Backfire under throttle?!

[Sean80]

Today I heard a backfire while under throttle (not quite WOT). From what I have read, this probably isn't good. I have been wondering for a while if I have a boost leak somewhere. I have taken apart all the hose clamps and reconnected them, but my AP is reading a boost of -10 at idle. Shouldn't it be a little closer to -20??

Cobb SRI, RMPC inlet, CPE DP, denso IVT 22's, PTP FP (steady in 1800's at WOT), stock BPV, Stage 2 + SF 93 map.

Any ideas would be appreciated. Thanks

[Fobio]

without a log, there's nothing meaningful we can offer. bad gas might be a reason tho, but I assumed, you filled up 93+ octane @ a reputable station?

if say your logs show rich afr's into the 10's with pulled timing, then it knocked and dumped fuel (likely running OL - Knocking values)...that kinda thing happens, even to tuned cars sometimes...you just gotta know your car enough to know why it did and if it's a pattern of symptoms. if it's doing it all the time, then there's something wrong...but pulling tubes and clamps whenever anything happens may cause problems of its own.

sometimes, it could be from soemthing as simple as you not getting on it for awhile (winter) and then blasting it...I imagine bits of dirty shit from the IM/injectors/pistons being blasted and cleaned, and chunks of carbon and soot flying off the pistons...just guessin'.

my car idles -10 psi when reading boost.

[WeatherB]

Like Fobio said, see if you can get us a log.

At idle the vacuum should be ~ -10psi or -20Hg

[Sean80]

Thanks for the input fellas! I always fill up with ultra 94 and it's the first time I've heard it do it under throttle. Usually I get afterfire during shifts. Hopefully it was what Fobio said, cleaning the gunk out because I haven't been getting on it much lately. My last log the AFR's were steady around 11.76ish and fuel pressure was in the 1800's. I'll keep an eye on it to see if it does it repeatedly. In the meantime, the car still goes like stink!

[Flagrum_3]

Backfire at throttle ususally means 'unburned fuel' getting thru.It could be as simple as what Fobio said, which I would suggest some fuel-injector cleaner (full bottle) and some spirited WOT runs to clean her out.(WOT under load).Another suggestion is check your plugs, even if they are relatively new, could be one is running too cold or hot or not at all. also check your plug connectors....Just a couple of simple suggestions...

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[Tokay444]

^^^ isn't that after fire, not back fire?

[Flagrum_3]

^^^ isn't that after fire, not back fire?

Sorry, never heard the term 'after-fire'.

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[Tokay444]

Oh.
Here.
http://forums.nasioc.com/forums/showthread.php?t=1724076

[WeatherB]

Did you see more than the usual amount of smoke out the tail pipe when this happened? If you don't have an oil catch can, you'll be surprised how much crap will collect in the manifold after a while of slow driving and then get pulled in the first time you boost.

[Flagrum_3]

Oh.
Here.
http://forums.nasioc.com/forums/showthread.php?t=1724076

I see, basically always used the same term for both types as everyone else I know.But thanks.

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[Tokay444]

How did you differentiate the two?

[The Wolf]

Why do you take every thread off-topic?

[Tokay444]

Sorry, thought afterfire was the topic.

[Sean80]

Did you see more than the usual amount of smoke out the tail pipe when this happened? If you don't have an oil catch can, you'll be surprised how much crap will collect in the manifold after a while of slow driving and then get pulled in the first time you boost.

I didn't happen to notice, but when I pulled the intercooler off I noticed a small amount of oil residue inside the connecting hoses. Is this the oil that an oil catch can would get?

[Tokay444]

Yes. Get one for the mani, and one for the intake. And see if your bpv is leaking.

[Flagrum_3]

How did you differentiate the two?

Easy, By the symptoms.

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