VR6 Pinking

[Roger Blassberg 0]

This is becoming a long-running saga.

 

I had the complete cylinder head replaced a year ago. Ever since, the engine has pinked on acceleration, especially badly when the engine is hot after sitting in traffic and/or hgh air temperatures.

 

I run exclusively on 97/98 RON fuel. The knock sensors give no fault on 1551/VAGCOM. New plugs. The ECU has the standard chip. I had a run on Stealth's rolling road and had acceptable power and torque figures (190.1 PS).

 

Following a recent thread from ChrisP, I suspect a faulty injector as a possible cause and rang my local Bosch specialist to ask for a check on them. He suggested that he would need to check the cam timing first to eliminate that in view of the recent top end renewal.

 

Questions; is it likely that cam mis-timing would cause pinking? Would the engine run smoothly, idle well and give full power if the cam timing were out? Is he looking for an extra couple of hours on the bill.......?

 

Best Wishes

RB

[dr_mat 0]

From reading of such problems on here I was under the impression that you'd know if the cam timing was out - as you say it'd idle a bit rough, it'd run a bit rough, and it'd probably not pull very well. What was your torque figure on Stealth's rollers btw?

Tell us more about the pinking: does it only occur on full throttle or only on part throttle? Only in a particular rev range? Is there any suggestion that you're having MAF problems? (What's the MPG like?)

 

Oh - and if anyone's going to double check the timing, surely it should be the people who did your top end rebuild first!

[Roger Blassberg 0]

The pinking is fairly constant on acceleration, probably worse on full throttle, and definitely temperature-dependent (worse at higher engine and/or ambient air temperatures). It doesn't seem to be so bad in the upper rev range, say above 4000.

 

I can't say if there any MAF problems for sure, but fuel comsumption is about 28mpg on my 20 mile commute through moderate traffic, up to 32 on a decent motorway run, driven at a speed where nobody overtakes. :) Maybe that is indication of a lean mixture. (These figures are from the MFA, not corroborated by long-term records of fuel consumed vs. miles driven) Certainly the exhaust analysis figures are well within limits.

 

The engine runs evenly and smoothly, but stalls very occasionally as you coast up to set of lights..."they all do that".

 

Would a MAF fault (other than an outright failure) come up on 1551 / VAGCOM? Are there any tests, other than substituting another one into the induction system and comparing results? This certainly is an avenue for further investigation which had not occured to me up to now.

 

Water temperature is 70 - 80 when bowling along, goes up to 105 max in heavy traffic. Oil temperature is around 100-102 at constant open road driving, but approaches 120 if really pushed. The oil reading, gave me cause for concern when I first had the car; my ABF engined Passat oil temperature gives much lower values. Reading through many threads here has reassured me that this is not unusual for an ABV however.

 

I don't recall the torque figures exactly, but the peak value and the shape of the graph were unsurprising one way or the other.

 

I agree absolutely with your comment on liability for checking the cam timing; it just seems unlikely to be a cause of pinking. Quite honestly, I trust the people who did the cylinder head to have done a good job, but of course mistakes happen...

 

All further contributions to the solution of this will be gratefully received and acknowledged.

 

Best wishes

 

RB

[Timo. 0]

you can try unplugging the maf whilst the car is running. The engine should at least dip in revs if not stall completely. If nothing happens it totally dead. They can often run out of spec though and not come up on diagnostics.

 

Best way is to borrow someones that is defintely working fine and put it on. At least you can eliminate that from the equation then.

 

Timo.

[dr_mat 0]

It's a teaser, no question. And your engine is completely standard?

There's nothing out of place in any of the figures you've quoted, nothing to indicate concern at least. Which makes it all the more weird that a completely standard engine is pinking at medium revs when the engine is warm.

There's no reason to doubt the operation of the knock sensors though - the ECU retards the ignition each time the knock sensor hears that sound, and you should then notice the car feels a little less lively afterwards, but it can still pink after. Once the ECU reaches it's maximum retard (around 11 degrees, IIRC) that's yer lot. If it's still pinking it will still pink, nothing more the ECU can do about it. I don't think it's smart enough to increase fueling in to compensate.

 

Maybe you should consider the possibility of an air leak around the inlet?

Also worth looking for contamination from other sources. Would an iffy head gasket and water in the cylinder cause pinking? (This is pure speculation on my part I don't remember ever reading that this is the case..)

[Roger Blassberg 0]

Anyone in the Herts area with a known good VR6 MAF would be welcome to contact me - Timo, you are a bit too far away, but thanks for your suggestion.

 

I have a horrible feeling that a new MAF is expensive - anyone have information, please?

 

Best wishes

 

RB

[Timo. 0]

yup, they aint cheap. I see them on ebay quite often, obviously they are second hand and you cant guarantee they are working properly.

 

Timo.

[dr_mat 0]

Mario_vr6 was ordering a reconditioned VR maf from the us for about £140 all in. But a new one is £300+ ... VW won't sell you a recon unit. Bosch will, however, but I'm not sure of the pricing.

[Kevin Bacon 5]

From Bosch, MAFs are £150 + VAT recon (new guts in existing housing) or £200 + VAT new. That was last year's pricing, so they may be cheaper now - or more expensive!

 

And meanwhile Corrado owners are still being kicked in the teeth by the dealers charging us £300 for one, whereas R32, 4Motion etc people get them for less than £100 exchange with a 2 year warranty.

 

Shall we put together a petition to send to VW UK? Might be worth a go....

[Timo. 0]

DO IT!!!!!!!!! The maf is about the only thing left to break on my vr. I've had all the rest go.... :cry:

[Kevin Bacon 5]

I've been through 3 of the darn things in 21 months.

 

I just think owners of VW's "Flagship' Coupe are treated like sh1t when it comes to parts. Instead of showing some recognition to the people that bought their hideously overpriced car, they still fleece us on parts 10 years on.... £150 MAF from Bosch, or £300 from VW..... they should not be allowed to double the RRP price. Damn W1kners.

 

I vote a VW dealer boycott..... let's all get our parts from Audi instead. I know they're still sourced from the same place in germany but the UK dealers will lose out.

[dr_mat 0]

Don't put together a petition. All that's going to do is get VW to pre-order the right number of £300 MAFs, and bin the rest...

BUT they have a requirement to provide parts for these cars under european law for another two years (the last Corrado was registered in 1996 ish so + 10 years), so any part that you find obsoleted and unavailable we should write a petition to them about, pointing out their legal obligations to Corrado owners.

[Kevin Bacon 5]

No they won't and can't because the MAFs are supplied by Bosch. My gripe is why we are paying double the Bosch price at the dealers for exactly the same part and why exchange VR6 MAFs were made obsolete in August when current V6 VWs still qualify for this exchange agreement.

[dr_mat 0]

Hey - thought occurs to me Roger. Did they skim the head when it was off? Did they use a good quality head gasket? Increased compression might be a cause for pinking...

[Kevin Bacon 5]

I thought that too but people have used the thinner MK4 steel gasket on the 12V successfully with no pinking.....

[Heardy 0]

These guy's are Bosch agent's,we use them at work http://www.andrewpage.com/products.asp give them a call and see how much a new MAF is from them

[Roger Blassberg 0]

No, the head was a VW exchange unit, complete with cams, followers, valves, the lot. I assume that that means it was a standard-spec combustion chamber volume and therefore a standard CR. I had bl@@dy well better be for the money I paid for it !!

 

I'll do the MAF disconnect test tomorrow, when it has stopped raining, and let you know. Ironically, today the pinking has been much less notieable in the cold, damp air.

 

I greatly appreciate everyone's advice.

 

Best wishes

 

RB

[Roger Blassberg 0]

Looking at the thread "VR6 ECU reset". Maybe I'll do that as well and see if the MAF settings are adjusted.

 

All you have to do is wait long enough, and the answers turn up eventually....

 

Best wishes

 

RB

[Kevin Bacon 5]

If you've got VAG-COM, get the knock sensors checked too. I think you did that with VW 1551 but how long ago was that?

 

The knock sensors are delicate and need to be torqued to the block carefully. The ECU just concerns itself with the connection and not so much the state of the fitment to the block. But as a rule, if the pinking lasts for a second or two at the most and pulls back, they're working. If the pinking is very loud and prolonged.....get the sensors checked. I've seen a KS crumble to pieces when removed (the rear one), so maybe some fresh ones might be a worthy investment.

 

Find a steep hill and press the gas pedal right down into the carpet in 3rd at about 2000 rpm. All you should get at best is nothing and at worst a quick crack of detonation and that's it. Anything more indicates trouble and needs looking at.

[Dan_Storm 0]

Roger, just to make things more confusing for you.....

 

I was always under the impression that you should expect a change in the RPMs/running after disconnecing the MAF on a warm engine. I do no believe this is the case for ALL engines, just most.

 

When I disconnect my MAF i get no change......but I still assumed it was dead so bought a new one. I installed the new one expecting more power/smoother delivery but it drove exactly the same (yes I reset the ECU).

 

I also read posts from a couple of people on here who have found the same. And i'm sure someone explained that if it runs the same after disconnecting the MAF it does not necessarily mean its dead. I believe this was only newer engines.

 

I know my engine is running ok - I got it rolling roaded at 207bhp (after a chip) and the delivery is smooth. I disconnected the MAF and went for a drive it felt a bit rougher and slightly down on power....but not particularly noticable.

 

Can someone else back me up on this? I'm not sure if i'm 100% correct but I don't want you to waste your ££ unless you need to.

 

If I get time later I'll try searching for the relevant post(s).

[Kevin Bacon 5]

If you disconnect the MAF and drive it (without resetting the ECU) and it feels no different, then it's not doing it's job and the ECU is using the throttle position sensor as a substitute. Wth the MAF disconnected, it should drive like a dog.

[dr_mat 0]

If the MAF is bypassed by the ECU, that fact will show up on a VAG-COM scan.

[Kevin Bacon 5]

Incorrect I'm afraid. The ECU is only concerned with the MAF's physical connection, not it's operation - from an error reporting POV. The two errors you're most likely to see on VAG-COM relating to the MAF are:-

 

Short to ground - intermittant

No signal

 

The MAF could be dead, it could be alive - the ECU simply won't tell you either way.

 

Not even putting the MAF on an Oscilliscope will tell you for sure. It is without doubt the most difficult component to monitor and test.

 

If only the ECU monitored and reported MAF volume in CFM per minute/second or what ever.... that's the only way to be sure.

[dr_mat 0]

I'm not going to argue with you, because I can believe that the ECU might happily believe the MAF is fine when it's not. But there's plenty of reason to believe that an ECU fault code: "adaptation limit reached: air/fuel mixture" points to the MAF being faulty and the ECU knows that's what's wrong.

[Kevin Bacon 5]

That error could be anything......siezed ISV, air leaks, duff HTs/plugs..... adaption limit reached *could* point to a MAF but it could also be a myriad of other things.