LT4 Injector Data for E90 ecm LT5 vs LT4

[MeanMike]

I have flex fuel working in my truck and need more fuel. The truck is an L84, L8T cam, Magnuson 2650. I bought LT4 injectors and pump and swapped them yesterday keeping my L84 solenoid on the hpfp. I loaded the 19 ZR1 (LT5) injector and pump data. I loaded it by going to the compare log and copying over differences for everything under injector control and everything under high pressure desired, fuel pressure feedback, transition rate, monitors and everything in the fuel pump tab.

Before the injector swap, I had the maf error at +-2 with an almost stock maf calibration. I had a max of 9 g/s difference from stock at higher flow, mostly less than 1 g/s difference in the cruising areas of the curve. After the injector and pump swap, I'm mostly 7-10% rich across the board.

So with that error, I assume the injector data is off. I tried the LT4 injector data for flow rate, multiplier, offset and short pulse adder. The maf error was similar but more varied at idle. So ultimately I went back to the LT5 data. The pump data is the same between the two so I'm not worried about that and I'm getting measured pretty much matching commanded.


My question in all this. How can the same injector in two different situations have such different data? Is the injector driver different in an E99 vs and E92? Perhaps higher voltage on the coil. Do you all see similar error going from L83/6 injectors to LT4 in and E92? Could my L84 injectors have had enough wear (68k miles) to have been flowing more fuel which I corrected back and now the new injectors show as rich?

Since we are back calculating air flow from known injector data, having correct injector data is critical. I don't know which one to trust. Both are going to have significant effects on my air flow and thus going to require changes to my torque tables. I just want to get it right and getting the injector data right is the foundation for all of this.

[TrkNrrs]

I have flex fuel working in my truck and need more fuel. The truck is an L84, L8T cam, Magnuson 2650. I bought LT4 injectors and pump and swapped them yesterday keeping my L84 solenoid on the hpfp. I loaded the 19 ZR1 (LT5) injector and pump data. I loaded it by going to the compare log and copying over differences for everything under injector control and everything under high pressure desired, fuel pressure feedback, transition rate, monitors and everything in the fuel pump tab.

Before the injector swap, I had the maf error at +-2 with an almost stock maf calibration. I had a max of 9 g/s difference from stock at higher flow, mostly less than 1 g/s difference in the cruising areas of the curve. After the injector and pump swap, I'm mostly 7-10% rich across the board.

So with that error, I assume the injector data is off. I tried the LT4 injector data for flow rate, multiplier, offset and short pulse adder. The maf error was similar but more varied at idle. So ultimately I went back to the LT5 data. The pump data is the same between the two so I'm not worried about that and I'm getting measured pretty much matching commanded.


My question in all this. How can the same injector in two different situations have such different data? Is the injector driver different in an E99 vs and E92? Perhaps higher voltage on the coil. Do you all see similar error going from L83/6 injectors to LT4 in and E92? Could my L84 injectors have had enough wear (68k miles) to have been flowing more fuel which I corrected back and now the new injectors show as rich?

Since we are back calculating air flow from known injector data, having correct injector data is critical. I don't know which one to trust. Both are going to have significant effects on my air flow and thus going to require changes to my torque tables. I just want to get it right and getting the injector data right is the foundation for all of this.

Did you change the leading angle table as well?

[MeanMike]

Yes, I copied over the fuel pump data

[TrkNrrs]

I didn?t understand the post perfectly I guess, but are you saying you put the l84 regulator on the lt4 fuel pump? If so that was going to be my next suggestion.

[MeanMike]

Yes, I swapped the regulator/solenoid from the L84 pump to the LT4. I'm having no issues with the pump. I'm not having issues with the injector either as the error is easily tuned out, but is that right?

I'm questioning why the same injector in two different applications has different injector data. Is there something behind the scenes we don't know about? Or is it really the same injector?

[smokeshow]

DI requires more finesse than just delivering a pulse. I have found it necessary to calibrate the fuel pump to match the fuel flow demand of the engine. A smaller engine on relatively low boost isn't going to draw down on the high side as much, so the factory LT4 pump cal is likely a bit aggressive for the setup. It will average out around target pressure, but the peak-to-peak on the pressure oscillations can drive some instability into the fuel system. It's hard to spot too because its such a fast disturbance. Injection scheduling warrants a close look as well...bigger injectors means the stock settings will not be optimal. Injection timing can have pretty big impacts on what you see in the fuel trims.

[MeanMike]

Good idea about the pressure oscillations. I'm sure my IPW is much smaller all across the board in a 5.3 vs an LT4. I also used the L84 size fuel lines and inlet line/check valve. I listened to a couple long Sam Barros podcast where he explained how it all works as a system for those pressure oscillations and I have no idea how my combination of parts is acting.

I've been thinking about the needed pressure and I certainly don't need what the ZR1 uses as a base file. My EOI is ~20* before bdc on the intake stroke with 20 MPa pressure, I could certainly reduce the pressure and stretch that EOI closer to zero and all through the range. My only negative to that is what happens when I run E85. We need a pressure multiplier vs ethanol content. Or I'll just have to load a new cal.
Screenshot 2025-02-03 185342.png

I know the LT4 injectors were never meant to spray into the smaller 5.3 bore. Their pattern is probably not great for that size bore either. I don't even know how to tune for most efficient SOI. I'm guessing that GM does that with some computer modeling that the rest of us will never have access to.
I was blown away with how much power I gained by getting all the fuel in by bdc with the stock injectors, but that basically put them at the limit on 93 which is what triggered this whole fuel system change.

[MeanMike]

I ended up using the LT5 data. When I did the "copy differences" in the comparison log, one of the axis in injector control didn't update. Once I fixed that, the difference at idle got better. I still ended up with about a -6% error at high maf flow, but I made that change and all is well. I put my first tank of E85 in and fuel is still tracking correct. I used the stock L84 SOI table and with the added injector flow, it still keeps EOI before bottom dead center on the intake stroke. For ethanol, I added to the Alcohol SOI adder table at high fuel flow and rpm.

I had done a couple injector upgrades in my CTSV(2) going from ID850 to 1050's and then to 1300's and they never showed any difference. That doesn't seem to be the case with OEM DI injectors.