Odd phenomenom - Occasionally get a LOUD pop from under the hood when energizin

[ktm]

....the fuel system. I am not starting the car, simply turning the key to the ON position. You will hear the pump energize and then an incredibly loud BANG! It only happens occasionally and the car will start up and idle fine afterwards. Most of the time when I energize the fueling system nothing happens, but when it does go BANG! it scares the crap outta me.

I have checked all over for fuel leaks, etc. and do not see anything. It HAS to be fuel system related as that is the ONLY thing that is energized when the key is in the ON position.

Anyone have ANY idea what the @(#&$(@#& it is? I am stumped.

[Tony D]

Disconnect the coil wire and see if you are getting a spark on initial powerup.

My Megasquirt does that, explaind at 'the other site'...

[ktm]

Just happened again. Sounds like a damn M80 going off!

[WingZr0]

what about Back Fire through the AFM mazybe..

[sblake01]

Do you have EFI?

[ktm]

The build:

Garrett T03/04E water-cooled turbo, Supra 440cc injectors, Wolf V500 EMS, LS1 Coil-on-plugs, etc.

No AFM as I am using a MAP sensor. Tony D indicated at "the other site" that his MS'd car does the same thing.

"What I believe it is, after careful observation, is the ECU is giving a SPARK concurrently with the initial energization. It SHOULD jump to a spark terminal with closed valves and therefore be muted (if the cylinder has enough of a combustible mixture at all.

But if your ignition system is like mine (jumps almost 4" now, WOO HOO!) that jump could just as easily randomly go to another cylinder where one of the valves is open and residual fuel vapors flash in the intake or exhaust causing one hell of an explosive backfire!

Mine is occasional, random, and made me question everything I did. Then one day when doing a power-on I noticed that spark from the coil terminal. EVERY time I power on the ECU. EUREKA! That is the ignition source! From there the logic followed.

There has been nothing I have done since to lessen it, or stop it. It just happens. Short of a relay that momentarily direct shorts the coil's signal at startup to prevent the coil from making that primary field and discharging, I don't know what you could do to stop it."

I am looking for other explanations, though Tony's makes the most sense.

[Zs-ondabrain]

You obviously have great spark. Could your timing be too far advanced?

Mine did it the other day, Just after I advanced the timing 5 degrees.

Dave.