Back Fire

[Jayme]

I was reading somewhere that dfco at least in ls1s doesn't cut 100% of the fuel. Just most of it. So you are left with a super lean slow burning mixture on decel. If the timing in this area is too retarded then the exhaust valve closes before the mix has burnt completely causing the popping. Generally people on other forums have observed that turning dfco off can help reduce the crackle or if you want to keep dfco on then increasing timing on decel will also reduce the crackle.

Based on that I would suggest increasing the timing in the 20kpa area. Holden generally leave that column fairly retarded.

[VL400]

Its the transition periods to/from DFCO that normally does it. Look at a log with spark advance as it enters and exits - will see spark advance go to "EST params - DFCO Mode Forced Advance", but its not instant and is only when it reaches the target value does DFCO actually occur. With this being such low advance it causes the crackle when fuel is injecting.

Example...

[Jayme]

This must be why I was reading people say that increasing dfco forced advance solves the problem...

[vlad01]

I was reading somewhere that dfco at least in ls1s doesn't cut 100% of the fuel. Just most of it. So you are left with a super lean slow burning mixture on decel. If the timing in this area is too retarded then the exhaust valve closes before the mix has burnt completely causing the popping. Generally people on other forums have observed that turning dfco off can help reduce the crackle or if you want to keep dfco on then increasing timing on decel will also reduce the crackle.

Based on that I would suggest increasing the timing in the 20kpa area. Holden generally leave that column fairly retarded.

I have very high advance in that area. would explain why its hard for mine to do it. Is that area much lower timing in the v8 bin compared to v6?

[v6bucket]

So I should bump the setting from 9.84 deg to something higher, is this correct? If so are we talking 1-5° or 5-10°?

[Dylan]

Post up a screen shot of your advance table?

By the look of VL400 screen shot it runs a fixed advance when DFCO is active.

But I run high advance in my cars and they don't do it either.

[Jayme]

as a stab in the dark, and based on VL400's screenshot, try upping it to 20 degrees and test. also take a recording of it happening and post it up so we can see the results.

[VL400]

Yep, raise it up to tame the crackle! Can make it closer to something in the 20kpa column.

[v6bucket]

This is not directly related to the backfire issue, but saves starting a new thread.
We had the Dato on the dyno again on Monday, warmed the car up checked a few things ready for the 1st pull, when I moved the ecu that was on the floor & the car faulted lost communication between the laptop/ecu, couldn't reconnect, so we shut down & I noticed that the led on the nvram went out as soon as ign was off, cal was corrupted & I didn't have the burner with me. So fitted the memcal that was the same bin as the nvram so that we could log on the dyno & make any necessary changes later. Laptop wouldn't connect, I then remembered that when I opened TP5 after being connected to the car, that it didn't give the connection beep, but when I hit the Connect/Disconnect arrows it connected. I checked the wiring near the ecu, had the engine running, pulling pushing wires etc. to find an issue but engine ran like a charm. I copied the correct bin onto the nvram plugged the laptop in & connected in the correct manor with beeps in the correct place etc. The only thing that has changed is that the laptop was shutdown & restarted. Could the laptop have had a stress out & corrupted the nvram?

[Holden202T]

if there was some sort of serial port/usb error it might not have closed the port properly and usually reboot is required to reset it ....

hard to know for sure though, but I've had issues in the past just turning the ignition on, crank the motor a bit and it drops power bad when it gets a lot of fuel in a cylinder then the nvram corrupts...... it hasn't happened for a long time, but I also changed ecms when I went from serial port to usb port etc