VTC_CiViC

And I'd like your opinion guys..

What I noticed, was that at higher boost levels (10psi+), I was getting a very loud very rapid backfire comming out of the exahust, kinda of like setting off a batch of firecrackers in a tin garbage can. It was really weird and I couldn't figure it out, but it felt almost like I was over fueling the motor even though I hadn't changed V-AFC settings at all latley. Anyways, I figured what the hell, let me lean back a little and see what happens. I drop the trim from -35% to -38%, and immediatley notice the backfiring lessend, but some was still present. Ok, I lean it out some more to -40% accross.. very little backfiring at all know, only an occasion pop at 12psi.

I couldn't help but think it was the strangest thing why now I have to run so lean, but then I reasoned this:

The MSD enhanced spark is so much greater than the stock spark, that it is igniting FAR more fuel that my stock spark could, hence more fuel was burning and I was backfiring from the excess fuel. And why only at higher boost? Because with the AFC mod, the MAP reads boost as normal pressure, the more boost it see's, the more fuel it adds so the more it'd backfire at higher boost levels.

Well to me it all made sense, but i'd never heard of anybody esle experienceing this issue. I checked the plugs, all look good, no pinging, A/F shows good temps @ WOT. So does it sound rational to you guys or what??

rtype11

you still have ignition problems, more timing advance, see if that works, this can blow your turbo up if it makes its way back up the exhaust. just for safety add more fuel earlier.

VTC_CiViC

But if I add more fuel, isn't that gonna only add to the backfiring?

rtype11

can I call you sometime to explain, I have seen this before, even tuned it out of my car, it is lots of fuel, but at the wrong time, it is leaving the cylinder during intake stroke while exhaust valve is still open, your motor is built to scavenge the fresh air charge, you need to dial out that overlap of the valves, and add the fuel earlier, I say add fuel now , so you can back it out later for safety, the fuel is burning right after the turbo basically, dangerous stuff. adding more fuel will make it too dense to backfire in the exhaust, you need (lean) vapour to explode for that firecracker noise.

csufweed

yeah you got ignition problems... either you installed the MSD incorrectly or stock parts are just on its way out.

VTC_CiViC

Well if the MSD was installed incorrectly, I'd have no spark at all, so that cancells that out. And my block as far as my plugs and compression numbers are concerned is in mint shape, so I doubt that. Seems like a tuning issue to me like rtype stated.

VTC_CiViC

See that's my point exactly, it never happend b4 the MSD, only since, and it will only happen at boost levels higher than about 10psi. Being that I run the AFC mod, the ECU is just dumping more and more fuel the higher the boost, almost like a factory turbo car would do, and it's this excess fuel at 10+psi that is causing the backfire, which explains why when I lean it down up top, the backfiring goes away.

But at the same time, what rtype said makes sense to, but it's odd. The way he explained it, he said adding fuel would help quell the igniting of the raw fuel, yet when I lean it it goes away? Weird stuff undeed!

csufweed

are you using the MSD BTM? If so take it off cuz that is the problem.

VTC_CiViC

No, straight MSD 6A, internal coil.

X2BOARD

The more I think about it, the advance on the ignition timing stated by rtype11 makes more sense. I am not sure on the addition of fuel, but upping the advance sounds logical.