Interesting info on B3702 Injection timing

[eficalibrator]

...you need to pull time out of the voltage adjustment and short pulse width tables. I've searched around and found what appears to be the right voltage adjustment numbers. But even with the short pulse table zero'd out, I'm still seeing 11:x AFRs at idle, which is why I was pulling more time out of the voltage table.

I'm inclined to agree with you here. I just didn't go that far down the path in my first post since I thought it was self-evident. What you're most likely finding is that the ACTUAL offset really is shorter and needs to be recalibrated. The offset and short pulse adjust make up a very large percentage of the total idle pulswidth, so an oversized offset can have a very real impact upon your ability to get back to stoich. You're heading down the right path, it's just easier if you start with the proper data rather than trying to stumble upon it.

[dfe1]

This thread still seems to be going sideways. If an injector in a sequential system fires against a closed valve, then as cam duration increases, the question is should injector offset be increased or decreased? Lee's testing showed improved performance be increasing offset, but to me that doesn't match the logic of the concept-- unless there's a benefit to firing the injector closer to valve open, or after the valve has opened. The reference pulse has to occur before the injector fires and that being the case, increasing offset will delay injector firing. If the idea is to give fuel more time to vaporize, then offset should be reduced to compensate for an earlier opening intake valve (than with a stock cam).

It's interesting to note that the injection timing tables (B3702) for truck, LS1 and LS6 are identical, (even though cam duration varies quite a bit) although the values for the G van are slightly larger. What's also interesting is that the E40 and E38 ECMs have injector timing versus RPM tables and the values (expressed in degrees) generally increase with rpm. On the other hand, values in the timing versus ECT table (also expressed in degrees) are higher at low coolant temps than they are at higher temps. (Opposite of value change in an LS1 PCM). I'm trying to make sense of all this and not being very successful. Every time I think of a reasonable explanation, I find something that contradicts it. Any ideas?

[drdarthinvader]

1. is b3702 a delay in opening the injector?
2. is b3701 a compensator to a slow opening injector? note :that aust and usa tables are different but tables in b3702 are the same

[5.7ute]

This thread still seems to be going sideways. If an injector in a sequential system fires against a closed valve, then as cam duration increases, the question is should injector offset be increased or decreased? Lee's testing showed improved performance be increasing offset, but to me that doesn't match the logic of the concept-- unless there's a benefit to firing the injector closer to valve open, or after the valve has opened. The reference pulse has to occur before the injector fires and that being the case, increasing offset will delay injector firing. If the idea is to give fuel more time to vaporize, then offset should be reduced to compensate for an earlier opening intake valve (than with a stock cam).

It's interesting to note that the injection timing tables (B3702) for truck, LS1 and LS6 are identical, (even though cam duration varies quite a bit) although the values for the G van are slightly larger. What's also interesting is that the E40 and E38 ECMs have injector timing versus RPM tables and the values (expressed in degrees) generally increase with rpm. On the other hand, values in the timing versus ECT table (also expressed in degrees) are higher at low coolant temps than they are at higher temps. (Opposite of value change in an LS1 PCM). I'm trying to make sense of all this and not being very successful. Every time I think of a reasonable explanation, I find something that contradicts it. Any ideas?

The offset when increased will have the injector fire earlier not later.

[LS1_Dragster]

I was reading an article the other day about direct port injection and one of the things it mentioned was firing the fuel near the top of the piston stroke on a cold motor for better emissions etc. This would explain why the injection times are lower when cold, they are firing the injector with the valve open. I guess they don't need the raw fuel puddling when it's cold.

[dfe1]

The offset when increased will have the injector fire earlier not later.

That appears to be the case, I'm just trying to understand the algorithm. If a larger number means the injector is firing earlier, then the value would have to be subtracted from a base delay, I'd guess. If that's the case, then the injectors fire at reference pulse+delay-offset.

[Gelf VXR]

Some of us are trying to figure out what crank/cam/valve event the injector timing tables are relative to (e.g. time BBDC...?)...

We appreciate your efforts in experimenting with this...

5.7ute (Mick) is very interested in this.

Hi Joe

I believe the injector timing is in crank regress and relative to TDC on the compression stroke?

Foe example on the LS2 the advance is 490 degrees when cold and 220 degrees at normal running temps, so the timing events for the LS2 are as follows:


Engine cold

Inj fires. 130 BTDC. CLOSED INLET VALVE
IVO. 16 ATDC
ICL. 118 ATDC
IVC. 40 ABDC


Engine hot

IVO. 16 ATDC
ICL. 118 ATDC
Inj fires. 140 ATDC. INLET VALVE BEGGINING TO CLOSE
IVC. 40 ABDC

[LS1_Dragster]

From what I've been reading, the cold injection event is more beneficial to happen when the valve is open and closer to TDC, they dont want raw fuel puddling up on cold walls. Also, the articles state that it helps light off the catalytic converter.

Lee

[joecar]

Hi Joe

I believe the injector timing is in crank regress and relative to TDC on the compression stroke?

Foe example on the LS2 the advance is 490 degrees when cold and 220 degrees at normal running temps, so the timing events for the LS2 are as follows:


Engine cold

Inj fires. 130 BTDC. CLOSED INLET VALVE
IVO. 16 ATDC
ICL. 118 ATDC
IVC. 40 ABDC


Engine hot

IVO. 16 ATDC
ICL. 118 ATDC
Inj fires. 140 ATDC. INLET VALVE BEGGINING TO CLOSE
IVC. 40 ABDC

Hi Gelf,

That does make sense (relative to TDC compression stroke)...

The LS2 injector timing is directly in degrees... makes visualization easier...

The LS1 injector timing is in milliseconds, so I have to convert that to degrees based on rpm:

offset[°BTDC] = 720 * Toffset * RPM/120000

where Toffset is in ms,

range of Toffset B3702 is 0° to 8°, so offset[°BTDC] range is 0° to 288° (at 6000 rpm)... does this make sense...?



BTW: oh, your IVO would be 16° BTDC (to give you ICL 118°).

[Gelf VXR]

BTW: oh, your IVO would be 16° BTDC (to give you ICL 118°).

Are you sure? 118 centre line, intake duration 204 degrees @ 0.05

118 ATDC - 102 = 16 ATDC