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Exhaust Backfiring & Sooty Exhaust

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My car has been backfiring since i got it really and the bumper around the exhaust is pretty sooty. It also smells nicely of petrol and isnt so economical. I've had a lot of people look at it and no one can seem to work it out, my last step is to take it to NI$$AN which i dont really want to do unless i have to.

I've just replaced the BOV to a Forge on (recirc) and this didnt seem to help. I havent been able to see if its still producing soot, but there is still banging..

If anyone has an idea of what it could be.. it'd be helpful. I've been assured the mixture in combustion is fine as well, which is why I changed the BOV as this is after the initial combustion process.. but anyways, advice please!!
 

DeanS15

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bov isn't to do with the process of combustion mate, it's afm readings not tallying up with the air in the combustion chamber that causes overfuelling and rich running. have you cleaned your afm element and plugs as a precaution? also see if you can check that the lambda sensor is working correctly - but in all honesty it sounds like its dump valve related to me. if you changed from a vta back to recirc and it didn't make a difference then i'd start looking at how the valve is plumbed in to make sure it has a correct source - make sure the valve isn't sticking etc, then check for boost leaks but this is normally accompanied by loss of power as well as lots of funny pops/bangs and smoke. i wouldn't take it to nissan for diagnosis as they will probably take ages to find the problem and charge a bomb to fix it ;)
 

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also see if you're timing is correct - if it's out then the egt 's could be through the roof and this will cause a lot of pops etc too
 
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it was using the standard recirc bov, but i swapped it for the forge recirc that you guys recommended, and that didnt help. i've swapped a lot of the boost pipes around and tightened them up and cant 'feel' any leaks (had my dad assist in checking for leaks)..

i'l go clean the afm element now, and the spark plugs have only got about 1000 miles on them (NGK Platinums) as the last ones were 'hanging out'. havent checked these since fitting, but again, they didnt solve the problem when i did change them. where abouts is the lambda sensor?

also it boosts to 0.5 happily, and only goes to 0.6 when its nearing 6000rpm and doesnt go higher. engine is standard bar hks air filter & i believe the exhaust is aftermarket, but not a 3'' system. oh and got a decat fitted, but problem was there before that.
 

S15_SAM

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I wouldn't clean your AFM mate as they don't take kindly to it, you'll just damage the hot wire. What symptoms have you got, I.e is it stuttering under full throttle, partial throttle, or is it really missfiring under heavy load? Or when it comes on boost?
My AFM was causing it to very slightly hesitate under partial throttle and only slightly when on full throttle. Put a second hand one on and bingo it is perfect.
 

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cleaning is fine if you do it with a solvent spray like brake cleaner and just spray the element.....
 
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Ok well i've had a look at the AFM sensor and to be honest it looks brand new. but never the less i gave it a wipe down with some little bits of cotton wool. checked the spark plugs and theyre pretty black looking, so i wiped them down. I re-gapped them too to 0.75mm to see if that makes a difference (did a google search and picked the middle number) as they were previously around 0.9mm i reckon. just did a foolish thing too and over tightened a jubilee clip on the boost sensor and snapped the connector. so just had an effort trying to make that airtight using all sorts of clips and glue. will have to see how that copes under pressure later once the glue has set properly.

SAM - no stuttering under any throttle, it used to last year when it was cold but seems fine now.. i'm not sure how to diagnose misfiring though. help?

Dean - where is the lambda sensor mate? i've checked all boost pipes and theyre all as tight as i'm willing to do them so dont think i've got a boost leak.
 
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Lamda sensor is bolted into the turbo elbow. I've been told to replace mine as it's running rich on idle and at low revs. AFR starts off at 14 then levels out to 11.8 in higher revs.
 

S15_SAM

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Well you'd know it was missfiring. You can't really tell if your AFM is good by looking at it mate, it all works off small wires etc and is a reduction in their sensing abilities which causes a fault. but doesnt sound like AFM fault anyway.

Hmmm tbh it's impossible to diagnose stuff over the Internet, if your competent enough mechanically to change your o2/lamda sensor then try it (located in the turbo elbow, near the baulkhousing and exhaust manifold) otherwise I would suggest taking it to horsham developments, or someone experienced with nissans sr20.
 
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Lamda sensor is bolted into the turbo elbow. I've been told to replace mine as it's running rich on idle and at low revs. AFR starts off at 14 then levels out to 11.8 in higher revs.
ah cool cheers. whats AFR? and how much is a replacement sensor and where can you get it from? please dont say nissan.jp haha
 

S15_SAM

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Ok just seen your in York, that's abit far to horsham. But have a look on sxoc traders section for one of the garages closest to you and book it in. It could be impossible for you to find the fault by guessing.
 
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Ok just seen your in York, that's abit far to horsham. But have a look on sxoc traders section for one of the garages closest to you and book it in. It could be impossible for you to find the fault by guessing.
theres no one up north that i've found who has a clue about the sr20 haha. even when i tell them its the same engine as a uk spec s14, they still arent having any of it.

I found replacement lambda sensors on the horsham website, and i've got access to a pit so i can jump down and clean the sensor without too much hassle (hopefully).
if needs be i'l get a replacement as theyre only £70, and if that doesnt help, at least i'l have a spare haha.
 

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lambda sensor is in the turbo elbow mate - the plug and wiring are attached to the original bracket above the exhaust manifold. there should be a guide to testing it in the workshop manual - it involves monitoring the output voltage on the black wire of the afm to earth at certain rpm's but i don't recall the specifics... i will have a look for more info. it would be handy if there was someone local that you could borrow the bits from, such as swapping afms and sensors and seeing if it does the trick. then you know which part to replace ;)
 

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It may be worth buying yourself a copy of DataScan and a consult lead too. Then you can check your fault codes, monitor live read-outs etc too..
 
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Cheers Dean!

It may be worth buying yourself a copy of DataScan and a consult lead too. Then you can check your fault codes, monitor live read-outs etc too..
Unless DataScan is mac compatible, then its a no go :( thanks though!
 

craig8585

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You must know someone with a laptop that runs Windows! :p Just an idea to save you paying someone to do the same thing for you..
 

S15_SAM

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Just do some research on garages up north as if you don't know where or what a lamda sensor is you'll never fix it tbh mate.
 
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Just do some research on garages up north as if you don't know where or what a lamda sensor is you'll never fix it tbh mate.
i know what one is and i just wasnt sure where abouts exactly it is, instead of having to scout the whole exhaust for it.. :rolleyes:

be positive! if you never try you'll never get anywhere in life! :)

You must know someone with a laptop that runs Windows! :p Just an idea to save you paying someone to do the same thing for you..
Maybe i'll do that.. haha

Links if anyone is interested:
Cable - http://www.blazt.biz/products/cable.php - ~£37
Software (Nissan DataScan I) - http://www.nissandatascan.com ~£33
 
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My brothers s15 pops and bangs and had a slight missfire, Horsham diagnosed it to be the knock sensor playing up? You could try getting it plugged in and checking that??
 
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My brothers s15 pops and bangs and had a slight missfire, Horsham diagnosed it to be the knock sensor playing up? You could try getting it plugged in and checking that??
cheers mate, looking into getting DataScan now :)
 
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