Fuel Injectors Rating

[buddy]

I have observed output of the PMD to the FS, while watching on the scanner the pulse width sent to the PCM by the PMD. The pulse width does increase with load to get more fuel. At idle, no load, I could see voltage increase, the amplitude of the signal from the PMD to the FS, while the PMD reported no change in pulse width. You hit a wall in terms of going faster or pulling load in limp mode because it will reach the limits of increasing fuel by increasing the amplitude (higher peak to peak voltage), and cannot increase the period (pulse width).

I'm throwing out all suggestions to get all the opinions, since others have told me I was wrong when they didnt actually know the facts and reported wrong information as fact.

 

[gmctd]

If this is true, then how does the timing ever advance?

Regards,

Because the rollers ride up the ramps quicker as rpm increases, with resultant quicker pressure rise - the rollers do not need to make the entire transition from the valley to the ramp peak to generate pop pressure - residual pressure in the pipes mean the pressure does not have to build from 0 - housing pressure @25psi at idle rises above 125psi as rpm increases, so pressure is greater than 0 when rollers are in the valleys at the start of the ramp

 

[gmctd]

The IP only receives the one PMD signal for injecting fuel, so how does it vary fuel flow at a constant pulse width if the FS is only open or closed?

PCM sends the signal to the FSD module to close the FS valve to begin pumping for the injection - FSD sends a valve closure-time signal back to the PCM to indicate valve is seated and pumping has begun - this signal is resulted from the change in applied current as the solenoid engerizes, the valve begins moving, valve is moving, valve stops moving, is held in place against rising pressure - the waveform can be seen to vary in width on an oscilloscope according to rpm

 

[buddy]

The injector does not regulate system pressure for the entire system. The pop pressure (and pressure just after the delivery valve) at idle may indeed both be the pop off pressure, but as soon as you raise the RPM, the pressure required to move that same amount of fuel in the decreased amount of time REQUIRES that the pressure at the pump increase. The lines are factory sized such that the peak injection pressure for the pump is never exceeded under normal operating circumstances. Start pushing more fuel or exceeding rated engine RPM and all bets are off.

I have seen several twisted pump shafts in the tractor pulling world. These are ALL due to undersized lines and/or injectors for the given flow rate and RPM combination.

To demonstrate that peak injection pressures regularly exceed pop-off pressure, I refer to EXHIBIT A.

Regards,

That is why I dont believe the pop pressure will shift the injection pressure. It wont make the peak pressure higher by increasing the minumum pop pressure. I agree it could add some wear ove the life because it could bring the idle pressure up above where it would normally hit.

With a larger nozzle, peak pressure should actually be lower, because more volume can be pushed through it easier. Volume of fuel being injected will be a factor in peak pressure. So if you increase from 60mm3 to 80mm3 you just increased the peak pressure the IP sees, so we all must be killing our IPs. I dont believe that to be true because we most likely have not yet hit the limits of the DS4.

So what actually drives the pressure? What is driving the valve that pushed the fuel to the injector and where does its force come from?

The PCM determines desired fuel rate and sends the injection signal to the PMD, which is what determines your fuel rate in that single signal sent to the FS. So what part of the IP does the metering of fuel and how does it do it?

How does the IP know how much fuel to squirt? Does it know, or does the FS meter the fuel that could be squirted by opening more or less and for shorter or longer periods of time? So only as much fuel as is allowed in is what gets squirted?

 

[buddy]

PCM sends the signal to the FSD module to close the FS valve to begin pumping for the injection - FSD sends a valve closure time signal back to the PCM to indicate pumping has begun - this signal is resulted from the change in applied current as the valve stops moving

Yes, I agree with that. That is what the PMD reports, when the valve closes. That signal is determined by current stopping, but there is still the fact that the PMD drives the FS.

The inject signal sent to the PMD from the PCM will determine what the PMD is going to try to tell the FS what to do. The PCM wants a certain fuel rate, so it tells the PMD what pulse width to tell the FS to do. And it also varies the voltage.

But I totally agree than FS closure reporting is totally current based, because that is the only way for the PMD to know, since it doesnt get feedback from the FS, only knows what its sending to FS. That does not mean however that the PMD is not voltage output based.

 

[Matt Bachand]

For what this is worth. After a recent alternator swap my voltage was up around the 16's, I swear my truck felt peppier and lighter, I even mentioned this in a thread about possible over-volting the PMD can boost gains.

Just about all I can add to this. Reading with great interest.

 

[schiker]

So what actually drives the pressure? What is driving the valve that pushed the fuel to the injector and where does its force come from?

The PCM determines desired fuel rate and sends the injection signal to the PMD, which is what determines your fuel rate in that single signal sent to the FS. So what part of the IP does the metering of fuel and how does it do it?

How does the IP know how much fuel to squirt? Does it know, or does the FS meter the fuel that could be squirted by opening more or less and for shorter or longer periods of time? So only as much fuel as is allowed in is what gets squirted?

I took apart an IP and don't understand it all but its a mix of checkvalves and timed ports with cams and rollers etc.

On the back is the distributor and fuel metering solenoid (that the PMD/FSD drives). Here are some photos. It was suggested in another post that the solenoid only has to overcome the differential pressure of injector to cam/rollers.

The rotor turns with timing gear valve cam/crank and drives the plungers around a camring and creates the pumping action that always pumps. The timed ports and solenoid deterimes where the fuel goes.

 

[schiker]

That picture was the metering valve I believe. The plunger of the fuel solenoid pushes this inward to seal off the passage to the spill chamber. With the spill chamber sealed off fuel has to go out to the injector. When the valve opens (spring and fuel force) fuel can spill into spill chamber and does not get injected. I am not sure how fuel makes it back to the fill chamber but it does.

The rotor and distirbutor has many timed ports and a few check valves are in various places. Here are some more pics.

 

[gmctd]

Correct Schiker - the FS solenoid closes the valve onto a passage - when the passage is open, pumped fuel is spilled, when the passage is closed, pumped fuel goes thru the timed port to the injector

Pumped fuel at idle has max capability of ~35mm3 - pumped fuel at some upper rpm is ~66^mm3 - the DS4, like most other variable rpm pumps, is variable volume, lo at lo rpm, higher at higher rpm

Fuel solenoid timing from PCM meters the fuel - since pressure is fixed by the injectors, that timing must also be variable due to the variable volume

 

[buddy]

So the inteligent fuel metering part of the IP is the PMD and FS correct? How does it allow variable fuel volume to be injected? What does the solenoid do to make RPMs go up? How does it make more fuel get injected to increase RPMs. Does PMD current close it or open it? Does that valve move further, allowing greater fuel amounts to spill at higher PMD voltages? With the AC voltage I imagine the valve is open its max amount at the peak voltage and as the AC wave comes down the valve is closing and seats when the AC signal is at 0V, then it starts opening back up as the voltage wave is heading back up and is open as much is will go at the peak voltage it reaches, then seats when voltage is back at 0V. It follows this alternating current wave. And peak voltage may determine the amount the valve opens, and when current goes to 0, when voltage hits 0 the solenoid/valve is closed.

The pulse width could be the time it takes the AC voltage wave to go up and come back down. So higher pulse width allow longer valve open to allow more fuel to spill, per timed injection event.

The Alternating current (AC) could be a square wave too, where its up then down instantly at high frequency. I'll see about "borrowing" an O-scope from work to get a good look at it this long weekend.

And the force to create injection pressure is compliments of the variable RPM spinning armature shaft? So really it cannot create a higher pressure unless you increase RPMs and fuel volume. the injector pop pressure has nothing to do with peak pressure. The injector will impact peak pressure based on nozzle size, smaller nozzle goes to higher peak pressure.

 

[schiker]

So the inteligent fuel metering part of the IP is the PMD and FS correct?

PCM controls fuelrate - fuel delivery logic. The PMD /FSD just amplifies the PCM signal to be able to do the work.

How does it allow variable fuel volume to be injected? What does the solenoid do to make RPMs go up?

The IP is constantly pumping fuel and has some excess. So to accelerate PCM just squirts more fuel in by keeping solenoid closed. As you probably already know Diesel works on fuel metering and the rpm it achieves is dependant on fuel injected and load. If over fueled for load it will naturally increase rpm. Fuelrate per injection and is timed so if the rpms increase the event gets cut off.

How does it make more fuel get injected to increase RPMs. Does PMD current close it or open it?

Current closes it cuts off fuel to spill chamber causing fuel to go to injector. More fuel naturally increases rpm. Increases fuel delivery by increasing valve close time.

Does that valve move further, allowing greater fuel amounts to spill at higher PMD voltages? With the AC voltage I imagine its open its max amount at the peak voltage and as the AC wave comes down the valve is closing and seats when the AC signal is at 0V, then it starts opening back up as the voltage wave is heading back up and is open as much is will go at the peak voltage it reaches, then seats when voltage is back at 0V. It follows this alternating current wave. And peak voltage may determine the amount the valve opens, and when current goes to 0, when voltage hits 0 the solenoid/valve is closed.

The pulse width could be the time it takes the AC voltage wave to go up and come back down. So higher pulse width allow longer valve open to allow more fuel to spill, per timed injection event.

Not real sure how to explain my understanding its not very clear to me.

And the force to create injection pressure is compliments of the variable RPM spinning armature shaft? So really it cannot create a higher pressure unless you increase RPMs and fuel volume. the injector has nothing to do with peak pressure, only the pop.

Yes, that is my understanding too. And kinda brings the discussion back to the beginning. Boats tend to be higher fuelrates and higher rpm than trucks and hence the marine injector orifice being bigger. This helps in timing and reduction of line pressure

See above

 

[schiker]

To try to clarify the IP is stroking away and the fuel delivery map of the PCM has a known fuel curve according to IAT, boost, and RPM (not sure what else). Then sends the appropriate signal with the proper request from the right foot go pedal sensor TPS. That's what makes the programs different and one better than other. You can increase acceleration factors but loose on emissions etc.

The fuel map is a compromise on emissions (black cloud accelration), power, and economy.

 

[buddy]

Thank You, anyone have a n exploded picture of the IP parts where fuel flows?

Cranking the engine causes the fuel to pump.

And that fuel, if PMD were dead, would only go through the spill valve because it would be forever open? How does the open spill valve prevent the fuel from being "distributed" to injectors. Is that blocked off until the valve is pushed in?

Is the plunger and valve in the spill chamber, is that what this picture is of?

I still wonder how does fuel injection change at constant pulse width. Does the valve have to fully seat to begin injection?

 

[gmctd]

E=IR(impedance)
I=E/R(impedance)
ELI
DVM's do not tell the tale - PCM\FSD\IP signals are largely digital

Thank You, anyone have a n exploded picture of the IP parts where fuel flows?

Cranking the engine causes the fuel to pump. = (CAUSES THE PUMPING PLUNGERS TO MOVE IN THEIR BORES IN THE ROTOR, PUSHING FUEL INTO THE CENTRAL ROTOR PASSAGE TOWARDS THE OPEN FS METERING VALVE WHICH IS SPILLING THE FUEL, PREVENTING ANY PRESSURE RISE UNTIL PCM FIRES THE FSD TO CLOSE THE VALVE)

And that fuel, if PMD were dead, would only go through the spill valve (NO SUCH THING AS A SPILL VALVE!) because it (FS METERING VALVE) would be forever open? = (CORRECT) How does the open spill valve (AGAIN, NOT!) prevent the fuel from being "distributed" to injectors. = ( FUEL SPILLED BY THE OPEN METERING VALVE CANNOT GO THRU THE SELECTED PORT TO THE INJECTOR) Is that blocked off until the valve is pushed in? = (VALVE CLOSES, SEALING ROTOR PASSAGE FROM SPILL CHAMBER, FUEL IN ROTOR PASSAGE GOES TO SELECTED DISTRIBUTOR PASSAGE - PRESSURE RISES THRU SELECTED PORT TO INJECTOR)

Is the plunger (IN ROTOR PUMP BLOCK) and valve in the (ROTOR) spill chamber (IN THE DISTRIBUTOR), is that what this picture is of? = (END OF ROTOR AND METERING VALVE, THE SPILL CHAMBER IN THE DISTRIBUTOR, MINUS FS SOLENOID, ARMATURE, AND ONE-WAY PORT VALVES -THAT SPRING-LOADED ROD OPENS THE VALVE WHEN FS DRIVE-CURRENT IS REMOVED - METERING VALVE OPENS THE ROTOR PASSAGE TO THE SPILL CHAMBER, FUEL PASSES BACK THRU TO THE PUMPING PLUNGERS - ADDITIONAL FUEL AT HOUSING PRESSURE ENTERS THE PLUNGERS THRU THE CHARGING ANNULUS PASSAGE IN THE DISTRIBUTOR HEAD)

I still wonder how does fuel injection change at constant pulse width = (CLOSURE DURATION IS CONSTANT, hopefully - HOLDING\METERING PULSE WIDTH IS VARIABLE PER DEMAND). Does the valve have to fully seat to begin injection? = (MUST BE FULLY SEATED TO BEGIN PUMPING\PRESSURE RISE WHICH POPS INJECTOR - PUMPING\INJECTION EVENT BEGINS WHEN PCM RECEIVES FS CLOSURE SIGNAL, INDICATING VALVE IS FULLY SEATED - PCM OPENS VALVE TO END INJECTION, SPILLING REMAINDER OF FUEL MOVED AS ROLLERS HEAD UP REMAINDER OF RAMPS TO THE PEAKS - THEN OVER TO THE DOWN-RAMPS TOWARD THE VALLEYS TO BEGIN AGAIN)

I explained most of this up in the main DS4 thread, Buddy - it would be a crying shame if you continue spreading all over the internet how wrong I am, simply because you cannot comprehend it - knowwhuttimean, Lt JG jellybean?

 

[gmctd]

Sun was behind huge cloud-bank, was a cool breeze, so I headed out to compare TECH2 with GMTDScan Tech and 'scope to clarify definitions - been over 5yrs since I thought in depth about any 6.5 stuff - soon's I hooked 'scope and PC up, invoked GMTDScan, and ECT reached op temps, sun came out, breeze died, ambient 98* temps summed with 195* ECT and 365*EGT, so I had to shut it down to keep from drenching my old Dell Latitude - and the LCD screen on the scope started darkening from the heat

Bummer! This may have to wait till autumn and cooler climes................

 

[Acesneights1]

Just to clarify something that was brought to my attention in another thread and as per GM Fac manual. Our trucks don't have "injectors" where injection event happens at the injector nozzle ?? do they ?? They actuallu have "nozzles" being that the injection event happens at the IP. only engines such as 2 stroke detriots etc etc have actual injectors. Is this correct or incorrect ? Because a freind on another forum kept reffering to nozzles and I got confused.(which happens easily).

 

[schiker]

And that fuel, if PMD were dead, would only go through the spill valve because it would be forever open? How does the open spill valve prevent the fuel from being "distributed" to injectors. Is that blocked off until the valve is pushed in?

The distributor times the passages to appropriate injector. The injector has a pop pressure. If spill valve open fuel takes path of least resistance to spill chamber. Fuel solenoid has to close off spill chamber passage so pressure will rise enough to pop injector. If a PMD/FSD dies and won't close spill valve. Fuel won't build enough line pressure to pop injector = no fuel in cylinder and classic pmd failure no start stall. If FSD/PMD shorts to fuel solenoid and closes valve all fuel is injected and runaway engine occurs then PCM reacts and will shut off fuel to IP with inlet fuel shutoff solenoid.


Is the plunger and valve in the spill chamber, is that what this picture is of?

I am not sure of exact path of fuel but yes I believe this the valve to the spill chamber that the fuel solnoid plunger closes off and dead heads the pumping diesel in the rotor and it must go out the distributor to the appropriate injector.
I still wonder how does fuel injection change at constant pulse width. Does the valve have to fully seat to begin injection?

More or less has to be closed to build injection line pressure but actual dynamics it might start injecting when its real close to closed. How close might depend on rpm and fuel rate requested fuel temp viscosity lubricity etc. Thus the precise control of fuel metering has to be variable.

Its fuzzy to me but I think I get some of it. The control "pulse width" can be variable due to the variable rpm of engine and dynamics of variable fuelrate and variable time of acceptable injection variable fuel viscosity etc etc. And importantly how close the PCM and thus the PMD corrects the injection event.


I think there is some indirect feedback going on the pcm doesn't know how much fuel gets injected exactly but it knows closure time of valve and desired fuel rate plus the crank speed and can adjust accordingly to hold steady rpm if the PMD/FSD and fuel metering solenoid and valving are in good shape. If the system deteriorates you'll get things like rough idle or fishbite.

 

[buddy]

E=IR(impedance)
I=E/R(impedance)
ELI
DVM's do not tell the tale - PCM\FSD\IP signals are largely digital


I explained most of this up in the main DS4 thread, Buddy - it would be a crying shame if you continue spreading all over the internet how wrong I am, simply because you cannot comprehend it - knowwhuttimean, Lt JG jellybean?

Yes you did and you keep making it a point to tell me how wrong I am, and then saying something like, you keep telling it how you think it works until someone tells you youre wrong. So now I am trying to get more input from other people too.

And somehow explain how a constant pulse width can still vary fuel flow, such as in limp mode. Is the FS a digitial component, or just repsond to an analogue signal?

 

[buddy]

Just to clarify something that was brought to my attention in another thread and as per GM Fac manual. Our trucks don't have "injectors" where injection event happens at the injector nozzle ?? do they ?? They actuallu have "nozzles" being that the injection event happens at the IP. only engines such as 2 stroke detriots etc etc have actual injectors. Is this correct or incorrect ? Because a freind on another forum kept reffering to nozzles and I got confused.(which happens easily).

Well in other vehicles they dont run high pressure to pop the injector. So I can see what they mean. The computer tells the injector to push the fuel into the cylidner, whereas our IP does that.

 

[gmctd]

Our trucks have actual injectors with nozzles, 8 of 'em - pumped fuel is injected thru the nozzles into the precups in the heads - pumping the fuel up to injection pressure, which is part of the injection event, is begun, controlled, and ended in the DB2 and DS4 - there are several types of injectors and many sizes and shapes - the 6.2 has a long injector, but identical to the shorter 6.5 injector, both with replaceable nozzles with a spray pattern suitable for indirect injection with precups and glow plugs - injection occurs at the injector nozzle - the injection event is managed at the IP

What you may be describing is unit injectors, where a special pump pressurizes engine oil which is pumped to the injectors to drive the pumping plunger - fuel is pumped to the injectors at ~80psi - when the ECM energizes the injector solenioid , the hi-pressure engine oil drives the plunger to create high pressure on the fuel, which is then injected into the cylinder - other types use specific lobes on the camshaft to drive the plungers to inject the fuel - more electronic and less mechanical control = more efficient engines