LML LML fuel sys info: [Archive] - Duramax Diesels Forum

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McRat
11-10-2011, 10:29 AM
Two Fuel Rail Pressure Regulators (FRPR) are used. FRPR1 is still located on the injection pump as on previous Duramax engines. FRPR2 is located on the front of the left fuel rail. This solenoid is normally open. The ECM supplies pulse width modulation to change the duty cycle of FRPR2 to control the amount of fuel returned to the fuel tank.

The new Duramax engines are equipped with Bosch piezoelectric fuel injectors. These injectors operate a high voltage, indicated by the orange color of the injector harness.

IMPORTANT: Do not make contact with the fuel injector harness, ECM or fuel injectors while the ignition is in the On or Run position. Use certified insulated gloves EL-48286. These Class 0 gloves are rated at 1000 v. Check for functionality and check the expiration date of the gloves.

The ECM supplies high voltage and provides a ground. Voltage is supplied up to 160v at 20 amps, and can peak up to 240 v. This causes the injector to open. The capacitor discharges through an injector for initial opening and holds open with 12 v.

Injectors are grouped into four pairs: 1-4, 6-7, 2-5, and 3-8. If a condition is detected in a group, that group is disabled and a DTC is set.

On the fuel system return side, the return lines are now equipped with snap-in connections. The return side is under pressure.

A pressure retention valve maintains 0.4 to 1.1 mPa of pressure within the return lines to provide proper fuel injector operation.

TIP: Improper injector return line pressure may cause a no-start or performance concern.

If the engine runs out of fuel, or if the fuel system is serviced, the system must be primed. After priming, a feed line from the low pressure side of the pump backfills the injector return lines. The feed line will also backfill if pressure falls below 0.3 mPa in the injector return lines.

From:

http://www.sandyblogs.com/techlink/2010/06/new-duramax-diesel-engines.html

Chevy1925
11-10-2011, 10:35 AM
Interesting, so they did away with the FPRV and put a FPR in its place from what i gather? boy if only EFI was setup for LML, it could make for interesting tuning

McRat
11-10-2011, 10:40 AM
What I find interesting is that it uses retained pressure from post-injector fuel to assist in closing the injector. Or at least if I'm reading that right. About 150 PSI doing the math in my head. The LB7-LMM don't have pressure in the return lines.

And that the high voltage, up to 240v, is a spike to get the injector to start to open, then it holds it open with 12v.

Chevy1925
11-10-2011, 10:53 AM
What I find interesting is that it uses retained pressure from post-injector fuel to assist in closing the injector. Or at least if I'm reading that right. About 150 PSI doing the math in my head. The LB7-LMM don't have pressure in the return lines.

And that the high voltage, up to 240v, is a spike to get the injector to start to open, then it holds it open with 12v.

Yes thats also interesting, i could see that for closing but it then makes it harder to open, so i ASSume thats why they have such a high spike to open the injector. the LBZ/LMM dont spike their injectors do they? or is it a constant 24v to open them?

Bryce418
11-10-2011, 11:06 AM
Interesting, so they did away with the FPRV and put a FPR in its place from what i gather? boy if only EFI was setup for LML, it could make for interesting tuning

Correct there is no high pressure fprv on a lml/lgh.

DIESELMAFIAPER.LB7
11-10-2011, 11:06 AM
240v?? Wow didnt some people say high voltage was why lb7s are so bad with injectors? Cant remember but i thought some blamed voltage that they fired at...

Very interesting info though

Chevy1925
11-10-2011, 12:36 PM
240v?? Wow didnt some people say high voltage was why lb7s are so bad with injectors? Cant remember but i thought some blamed voltage that they fired at...

Very interesting info though

yeah i was thinking the same. i think the LB7s fire off a constant 96v and dont ramp up or down like the LML. What id like to know is just how long the injector actually stays at 12v after the "up to 240v" initial shot and why it is worth that kind of effort to drop teh voltage. Or is the initial voltage gauged upon rail pressure so as pressure goes up, the initial firing voltage goes up? very interesting stuff

McRat
11-10-2011, 01:08 PM
yeah i was thinking the same. i think the LB7s fire off a constant 96v and dont ramp up or down like the LML. What id like to know is just how long the injector actually stays at 12v after the "up to 240v" initial shot and why it is worth that kind of effort to drop teh voltage. Or is the initial voltage gauged upon rail pressure so as pressure goes up, the initial firing voltage goes up? very interesting stuff

It was a long time ago, but IIRC, when I was doing cyl pressure testing on Big Blue (LLY), the injector voltage stayed up. I just don't remember the voltage. Or much of anything else about the project. :D

duratothemax
11-10-2011, 01:49 PM
actuating a piezo transducer is completely different from activating an electromagnetic solenoid. Fingers has more of the nitty-gritty technical details about this.

They arent even CLOSE (electrically), when it comes to driving them.... You really cant compare them to LB7/LLY/LBZ/LMM injectors in any way.

duratothemax
11-10-2011, 01:50 PM
boy if only EFI was setup for LML, it could make for interesting tuning

Why do you say this? :confused:

duratothemax
11-10-2011, 01:53 PM
What I find interesting is that it uses retained pressure from post-injector fuel to assist in closing the injector. .

They also need pressure in the return line system because thats what the 9th injector (for regen) is tied into....

Fingers
11-10-2011, 06:12 PM
Return line pressure actually helps the injector open.

whitetrash21
11-10-2011, 06:18 PM
Injectors are grouped into four pairs: 1-4, 6-7, 2-5, and 3-8. If a condition is detected in a group, that group is disabled and a DTC is set.

Whats the point of this??? Why not individual conditions for each injector. Doesn't that make it harder to diagnose any issues that injector specific???

duratothemax
11-10-2011, 06:39 PM
Whats the point of this??? Why not individual conditions for each injector. Doesn't that make it harder to diagnose any issues that injector specific???

Its just the way the internal electrical architecture of the ECM is designed...

When Bosch was designing the ECM and sourcing driver "chips", maybe they could only find drivers that were grouped in pairs? Or they did it to save space on the circuit board?

Either way...its only TWO injectors...how hard is that really to diagnose? ;)

remember LB7/LLY's had FOUR injectors per "positive supply bus/rail", and nobody really has any huge trouble diagnosing that...

ripmf666
11-10-2011, 08:16 PM
http://www.duramaxdiesels.com/forum/showthread.php?t=29599

http://www.duramaxdiesels.com/forum/showthread.php?p=517747#post517747

McRat
11-10-2011, 09:42 PM
Something seems odd or a misprint.

Henry's link says the injectors use 250v x 20 amps. That's 5000 watts, or about 7 hp. That over 400 amps at 12 volts. Think alternator the size of a soccer ball.

That's got to be very brief discharge, it can't be holding that current.

quadracer37
11-10-2011, 10:32 PM
i think the cp3.X? Is pretty interesting with the dual hi pressure outlets! :woott:

coker6303
11-10-2011, 10:45 PM
Something seems odd or a misprint.

Henry's link says the injectors use 250v x 20 amps. That's 5000 watts, or about 7 hp. That over 400 amps at 12 volts. Think alternator the size of a soccer ball.

That's got to be very brief discharge, it can't be holding that current.

Has to be a capacitor somewhere

Sent from my ADR6400L using Tapatalk

ripmf666
11-11-2011, 12:21 AM
Has to be a capacitor somewhere

Sent from my ADR6400L using Tapatalk

Yes have to find were I save the gm info its built into the new ecm's.

whitetrash21
11-11-2011, 12:57 AM
Its just the way the internal electrical architecture of the ECM is designed...

When Bosch was designing the ECM and sourcing driver "chips", maybe they could only find drivers that were grouped in pairs? Or they did it to save space on the circuit board?

Either way...its only TWO injectors...how hard is that really to diagnose? ;)

remember LB7/LLY's had FOUR injectors per "positive supply bus/rail", and nobody really has any huge trouble diagnosing that...

I thought the lb7/lly were individual. Am I thinking of something different when I think of being able to control individual injector vs the ecms detecting something amiss and setting DTC's???

duratothemax
11-11-2011, 06:23 AM
Something seems odd or a misprint.

Henry's link says the injectors use 250v x 20 amps. That's 5000 watts, or about 7 hp. That over 400 amps at 12 volts. Think alternator the size of a soccer ball.

That's got to be very brief discharge, it can't be holding that current.

Its not a misprint........capacitors are wild things....... ;)

duratothemax
11-11-2011, 06:25 AM
Why is everyone all drooling over this LML setup and thinks its so cool? Its not anything special. The pump sucks, it flows maybe only 75% of what an LB7/LLY CP3.3 flows.

The LML's have been out for almost a year, why do you think no one has gotten one to actually go fast?? :(

Chevy1925
11-11-2011, 07:20 AM
Why is everyone all drooling over this LML setup and thinks its so cool? Its not anything special. The pump sucks, it flows maybe only 75% of what an LB7/LLY CP3.3 flows.

The LML's have been out for almost a year, why do you think no one has gotten one to actually go fast?? :(

its not really drooling that im doing, more interested in why GM did things the way they did. its a new system and i love to learn about new stuff that has come out on the dmaxes. i was always that kid that asked "Why" waaaaaaaay too much :D. When ever you make it to the west coast ben, i owe you a dinner just so i can pick the heck out of your brain :hug:

stacks04
11-11-2011, 08:56 AM
The return side pressure is not for the hydrocarbon injector that burns the dpf. The hci is fed from the cp3 directly from in between the supply and pressure sides of the pump. The return line pressure is just for proper injector operation.

The cp3 is now a timed unit, it has to be installed matching marks on the gears. This was never the case with any dmax pump to date. It is a two chamber unit supposedly to have more evenly matched fuel pressure in the rails.

The fuel rail pressure sensor is now in the back of the driver rail, there is 2 regulators like Pat said, there is a fuel supply side pressure sensor also. It monitors the supply pressure to monitor vacuum of the supply system. It is used as a driver warning to alert of fuel filter clogging. It is normally closed and opens if vacuum gets to 13" hg. The ecm then alerts the ipc iirc.

duratothemax
11-11-2011, 09:16 AM
ahh yes you're right, I was wrong!! What I was thinking of (and what threw me off), was that on the feed line to the 9th injector is connected to the return line through a check valve, which apparently (if the truck is run out of fuel) allows the low pressure fuel that feeds the 9th injector to "backfill" into the "main injector" return line circuit to build the required ~150psi in the return line circuit. I read the LML fuel system description a long time ago and got mixed up. :o

Just to be clear though, the 9th injector is NOT a high pressure injector like the main injectors. It is fed off of the low pressure side of the pump.

1lowdiesel
11-11-2011, 10:11 AM
Only thing I have to add on this subject is that from a fuel supply stand point you can supply the engine with 15-20 psi of pressure without any adverse affects :thumb:.

McRat
11-11-2011, 11:29 AM
Why is everyone all drooling over this LML setup and thinks its so cool? Its not anything special. The pump sucks, it flows maybe only 75% of what an LB7/LLY CP3.3 flows.

The LML's have been out for almost a year, why do you think no one has gotten one to actually go fast?? :(

Not drooling, just thought all the changes to the fuel sys were interesting.

The 2 GM docs conflict. One says it's held open at 250v/20a, the other says it's fired at 160-240v/20a, then held open with 12v. I'm going to go with the second story, since there is no way there could be that much power going through the injectors, just based on how much heat would have be dissipated.

I still don't get the 20 amps though. It's a huge amount of power even if just for a short burst. Maybe they mean the ECM requires 20 amps?

stacks04
11-11-2011, 02:41 PM
ahh yes you're right, I was wrong!! What I was thinking of (and what threw me off), was that on the feed line to the 9th injector is connected to the return line through a check valve, which apparently (if the truck is run out of fuel) allows the low pressure fuel that feeds the 9th injector to "backfill" into the "main injector" return line circuit to build the required ~150psi in the return line circuit. I read the LML fuel system description a long time ago and got mixed up. :o

Just to be clear though, the 9th injector is NOT a high pressure injector like the main injectors. It is fed off of the low pressure side of the pump.

I did not know this. Thats a good bunch of info. And yes your correct on the hci. It is nothing more than a impala fuel injector from bosch.

Fingers
11-13-2011, 06:39 PM
Not drooling, just thought all the changes to the fuel sys were interesting.

The 2 GM docs conflict. One says it's held open at 250v/20a, the other says it's fired at 160-240v/20a, then held open with 12v. I'm going to go with the second story, since there is no way there could be that much power going through the injectors, just based on how much heat would have be dissipated.

I still don't get the 20 amps though. It's a huge amount of power even if just for a short burst. Maybe they mean the ECM requires 20 amps?

The Piezo, once charged, does not flow much, if any current.

Probably an inductor ala ignition coil type setup. Not a cap.

duratothemax
11-13-2011, 07:18 PM
I think I remember reading in SI that the ECM had an internal capacitor bank...ill double check on that though

Michael
01-20-2012, 01:46 PM
Does anyone know what the pressure/voltage curve is for the LML rail pressure sensors? I ordered one and ran it on our test bench, but we could only get a stable reading up to 15,000 psi (due to the tester), but the curve appears to be 2200 bar (versus 2000 bar on the LBZ/LMM).