Backfire On Decel And Idling After Some Full Throttle Runs. Fairly Stock R33 Gtst

[benl1981]

Need some advice on this. Have read a few different threads.

Details:

Car runs stock bov. 10psi boost stock airbox and turbo. R33 gtst. 3" exhaust turbo back with unknown brand of cat and stock ecu

Problem:

Car runs ok using 10psi. However if you do more than about 4 or 5 bursts of full throttle there is some big bangs from exhaust on decel and you can even hear small bangs when back at idle.

Tps signal seems ok. Checked that on the PFC. Will switch to PFC once I get the Wideband in but would like to sort this first

Exhaust doesn't appear to have a leak. Not sure how old cat is.

When I changed the exhaust the mechanic thought there may be hairline crack in exhaust manifold but there us no soot or any signs of leak from it.

Problem may be slightly worse after fill up.

It still has a charcoal canister connected but one of the pipes on top of engine is blocked off. I.e only one line going to canister so assume no feed back into engine?

What I though it could be:

1. Leaky injector. But wouldn't it not just be after a number of runs.

2. Exhaust leak. Can't see soot anywhere or hear any leaks

3. Overfuel of stock ecu. I had a previous r33 that got down to about 9:1 and still didn't bang so don't think it's that. Running lower boost doesn't seem to change that much

It's just strange that it's only after car is really warm etc that it does it.

The exhaust installer did say the manifold looked as if it had been quite warm at some stage. Metal is very grey from heat. But I think most manis look like that after a few years..

One strange thing that after a fuel fill up I can sometimes hear a vibration noise that cones and goes from near the filler cap.

I opened the cap and the noise stopped and sounded like a pressure release. So might need to check that out. But if there is no return in the charcoal canister and the fuel injectors are shut on decel this shouldn't really be causing the issue

Sorry about the essay.. Got a few things to check I guess. Anyone had this or got ideas?

Cheers

[Manuel Kasko]

My guess is your cat had gone.

Collapsed most probably if it's the stock one.

My car never used to do it but now does it because it's got no cat.

[benl1981]

Thanks for that. So are your symptoms similar. After a few full throttle runs it starts banging on decel etc.

I might try another stock cat I know worked fine then

[Manuel Kasko]

Yeah after a few runs it will be running rich to protect the motor and thats when it seems to bang.

I can do a brap here in there then on decel it will pop and play up.

Shouldnt be to worried.

Maybe chuck the FC in and get it tuned for the boost its running?

[benl1981]

Can somebody tell me where the charcoal canister lines run?

Near the crossover pipe there are 2 small tubes.

The top one runs to the charcoal canister (looks like after market as mounted lower than the stock one)

The bottom tube has been blocked off.

Is the bottom one the feed back into engine?

There seems to be some pressure build up in the fuel tank. You can hear some noise around the cap when fuel tank is close to full and when you undo the cap there appears to be quite a release and noise goes away .

I wonder if this has anything to do with the backfire I.e an incorrect functioning fuel tank vent

[benl1981]

Can somebody tell me where the charcoal canister lines run?

Near the crossover pipe there are 2 small tubes.

The top one runs to the charcoal canister (looks like after market as mounted lower than the stock one)

The bottom tube has been blocked off.

Is the bottom one the feed back into engine?

There seems to be some pressure build up in the fuel tank. You can hear some noise around the cap when fuel tank is close to full and when you undo the cap there appears to be quite a release and noise goes away .

I wonder if this has anything to do with the backfire I.e an incorrect functioning fuel tank vent

[GoHard]

Dude, one of the lines comes from your tank to vent fumes. MAKE SURE this line has not been blocked off...

[benl1981]

Thanks. Yes - that sounds pretty important!! Is this the one? Looks like the hose is crushed and quite old..

Anyway - the setup doesn't appear stock. Will need to look at it. It's a huge canister mounted low. See some photos.

Hopefully fixing this may alleviate the issue.

[Manuel Kasko]

The hose that has been blocked should run back to the canister.

Dont know what the f**k they would block that.

I will try get a photo of how mine runs this afternoon and post it up for you

[benl1981]

Thanks mate that would be great. If you take a photo near your canister also that would be good.

Looks like someone has fitted a bigger charcoal canister at some point and botched the standard setup! Might try and get a stock canister and plumb things up as per stock

[Manuel Kasko]

Send me a pm with your number and ill send you a pic at lunch time

[GoHard]

I found these diagrams a fellow forum member posted up if it helps.

Cheers Browny!

Edited July 9, 2012 by GoHard

[ARTZ]

What's leaking out of your intake pipe?

[GoHard]

What's leaking out of your intake pipe?

Who-oah! das sum bad ass blow by

[jattsta]

i did have this issue once aswell with a mates 33.. seemed to have fixed it by putting on a pod..

[benl1981]

Hmm. Think it's been like that for a while re. wetness around pipe.

Might have to check the PCV and around turbo.

Engine doesn't blow any smoke and doesn't use any oil so dont think blowby could be THAT bad??

There isn't any leaks around the rocker covers which is where you would expect it if it way that bad??

thanks

[benl1981]

Thanks guys.

Problem solved. I think the vent into the canister was being blocked causing the backfire.

Seems to be all good now with it venting..