Excess Backfiring All Of A Sudden?

[TommO]

Well today I went to Bathurst and back and came across a problem with my car.

After a hammering, it would backfire really really badly when off the accelerator... like one every half a second or so. It would do this constantly until the clutch went in and it idle'd down. It progressivly got worse during the day.

Also something that the car has always done, but got much much worse today (when the back firing started), is that the car won't idle when first started after a > 5 minute break.. I'll have to hold the revs up, or it hunts for an idle between 100rpm and 1500rpm... .... however after I drive it through a couple of gears, and clutch goes in, it idle's fine ??

Any help would be great. I'm always scared of my car running lean

[gun32gtr]

yeh noticed that tommo...hope it gets sorted mate

[GTRsean]

my car hates hot starts and just dies after trying to correct itself. usually you have to keep the revs up via throttle input. A temp sensor issue?

[d00dz]

Checked the sparkies?

[Lazy-Bastard]

backfiring could be an exhaust leak, maybe you spat a gasket somewhere along the line

[Links]

Mone does this - however not constantly.. it'll pop 3 or 4 times. when I back off the accelerator.. even 10/15 seconds later.. my thoughts are excess fuel being burnt + the temperature of the engine..

similar with restarting when warm.. has issues occasionally and dives down to 500rpm sometimes your issue seems to be a bit more hightened..

Could be a faulty sensor somewhere would be my thoughts.. see if it does it this week..

[benl1981]

clean your afm for a start possibly - using either contact cleaner or brake cleaner

[XSIVE]

the hunting at idle is pretty common for skylines, usually relating to the oxygen sensor, its probably filthy, or f#@ked, get a new NTK one from Petroject for about $100-120 and should fix your problem. May have something to do with AFM too so i'd probably try cleaning both the oxygen sensor and the airflow meter and see how it goes after that.

[TommO]

Thanks guys,

I'll pickup a new O2 sensor (it's good mainteance anyway) and clean the AFM on Wednesday and let you know how I go.

If it doesn't resolve the issue, i'll get new fuel filter / spark plugs, as I've gotta change my oil this week anyway.

Hopefully that resolves all the problems.

Cheers!

[C_DawG]

Sounds like what mine started doing right before the fuel pump died.

Was missing a bit and popping when I backed off. Went to start it the next day and it wouldnt fire! Turned out the pump was fubar, took it out and gave it 12V and it would surge then, stall, surge then stall. Just stuck a Bosch one in.

[GtstCoupe]

yeah my cat back came loose and would pop and backfire heaps not to mension the car was louder

[TommO]

Interesting point on the exhaust, I could defintely here a few weird noises from it over the last two months and then it stopped a couple of weeks back. I might take it to an exhaust shop and get them to chuck it on the hoist.

I've got a Walbro 500HP fuel pump which has a 12V connection, so unless thats having problems I don't imagine it will be that.

Cheers again for all your help and ideas,

Tommo.

[TommO]

Replaced fuel filter and put it on the dyno last night

Everything checks out OK, AFR's are all normal and timing is fine.

So it looks like it's simply a dead cat... getting a new 3inch cat and dump pipe put in today to rectify this

[Scandrew]

How does a dead cat cause popping? My car backfires and pops a lot as well. I heard my exhaust making weird noises as well.

[TommO]

Not sure on that one mate, i'm simply going off there recommendations

Either way the muffler is great very ver hot due to the dead cat

[morlock]

if the cat is stuffed then basically the exhaust temps are increased and causes backfiring.

[Amaru]

Well today I went to Bathurst and back and came across a problem with my car.

After a hammering, it would backfire really really badly when off the accelerator... like one every half a second or so.  It would do this constantly until the clutch went in and it idle'd down.  It progressivly got worse during the day.

Mine does this after longggg drives as its just the exhaust getting extremely hot and burning every single bit of fuel going through the exhaust whereas it would normally just spew it out as black smoke.

Also something that the car has always done, but got much much worse today (when the back firing started), is that the car won't idle when first started after a > 5 minute break.. I'll have to hold the revs up, or it hunts for an idle between 100rpm and 1500rpm...  .... however after I drive it through a couple of gears, and clutch goes in, it idle's fine ??

Any help would be great.  I'm always scared of my car running lean 

<{POST_SNAPBACK}>

Just sounds like the air intake temperatures are very high. I have noticed on my Power FC if the inlet temp is above 50 degrees (which happens quite easily after youve hammered your car, turned it off and it just heat soaks through the engine bay) it doesnt want to start and idles like crap until you drive for a bit to bring the temperature back down.

[jezzerrr]

I had the annoying idle hunt, pulled out the aac vavle and it looks like it's brand new! so i did the second thing that i suspected, and thats that little thing on the back end of the plenum (not sure of it's name). pulled it off, pulled it as apart as i could, soaked in in petrol and scrubbed it as best i could with a brush. The piston that looks like is regulates air was very carboned up, and now that it's clean I have a beautifully smooth idle! although it idles a bit high at the mo.

I have the exact same problem with my exhaust! I thought it was just running rich, I should have been wise to the leaking gasket possibilty.. plugs were changed 15000 k's ago so I dont thing they are a problem. I have suspected that my cat is shagged for a while as it has an annoyingly loud vibration at around 2000 rpm. so I'll be checking for fooked gaskets first, and then I'll be replacing that cat!

So how did you go Tommo? what was your cat worth? Lucky me, mine came with a dump pipe i think it's still the standard cat too, so I might be up for a little power increase that's if i dont find out that the vibration is a piece of turbo !!!!

[Duncan]

Thommo I reckon it is a leak on the intake or exhaust side somewhere. The engine gets the wrong amount of air compared to what the afm tells it. Is it only when there is no boost? The leak might be sealing under boost but sucking air in when under manifold vacuum.

[TommO]

I think I found the main cause of the idle problem today actually. Was out playing around with tools and acting like I know what I was doing!!

Anyway the gasket between the AAC valve or whatever and the manifold (where there's the two bolts from the valve into the manifold, there's a gasket there)... the gasket looked pretty dodgy, so got out the socket set and tighened it up so it was a better seal... and I did 100km's today and it seems to idle much better.

Not sure if this was the pure cause of the problems, but combined with replacing exhaust and cat, and doing that, the car seems perfect now.... I'm getting my injectors cleaned next week as well (good mainteance) and getting a heavy duty clutch whilst i'm there, so i'll get them to have a check over everything too. I'll get them to put a new gasket in there as well to prevent any furthur issues.

Damn it's nice having a car that idle's smooth again...

Thanks for all your help and ideas - without it, I would have just sent the car straight to the mechanic, but I enjoy playing around and learning.

Edited October 7, 2005 by TommO