I have a 416 LS3 stroker running Holley Terminator X that for whatever reason commits a nasty back fire as soon as I turn the key when the motor is warm. Not hot mind you, it starts up perfectly fine both when completely cold, and after it's fully warmed up. However if the coolant temp is somewhere between 90-150 degrees, and the car had been run earlier, as soon as I bump the key I get a shotgun level blast through the intake and smoke pours out of the air filter. Additionally, the engine will not start in this state, after the back fire. It will just crank and crank and crank, unless I open the throttle partially myself, and then it will stumble to life.

Engine specifics:

Forged LS3 4" stroke 4.070" bore
-6 cc flat top pistons, 10.8:1 compression
Naturally asperated, LSXR intake
60 lb LS3 injectors from SEP
Holley 340 lph fuel pump dialed for 60 lbs on a return style fuel setup
1-7/8" long tube headers

I have attached my current config file, as well as a log of a start attempt where a back fire occurs.

I have gone through the startup tips posted elsewhere in this forum, and adjusted my hot idle for 2-3% IAC position via the throttle body (with a TPS auto-set completed afterward, of course).

What could possibly be the cause here? Needless to say, it's rather embarrassing to show off your car to some buddies in the parking lot after you drove it there, only for it to sound like ole cleeters jalapy popping and banging down the street.

Thanks in advance for any assistance or tips anyone can provide!

https://www.dropbox.com/s/y1kxhz4qz7...-0002.dlz?dl=0

https://www.dropbox.com/s/0tfk3mdq00...earn.terx?dl=0

 

Let me get out my Cap'n Crunch decoder ring so I can reveal the invisible text.

 

lol, trying to keep it interesting.

Sorry, I have the 'dark mode' on, and it had my original black text hidden so I changed it to white. Lemme fix that quick...

 

I don't have software for Terminator X and was waiting for somebody to help you but it's not happening yet.

First thing I'd check with backfire is ignition timing during cranking. Timing should be around +15 degrees in the cranking parameters, and Crank To Run RPM at about 400 rpm.

Cranking Fuel should be around 9 or 10 lb/hr hot, and somewhere around 13 to 16 at 100F coolant temp.

If you have cable throttle body then open up the IAC Parked to 80%. You have a big engine and it needs air.

Disable the Fuel Prime Percent while troubleshooting. It's just going to jack up your efforts to dial in the fuel during cranking. After you get things dialed in I'd suggest to keep that number fairly low around 125%. All it does is give your engine a little kickstart of fuel before timing pattern recognition is achieved and normal fuel injection occurs. You shouldn't depend on it for starting, it's only there to help the engine start a fraction of a second quicker. And keep in mind that little shot of fuel happens every time you cycle the key switch on, so it can load up things with fuel if you're turning the key switch multiple times before cranking.

 

Thanks for your response! I actually got a decent bit of traction on this over at the Holley forums. It turned out I may have missed the fact that my injectors were rated for 60lbs at 43 psi, not 60 psi. I dialed my regulator back, updated the injector data in the Terminator X software, and also reduced clear flood to 125%. I took 10% off the full range of cranking fuel, so it's 7 lbs/hr hot, and tapers from 21 lbs at 100F coolant temp (might still be a little much here). Crank to run is 400, and cranking timing is 15 degrees. IAC park is right at about 80 at 100F as well. So far, it hasn't backfired after making these changes. I think the core of the issue was my mistake in how I had the software thinking they were 60lb injectors at 60psi, not 43psi, which I believe caused it to scale the fuel tables way off.

 

Good deal. Oughta run more consistent in general with improved injector data. Might develop a few quirks in drivability until the fuel map smooths again, but that's going to happen when changing fuel delivery.