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  #1  
Old 05-27-2013, 11:29 AM
srpsinu srpsinu is offline
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Default How does Stanadyne DB2 pump maintain correct injection timing?

Hi all

I am a new member & this is my first post. So if this question sounds noob then please bear with me.

I am unable to understand how rotary diesel injection pumps with opposed piston plungers like Stanadyne

DB2 & Lucas DPA maintain correct start of injection time because as more fuel is sent to the pumping

chamber the plungers move apart more & meet the cam lobes earlier( so timing must have been advanced more at higher throttle than at lower throttle). How does this maintain consistent injection timing?

Thanks in advance for all replies.
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Old 05-27-2013, 02:00 PM
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stodg73 stodg73 is offline
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First off, Welcome to The Diesel Truck Site!

With regards to the rotary injection pumps, like the Standyne Pump, the Lucas DPA or the Bosch P7100, they all have a mechanical advance built inside the pump that rotates to advance/retard the timing of the injection cycle. The Standyne pump has only one (1) metering hole that as it is turning, it will deliver fuel to that injector.


Since more fuel is needed at faster engine speeds, the pressure from the lift pump forces a little bit more fuel into the plunger chambers and the plungers are moved closer to the cam lobes, thus making the timing advance somewhat. There is a mechanical advance built into the pump as well, to advance the cam lobes therefore advancing the timing of the engine.

So, on faster engine speeds, the mechanical lift pump adds a little more fuel into the plunger chamber, advancing the timing somewhat, and a mechanical advance also moves the timing more advanced.

If you know how an older gas engine distributor works with a mechanical advance, you can apply the knowledge to the rotary injection pump and get a feel of how the mechanical advance works.

Hope this helps.

Again, Welcome to The Diesel Truck Site!
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Old 05-28-2013, 12:27 AM
srpsinu srpsinu is offline
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Thanks stodg73 for the reply.
That means without the cam ring moving some timing advance takes place if the metering valve is opened more. The movement of cam ring at higher rpm causes even more advance. Is this correct or am I missing something. The beginning of injection (at constant rpm)is not constant like the bosch ve pump. Am I right?
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Old 05-28-2013, 07:53 AM
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stodg73 stodg73 is offline
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Quote:
Originally Posted by srpsinu View Post
That means without the cam ring moving some timing advance takes place if the metering valve is opened more. Correct, as the fuel pressure rises, the injector will pop off earlier.

The movement of cam ring at higher rpm causes even more advance. Correct, the movement causes the injectors to pop off at 20* BTDC rather than at 16* BTDC.

Is this correct or am I missing something. The beginning of injection (at constant rpm)is not constant like the bosch ve pump. Am I right? Right.
Answers in red.
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Old 05-28-2013, 12:14 PM
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Dang, good answers Stodg!! You even taught me something!
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Old 05-29-2013, 08:23 AM
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Only one small problem. With the 12V fuel system the mechanical lift pump does increase pressure with RPM's but with high demand volume like WOT the volume rate of the mechanical lift is reduced.

http://www.torkteknology.com/news/5/...Lift-Pump.html

Quote:
Contrary to popular belief, the Cummins lift pump produces flow on the return stroke of the piston, not the forward stroke. Spring pressure on the return stroke, NOT the forward plunger movement, is what produces the flow in the fuel system.
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Last edited by Mopar1973Man; 05-29-2013 at 08:27 AM.
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  #7  
Old 05-29-2013, 09:56 AM
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Quote:
Originally Posted by Mopar1973Man View Post
Only one small problem. With the 12V fuel system the mechanical lift pump does increase pressure with RPM's but with high demand volume like WOT the volume rate of the mechanical lift is reduced.
I realize the demand is higher, so why does the lift pump pressure increase during higher RPM's as reported by several sources? I also realize that the pump can only deliver so much fuel to the injection pump.

Another question that needs to be answered is, how much fuel is needed at idle and how much at WOT. I bet the lift pump is providing ample amounts at both RPM's.

My dad's VE pump went from 3 psi to 10 psi when the RPM's went to 2200 +. This is a significant increase in pressure to force the injection pump fuel plunger open more, therefore giving a little bit more fuel for the IP to deliver, therefore increasing timing(popping the injectors off earlier).

The spring tension/pressure of the injection pump needs to be measured to see how much it changes from idle to WOT, in order to see if there is more fuel being pumped into the fuel plunger.
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Toys:
'79 CJ5, 258ci, 3" lift, 33x12.50x15, Stock Engine and 3 Speed Tranny
'05 Suzuki, GSX1300R, Hayabusa, All Stock, #3('00 blown engine, '00 stolen, & '05)
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  #8  
Old 05-29-2013, 11:08 AM
srpsinu srpsinu is offline
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Actually this type of pump( opposed plunger type) is used in a very popular diesel car in India, the TATA INDICA V2. The FIP used in this car is made by LUCAS TVS & I believe is a variant of the LUCAS DPA pump. I would like to know the range of variation of injection timing change from idling fuel delivery to full fuel delivery( with advance piston constant). Seeing the shape of the cam on which the two rollers ride, the timing variation range can be about 45 deg cam ie 90 crank. So I am reaally curious to know if such a large variation in injection timing can allow an engine to run normally. Any idea about how the cold start advance works in this type of purely mechanical pump( except for the 12V stop Solenoid). The reason why I am so much into this is I am currently facing this problem of knocking at idle. would like to add that there is no lift pump in this car. the fuel is sucked from the tank through filter only by the transfer pump inside fip

Thanks for the replies
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  #9  
Old 05-29-2013, 01:04 PM
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Have you tried the gravity feed the IP instead of having the pump pull the fuel from the tank, to see if you will get rid of the knock. Doing this will see if there is a blockage in the fuel line and may indicate the need for a electric transfer pump near the tank.

Here is a link as to how the Lucas Pump works.
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O.O., 01.5, Dodge, 2500, High Output (H.O.) Cummins Turbo Diesel (245/505), Quad Cab Long Bed (QCLB), 4x4, Sport, Original Bosch VP 44 Injection Pump, 6 Speed/NV5600 Transmission, 3.55 Gears, 105k, currently stock engine, Fram Air Filter, 285/75R16s, Glow Shift Gauges: Fuel Pressure (FP), Boost, Exhaust Gas Temperature (EGT), Oil Temperature, SMARTY@1, Airtex lift pump 19 psi @ idle, 14 psi @ WOT, Propane Injection, 2 Stroke Oil, Intake Air Temperature (IAT) Fooler = Better MPG, Bed Lined, Chrome Nerf Bars, more to come!!

Toys:
'79 CJ5, 258ci, 3" lift, 33x12.50x15, Stock Engine and 3 Speed Tranny
'05 Suzuki, GSX1300R, Hayabusa, All Stock, #3('00 blown engine, '00 stolen, & '05)
The complete live & learn and pass it on by H. Jackson Brown, Jr.
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  #10  
Old 06-06-2013, 06:42 AM
muttonn2586 muttonn2586 is offline
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a lot of fuel is required at quicker engine speeds, the pressure from the pump forces slightly bit a lot of fuel into the plunger chambers and therefore the plungers area unit affected nearer to the cam lobes, therefore creating the temporal order advance somewhat. there's a mechanical advance engineered into the pump moreover, to advance the cam lobes so advancing the temporal order of the engine.

So, on quicker engine speeds, the mechanical pump adds slightly a lot of fuel into the plunger chamber, advancing the temporal order somewhat, and a mechanical advance additionally moves the temporal order a lot of advanced
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