10 PM   #7 (permalink)
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20 is a lighter gauge wire, and would probably only worsen the problem, maybe go with 16 or 14 instead.
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Old 06-30-2004, 07:25 AM   #8 (permalink)
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Excellent stuff, here, TDG - it is appreciated.


Do you know how TDC Offset is related to the wide slot for #1 tdc in the encoder wheel?


I see how it can relate, but what is the official stance on it?Edited by: gmctd
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Old 06-30-2004, 06:52 PM   #9 (permalink)
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To be honest with you, I really dont know why they made #1 a wider slot, obviously so the computer can tell it from the other 7, but why it would care, I dont know. I never really thought about it to tell you the truth but sure the computer could just look for that longer pulse to set TDC Offset, or it could use all 8. Its also very possible that it might be there and completely ignored by GMs, stanadyne made DS pumps not exclusively for GM mind you, they designed the pumps and GM was their first customer for it. John Deere was planning to buy clockwise DS pumps, but for some strange reason they backed out...hmmm...I cant imagine why?? Just a thought, I really dont have a good answer for you TD.
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Old 07-01-2004, 07:48 AM   #10 (permalink)
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According to what I've read, Stanadyne wanted GM to do further field testing, but GM insisted on '94 DS-4 product release.


Money rules....


Logically, the wide #1 slot is for the 5deg (+2.5, -2.5) max TDC Offset spec - allows electronic measurement and adjustment, similar to what you do with the mechanical optical sensor adjustment.


OBD-II PCM's are limited to +2, -2 to set the DTC.

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