backfires?

[JFISHTHECREATOR]

I have a full megan racing exhuast on my f22a4. The header/downpipe gasket keeps burning/blowing out. it gets loud , and sometimes when i rev it , it will backfire. does anybody else have this problem?

[sonikaccord]

Did you reset the ecu? How long have you been driving it with the new exhaust?

EDIT: Is the ECU stock?

[johnl]

Poor quality gasket? Perhaps the flange surfaces of the header and / or the downpipe are not flat enough? If so then parts of the gasket may not be in good enough contact with the flanges, and as result get too hot and burn out.

The backfiring is caused by negative pressure waves inside the exhaust causing atmospheric air to be 'sucked' into the exhaust through the leaking gasket. This causes an excess of O2 inside the exhaust, which causes unburnt fuel to burn ('explode') inside the pipe.

Excess O2 won't get into the exhaust only on the 'over-run', but since there are always positive and negative pressure fluctuations within the exhaust, it will affect exhaust gas O2 content most of the time (i.e. increase it). This will affect O2 sensor output, and the ECU will 'think' that the engine is running lean, so the ECU will inappropriately enrich the AFR...

[JFISHTHECREATOR]

Did you reset the ecu? How long have you been driving it with the new exhaust?

EDIT: Is the ECU stock?

Have not reset ecu. Ecu is stock(91 ex 5spd). Been driving it since about may.

[JFISHTHECREATOR]

Poor quality gasket? Perhaps the flange surfaces of the header and / or the downpipe are not flat enough? If so then parts of the gasket may not be in good enough contact with the flanges, and as result get too hot and burn out.

The backfiring is caused by negative pressure waves inside the exhaust causing atmospheric air to be 'sucked' into the exhaust through the leaking gasket. This causes an excess of O2 inside the exhaust, which causes unburnt fuel to burn ('explode') inside the pipe.

Excess O2 won't get into the exhaust only on the 'over-run', but since there are always positive and negative pressure fluctuations within the exhaust, it will affect exhaust gas O2 content most of the time (i.e. increase it). This will affect O2 sensor output, and the ECU will 'think' that the engine is running lean, so the ECU will inappropriately enrich the AFR...

I used the gaskets megan racing sent me, i cleaned the surfaces on each pipe. Should i try the permatex copper gasket stuff and spray it on the gasket?

[johnl]

I used the gaskets megan racing sent me, i cleaned the surfaces on each pipe.

I'd put a straight edge across the header and downpipe flange surfaces (in every direction, including diagonally) to make sure one or the other isn't warped. The gasket needs to be tightly clamped at all points, if one of the flange faces is warped (enough) then this may not happen, and some part of the gasket may get too hot.

After fitting the gasket and running everything up to temperature, let it cool down and retighten the nuts. Check nut tightness again after a few days normal running.

Should i try the permatex copper gasket stuff and spray it on the gasket?

Never used it, so can't recommend or not. Don't use anything that has a silicon content that isn't specifically marked as 'sensor safe' (it will kill the O2 sensor and may damage the cat). Personally, the first thing I'd try would be some 'muffler putty' between the flanges and the gasket.

[JFISHTHECREATOR]

i put a new gasket on it, tightened it , warmed the car to operating temp , jacked it up , then re tightened. its fine right now - been a week. if and when it goes out again i will spray some permatex copper spray a gasket onto the gasket. if that dont work i have one more after it , so i would use it. then either buy more gaskets , or go back to my stock A4 headers. although i did see a significant change in power with these megan headers/pipes.

[johnl]

i put a new gasket on it, tightened it , warmed the car to operating temp , jacked it up , then re tightened. its fine right now - been a week.

Now is the time to recheck the nut tightness.

[802cb7]

i put a new gasket on it, tightened it , warmed the car to operating temp , jacked it up , then re tightened. its fine right now - been a week. if and when it goes out again i will spray some permatex copper spray a gasket onto the gasket. if that dont work i have one more after it , so i would use it. then either buy more gaskets , or go back to my stock A4 headers. although i did see a significant change in power with these megan headers/pipes.

how significant? can you also double up the gaskets if needed?

[johnl]

how significant? can you also double up the gaskets if needed?

I've heard of it being done, but if you need to it's a Band-Aid on the flange faces not being flat enough. Doubling up on the gaskets results in an effectively more compressible gasket, so it (they) may be more able to seal what would otherwise be a leaky connection. For how long it might work is another issue.

Doubled up gaskets may possibly result in the gaskets running hotter because the faces of the gaskets in contact with each other are further from the flange faces (and insulated by the non metallic layers of the gaskets). The gaskets will lose heat into the metal of the header and the downpipe (which are always radiating substantial heat away in use), so the further parts of the gasket are from the flange metal the less heat they may lose...?

[JFISHTHECREATOR]

how significant? can you also double up the gaskets if needed?

I don't know if I can double up the gaskets , but as Johnl said, it could possible be done.

as for the power increase , i cant tell you hp, because this thing has never hit a dyno. but the acceleration from 0-60 , and 60-100 was quicker.