Pete Croney

I meant to add that all the very hot oil from your turbo goes back into the block in cylinder 3 head.



It would be sensible to modify the sump to receive this oil direct on cars that are running high boost/used at high speeds.

Jay m A

iTrader: (2)

What about abrupt lifting off at high speed? Are there different stresses involved when engine braking? How does the ECU fuel when the throttle is snapped shut yet the car is at high rpm in 5th?

Justin

ustolemyname??stevieturbo

iTrader: (1)

Would I be wrong in saying that it seems to be more common on later engines?? I have heard of more approx 98 onwards failing than earlier engines. The oil surge thing may have some foundation, as perhaps at high speed running, ( and not specific to cornering ) there could be a lot of the actual engine oil flying around the crankcase, and building up around the cylinder heads, which would possibly leave the sump with less than desireable oil levels, which would be made worse by a static low oil level. Perhaps a larger capacity sump may help if this is possible. I would also think that a proper oil cooler would be a good preventative measure, as it would help the oil maintain its properties. As always though, good oil is a must. Semi-synths arent worth it, go for a top notch fully synthetic oil, that isnt too thin.
Curious as to why you say 3 and 4 are the last to receive fuel on the rails Adam?? 3 and 4 are on opposite sides of the engine, both being the rear cylinders, so on will be first, the other last.

Bob Rawle

For some real reading try this,

http://www.scoobynet.co.uk/bbs/thread.asp?ThreadID=29769&Page=1

the subject was extrensively debated in this thread.

The theory re scoop and air delamination has been heard before, whilst it may happen I checked my own car with an airflow meter, flow thro the scoop just increased with speed. I only checked my car practically, theory is ok but practice sometimes different, be good if a few others could do the same.

Det can cause it, you would see evidence though, on Phase 1 engines no4 cylinder will always be richer than any other due to manifold design, phase 2 is much more evenly distributed, most cars that det badly blow the piston first though, quite often the big end is still ok.

Certainly starts as pick up causing a hot spot, that may then clean up or degenerate into failure at a later date.

Hard running at high revs high load will do it, engine (std) not designed for that, temps get too high.

Lots of evidence that servicing technique is an influence, oil quality, oem or aftermarket filters, yes you must pre fill the filter, then let it stand to soak up oil into itself then fill again and repeat till it stays full ... but also take off the crank sensor and crank till the oil pressure light goes out (be carefull not to burn out the starter) then replace connector and start normally.

Oil temp over no three is no different to anywhere else, checked it every where including sump.

Fuel pressure at no 3 will be as per factory design since that is where the regulator is, other cylinders will probably see higher not lower since the fuel flows around each injector to get to the next.

Just a few additional thoughts but the indicated thred covers it all in detail.

cheers

nom

Just reading the first few on that old thread reminds me - a couple of months ago, someone was on here having had 3 big-end failures, each fixed replacing sensible parts, except for the MAF which somehow wasn't broken... And Subaru thought it was the ECU. Two things - how would the ECU manage to do this, and more importantly, if all relevant parts are new, why does it do it again twice more when it's, well, new?
Confoosing.

Fuzz

Couldn't the fuel thing be ruled out by fitting lambda senors to each exhaust port and measuring independantly or is that point to "hot" for the sensor.
has anyone tried this already.
even if expensive, surley it's cheaper than a re-build

WREXY

To add to what Gravelexpress said in his post, I was speaking to my friend who is a scooby tuner in OZ and he said that big end bearing failures were not common on street driven cars in Australia. He said that bearing failures usually happened to cars that were used on the track, hence my suggestion that it could be due to oil surge or even top end speeds. The speed limit in OZ is 110kph which is roughly 70 mph. It is strictly monitored with lots of speed traps, including gatsos, laser, minigatsos and radar traps and people rarely do top end speeds. They mainly accelerate quick then back off. It may be the reason street cars aren't having big ends let go over there.

Cheers,

Wrexy.

mutant_matt

Just to throw another one in the pot....I recently found out that apparently, there is a known problem with some 98 (ish) UK cars having a bug (or something like that) in the ECU which can cause Det. This is on a completely standard car.

I know of a UK car which has blown up 6 times under warranty (admittedly driven badly (hard from cold etc.)) and IM paid out each time.

I can try and find out some more detail if anyone thinks it's relevant?

Matt

Bob Rawle

More no 4's go than no 3's ... so does not compute and since the ecu overfuels wildly in most cases there is plenty of scope there. Also just as many std cars go ... fuel pump more than adequate for those. No its not that ... have to consider the whole not just focus on one cylinder, "Big End No 3" is the nickname but is reality its any of them and mostly no 4.

Also the evidence does not support cylinder 3 overheating in particular. In fact no 2 cylinder is the leanest in practice especially on phase 1 engines.

nom

OK, any cylider could go, but from the stats collected so far have any of those that have let go had uprated fuel pumps? As it could still easily be the weak link, even if the actual cylinder differs...

WREXY

Don't know if this is true but I was told that the MY00 stock fuel pump is better than the MY99 one. Is this true? If so, there are still plenty of MY00 stockers that have had big ends go on them. Quite a few have broken here in Greece.

Cheers,

Wrexy.

nom

That's another bit of info I haven't seen - which may give more 'hints' - is there a particular time of year that engines go? You never know - if ambient temperature is a contrubuting factor, it could tell us something? Maybe?

fivepint

just to add my 2 cents, when 'we' say high speed running do we mean road speed ? not too sure why a 112mph limiter would prevent an engine from being driven at high revs for extended periods, I only say this as a personal observation that during a hi-speed 3rd/4th gear back road blast my car would be reving high for extended periods, has the paralel/series fuel rail mod been done on alot of UK cars?

Cheers

ps: Pete if ur still reading this do u do a modified Carbon scoop for the "classic" impreza (MY00)?