exhaust poping

[Bournemouth James 0]

i have a popping noise coming from the exhaust when let of the accelerater, what does that mean?

[Bruno 4]

a popping noise ....exhaust ..let off the accelerater...

 

Its fuel burning in the exhaust, hence the extra sound of a mini explosion - sounding like a pop. Its caused by a number of things

(i) your driving tactics - loading up the injectors and then rapidly closing the throttle, leaving a ball of unburnt fuel on the next stroke (it can be done)

(ii) leaky valves - VR6s used fireball concepts in the head design, hence their valves need to be tight

(iii) cam timing off, or an excessively hot cam for a car that has a catalytic convertor still plumbed in (if you have put in a wild cam then you need to get the ECU remapped)

(iv) plugs not firing at the right time with a rich fireball waiting..,

(v) a combination of the above.

 

Check your plugs, leads, throttle body. Make sure they are all clean and sorted. Then if that makes no difference, get a VAG 1557 on it and check for cam sensor pulse problems, or O2 sensor failure. If they look OK, then get a compression check done by someone who understands these things and search for a leaky valve set.

 

If its that obvious and its a VR6, I suspect that two cylinders, not one, are affected - one cylinder is unlikely to upset the balance enough for the popping sound.

 

Is it a problem? YEP. Unburnt petrol wrecks your cat convertor and that is expensive. Cheaper to find the problem quickly. My garage took a year to find it and then sheepishly told me that the cat had been wrecked by petrol, but of course that wasnt their problem....!

[Bournemouth James 0]

if its any help, its 20v turbo engine

[dubster82 0]

If you dont have a cat? is it then, not a problem? :D

[LowG 0]

check spark timing on the distributor,advanced or retarted timing can cause this and also have an effect on your fuel consumption.

[Bournemouth James 0]

Would a dump valve help this problem, or am i barking up the wrong tree here?

[dubster82 0]

think you'r barking up the wrong tree, the dump valve just lets the excess boost out to let your turbo spin up quicker.

 

Welcome to the world of Forced induction :)

[Andi 2,147,483,647]

think you'r barking up the wrong tree, the dump valve just lets the excess boost out to let your turbo spin up quicker.

 

Welcome to the world of Forced induction :)

 

Dump valves redirect the vacuum caused when lifting off the gas to change gear (under acceloration), therefore allowing the turbo to freely spool-down, not be forced to a complete stop, then have to spool up from 0rpm when the gas is pressed again in the next gear.

 

I get a pop from my VR6 at 1.5k revs. Good fun blipping the throttle in traffic when bored. Only ever done it since the Miltek was installed though. However, I wouldn't be suprised if my 190k mile-valves are quite as tight-as-a-tiger as they used to be.

 

My MX5 used to burp flames like a bitch. But that was aggressively retarded cam timing. This is probably the same for the 20v Turbo - it'll be setup to get the best fuel/ignition timing under hard accelloration, as opposed to a more economical setup.

I wouldn't worry about it in the 20vT. You ever seen V8 Supercars racing in Australia? Watch them as they change down gears for corners... ;)

[Kevin Bacon 5]

Exhaust popping (or fuel explosions) is normally caused by a defective or missing over-run cutoff circuit.

 

Engines need some way of returning the fuelling to base idle level otherwise the engine just acts as a big air pump blasting unburnt fuel into the exhaust.

 

16Vs do this by pulling the air metering flap down on over-run.

 

VR6s (and AFAIK, G60s) control over-run shut off electronically based on measurements fed to the ECU from the numerous sensors.

 

If not that, then your valves could do with regrinding as Bruno pointed out, but if your'e going to do that, you may aswell rebuild the whole head!

 

Kev

[Beetlebug_2001 0]

Could it be a hole in the exhaust 2? my manifold gaskets where screwed on my old beetle and it caused it to pop when backing off the accelerater, i thought it sounded cool so i left it :lol:

[HiAsAKite 0]

My GTi does the same when the exhaust is about to go..... sounds fantastic as I come off the accelerator as it coughs and pops... but in truth I know the exhaust is about to go..

 

 

Where is the sound coming from... is out the back of the exhaust, or somewhere else? if somewhere else it may be the exhaust leaking..

[Dboy 0]

if its any help, its 20v turbo engine

 

gwaaan u bad boy 8)

[Bournemouth James 0]

The car has a magnex performance exhaust (noisey) and has no cat fitted, but the engine should have a cat, could this be a reason?

[Bruno 4]

The car has a magnex performance exhaust (noisey) and has no cat fitted, but the engine should have a cat, could this be a reason?

 

Now yr talking. Your ECU map needs to be redone. You've got two problems with a no cat system (i) NO oxygen feedback to the ECU (whoooops); and (ii) unburnt fuel in the exhaust line. Most VW ECUs bias the opposite way to Ford ECUs, ie they run rich and require the lambda probe to pull back the timing and drive up the oxygen ratio. If you dont have a cat, your lambda probe shouldnt be there any more. Now unless you ran an intake mod and remapped the wire-only-ignition that seems to be where the problem is.

Assuming u like the no-cat system (I dont understand how you get thru the MOT) your only option is to have it remapped.

 

If Im right thiscould be replicated by driving up a hill, foot down. As the car gets to the top and the revs become easier and the engine works less hard, you the immediately lift off completely and - it should pop.

[W3RKD 0]

hi guys been having a read through this thread... and even though the car has no cat surely it must have a lambda probe in the bypass ?? also what management is it running james?" and what spec is it tuned to ? personally i wouln't worry to much about it as long as you do have a lambda probe in there and everything is running correctly.

[Bournemouth James 0]

its the standard golf ECU, in standard 150bhp form

[G60Jet 1]

i get flames lighting up the tunnel on the way to work each morning, just need to change down, boot it and blip the throttle changing back up and if you get it just right the exhaust pops and you can see the flash in the mirror nothing to do with the problem you've got but i like it!!

[kongo127 0]

Hi guys!

I have exactly the same exaust popping! I can avoid it if i advance manualy the timing turning counter clockwise the distribuitor just a little before knocking occurs! The car runs much better and quicker of the line! The popping dissapears!

But everything points to a dead lambda probe. Because there is no oxigen feedback to the ECU and automaticly it runs rich (to much) and that is why we need to adjust manually the timing, because the ECU doesn´t make it! And the fuel gets burned in the exaust! The best thing to do is to buy an Original Bosch Lambda Probe!

And the car seller told me that had to remove the catallitic converter, because it was noisy (looks like a coffee can with some coins in there). So i really believe it a faulty lambda probe!