Tuning supercharged C7 - Weird issues

[mowton]

Andy,

I have been reading up on DI and as stated above, it is a complete divergence from the port injection. Here is my understanding to tis point. Much smarter posters can correct or affirm.

Based on the extensive calculations the PCM does to convert Driver demand (pedal) into the various critical engine data like throttle position, injector timing, injector pulse width, Fuel pump pressure etc, perhaps maxing the tables is not the correct approach. Again, I don't have any physical experience yet, just what I have read and theorized.

The injection of fuel in the high load/RPM area's is critical and directly dependent on correct fuel pressure and injector timing relative to the intake stroke. Look at the fuel pressures being used and injector sizing to allow the proper amount of fuel flow into the cylinder at the very high load scenario's....2000+ PSI! During low load/rpm, the injector I believe is fired as the compression stroke reaches the top of its travel thus allowing for the very lean cylinder mixtures (not sure how that relates to the WB readings yet). Due to decreasing time to inject required fuel volume as the piston travel/charge mass increases, the fuel is injected during the intake stroke in a more conventional manner. My understanding is this cylinder AFR would be closer to conventional, but still a bit leaner than we have experience in the port injection tuning. I have to assume Boost further exacerbates the fueling injection model and needs to be adjusted to be increased through Fuel Pump pressure settings or other injector tables (different profiles) which I am still researching.

The above PIDs will identify the calculation results and show any throttle limits being imposed as a result of the Torque model processing. Based on the pedal demand, you should be able to correlate the actual opening of the Throttle blade to the expected percentage. If it gets to max as expected, the proper charge mass should be presented to the cylinder. Now we have to make sure that proper fuel mixture is added, at the right time, to allow the mixing of the air/fuel to the proper AFR (still not sure how this is done...numerous injector/fuel pressure tables), before the compression is complete and fire off the spark plug and the rest is magic.

Sorry I don't have the keys to the crypt yet but working it.

Ed M

[mowton]

Guess this thread ran out of steam or everyone else figured it out.....I feel so alone

Ed M

[5FDP]

Want a hug?

[Chris@HPTuners]

The LT1 operates only in homogeneous mode, there is no stratified ultra lean burn mode. All injections are done during the intake stroke. The only exception is catalyst warmup which can use split injection (inject a second pulse later in the compression stroke) to heat the cats faster.

The combustion process depends on a lot of complex factors unique to GDI. There is a ton of CFD modelling that goes into the design and positioning of the injector, its spray pattern under various pressure conditions, the shape of the piston crown, the intake port, the spark plug position etc. to make the mixture stable, atomize the fuel completely to make combustion uniform across the wide operating range. The GDI engine is very sensitive to the timing, pressure and pattern of the fuel injected. Just spraying more fuel into the cylinder for it to hit the piston, the cylinder walls and not vaporize and burn efficiently doesn't help at all.

I think we are going to see a lot of development on the piston, cylinder head, fuel pump and other areas optimized for pure high performance only. My guess (just a guess) is they will be wildly different to the stock configurations. But it will take a lot of experimenting or some CFD geniuses (or both) to bring out the big gains.

The good news is I think the E92 ECM is up to the task and software flexible enough to see some big modifications.

Chris...

[mowton]

The LT1 operates only in homogeneous mode, there is no stratified ultra lean burn mode. All injections are done during the intake stroke. The only exception is catalyst warmup which can use split injection (inject a second pulse later in the compression stroke) to heat the cats faster.

The combustion process depends on a lot of complex factors unique to GDI. There is a ton of CFD modelling that goes into the design and positioning of the injector, its spray pattern under various pressure conditions, the shape of the piston crown, the intake port, the spark plug position etc. to make the mixture stable, atomize the fuel completely to make combustion uniform across the wide operating range. The GDI engine is very sensitive to the timing, pressure and pattern of the fuel injected. Just spraying more fuel into the cylinder for it to hit the piston, the cylinder walls and not vaporize and burn efficiently doesn't help at all.

I think we are going to see a lot of development on the piston, cylinder head, fuel pump and other areas optimized for pure high performance only. My guess (just a guess) is they will be wildly different to the stock configurations. But it will take a lot of experimenting or some CFD geniuses (or both) to bring out the big gains.

The good news is I think the E92 ECM is up to the task and software flexible enough to see some big modifications.

Chris...

Thanks Chris for the update. Is there someplace one can go to try and research the injection profiles/pressures that we see in the LT1 tables. I assume that for the standard power adders like CAI, Headers and maybe low boost, the current configured piston/head combinations will work with tuning. I think I might understand the Torque model for Throttle control, but the fueling portion (timing, fuel pressure, limits etc) is still very foggy.

Thanks again,

Ed M

[Chris@HPTuners]

Thanks Chris for the update. Is there someplace one can go to try and research the injection profiles/pressures that we see in the LT1 tables. I assume that for the standard power adders like CAI, Headers and maybe low boost, the current configured piston/head combinations will work with tuning. I think I might understand the Torque model for Throttle control, but the fueling portion (timing, fuel pressure, limits etc) is still very foggy.

Thanks again,

Ed M

Not that I know of, I have a couple of books but they are very general. Most of the detailed stuff seems to be in patents and research papers at the moment but even then there's not much there. Most of the discussion is around stratified mode, positioning the ultra lean mixture near the plug so it ignites, swirl patterns, injector spray etc. There's also a lot of stuff on the exhaust treatment for the stratified mode dealing with the high NOx emissions that come with it and suboptimal catalyst operation. I have found almost nothing in relation to GDI and performance applications.

[Area47]

Ed, it died when the light was seen at the end of the tunnel with guidance. Now just needs to work past the torque tables to get the power where it needs to be.

[jim2092]

Andy,

On another forum you said you corrected this problem. But no update here. Those who have tried to assist would like to hear about it.

[Pekka_Perkeles]

But no update here. Those who have tried to assist would like to hear about it.

In a public forum?

Web-forums are old-fashioned and overrated. You'll get better results by calling the person directly.. :-)

[mowton]

In a public forum?

Web-forums are old-fashioned and overrated. You'll get better results by calling the person directly.. :-)

The Public Forum is good enough to air a problem, ask questions, enter into a public discussion and get help/advise.....I see a many of these type threads just die out without a specific "here's what helped or how I fixed it". At a minimum you could at least see what advice helped correct the OP's issue. It's like a grownup movie, some times you just have to create your own ending with what you have just seen. Just the way it is.

It's still better than throwing wrenches, alone, in a cold, dark garage

Ed M

[Pekka_Perkeles]

The Public Forum is good enough to air a problem, ask questions, enter into a public discussion and get help/advise.....I see a many of these type threads just die out without a specific "here's what helped or how I fixed it". At a minimum you could at least see what advice helped correct the OP's issue. It's like a grownup movie, some times you just have to create your own ending with what you have just seen. Just the way it is.

It's still better than throwing wrenches, alone, in a cold, dark garage

Ed M

Yep.

I guess I was bit sarcastic.

On the other hand; just reading public forums doesn't make you an expert, but connecting directly with others with similar goals may just do the trick - if you have something to share as well. I haven't contacted anyone with C7 tuning, but it's easy to imagine that some folks do exactly that to solve problems. And that's fine, I think.

[jim2092]

On the other hand; just reading public forums doesn't make you an expert, but connecting directly with others with similar goals may just do the trick - if you have something to share as well. I haven't contacted anyone with C7 tuning, but it's easy to imagine that some folks do exactly that to solve problems. And that's fine, I think.

I would love to agree but I am not sure what this means. lol

[Pekka_Perkeles]

I would love to agree but I am not sure what this means. lol

It's been a while and no comments anymore in this thread. Surprise or so called "lol"?

[jim2092]

I guess everyone lost interest. There was a highly respected member of this forum who told us that "Web -forums are old-fashioned and overrated. You'll get better results calling the person directly". We are now calling each other and sharing all the secrets. Hasn't anyone called you? LOL

[ingsteve]

Check on YouTube...LMR state it is working...

[c.u]

Must be nice.http://api.viglink.com/api/click?for...78160658988.:p

[BGolden]

I have an auto car in my shop with a Pfadt system (obviously I cant call them) on it and the car is running out of fuel at 5500 rpms. With their tune it ran out of fuel at 4800 so I removed their tune and started from scratch with the car. No matter if I have it at 12.2 or 11.5 it will run out of fuel. It will command 2200 psi on the HPFP but it will only produce 1200 psi. I know its a fueling issue from the LPFP as pressure from it will drop to 45 psi. The car runs perfect until this happens. All torque management has been turned off and the throttle plate is holding 84% the entire run. Has anyone else run into this issue?

I tried a boost a pump but the stock voltage exceeds 17 volts to the stock pump and the boost a pump did not like that. I am considering an inline pump between the LPFP and the HPFP. Unless there is a table I am missing that allows me to up voltage to the stock pump or another way around it.

Any help is appreciated.

[yonson]

How much boost are you running and what kind of power is it making when you run out of fuel? Did you change anything mechanically with the factory fuel system? If you are under 8 psi, you shouldn't need an additional pump etc... post your file or at least a log of the issue and we should be able to tell more...

[BGolden]

7.25 psi on stock map sensor. I have not verified with a mechanical gauge. 540 trq low 500's with 5* of timing but pulling timing to 0* due to the lack of fuel. Fuel system is stock. I'll try to post a file in a bit busy day.

[veee8]

Any updates on this issue?