A Query for those technical out there

[adsgreen]

If it's the vac line or one way valve under the manifold then I could see it - the vac lines have been known to "pop off" and the one way valves are not great. Just a piece of rubber in a sealed unit so will fail eventually 9why MRC change them whenever the manifold is off and why I advised the DIY'er doin the manifold to extend the vac line to make the one way valve changeable without resorting to manifold off.

Anyway if either have failed or another vac line has popped then would explain why it went so quickly. The reason you'd have got occasional misfires was down to the vac leakin and the levels getting really low. As soon as you stopped the car then no vacuum being generated but the leak would have been on going and when you restarted you'd have been in the same position as me and the car just freaks out.

[P_G]

adsgreen (or anyone else who knows for that matter), given you have replaced the one way valve and by the sounds of it the solenoid as well can you get these form Audi? I was always under the impression it came as part of the IM as a complete unit?

And what are the costs for the valve and solenoid?

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The one way valve is under the intake manifold and is under a tenner- it's why mrc replace them whenever the IM is removed.
As for solenoids, there are quite a few dotted about but the only one part of the IM is the runner flap control.

[P_G]

I gather you can get them all individually though?

[adsgreen]

One way valves definately. Runner flap solenoid pretty sure you can.

[P_G]

No call today from Audi so I called them and it was still being diagnosed but nothing yet, likely to get a call sometime on Monday. Haven't even been quoted a price for diagnosis. So I have organised a flatbed to pick the car up as I suspect it will be going elsewhere to be fixed.

[ArthurPE]

the fact that you just had the manifold off and the flaps removed (they are vacuum operated) implies a possible vacuum issue
the IM sensor codes are due to the removed flaps?

don't know if it's related to the misfires
N145 is the Right Electro-Hydraulic Engine Mount Solenoid Valve (the right side is also the majority of the misfires)
page 35 http://sandbox.enjoybeing.net/audi/4.2-fsi.pdf
since it's saying and open ciruit perhaps a wiring problem for sensors in the same loom?
perhaps if the mount is bad movement has damaged/broke some wiring?

this might help http://forums.quattroworld.com/allroad/msgs/62853.phtml
an Audi mechanic comments in the thread bad mount = misfire(s)

after some more digging: there is supposedly a TSB out that relates to this: bad mount wiring = misfire

[adsgreen]

'open circuit' is a bad description. The ecu is expecting a voltage change with the engine mount but ad the mount is vacuum controlled and there appears to be a big vac leak.
My money is on a hose under the im.
Edit: ah rs4 mounts don't look like they hook into the vac system so a shorting mount could cause havoc too.

[P_G]

So the two potential issues are either bad engine mount / wiring to the solenoid on that mount or vacuum related but likely to be the latter since the IM has been off.

[adsgreen]

Yup - sounds reasonable to me.
You could easily test the mount by unplugging it, clearing fault logs and seeing how the car idles.
A vac problem will be obvious but a mount should mean it runs ok.

[P_G]

So, the official diagnosis from Audi this morning is that one of the manifold core plugs over cylinder 5 has gone AWOL (don't know how I missed that on visual inspection but I did! ) so lots of air getting in / out that isn't supposed to. More worryingly the spark plug in cylinder 1 is damaged although when they have run the engine plugging up the hole in the manifold Audi reckon it runs perfectly OK and no codes but low compression (probably because there's a hole in it and deflapped). The side electrode is effectively bent over the central electrode.

So the car is now at Revolution awaiting my Thursday workshop slot so they can open it up again, change all the core plugs as a precautionary and go on the hunt for the missing one assuming it has gone in rather than out and borescope cylinder 1 to see what's what.

Very odd.

[adsgreen]

wow - thats a pretty extreme case. Don't beat yourself up for missing it... definately not an obvious cause.

Depends on how the plugs look - they can bend without being mecahnically hit. I've had plugs damaged when they've been changed. Would be obvious on the piston if anything had clunked it. If the core plug had got in there it would have trashed everything very very quickly and most likely still be rattling about.

The symtpoms you decribed completely fit with a sudden massive loss in vacuum which a hole that size would cause.

[P_G]

It's just the one plug that is mishapen in cylinder one and the side electrode is still in place and in one piece, like said just bent over the central electrode. All the other plugs are fine but were replaced as a precaution. Soon see what the borescope shows on Thursday but when they were checked the last time the IM was off all were clean as a whistle and score free.

It would surely be very difficult for a 1p sized core plug to get past the inlet valve anyway and if it has bang goes the theory that carbon build up occludes airflow on the valves because there would be no way a core plus would get through in such circumstances!

[2manytoys]

I hope all is well.

If you are talking about the little caps, that when popped you can access the flap screws, I also think it would be hard for the engine to swallow one of those (not impossible though if it bounces around on/off the valve).

You may have run so lean that Cylinder 1 got VERY hot. That may have damaged the spark plug (and piston). Here is a pic of a plug from my race car. Once we pulled it apart I had no valve tops and a massive hole in the piston (that happened at 8000rpm down a back straight though). Still don't really know the cause



Let's hope things aren't too bad. Good luck.

[P_G]

Damage was not the right word to use in my statement from yesterday as there is no physical damage to the side electrode, it is just squished / bent over the central electrode but in one piece with no marking on it. Not like the pic you or Gumball0r has posted up. So heat may well have bent it. Audi were happy enough to change the plugs, plug the hole where the core plug was and run compression testing after clearing the codes and they would not come back on although compression was down on some cylinders

Will know on Thursday but fearing the worst as that costs most money!