Why do Impreza's let go?
 

Thoughts please why does it always seem to be on no three?
This particular car has spun a shell on no. 3
Evidence of hot spots/being dry on no .3
Any further thoughts from
det.
oil starvation
sods law?

it isnt getting enough fuel.. thus burns up the piston because fuel cools down the pistons, My car has been mapped for slightly more fuel to overcome this,
lot of MY99 cars here in Iceland suffered from this

I thought it was of No3 being the furthest away from the oil pump(starvation),hence one of your quotes ...
Not 100% on that tho

The are also concerns that the up-pipe runs alongside No 3, which is one reason I've heard for ppl heat wrapping up-pipe and why standard have the heat shield. Don't know how much of a factor this is combined, I should imagine, with det.

I think it's the furthest away on the fuel rail mate.

Ns04

maybe both then..:wonder:

So fuel starvation possible
Oil starvation possilble
wrong fuel? causing det??

I am worried also regards this particular car as the owner had carried a service out just 100 miles before..Not clear what oil/filter was used.He doesn't remember:wonder:

thnaks for feedback peeps;)

If you are rebuilding it you would be wise to fit an RCM oil pump and swapping the fuel feed to either reverse the supply (Feeding number 3 first) or IIRC Mocom Racing are doing some quite tidy parallel fuel rails..
Carry out a search on the rails...

done 2x P1's recently and both had MAF faults..................

various reasons in the main, det problems on early cars (mainly no.4 piston)
as stated poor grades of oil or bad servicing, various reasons really..........

alyn

Car had a new maf 900 miles ago

All points to bad service/maintanace I think

could be just one of those things. When my car was mapped, it was mapped to add slightly extra fuel on that cylinder.

There are a number of reasons and it is not always No. 3.
Many cars are run with DET and the owner is blissfully unaware.
This can be caused by poor quality fuel eg 95 RON when the car is intended to run 100 RON.
Weak mixture for a number of reasons including bad mapping if the car has an after market ECU or Ecutek.
The top mount intercooler is insufficient to adequately reduce charge temperatures at sustained WOT.
Oil of the wrong spec and of inferior quality.
The O/E fuel rails are capable of well over 500 bhp but as Martyn says above, you can reverse fuel flow direction. I cannot prove why but having done this on numerous Scoobs, it does seem to result in smoother running. Might just be the placebo effect but I believe it is worth the modest effort, even though I cannot prove the gains.

Is reversing the fuel flow as in depth as the parallel fuel mod, i.e. does the inlet manifold have to be removed?

With any well designed and manufactured engine, one part must fail first.
Not to be confused with an inherent weakness. It's just a fact that one part will always fail first.

How do you reverse the feeds to the rails?

hi m8 dont now if this link will help but it might .it's got info on fuel rails
Modifications

So the standard serial set up feeds 4-2-1-3?

The fuel flow standard is 4-2-1-3 and through the fuel pressure regulator and back along the pipe to the bulkhead and back to the tank.
If you are replacing the FPR, then you can reverse the flow simply by swapping the feed and return pipe on the passenger side of the engine, on top of the inlet manifold. Feed then is 3-1-2-4, then the replacement FPR and back to the bulkhead return.
On the O/E system, the fuel comes from the tank/pump to the filter and from the filter to the top fuel feed line at the middle passenger side of the inlet manifold and the return is from the pipe underneath the feed pipe above and back to the tank via a grey coloured pipe that goes through the bulkhead.

I thought it was down to the Center Main bearing journal having to feed No.2 and No.3 Big End, whereas No.1 Main bearing journal feeds No.1 Big End, No.5 Main bearing journal feeds No.4 Big End.
Just my Opinion though
:thumb:

It's a combination of factors....

Driving hard without taking into consideration that you need to either use better oil, OR change it more often. Same goes for short journeys.

Actually bothering to check the oil level between services.

Jap 280ps car not remapped for UK fuels.

Dodgy mods. (MAF killing stainless mesh, foam or mega oily cone filters), Fuel cut by-passing, Bleed valves etc.

Remaps not taking enough consideration to varying fuel quality and engine longevity.

Sensor (partial) failure, causing lean air/fuel mixtures.

Essentially, all of the above can either lead to excessive tempratures, oil breakdown, oil starvation, Detonation and overloading of bearings. Resulting in increased wear, and cumlative damage reducing the engine's expected lifespan

Also bear in mind, any of the above may have happened at any point in the vehicle's past. The problems could be rectified, but the damage is already done, so the overall expected lifespan of the engine is reduced. Thus what you could see is a failure rearing its ugly head several years later, seeming out of the blue.

Cylinder no.3 is the last to receive fuel due to the OE fuel rail design. It is also closest to the turbo so in theory should be slightly hotter than the rest.

A parallel fuel rail mod would help.

How about another theory

Just serviced, oil level up to max which is too much, high revs/high cornering loads, oil in breather system contaminates MAF, runs lean and therefore dets, finds weakest point in engine (doesn't mean engine is weak but every mechanical part ever made has a failure mode as pointed out above) and fails.

Mike

Mike,

Would fitting a catch tank make much difference?
Obviously I realise its best not to fill the oil up that much in the first place.


Dave

Dave

Maybe, but we haven't tried it on a road car.

Mike

Thanks for the reply Mike :)

My thoughts exactly although, I've still to hear an explanation of how with a pressurised fuel system, with the regulator at the end rather than the beginning of the run, you can get less fuel at one end than the other? Surely pressure is pressure? But there is plenty of anecdotal evidence that reversing the fuel flow or doing a parallel fuel rail mod helps. It certainly seems neater that way.

TBH, that 'Number 3' corner of the engine bay is easily the hottest - turbo, uppipe, downpipe, intercooler, brake and clutch systems, it's all over in that corner. And whenever rocker cover gaskets go, they're always in that back corner as well. No wonder it's often number 3 cylinder that causes a problem.

Having seen cars run perfectly happy on a serial fuel rail feeding 12 injectors without showing diferential fuel distribution between cylinders despite having smaller ID piping. I fear that without hard factual evidence, this is not a problem on a STANDARD or mildly modified car and leads me to suggest that this is just conjecture. Possibly the idea is based on 500+bhp cars which may suffer issues owing to them needing a hell of alot more fuel.

The O/E fuel rails are capable of well over 500 bhp.

Thought as much :) (apologies, I missed out a "not" in my above post :o ). Does make me wonder why people do it though. Stuff spread about on forums probably didn't help, no doubt ;)

Depending on model year, the main breather (crancase) Tees off the return pipe from the dumpvalve just before the turbo, which is down stream of the MAF sensor. There is also a PCV valve somewhere that also sucks directly into the inlet manifold when off-boost. The rocker cover breathers draw in fresh (filtered) air (well, they are supposed, at least)