Exhaust backfire

[GodziRRa]

Hello guys!

Lately, I've noticing that my car would have a little backfire (pop pop) sound on the muffler during idle or sometimes during deceleration. Running aftermarket exhaust by the way, 3.5 or 4 I think.

What do you think is causing this? Do I need to worry about it? I heard that Nissan turbo engines love to do that. The flame and the sound is awesome, and scares the heck out of some ricers behind you sometimes. But just to be sure.

Thanks!!

[Skym]

Stuffed o2 sensors (x2 on GTR and slow to react due to being clogged with carbon deposits) can make stock ECU run engine richer for longer. When it does this you get flames from exhaust (poping sound). Sometimes running rich on decel can be due to atmosphere vented BOV. When running properly it shouldn't do it, unless you tuned engine to do it (run it richer after fitting cams).

Easy way is to unplug o2 sensors and see if idle is smooth and problem goes away. But be aware that o2 sensors could be picking up a intake airleak or exhaust airleak and running engine rich. Those problems + unplugging 02 sensors could make engine go lean, blow up.

[GodziRRa]

Stuffed o2 sensors (x2 on GTR and slow to react due to being clogged with carbon deposits) can make stock ECU run engine richer for longer. When it does this you get flames from exhaust (poping sound). Sometimes running rich on decel can be due to atmosphere vented BOV. When running properly it shouldn't do it, unless you tuned engine to do it (run it richer after fitting cams).

Easy way is to unplug o2 sensors and see if idle is smooth and problem goes away. But be aware that o2 sensors could be picking up a intake airleak or exhaust airleak and running engine rich. Those problems + unplugging 02 sensors could make engine go lean, blow up.

I'm running HKS BOV. The small popping sound happens at idle. It will disappear when I step on the gas, but there was a time it popped loud during deceleration. Most of the time my exhaust 4" exhaust piping will hit humps in some roads, I'm also thinking maybe some loose exhaust bolts can cause it?

[mitch32]

It shouldn't pop on idle, like Skym said either clogged O2 sensors or your BOV is leaking. HKS BOV's have a tendency to leak if they aren't cleaned regularly (once a year). They leak because when you let off the gas for a split second after the BOV releases pressure it sucks air, there is no filter on HKS BOV's so sand and bugs get stuck on the gasket and then they leak. Also your MAF's could be dirty but you'd have other issues besides a pop on idle.

Sometimes a car when its tuned the idle isn't smoothed out and it has some small popping sounds but they are very small.

Lastly the pop on deceleration is 100% normal when you have a BOV, an aftermarket exhaust, and MAF's sensors. I love those backfire pops, lol....

Good luck
Mitch

[GodziRRa]

It shouldn't pop on idle, like Skym said either clogged O2 sensors or your BOV is leaking. HKS BOV's have a tendency to leak if they aren't cleaned regularly (once a year). They leak because when you let off the gas for a split second after the BOV releases pressure it sucks air, there is no filter on HKS BOV's so sand and bugs get stuck on the gasket and then they leak. Also your MAF's could be dirty but you'd have other issues besides a pop on idle.

Sometimes a car when its tuned the idle isn't smoothed out and it has some small popping sounds but they are very small.

Lastly the pop on deceleration is 100% normal when you have a BOV, an aftermarket exhaust, and MAF's sensors. I love those backfire pops, lol....

Good luck
Mitch

Thanks for the awesome info guys.

Ah so the HKS BOV has this problem? It has been a year and I really haven't touched it. The popping sound at idle happens maybe twice in 1 minute. I just had this problem recently out of the blue, haven't done any thing on the engine.

But what do you guys think about exhaust leak causing idle misfire? Actually, I have decided to put a flex pipe on my exhaust, it would hit humps regularly that's why. I was thinking maybe all those hit it took maybe it has a leak somewhere. I hate the fact that Apexi did not put any flex pipe on it though.

[cobrAA]

i love it too, don't fix it people tells me at the red light, I should bring my car right away to the garage because there's flame coming out

[Oakville]

those backfire pops on decel are unreal...i get them in my dads car all the time, tis a great feeling

[bellis_GTR]

One of the reasons why I got this car is to see flames! Still have yet to get one captured.

[Skym]

Only time my car threw flames from exhaust was due to stuffed o2 sensor. Unplugged o2 sensor, problem went away.

Pop on idle is normal because factory ECU tune runs engine rich at idle and mixed with o2 sensors telling ECU to run engine richer because engine is running too lean = idle rpm drops, engine misses. Then o2 sensors tell ECU engine is running too rich and ECU leans engine out and it stops missing, idle rpm rises. Gets worse if you have intake airleaks, as o2 sensors are picking up that there is a airleak and idle rpm fluctuates more.

If you want to check o2 sensors, hold at 2000rpm and count how long in seconds it takes o2 sensor voltage to fluctuate from lean to rich and rich to lean. Long time = o2 sensors are stuffed. From memory 5 sec each way is normal, but could be wrong. You're meant to check and replace stock o2 sensors every 40-60,000km.

On GTR, check intake piping for airleaks before and after intercooler. Sometimes that can be the cause.

[krarks]

Mine was popping on every decel (has stock recirc, 3" exhaust) and found an exhaust leak. Fixed the leak and the popping went away. Only can get the occasional pop on a very hot day. If you don't have leaks or symptoms of faulty o2 sensors, then I wouldn't worry about it man!

[Skym]

Exhaust manifold leak makes more oxygen enter exhaust and o2 sensor (o2 = oxygen) voltage goes down (more oxygen inside exhaust) and triggers lean trigger on ECU and ECU makes engine run rich.

[M13]

I used to get lots of backfire, but once I tuned my car, got rid of exhaust leaks, I only get little pops on high rpm decel.

[GodziRRa]

Still checking, it's driving me nuts since I know the car is running very rich. By the way, is it normal for a GT-R to show different voltage readings in the 2 MAFs?

[bobbo]

Yes but should be within .4 or .7 volts of each other.
You should download a service manual aswell. There are so many problems you can diagnose and trouble shoot with a volt/ohm meter and using the diagnostic mode in the ecu.
One thing I did was ask my local Nissan dealer to hook Consult (Nissan's diagnostic system) up to my car. They can go through all the sensor values, reset perameters and give you a printout of all of the information. They'll probably charge you for an hour of labour but it will certainly let you know what everything is doing.

[Skym]

On the stock R32GTR ECU, rich trigger voltage for o2 sensors is set at 610mv and lean trigger voltage for o2 sensors is set at 230mv.

o2 sensor is a 0-1V sensor or 0-1000MV sensor (multimeter at o2 sensor plug or ECU pinouts on ECU). So basically 1V is very rich, 0V is very lean.

I think at idle, should be around 0.5V / 500MV or 14.7:1 (stoichiometric) when converted to A/F ratio for stock engine.