Overrun Questions

[ardandy 0]

The situation:

 

My VR6 is blue smoking one the overrun, I can go down a hill say for only quarter of a mile and then when I get to to the bottom and accelerate it plumes blue smoke out. The longer the overrun, the more the smoke.

 

Doesn't do it when I'm booting or tootling around (at least not yet).

 

Questions:

 

1, If it is the pistion ring thingy, if I get it sorted, will that be it then for that problem, or can others arise when getting that work done? (if that makes sense). Basically, is it worth spending £600 on getting them sorted out on a 14 year old engine, or save up for longer and go for a complete rebuild, which would mean I wouldn't have any engine probs after that. I dont want to spend £600 and then find I need a rebuild for some other reason later on.

 

2, Can a garage tell if its a piston ring issue without it costing me a fortune? What sort of diag price?

 

3, My car didn't do this 2 week ago, and now after 0.4 miles down a hill on overrun, I almost covered the car behind me in blue smoke when setting off. Surely somethings gone? Is piston ring a sudden or gradual change?

 

4, Will I ever go a month without fixing something? :cry:

 

I'm going to try the Silkolene oil solution next and see what happens.

[ardandy 0]

Well, it's going into Andy W at PSI on thurs for his expert opinion.

 

Just had a VAG-COM check done by VW (£36 inc VAT) and the only thing they brought back was a engine speed sensor, which I've being reliably told by Andy W that they didn't have the engine running when it was tested!

 

Monkeys!

 

PSI reckon its a fuel thing rather than oil, as its only doing it after overrun and no other time.

 

Fingers crossed.

[dinkus 10]

Have a search for smoke on overrun - it's a common VR thing and could well indicate shagged piston ring(s) and/or excessive bore-wear on cyl 1 and/or 6.

 

An easy check is to look at the plugs and see if they all look the same - if 1 and 6 are black then it could well be bore wear.

 

If you want it checking out in more detail, you need a leak-down test (again have a search) to see which cylinders are causing it and/or whip the head off and take a look inside (not cheap).

 

If the bores are worn, then it's new block time, which is not a cheap job at all...

[Kevin Bacon 5]

Mine used to kick out a small bit of blue after a lengthy bit of over run and then I had the head rebuilt and it did the same, but much less often.

 

That was with Quantum silver.

 

Since switching to silky it doesn't smoke at all. Only uses about 100ml or so over a month under normal driving (50 miles a day) and about 1/4 litre over the same period if I regularly drive it hard.

 

That's good even for a healthy VR, let alone one that's just turned over 133K on the original block.

 

If you suspect it's pistons, check bores 1 and 6 for oil fouling on the plugs.

 

My advice is to fit some strong brakes and not over run the engine, just coast down hills and up to junctions, saves a bundle on oil :-)

[ardandy 0]

Whatever it is, Andy Walker I'm sure will find it.

 

Got plenty of time, I'm off on hols for 10 days so he's got the car for that long. :)

[Kevin Bacon 5]

Hopefully he'll say the bores OK as head work isn't too horrendous cash wise.

 

I was ready for a full rebuild when I had my head done but Stealth said the bores still had the factory honing on them (@ 93K) and didn't need reboring.

[ardandy 0]

He reckons its not a piston/bore thing as it only does it on overrun and no other time. Reckons it's more likely fuel and not petrol thats burning.

 

Car still runs sweet.

 

We'll see!

[Kevin Bacon 5]

Can't see how it's fuel related unless the over run is so rich that it's thinning the oil down.

 

On the overrun the injectors are barely open. Sorry, not buying that.

 

I think the oil is just being pulled in through the guides. You get huge vacuum on the overrun, which will soon highlight worn valve guides and seals.

 

He's probably right on the bore wear tho, it would smoke a lot more if they were knackered.

[ardandy 0]

He was thinking more on the dodgy sensor side of things, (did explain but I'm not very technical!) and that the fuel is getting burned in the exhaust??? (might have that last bit wrong)

 

Wouldn't a dodgy fuel/lambda/air sensor ever cause this?

[Kevin Bacon 5]

Yeah a dodgy lambda would cause permanent over fuelling, might be worth getting him to check that. VRs generally pop and fart on the overrun when too rich.

[ardandy 0]

Mine has started popping (exhuast popping) now, a lot more than it did before. All I have to do is blip the throttle to 2k rpm quickly and I get quite a cool "pop"! Same if I slow down in gear and let the engine go below 2kish rpm, sometimes get a pop then too. Don't think I got that before, cant rem hearing it anyway!

 

When I boot it, change gear, or engine break it doesn't pop then though.

[dr_mat 0]

You'd notice that much overfuelling on your MPG ...

[ardandy 0]

Get about 25mpg on average. Thats mainly town/bypass driving. No motorway.

[dr_mat 0]

Doesn't sound massively down on normal for that type of driving.

[Timo. 0]

If it was fuel related it would be grey/black smoke.

 

You said it was blue, that's oil burning!!

 

Sounds like busted value guides/seals.

 

T.

[dr_mat 0]

Also could be a suddenly broken piston ring...

[gradeAfailure 0]

Bringing this back... :)

 

Mine's started to give a little puff of smoke on acceleration after overrun, but it's more white smoke than blue, and strangely enough it only does it after low-revs overrun (2500 and below) rather than high-revs overrun. It does noticeable pop and fart on low-revs overrun and not when at the higher revs, so are the two linked? Doesn't seem to be using ridiculous amounts of oil, and it doesn't smoke on startup either. Head was done at Stealth 2 years ago by the previous owner, so I can't believe the valve seals and guides are shot after that short length of time...

[ardandy 0]

white smoke is petrol I believe. Possibly overfuelling? Mine had a temp sensor (about £9) replaced. From what I was told the faulty sensor kept telling the ecu it was cold and overfuelling, which on the overrun built up a bit in the exhaust and when you accelerate, poof, it comes out the back.

[Roger Blassberg 0]

Sounds like valve guides and/or seals if it's only smoking after over-running. The seals can be replaced without removing the head using compressed air to hold up the valves. Obviously the guides can only be changed with the head off.

 

Popping in the exhaust can be caused by a cracked flexible in the downpipe.

 

Best wishes

 

RB

[gradeAfailure 0]

andy, which temp sensor was that?

 

roger, i hear what you're saying, but i can't see how the seals would have gone in only 2 years, and surely Stealth would have fitted new valve guides if they were worn...

[ardandy 0]

air temp.

 

it was Andy at PSI that sorted mine out. Also cleaned the throttle body out and the breather pipes.

[Timo. 0]

white smoke is petrol I believe. Possibly overfuelling? Mine had a temp sensor (about £9) replaced. From what I was told the faulty sensor kept telling the ecu it was cold and overfuelling, which on the overrun built up a bit in the exhaust and when you accelerate, poof, it comes out the back.

 

Have you got a part number for that air temp sensor??

 

T.

[ardandy 0]

No idea, PSI did it all. Air temp sensor for a VR6 C should get you it no probs.

[Kevin Bacon 5]

It's the blue temp sender that makes the engine think it's cold. The intake air temp sender doesn't have enough adjustment scope to make the engine run too rich. Over fuelling smoke is black, not white. White smoke (steam) is usually water related, it could be a very light grey/blue which is oil.

 

Stealth defo replace the guides and seals, so it could be the onset of bore wear. Do the usual with plugs 1 and 6.

 

Gareth also had problems with the breather causing all 6 plugs to foul up with oil, so Stealth retro fitted a later PCV filter and ran the vacuum hose over to the brake servo outlet and that stopped the problem.

[gradeAfailure 0]

well, if it is bore wear, then so much for the "should be good for another 100k" hope that i had... :roll: or I'll just switch to the Silkolene... ;)

 

will check the plugs when i get time...