Bad compression on one cylinder, any ideas?

[PhatVR6 0]

Ok, so it's a 24v, but essentially it's astill a VR6.

 

Anyway, fitted a 2.8 in my mk4 last weekend and sold the 3.2, it was costing too much to run and i needed some money back if I want to keep the car.

 

it fired up first time, no probs.

 

I've only done about 50 miles in it, if that, all with no problems. Then, last night I went to reverse the car into the car port and it was running really rough. Then the CEL (check engine light) came on. I ran in and grabbed the laptop, ran vag-com on it. a few codes.

 

Firstly a "multiple cylinder misfire"

then a "cyl #1 misfire, upper limit exceeded"

 

it's definitely numebr one too, because it runs the same with number one coil unplugged.

 

I fitted a new set of bosch plugs today, still no better.

 

so I checked the compressions. all cylinders were 12bar.....except number one....2bar :-(

 

so, any ideas what it could be? the engine has been stood for about a year, but if anything was wrong with it casued by it being stood or getting any comtamination in it then why has it taken 3 days to surface?

 

My current thoughts:

 

I'm ruling out piston.bore damage, as it's not smoking at all, and the oil doesn't smell of petrol

 

I'm thinking it could be valve related, in that a valve either isn't seating right, stuck open, bent or all of the above!

 

suggestions welcome before I rip the head off on thursday.

[24V Renshaw 0]

Is the new plug tight?

 

Jay

[bigpants baby 0]

was the engine/doner car involved in a knock & might of had something sucked into the inlet? (bit of plastic etc)

Reckon it might of been a stuck valve which has turned into bent one now?

[s.g 0]

i would check the spark plug again could be a dodgy one or even the coil lead.

[Andy D 0]

Sounds to me that you might have a burn out valve what was the plug like that came out it was in one piece? The compression could be low due to there being no spark and it has bore wash with all that fuel going in and no spark. Have you tryed doing a wet test my putting a squit of oil down the bores to check the rings. if the comppression goes up big time then you have a problem with the compression rings. Not trying to take the piss but there is spark on number one ?

[andy 0]

Did you do the compression check with a warm or cold engine? One of my cylinders reads very low cold but fine when its warmed up which is when you should check it.

[PhatVR6 0]

most of you didn't read....

 

it ran fine for 3 days.

 

it went funny before I touched the plugs.

 

the inlet manifold wasn't damaged, but it has been stodd with just a bot of gaffer tape over the ports for a year, which probably hasn'tbeen a perfect seal.

 

compression checked it when it was cold. it runs no difference if it's hot or cold, it's crap at all temperatures.

 

the plug that can out was complete, but very black and very wet.

 

haven't checked for spark yet, didn't have a spare plug at the time, or an extra pair of hands.

[Roger Blassberg 0]

1.Broken compression ring(s), but intact oil scraper ring so no smoking.

2.Head gasket blown.

3.Sticking valve

 

Best wishes

 

RB

[CoxyLaad 0]

I am going for valve not seating properly.

I reckon its sucked some shit in from somewhere and the valve has mashed it against the seat, which is now stopping it shutting properly. 2 bar is pretty much a total loss of compression is it not?

Its got to be a valve.

[CorradoVR6-Turbo 0]

Sticking hydraulics? Lift the rocker cover off and look at the height of the buckets.Or do a leakage test.

Unlikely that it will be rings.Evan with no rings you will have more pressure than that

[H8RRA 0]

got to be valve train - i can't iamgine you'll have much problems identifying it paul once the head comes off - you may just have to wait to see what parts are needed.

 

What coxy and james say tie in with some sh1t thats benn ingested whilst its been stood.

 

valve seats would be the best bet as coxy says, mashed debris preventing seal or now damaged seat in head?

 

sticky hydraulics is a good one from james but i presume you would have a knocking/noisy tappet if that was the case.

 

Probably nothing you haven't thought of and your just after a sanity check on what it might be paul?????????

[CorradoVR6-Turbo 0]

The hydraulic wont be noisy as its expanded and the gap between Bucket and cam will be zero.

 

As for checking spark when you have more than one set of hands will rule out the obvious.

 

But its going to have to come apart to fully understand why its gone wrong

[Henny 0]

yeah, as said above in different places, I'd do the following until I found the problem:

 

Check the plug isn't damaged (as daft as it sounds).

Whip off the cam cover and check that the tappet is actually free and moving as it should.

Take off the head and get the valves and seats checked.

Drop off the sump, drop out the bottom cap and push out the piston to see if it's got damaged rings.

PANIC 'cos I'd have no idea what the F*** to check after doing all those things and not finding the problem... :| :lol:

 

Good luck matey! 8)

[h100vw 0]

Know anyone with a boroscope thingy???

 

Used on aircraft engines to inspect combustion chambers without having a million quid engine in bits.

 

I know Snap On do one. Maybe you could get the rep to demostrate it on your engine then tell him you'll have to think about it, with Christmas and everything :roll:

 

I am going with a valve stuck for whatever reason. Got to work top down IMO. Cam cover off, check that you get some clearance on all tappets. Cams out, tappets out see if all the valves are up the same amount.

 

Gavin

 

EDIT leakdown check will tell you where the compression is going won't it. Smash up a plug and weld a length of steel tube on it, connect to the airline and listen for the air coming out. Dipstick means bottom end, throttle body for inlet vavle and exhaust pipe for exhaust valve.

[borderair 0]

You can buy an adapter to fit an airline to the spark plug hole (under a tenner)

This will allow you to pressurise the cylinder.

 

Then you need a mechanics stethoscope (also under a tenner)

Turn the engine to the correct place when the valves would normally be closed.

 

Pressurise the cylinder

Then listen (using the stethoscope) down the dipstick tube, the inlet manifold and exhaust manifold.

You should hear air escaping down one of the above

This will tell you were the fault lies without stripping the head

[PhatVR6 0]

well, it was the gasket.

 

no damage whatsoever to the head, vales, bore or piston from what I can see.

 

there appears to be a bit of a smooth spot on the gasket, where there should be a ridge. and there's a corresonding water mak on the head too. The exhaust valves were wet, and it had actually lost about 10mm off coolant in a week.

 

got it all cleaned up. I was tempted to fit my spare R32 head, and inlet manifold as the valves, ports and TB are bigger, but I can't as the head bolts are a different diameter an length.

 

look out ofr a 24v thread coming up, showing all the differences between the 2.8 and the 3.2. you'll be surprised at how different they are when they look almost identical from the outside.

[Supercharged 2]

Nice one, glad you got it sorted with not much expense!

 

What do you think happened to it? had the engine been apart before or had it just do damaged as a result of being stored for a while??

[PhatVR6 0]

much much expense! think again!!

 

genuine head gasket and bolt set.....£105!!!!!!

 

I'm thinking that someone has had the engine apart to have a look at it, then put it back together without changing the gasket and bolts (not surprised at that price!!)

[Henny 0]

PhatVR6, that's still cheaper than a 1H block's bolts and gasket! :|

 

10x £8 for the bolts and £30 for the gasket... :(

 

Glad you've got it sorted though... 8)

[PhatVR6 0]

and......it wasn't the gasket after all!

 

got it back togheter today, still runs the same, still the same error codes, still 2bar compression on #1

 

f*cking fuming!!!!! and not got a clue what it is either.

 

I still have the original head, but I'l actually tempted to re use the original engine, and fit the crank out of this engine with new bearings. more f*cking about, but it's not like I'm stuck for time, I've got 2 weeks off work. biggest problem is getting the parts (and yet more expense of couse)

 

and ideas?

 

got some pics of the lump to post up.

[h100vw 0]

Are you 100% the valves are sealing?? No sign of broken ring/ Did you try the leakdown check? Thats what I would do before spending more time and money.

Gavin

[PhatVR6 0]

didn't do a leak check, but I will do now.

I'll dismantle the compression checker I just bought and hook my air line up to the pipe.

[CorradoVR6-Turbo 0]

If you had some spare hydraulics it might be worth changing them on that pot.or swap them with another pot but that to much pissing about.

[PhatVR6 0]

hydraulics?

 

tappets you mean?

[CorradoVR6-Turbo 0]

Ok Hydraulic tappets,or are they shimmed?