[urq] WX 000454 is RIP root cause?

[fdekat]

Hello Louis-Alain:

I too have had a blown head gasket, but I'm pretty sure I know why it blew.
Fortunately in my case, all it took out was the gasket.

(pic: http://pictureposter.audiworld.com/80066/headgasket.jpg   You'll have
to cut and paste into your browser, and AudiWorld doesn't allow links)

I was running a MC1 motor, with urq intake, and MAC 02 ECU.
To start with, I though I could hear 'pingin'. On investigation, I discovered
that the 'liquid separator' on the vacuum line between the  intake  and the
ECU had cracked from old age. So the ECU was seeing noting but 1 bar intake
pressure (atmosphere).  So no timing back off on boost. Pulled well, but the
pinging couldn't have been good for things. Replacing the 'separator' fixed
things, but didn't pull as well any more. :-(

Then, maybe a year later, (The week befoere Carlisel, wouldn't you know it?),
I hear pinging again..  On the highway, maybe a day later, I get on it good,
and all of a sudden, a BAD noise..

I shut down, and  pulled over, and all seems OK. Get going again, noise comes
back. So I *really gently* drive home again, and shut it off.  Couldn't find
anything, but put on a trailer, and take it to a friend's shop.   Compression
test on the back two cylinders ~40 lbs.  Pretty obvious what the problems
must be, so off comes the head.

Root Cause?  Back to the ECU again. Only this time, the pressure transducer
was not outputting *anything*. So instead of the ECU thinking manifold
pressure is always at 1 bar, it thinks pressure in the intake was 0 bar. Full
timing advance, probably.

What to do?  Apparently, the pressure transducer in a MAC 11 is
'electrically' the same as in MAC 02, but physically different.

But as I had a MAC 11 harness (and all the required bits), I could see no
sense in repairing the MAC 02 with bits from the MAC 11, when I could just as
easy go to (improved)  MAC 11 management.

So that's what I did. Moved to MAC 11 ECU/harness/bits. Used the original
timing sensors, and the urq fuel distibutor. I now get more boost, knock
sensing and active boost control. Easier to get chipped ECU too..!

Ideally if I HAD to replace the motor? I'd go to a MC2 motor because of the
better 'drivability' (smaller turbo and higher compression), dual knock
sensors and not too much fabrication work. Yet still preserving the 'stock'
look..

=Frank=



> -----Original Message-----
> From: Louis-Alain Richard [mailto:larichard at plguide.com] 
> Sent: Thursday, January 31, 2008 1:10 AM
> To: urq at audifans.com
> Cc: Geraint Lloyd; info at dynodoc.ca
> Subject: [urq] WX 000454 is RIP
> 
> Hi everyone,
> 
>  
> 
> My trusty WX had a little hiccup last Sunday, on the way to Mecaglisse ice
> lapping day. The head gasket blew between cylinder 4 and 5, and the result
> is a dead WX. The head, rebuilt less than 4 years ago, is shot, material is
> gone between the 2 cylinders, and the #4 piston is partly melted as well.
So
> a new engine is in the future for my car. We also found that the turbo as a
> small crack and the exhaust manifold is a little warped too. Oh well.
> 
>  
> I would too evaluate a MC swap, either with the WX CIS or the MC system. I
> want the car back on the road as fast as possible, to prevent the "car that
> sit too long for repair" syndrome.
> 
> Oh, last question: what would cause a gasket failure like this ? When I
> asked Geraint and Brady this very question, they answered (collectively
> laughing) : " Why bother, it's screwed, man ". Well, I want to be sure that
> the failure was not caused by a clogged injector, or an air leak, or
> something else that would resurface with the next engine. The shame is the
> car was going very well prior to that, accelerating hard without any
> hiccups. The failure happened after an half hour drive at 75 mph, then we
> left the highway to take a regional road. Starting from stop, I did my
usual
> 0-60 WOT acceleration, then kaboom ! I kept running for a few kilometers,
to
> find a safe spot to stop. That distance is surely responsible for the
> piston/head meltdown, (my fault), but what caused the first gasket failure
?
> The car was filled with fresh 94 unleaded from the day before. 
> 
>  
> 
> Enough for now, 
> 
>  
> 
> Louis-Alain