Loud 'POP' and blue smoke

[mackat]

Just went to start the 6 and as the engine was turning over there was a loud 'POP and loads of blue smoke - Am I correct in thinking that's a blown head gasket?

[thododd]

Not necessarily.
Blue smoke suggests burnt oil, so it COULD be that the HG has failed between and cylinder and an oilway, but it could also be a valve stem or piston rings

Have you got a compresion tester? That ought to rule out the rings.
Id also check your oil/ coolant for mayo (classic HG fail sypmtom) and whether the oil level has dropped

[mackat]

nah dont have a compression tester.
Did a oil change before driving to Scotland for xmas, I've covered over a 1000 miles and I've been for a drive couple hours before the pop.

Managed to take the spark plugs out before the rain started and they are looking very black..

[ginge191]

Does it still run? Sounds of it running? Does it crank?

[mackat]

Does it still run? Sounds of it running? Does it crank?

yes/no - pulled the battery terminal just in case a fire started (the first thing that went through my head) Once connected again, started up but proceed to rev out, so cut the ignition. Started again but died straight away. Third time gave some gas and it runs very rough, but need to keep my foot on the gas to keep from stalling.

[Redordead89]

Valve guides can blow blue too!

[adam b]

I'd say you have an electrical issue somewhere and it's overfuelling.

---

It wouldn't rev out and then not idle if you'd blown the hg or a ring. The pop was probably a backfire, maybe through the inlet

---

If turns out to be fuelling I'd change the oil again before using it.

---

If it's on a gti 6 check the resonator under the inlet manifold. They can pop loudly.

[thododd]

Wouldnt overfueling produce black smoke? It could explain the backfire/'pop' and black plugs though
The exhaust ought to stink of fuel too

[cully]

---

If it's on a gti 6 check the resonator under the inlet manifold. They can pop loudly.

this!

if you had a blowback this can split the resonator box then ther will be no idle control as air is free flowing into the manifold via the crack in the box

[mackat]

Thanks for the replies Chaps -


These are the state of the plugs:
   

Would say they have about 3000 miles on them by now.

Checked the oil and coolant levels, both are good. No leaks or puddles on the drive.

Cleaned the plugs up, dropped them back in, started the engine up and it does the same thing.
1st turnover, starts and then bounces off the redline
From then on starts but without any throttle it dies.

What are the normal symptoms of a blown HG?

I'll have a look at the resonator when I'm next outside. How could this blow?

---

---

If it's on a gti 6 check the resonator under the inlet manifold. They can pop loudly.

this!

if you had a blowback this can split the resonator box then ther will be no idle control as air is free flowing into the manifold via the crack in the box

Yes - it's the 6.
If I have free-flowing air wouldn't the engine rev out every time I started it?

[Niall]

Them plugs dont look bad at all tbh. The electrodes have been a bit damaged suggesting its not been running right. Your initial issue is going to be a fuel mixture issue but we can deal with that once you've found the issue with the high revs.

Its not a HG mate. As others have said, there is a resonator on the bottom of the inlet manifold. When these backfire it can blow the join apart on that resonator meaning there is unmetered air getting in hence your bouncing from the red line.
Take the manifold off and have a look at the resonator. Id put money on that being fooked.

These GTI engines dont blow head gaskets that often at all but if they did it would be the same symptoms of any HG failure. Loss/mixing of coolant/oil, pressurised coolant system, over heating etc etc.

[adam b]

They tend to just work but slightly lumpy with a blown hg.

[Paul_13]

If the resonator has cracked, it will suck in unmetered air and red line then cut out.

I had my resonator bung pop out and it did the same

[ginge191]

I was going to say resonator box; hence asking the above.

I'll put a fiver on it

[mackat]

Thanks for the replies fellas!!

Is there anyway to check without taking the inlet off?
And if I did take the inlet off, is it better to leave the fuel rail on and would I need a new gasket?

[Paul_13]

Take the inlet off as a whole, easiest way. Don't undo the fuel rail

[mackat]

New gasket afterwards or would i be ok to use the current one?

[cully]

its a paper gasket so it will be destroyed when removing the inlet,
so a new one will be needed

[mackat]

its a paper gasket so it will be destroyed when removing the inlet,
so a new one will be needed

Thanks

[mackat]

This morning I've managed to get more light into the engine compartment without taking the manifold off.
And Chaps, you're all right! The resonator has split down it's join and a nice hole blown off the corner.

Question now is, do I buy another resonator or do I buy a bung?

Also why would this have happened?

[Paul_13]

Bung!
I may have one lying around if you're in need

Back fire from a cylinder?

[cully]

cool now just fix it !

[Niall]

So now youve worked out the cause of the over revving, you now need to work out why its back firing. If you have a friendly garage near by, i would suggest getting an emissions test then we should be able to see whats going on from there.

[mackat]

Bung!
I may have one lying around if you're in need

Back fire from a cylinder?

Will give you a whatsapp chap - think I still have your number

---

So now youve worked out the cause of the over revving, you now need to work out why its back firing. If you have a friendly garage near by, i would suggest getting an emissions test then we should be able to see whats going on from there.

It's only just gone through its MOT, it did fail the first time with emissions, but by a very small percentage.

The mpg on the way up to Scotland was around 35.7 which is I think is good for a 6. Haven't worked out the mpg on the way back down yet.
But there is always a smell of fuel on startup until the engine warms up.

[Magenta Sunset]

slightly too rich?

[adam b]

Bet it's fine if you just start it. No back fire, just the plastic has failed due to age

---

PS - I win.....

[mackat]

Wanted to say thanks for everyone's help -

I thought it was a small hole in the res, apparently not:

   
   
   

I've installed a bung and fired up first time, although now it sounds a little off.
Sounds like a misfire or something else?

[cully]

video the engine sound not at the exhaust

[mackat]

 

The engine sounds ok me thinks:

[Eeyore]

wow that is really broken haha. the box not the sound!