Compression test results.

[dumptyboy 0]

I need some advice please everyone. I recently replaced the cylinder head on my VR6 because I believed the stem seals were knackered. The reason I changed it was because I was getting loads of black/grey smoke on overrun and it became more noticeable once the engine was up to temperature.The spark plugs on all cylinders seemed to get a fair amount of oil on them also.

So I bought a replacement cylinder head off a guy on eBay that had apparently had the stem seals replaced for new ones aswell as the stem guides. I fitted the new head over a weekend and when I took the car for its first drive afterward it seemed to be cured of its smoking habit!

Anyway recently it started smoking again just as bad as before, so I suspected perhaps the bottom end (piston rings) was at fault, unless of course the reconditioned cylinder head was Infact just as bad as my old one, and never had the stem seals replaced!?

 

So anyway, I've done a compression test to see if the piston rings are shot, and here are the results:

 

Cylinder 1: 174

Cylinder 2: 180

Cylinder 3: 174

Cylinder 4: 188

Cylinder 5: 174

Cylinder 6: 188

 

Now I'm not sure if these results are within Tolerance or not, so can someone please let me know?

 

And what would the general opinion be about what I should do next, is it the bottom end that needs sorting or should I try to replace the stem seals with fresh new ones and hope this will cure my smoking problem?

 

Any help appreciated.

Many thanks.

 

Rob.

[Critical_Mass 10]

Id say they look fine mate, maybe someone with a bit more knowledge can confirm that or say otherwise. Could be valve stem seals getting oil into the cylinders... VRs are known for it. hence the spark plugs.

[Harrier 1]

Your valve guides could be worn, which might make sense as you said it seemed ok initially. How many miles on engine ?

[dumptyboy 0]

I've just realised I have made a mistake with the compression test. I. forgot to open up the throttle whilst doing the test so this will obviously affect my results, D'oh!!

 

I got the engine upto working temp, disconnected intake hose, disconnected coil pack, removed fuse 18( fuel pump), and removed all spark plugs, but forgot to leave the throttle open........

 

When I removed my spark plugs today for the compression test they looked fairly healthy, with only oil on some of the threads? I only do about 15 miles a week in the car, I don't know if that makes a difference?

 

But I really need to sort the smoke problem as its quite embarressing.

 

I'm probably best to do another compression test tomorrow with the throttle open and return with my results.

 

Thanks for your help. :)

[Harrier 1]

Your compression figures are more likely to increase with throttle open (more air going in). I think they are fine

[dumptyboy 0]

Your valve guides could be worn, which might make sense as you said it seemed ok initially. How many miles on engine ?

 

133k approx. yeah I'm starting to wonder if the reconditioned head that I've bought is Infact just as worn as the previous one. I've actually started cleaning up the head that was originally on the car and I'm going to replace the valve guides and stem seals, so perhaps I should finish working on it and just spend another weekend pulling the engine apart to refit it! At least I will definetly know that the guides and seals are new then?

[vw rule 19]

Hello Rob

 

compression at 180 to 200 PSI is fine for the VR6

if they were down to 140 or slightly lower, then yes I'd say you would have a compression problem starting.

 

Black smoke from your exhaust is normally fuel, for petrol and diesel engines,

and blue / grey smoke is normally oil.

White / grey smoke is normally a sign of water loss.

White smoke from a diesel engine normally means that neat diesel is not being burnt correctly,

or is being injected at the wrong time.

 

You have 3 piston rings on the pistons,

the top and middle rings are the compression rings,

and the lower / bottom ring is the oil ring.

 

Your compressions seem to be ok so I'd say your compression rings are fine for now,

but your oil rings could be slightly warn.

The oil ring is designed to allow oil to pass through it and line the bore with a fine smear of oil,

some oil may pass the compression rings but this is normal in small amounts.

 

Most engines do burn a small amount of oil, but V4, V6, V8 engines tend to burn a little more,

due to the angle of the V-block, this includes the VR6 I know it's only got a 15 degree internal bore angle,

but they do burn slightly more oil than the other Corrado engine versions.

 

Rob you said that you fitted a reconditioned cylinder head,

a recon head should have been skimmed, and have new valves, new valve guides, and new valve stem oil seals,

and may be new or machined cam shafts, plus new cam lifters - (Hydraulic tappets)

 

Excessive oil consumption will be down to warn cylinder bores, pistons rings, valve guides, valves them self's, valve stem oil seals.

When I say valves them self's I mean the valve stem on the valve,

if you check for side movement in the valves when they are still attached in the cylinder head,

there should only be a slight bit of movement around 1/4 to 1/2 a millimeter,

1.2mm to 1.5mm is really too much movement, and at 2mm or more side movement valves can shatter or snap at the valve head.

But to get a true reading you'll really need to strip the head bare of the cam shafts, stem seals, valve springs,

just so there is no pressure on the valves then.

 

You can fit new valve stem oil seals but this will only work short term if the valves are worn or the valve guides are,

you can measure the valve stems to see if they are warn out or not, but you'll have to remove the valves completely to do this.

But usually it's the valve guides that wear out first as they are much softer.

 

Normally on start up from cold, blue / grey smoke is valve stem / guide wear or valve stem oil seals,

what happens is once the car has been left for a few hours or over night the oil in the cylinder head can seep,

slowly through the warn valve stem oil seals and line the valve guides with oil,

may even drip on to the valve heads so when the engine is started the suction from the piston stroke will draw the oil down,

and out in to the exhaust but you normally only see this on start up when the engine is cold.

 

Rob if you are still seeing smoke from the exhaust when the engine is hot,

then it could be your piston rings, mainly the oil rings, you don't always have really low compression.

What state were the cylinder bores in when you had the head off ??

Was there deep wear scratches or were the bores heavily glazed ??

Pitting in the cylinders is a sign that the bore lining is becoming thin,

in which case will need a re-bore or replacement liners fitted.

 

Rob if you can feel a deep ridge near to the top of the cylinder,

then that really means your bores have seen better days.

 

 

It is normal to have some by pass pressure in the crank case i.e engine block.

By pass pressure is the combustion fumes from the cylinders, that pass the piston rings in to the crank case.

Too much crank case pressure will force oil up in to the cylinders and some fuel in to the oil in the sump,

this usually means the pistons rings are shot or bores are warn in a oval shape,

or in some rare cases can be the breather box is blocked up.

 

vehicles that only do short journeys tend to have a smell of fuel on the dip dick,

plus the cylinder bores will wear out quicker.

 

Rob also the fuel regulator if it's a little warn can let too much fuel through,

which can make the engine run slightly rich hence the black smoke you have.

 

 

Hope this helps.

 

Si :thumbleft:

[dumptyboy 0]

Thanks for your detailed reply vw rule. Im actually colour blind so it can be hard to tell sometimes what colour the smoke is, haha.

I don't know whether this makes a difference or not but I've also been getting a load of soot type stuff left on my driveway if I let the car idle and then accelerate hard:

 

 

Does this indicate over fuelling?

I have changed the oxygen sensor and the maf for known working ones recently as I was getting a strong smell of fuel, and do still occasionally smell fuel but nowhere near as bad as before. I also tightened the fuel lines ontop of the fuel tank and below the fuel filter as these joints were leaking slightly.

 

The car drives really well, idle is perfect and it usually returns good mpg. But I'm still wondering if it is over fuelling slightly now.

Would over fuelling cause the smoke on overrun?

 

I does smoke slightly on cold start up, usually just white smoke that I assumed was just condensation.

 

I appreciate all of your help, I'm just secretly hoping its going to be something simple and I'm not going to have to pull the engine apart again.

 

Also I have a vagcom cable and ran a scan but it showed up no faults apart from the cam position sensor but I believe this would usually show if the engine is not running during the scan.

 

:)

[vw rule 19]

Hello Rob,

 

on the attached photo you've put up I'd say it looks like fuel soot,

the block spots on your drive look like the engine may well be over fuelling slightly.

 

Because to have engine oil spitting out of the exhaust that would mean you have a internal engine problem,

which would normally kick out blue / grey smoke from the exhaust.

To have oil coming out of the exhaust, it would be head gasket gone badly, or a cracked cylinder head, or a cracked damaged piston or rings.

 

Your exhaust Rob is it a DTM Stainless Steel box and system ?

It's just that with some of the stainless exhaust systems they do tend to get coated with thick soot in side,

mainly in the rear box as it's the coldest part of the exhaust.

I used to get this on my old MK2 VW Scirocco, I had a Janspeed stainless system on it.

 

It is normal Rob to have some moisture from the exhaust tail pipe,

as this moisture is mainly from the cat where the gases pass through the honey cone inside it,

so you will see a little white / grey smoke coming out,

the white smoke is the moisture and the grey smoke is where it has mixed with the soot and small traces of oil in the exhaust.

 

Your very short journeys Rob will mean your Corrado won't be getting right up to running temp for long enough,

so you will see moisture more often coming out of your exhaust.

 

Like I say I think you mainly have a over fuelling issue,

you still need to keep an eye on your engine oil level and coolant level.

 

The VAGCOM or any other scanner won't pick up a faulty fuel pressure regulator,

as they are normally vacuum operated and don't have any sensor on them.

I believe you'll need the engine to be running to check the fuel pressure,

this can be done at most workshop garages.

 

It could even be worn out fuel injectors as the centre needles do open up to a larger size,

due to the constant fuel friction going through them.

 

Plus in the past I’ve had the coolant temp switch go a little weak,

it still works but can be come lazy, which can course over fuelling problems, same goes for the lambda sensor.

 

I think the cam position sensor is mainly for the fuel injectors, it normally tells them when to fire,

plus does kind of work along side the crank sensor for the coil pack,

but the coil pack gets it’s main signal I think from the crank sensor, which tells the coil when to fire.

 

Rob normally thick black smoke out the exhaust is fuel meaning the engine is running too rich,

or a EGR valve is sticking or is choked up with soot.

 

 

Hope this helps mate.

 

 

 

Si :thumbleft:

[P3rks 11]

Just to add to this I have a similar issue with blue smoke on the over run.

 

My compression test results were..

 

Cylinder 1 - Dry 160 / Wet 185

Cylinder 2 - Dry 180 / Wet 200

Cylinder 3 - Dry 145 / Wet 160

Cylinder 4 - Dry 175 / Wet 190

Cylinder 5 - Dry 170 / Wet 180

Cylinder 6 - Dry 160 / Wet 170

 

I've done a bit of research and 160psi is factory standard with an upper limit of 189psi and a wear limit of 109psi. A 44psi max difference across the range. So i'd say mine are all within tolerance. If anything for a standard, original engine with the original headgasket with 130k on the clock is pretty damn good.. Although the Cylinder 3 does concern me though being lower than the rest...

 

I'd say your compression is good.

[dumptyboy 0]

Excellent thanks for your help everyone. The exhaust is a cat back stainless steel Scorpion system, and I currently have a decat pipe fitted.

When I removed the cylinder head I checked for any obvious damage to the bores but they all seemed perfectly fine to the naked eye.

Im thinking perhaps I'm best changing my coolant sensor and fuel regulator and seeing if that cures the problem ???

 

The only thing that is confusing me is why would the smoke be more obvious on over run if it is over fuelling, would it be more apparent after I accelerate after coasting down a hill for instance?

 

Many thanks for all your help everyone.

[coullstar 0]

When was the last time it had a good proper long blast?

[dumptyboy 0]

When was the last time it had a good proper long blast?

 

I drove from my house to Tenby ( approx 17 miles) about 3 weeks ago, I didn't thrash it but gave it abit of heavy acceleration where I could. The car only gets used on weekends and I might only do about 3 miles in it some weeks, but once the engine is upto temperature I tend to take it for a good hard drive for a couple of miles if traffic allows!

 

Do you think the cars lack of use could course the problems I'm having, should I try taking it for a longer drive and see if it clears thing up?

 

Cheers.

[vw rule 19]

Hello Rob,

 

the over run I think is when you take your foot off the throttle at speed, say at high rev's 2500 or 3000rpm or above,

this is when driving the car or just revving the engine on the drive, and you come off the throttle pedal very quickly,

which is similar to when the car first starts up from cold / hot,

I know it won't reach high rev's but will go to 1000 or 1500rpm

once the engine catches and starts.

 

This is the reason why you'll first see smoke from the exhaust from cold or you can still see it on the over run.

 

Same thing when you apply the throttle pedal down hard you'll see some smoke if the engine is using oil or water or if it's over fuelling.

 

If you look at a rally car or any other high performance car you will normally see flames,

coming out of the exhaust tail pipe this is due to the extra fuel being injected but doesn't quite get burnt in the cylinders,

it ignites in the hot exhaust, hence flames out of the exhaust pipe.

 

You won't see any flames from your VR6 Rob with the cat fitted but might do with it removed,

but it's normally when a engine has been highly tuned up that you'll see flames from the exhaust tail pipe.

 

Very aggressive over run can damage your cat as it tries to push the honey cone out or my smash it to bits,

but this is if you were driving your car at 5000rpm or above,

all the high performance cars have upgraded cats to suit the high engine out put and extra fuel.

 

Most normal road cars never really hit 5000 or 6000rpm if they do it’s really once in a blue moon.

 

 

Hope this helps.

 

 

Si :thumbleft:

 

---------- Post added at 6:33 PM ---------- Previous post was at 6:06 PM ----------

 

I think Rob your main problem is a lot of soot build up in your exhaust system,

this is due to oil or over fuelling.

 

oil being used / burnt in the engine will show it's self normally as blue / grey smoke from the exhaust.

 

Black smoke is normally related to too much fuel delivery in the engine.

 

Rob if you are just doing 3 miles a week in your Corrado then yeah I would say it is related to your smoking issue.

 

A car engine doesn't really get up to normal working temp until you've done about 5 to 6 miles,

say about 10 to 15 mins in time.

So your exhaust may not be getting a long enough time to stay hot and the same for the engine,

your engine by the sounds of it will only just be coming of it's cold start programme,

if you're just doing 3 to 5 miles.

 

I would give it a decent run say 20 miles or above, and drive it up to 70 MPH,

for most of the 20 miles to see if it clears up,

if it’s still the same or hasn't got any better (if the smoke hasn't reduced or cleared a little)

 

Then yes I would say you've got an internal engine fault (oil or fuel related)

 

 

Hope this helps Rob

 

 

Si :salute:

 

---------- Post added at 6:44 PM ---------- Previous post was at 6:33 PM ----------

 

Right I'm off home now, still at work :lol:

 

Thank god it's Friday, the weekend is here :dance:

 

 

Hope you get her running spot on mate,

 

 

Right laters :salute:

[coullstar 0]

I would take it for a good old italian tune up if it were me!!!