My first nitrous system pull today, I'm totally green and need some advice.

I could feel the nitrous kick in and all was well until deceleration popping backfiring through the exhaust. Unfortunately my wideband didn't record in the HP Tuners log (my fault for not checking opening the scanner) but with an eye on the gauge it was a little lean at 12.1 a/f for nitrous. DFCO is enabled and the wideband read in the 20's during decel. Should I just up the fuel jet and do another test? The popping has me on edge as you can tell by my cussing in the video lol.

LQ9 SBE
PRC 225 heads
TSP v4 cam (231/234 .629" .615" 111*)
TBSS Intake 92mm TB (cable)
1 -7/8" long tubes with duals

NX Express plate kit with 75 horsepower jets (41 Nos - 23 Fuel)
BR7EF Plugs gap @ .032
Removed 2* degrees of timing with 24* total
NOS Progressive Controller set at 3000 to 6500 RPM's (7000 RPM Limiter)

The second hit has the loud backfiring

 

Sounds like unburnt fuel igniting in the exhaust. I think your fuel jet is too large. Shouldn't it be a 22 or 23 fuel jet? What are you referencing for jet sizes?

 

Yeah the 43 fuel jet was a typo should have typed 23... sorry bout that.

On the first test I forgot to connect the green data plug to HP Tuners... yeah I'm a retard lol

The second test I brought the bottle pressure down a bit to 1000 PSI per NX Expresses recommendation and that helped. The log shows I'm still slightly lean so I'm going to up the fuel jet to the next size.

Second test backfire no so bad as the first.


NX Express Jet Chart

 

How much PSI is at the fuel rail? Assuming you fuel is coming off the rail...

Also, how much PSI at the bottle on the first pass?

 

Around 58psi from the inlet to the rail. My fuel rail doesn't have a schrader valve to tap from. Walbro 255 lph drop in modular pump at around 62% IDC at 7000 RPM.

The bottle pressure was 1100 psi first pass. Then I re-read NX Express recommendation and lowered the bottle to 1000 psi on the second test hit. The back popping wasn't as loud after the pressure drop. Over the weekend I was able to get some good data and the a/f is in the high 11's to low 12's so it's a bit rich. I need to weigh the bottle and see how much I have left before making a jet change.

Tapped into the fuel supplies quick connect.



No Schrader valve on the TBSS rails.

Attachment 712339

 

You don't need the BR7 plugs and you don't need to pull any timing on 75 shot. Have fun be safe.

 

Maybe I misunderstood, your video is no longer available. When in decel the n20 isn't active. Popping is normal with a lean decel. If you don't like it, richen up the decel fuel on your map and get the AFR back in range at 14-15. *shouldn't* have anything to do with the n20 kit.

 

Decel fuel cutoff in tune. Disable it and it will stay richer on decel.