I think the long-anticipated exhaust valve trouble may be rearing its ugly head on the missus's Fabia. 

AZQ-code, 1.2/12-valve engine at 174k miles. 

I bought a spare head about 7 years ago, after learning about issues with these engines: I think now might be the time to bring it into service.

 

The engine has been sounding steadily louder/exhaustier over the last couple of years, despite many attempts to remove all possible leaks in the external exhaust system.  Just recently it has got noticeably less smooth at idle, and driving it briefly yesterday morning, pulling away forward or backward at low revs feels like the engine's trying to jump out of the bay. 🙄

 

I suspect the idle unevenness is imbalance between cylinders caused by exhaust valve leakage; and this extreme jerkiness at low rpm is full-on, total misfiring of the affected cylinder(s).  Anyone agree, or got alternative explanations?

 

It still seems to run fine above idle, returning slightly above long-term average mpg, Hoping it will get home from its current location today, a reasonable distance. It's done same journey the last 3 weekends so I'm hopeful. Got a solid yellow emissions warning light halfway home last weekend with an upstream oxygen sensor code. Cleared and didn't re-appear during the week.

 

Any way to inspect the exhaust valves nicely with head still on?

 

I've borrowed a little USB camera that'll go through spark plug holes OK, but not sure I can get it to look upwards very easily, needs a teeny mirror that will have to go in ahead of it. 

 

What about with exhaust manicat off? Can't remember how much might be visible through the exhaust ports?

 

I don't have leakdown test gear, whatever that consists of. Compression tested relatively recently with good numbers IIRC.

 

Good compression figures = valves seating ok

 

First thing to try are new plugs (~£7 for a set of 3 bosch at ECP etc) and a healthy dose of fuel injector cleaner.

Could be some uneven carbon build up on inlet valves if its a bit of an oil burner. Fuel system/injector cleaner might help along with a good old italian tune up.

 

Might also have a weak coilpak, if you have a spare try a swap.

Thanks xman. There was a recent thread on a Polo forum in which a car (6-valve) had passable compression figures despite significant damage to two out three exhaust valves. I think this is possible due to the 'ratcheting-up' effect where the compression doesn't come back out of the test gauge, until reset between cylinders. I seem to remember that the test which concluded the valves were at fault was a subsequent leakdown test. @Tech1e has also often recommended this avenue of investigation if memory serves.

 

Will check plugs and coils anyway ta. 

Also have a spare set of injectors somewhere that were cleaned by someone on here so long ago that I've forgotten his name.

You wouldn't see enough of the valves through the ports with the camera I reckon. Check on your spare head?

Edited 21 June, 20205 yr by TMB

Great thought about checking on spare head! 😊

Today's very good news is that the car made it home, and its owner is not unduly perturbed by the idea of it 'going under the knife' shortly.

1 minute ago, Wino said:

Today's very good news is that the car made it home, and its owner is not unduly perturbed by the idea of it 'going under the knife' shortly.

 

Nice one. Dr. Wino can now proceed 😁

Hi ive recently bought a polo from the garage where i work at with a few issues. 

Firstly it failed the emissions on the mot.

second it started misfiring at idle but intermittent. 

Did compression all were ok so i assumed the valves were ok.

i removed the head to fit a headgasket as it had failed and was shocked to see how bad these valves were. 

If you zoom in they are the worst ive seen considering it ran not to bad tbh.

Replaced the valves and the valve guides.

Apparently its the guides which cause the issue.

Anyway doesnt really help you checking yours but just shows how poor they are.

passed the emissions straight away after!

^ Wow, look at the state of those!

1 hour ago, TMB said:

^ Wow, look at the state of those!

Bad arnt they!

 

11 minutes ago, Damo152003 said:

Bad arnt they!

 

 

Sure are mate.

18 hours ago, Damo152003 said:

Bad arnt they!

 

Odd how cylinders 1 & 2 exhaust valves are really badly cracked all around, but cylinder 3's is completely fine as far as I can see in that photo.

 

Anyhow, no wonderfully positive progress to report from a bit of work on ours.  

 

Took the spark plugs and coils out for a look, nothing to see. No codes for misfires, so nothing to go on in terms of swapping anything out, even though I do have spares.

 

Swapped in the refurbed injectors; no obvious change to anything. ☹️

 

Should've done another compression test while the plugs were out, but didn't think of it in my haste to check whether the injector swap had fixed things.

 

The symptoms are much worse during first minute from cold start, if that helps anyone form an opinion. Still very jerky to pull away at operating temp, without adding revs that never used to be necessary.

 

Couldn't see anything useful with USB camera

 

 

So many things to try, too much glumness ot do anything at the moment

 

 

Edited 22 June, 20205 yr by Wino
Numbering correction

Maybe makes no sense but how about cleanliness of the throttle body

 

 

TB is clean, but thanks.

 

I booked it in to a local garage for a leakdown test on Wednesday, then phoned back just now to ask what that was going to cost, cos I forgot during the first call. 

Spoke to someone different who helpfully admitted that they don't actually have leakdown test kit! 😣  Cancelled that one...

Edited 22 June, 20205 yr by Wino

Just redid compression test, and all about 15 bar.

 

Had a moment of hope when one of the three coilpacks had some little bumps in the top surface, the other two being smooth and flat.  No change when swapping in either of a couple of spares. 😞

Might do similar swapsies with cyl 2 and cyl 3 coils later. Belt and braces.

 

Next stop after that: lambda sensor investigation I think. The 16514 (B1S1 malfunction in circuit) - intermittent had returned, although not enough to put the fault light on.

If that throws up nothing, try to find another garage that will really do a leakdown test...

Might have to check for chain stretch too; just in case that could be the elephant in the room. TDC no.1 and see what the cam end slots are up to.

Just realised that with two spares available, I could test the remaining two coilpacks by substitution in about 5 minutes flat, in one hit, so I did.

It's not them. 

 

I imagine it wouldn't take much valve damage to make a three-pot engine run roughly. Hopefully a leakdown can shed more light.

 

I've read that the timing chains can jump on these engines but the engine would surely run like crap all the time if that was the case. Be interested to see what your valve timing check shows.

Edited 22 June, 20205 yr by TMB

A leakdown test is unnecessary with such good compression, it simply tells you whether the valves or rings are responsible for a low compression reading.

 

I'd be looking for an air leak somewhere, try misting all the inlet joints with washing up liquid solution and look for a telltale.

Isn't air inlet under vacuum?

33 minutes ago, pavinjo said:

Isn't air inlet under vacuum?

 

Yes, unless someone fitted a turbo when I wasn't looking.

 

Got a NOS genuine pre-cat oxygen sensor arriving (hopefully) tomorrow, bargain at <£35 delivered from the bay of e. Took some logs this morning and I think there may be something amiss there. The (only) fault code points to a problem with it; so it seems nutty to ignore that. Can't see anything obviously bust wiring-wise. 

 

Can't see anything wrong with the chain timing, although it's a bit tricky to be precise about TDC when you don't fit the crank locking tool, 'cos you've convinced yourself that it's pretty close and so probably isn't the issue. As you say @TMB, if the chain had jumped a sprocket tooth, or was overly elongated, it ought to run poorly all the time, not just in one small area of the operating range.

 

 

 

 

3 hours ago, pavinjo said:

Isn't air inlet under vacuum?

 

You get a slurping noise and some foaming, try it, you might like it.

It seems like the answer to the thread title is no.

What I should have asked was - is it time for a new pre-cat oxygen sensor?

 

Replacing that seems to have restored correct function, according to a chirpy voice message I just got from its owner, on the road.

Fitted and immediately took some logs yesterday, static and on a test drive.  Will review the data later, but it felt better if not perfect straight away.

 

Thanks for the suggestions and comments. 

 

 

Glad it turned out to be a much easier fix than taking the engine apart 👍

Spoke too soon actually Lee. Bloody thing went into limp mode a couple of miles from destination.  Cylinder 2 misfire code plus the precat lambda code. 

On the end of a whatsapp video chat she's just swapped out cyl 2 coilpack and is heading out for a short range test drive...