Airbox engine cover flap valve (engine pinking when hot)

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littlepolo
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Airbox engine cover flap valve (engine pinking when hot)

Post by littlepolo » Tue Aug 16, 2011 12:30 pm

I've had a longstanding problem, apparently one that occurs on many VW / Audi engines, in that the engine occasionally pinks under load (1800-2400 RPM) especially during hot weather. If I change down, and revs rise, the pinking stops. I checked all the usual things (plugs, coils, etc.), and even used an octane booster, but could not find an answer to this problem.

During a recent inspection, I decided to take apart the airbox (16V 1.4 BBY 2003) and found the flap valve that re-directs warm air from the exhaust manifold during cold temps. The lug on the flap/pivot seemed to be broken, and I thought it might be stuck open - feeding warm air to the intake at all times. I removed the flap and ran the engine without it. The pinking problem seems to have been reduced. It does pink at times, but not as bad as before.

Anyway, is it possible to get a replacement flap valve assembly? It seems to be part of the airbox... I guess its OK to run without it at the moment, but when winter comes it will affect warm-up times, and fuel consumption.

If you have the pinking problem you might want to take off your airbox, remove the air filter housing, then the housing (at the front) that contains the flap valve and see if its working or not. According to some information I received, you can use a hair dryer to open it (but I suppose that only works in cold weather). I read elsewhere that the flap is partially vacuum operated also.

Any other ideas on what might cause the engine to pink at times?

RUM4MO
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Re: Airbox engine cover flap valve (engine pinking when hot)

Post by RUM4MO » Thu Aug 18, 2011 9:20 pm

My wife has a late 2002 with a BBY engine (September build date), yes it does pink a bit and is always filled with either Esso or BP or Shell. Had car from new and have had the filter box open maybe 5 or 6 times but never noticed any problems with the air divertor - though I've never thought about that causing the pinking. I had always put it down to maybe low acoustic sensor output - or faulty acouster sensor, but never got round to trying to view that channel with VCDS if its viewable.

littlepolo
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Re: Airbox engine cover flap valve (engine pinking when hot)

Post by littlepolo » Thu Aug 18, 2011 9:50 pm

I thought maybe a hot air mixture in hot weather might affect fueling/ignition? Maybe not.

Do you mean the knock sensor? Would that be an easy swap/worth trying?

Thanks

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Re: Airbox engine cover flap valve (engine pinking when hot)

Post by RUM4MO » Fri Aug 19, 2011 5:45 pm

Yes I mean the knock sensor, I was always under the impression that when a knock sensor is part of the engine control system, that we humans would never be able to audibly detect any pinking as this sensor would hear it and back off the spark firing before it had got that severe.

littlepolo
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Re: Airbox engine cover flap valve (engine pinking when hot)

Post by littlepolo » Fri Aug 19, 2011 8:11 pm

Maybe that's it then. I'm surprised at how much it knocks, and only backs off when I lift my foot. But why only
in warm temps?

Incidentally, I found this interesting article. Not directly related to a VW 1.4, but the principles are the same.

http://dodgeram.org/tech/gas/Trouble/ping.htm

I might try a can of PowerBoost foam (decoke) first, as that's only 20.00, and the knock sensor is more expensive.

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Re: Airbox engine cover flap valve (engine pinking when hot)

Post by RUM4MO » Sat Aug 20, 2011 9:13 am

I have frequently thought about adding in some higher octane fuel, though nowadays higher octane probably does not mean that much higher than normal fuel. I used to treat my cars to Redex, but I reckon that the Redex currently being sold is not as effective as the previous stuff at clearing out any accumulated coke. With the previous Redex, it could be either used at normal "strength" as a regular additive or at double "strength as a cleaner - there is no such info/suggestion on the current containers. Also, I had always noticed an increase in MPG while running a full tank with a double dose Redex - a fact not just gut feeling, now with the newer Redex I have not noticed any increase in MPG while running on a dosed tank of fuel - that is with this 1.4 16V BBY engine and a 2.8 30V APR engine, so I've kind of given up with the yearly "double dosing with Redex" and rely on the fact that I only use Esso, BP or Shell fuel from branded fuel stations. One other thing, after you trying an octane booster, maybe try to find out if VW ever issued an engine ECU flash update for this engine that might have changed the maping to miss pinking. I don't know how you could find this out as I'd doubt is the service people at your local VW dealer will be clued up on this sort of thing. In the "grown up's" world, a central register of current desirable software issues etc would be held for checking - and all the reasons/changes for the up-issuing listed. But we are talking about nuts and bolts trade here so maybe what they don't understand is not worth their time knowing about! My car has only been to VW for its first service (and every MOT) so I have not exactly pushed this issue with them as that car is a personal import (so they claim that its built using different parts to a UK sourced one - this probably means that UK sourced VWs are built from UK sourced parts - aye right!).

What really annoys me with this BBY engine in this car is that pinking starts when the car is asked to do acceptable levels of work, not, when you are being unrealistic about what you are asking it to do in too high a gear (which with older cars would always lead to pinking). My car and our previous cars did not ever do this and they were a lot more powerful, maybe VW has gone a step too far in the ignition/fuel mapping on these engines. This could possibly be a situation where getting the engine remapped with a bigger (more points) map would get rid of this annoying and possibly damaging pinking AND improve the MPG - remapping tends to be aimed at increasing power output and is priced with that in mind, but in reality, if the car manufacturer does not try to make things work properly then it is a way to improve things, I'd guess that the ignition/fuel maps on our previous Fiesta 1.6SI & Cav GSI & my current Passat 4Motion were/are a lot bigger than the Polo with BBY one!

Have you never noticed that these engines, can and will, under high loading, even pink when the engine is cold and the ambient temperature is very low - if you are silly enough to ask for the impossible at low engine revs, ie at a point where you might expect the engine to bog down or even stall?

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Re: Airbox engine cover flap valve (engine pinking when hot)

Post by RUM4MO » Mon Sep 05, 2011 11:06 pm

Any update on this problem?

littlepolo
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Re: Airbox engine cover flap valve (engine pinking when hot)

Post by littlepolo » Tue Sep 06, 2011 9:26 am

I'm stuck deciding what to try next.

I made a 500 mile round trip recently, and during a rain storm whilst going up a hill (with a loaded vehicle) it started knocking
heavily (loss of power). The ECU went into limp home mode. Luckily, I had my code reader with me and found a 17772 CEL code. This translates to a bad ground on a coil pack (“17772 - Cylinder 4 Ignition Circuit: Open Circuit”). Left the bonnet open for ten minutes, cleared the code, and restarted - all seemed fine after that - with the exception of the occasional pinking problem. I had put an Octane booster in the tank following a cleaning of the fuel system, so octane is likely not the problem.

Reading yet more on this type of problem, coil packs seem to come up often. But then I've read of people changing coil packs and
the problem returns. If the engine was knocking/pinking under load at different revs, then I might be more inclined to suspect the
knock sensor. Given that it occurs under light loads, 1800-2200 RPM (approx), often in the lower gears, maybe it is some kind of fuel
map problem. And given that no CEL codes are present (usually), that might suggest the ECU fuel map thinks fueling mixture is correct?

In short, none the wiser. I'm thinking to take it to a non-dealer VW specialist. Maybe if I pay for a diagnostic check, they will be able
to tell me if they see the problem or not? Having said that, I had a diagnostic done over a year ago and they picked up that one
of the sensors was faulty. I forget which one exactly, but I think it was one that goes into the plenum chamber. Anyway, I changed that,
the car did drive better, but the pinking still occurred. My point is, if it had been an ECU firmware issue, surely the garage would have flagged it? They picked up on a lot of issues; cambelt - which was changed soon after, front suspension bushes, bulbs, etc. So its not as if they didn't give it a careful examination.

I did find a thread where someone with a Jetta had a 17772 code, and found a TSB that requires the cyl 4 coil pack ground wire to be re-terminated/routed to the ground point under the battery - but I'm not sure if this applies to the Polo 9n. And if that coil pack was the problem, surely I'd get the code frequently? Also, I think there is a difference between the pinking that occurs, and the 17772 (P1364) code incident - which was a definite misfire.

Anyway, the TSB is, basically: 1) remove battery and battery tray, 2) remove any other components to allow access for repairs, 3) remove terminal #1 from coil connector (6 pin "D" shaped) -numbers are under cover /backside - purple lock needs to be released - proper wire release tool is recommended, 4) Install new wire and seal into that terminal of connector -000 979 225 & 000 979 230 are wires -111 971 940 A & 357 972 741 B are seal and butt, 5) route to ground stud under battery tray. Clean any rust / corrosion from existing ground before reassemble check / clean main battery ground to body condition as well.

IIRC heat in failing electronic components exacerbates their breakdown. So it could be the coil pack. But, is it the ground wire? I could get a third-party coil pack off eBay, just to try it. But forums are full of people who report having swapped out components yet have not resolved the problem. And some dealers might say they have to do that as part of the diagnostic process.

Only other thing I've trawled up using Google is an air leak between the intake manifold gasket, and the cylinder head.

Its clearly a widespread problem. But the solution seems much less clear.

littlepolo
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Re: Airbox engine cover flap valve (engine pinking when hot)

Post by littlepolo » Tue Sep 06, 2011 10:15 am

Forgot to ask, is your Polo a manual, or automatic, transmission? And how much oil is she using? And what fuel are you using?

RUM4MO
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Re: Airbox engine cover flap valve (engine pinking when hot)

Post by RUM4MO » Tue Sep 06, 2011 9:32 pm

littlepolo wrote:Forgot to ask, is your Polo a manual, or automatic, transmission? And how much oil is she using? And what fuel are you using?
Car has a manual gearbox, does use a bit of oil - at a guess (without checking records) 1.0ltr every 1500>2000 miles, use "normal grade" ESSO & BP & SHELL.

I still think that the knock sensor is not outputing a high enough signal level (without checking anything) and in normal use us humans should never ever actually hear pinking if the engine managment system has built in knock detection. Maybe VAG either modified the knock sensors or the managment program - again maybe its a flash update that gets rolled out if the customer complains.

On the subject of induction air leak after the MAP or MAF sensor - again the knock detector signal should cause the ECU to move the spark timing to stop it happening - though it will have limitted range to play with. The other item that limits fuelling is the pre cat Lambda sensor, but I think that this car has pinked when fitted with its original "S1" sensor and still does with its new VAG supplied "S1" sensor.

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Re: Airbox engine cover flap valve (engine pinking when hot)

Post by RUM4MO » Thu Sep 08, 2011 8:53 pm

One other thought with respect to your BBY engine pinking, have you ever checked the brake servo with the engine off, most cars I've driven tend to hold vac so that even a day later you can get one of two servo'd brake applications without starting the engine. At the moment, my wife's Polo loses its vac almost as son as the engine is stopped - how does your car compare with that?

littlepolo
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Re: Airbox engine cover flap valve (engine pinking when hot)

Post by littlepolo » Thu Sep 08, 2011 9:17 pm

Interesting. I will need to check, but, IIRC, when getting in the car, and putting my foot on the brake to shift gear (Park to Neutral) there is no pedal pressure. So it seems not to be holding vacuum.

Just yesterday, when the weather was mildly warm, I went out around town - engine was at 2100RPM, and it was pinking like hell.

That made me resolve to do.... something...

The fuel tank is almost on empty, and I might try higher quality petrol - just to see if there's any difference with that, and an octane booster (which seemed to do nothing....). Some people claim 7%, or so, improved MPG - which offsets the higher cost. I'll be surprised.

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Re: Airbox engine cover flap valve (engine pinking when hot)

Post by RUM4MO » Sun Sep 11, 2011 8:26 am

Its also around 2?00 > 2500RPM that my wife's Polo pinks - could be that these are were meant to get a flash update to the ECU - I don't know where/how to find out what if any flash updates were needed to get done to these engines and exactly what the problem was that required these updates.

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Re: Airbox engine cover flap valve (engine pinking when hot)

Post by littlepolo » Mon Sep 12, 2011 5:06 pm

I think if there were a vacuum pipe/leak problem, it would result in idle problems, and occur more widely throughout the RPM range.

In old speak, this problem is like what would, on a carburetor engine, be called a flat spot.

Well, I have trawled Google-wide for TSB's on VW / Audi / Seat 1.4's and other engines, but cannot find any reference to a specific TSB
that relates to this problem/engine. I have a laptop with some diagnostic software, and if I have/can find a suitable interface will hook
up to the ECU and find out what Rev. the ECU firmware is at present. Do you have any idea what Rev. you are using?

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Re: Airbox engine cover flap valve (engine pinking when hot)

Post by RUM4MO » Wed Sep 14, 2011 9:48 pm

Sorry for the delay in replying, I have been looking on the VCDS site and the "component" field is meant to include firmware issue - but I can't be exactly sure which section relates to the issue.
My wife's Polo BBY engine controller is VAG P/N 036 906 034 DD and the component is MARELLI 4MV G 4555
Now I am assuming that your car has an auto box so probably has a slightly different version of that Marelli ECU, so comparing mine with your's might not be too easy.

I agree that this does not sound like an induction leak as it should show up low down the rev range when the engine is creating a large depression.

As for feeling any "flat spots", with that engine connected to a manual box, lack of flexibility is always a possibility - though sometimes its performance is surprising!

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