EddScott

I've been to see and enquired about a fair few P1s recently and each one, the owner has had a different story as to why the engine has blown.

Only one at 87K hadn't had a new engine but had been mapped for UK fuel. Some other sub 50Ks were on the OE engine.

Now I thought the story was that Prodrive didn't map the P1 for UK fuel. I've said this to one individual which almost started row over what a silly thing I'd said to imagine Prodrive doing such a thing. I thought they'd had these fuel pellets put it in the tank - again looks of shock and bemusement.

One guy said it was because the two halfs of the engine block move and become shaped rather than flat and a whole new engine is required - never heard that one.

[Cat mode]
"So what is it?"

New_scooby_04

iTrader: (4)

Not an expert myself mate, but IIRC a few well known mappers have come on here and said that the P1 ECU has a pretty much a STi 5 map i.e. not optimised for UK fuel.

Awaits clairification

j16jrf

iTrader: (3)

surely prodrive would have mapped them for uk fuel?

joz8968

iTrader: (13)

As you may, or may not, know, the P1 is based on a JDM STi Type-R Version 5. As part of the UK type approval process, Prodrive got STi to re-map the ECU so that the motor could run OK on UK 95 RON fuel. I've read that STi, allegedly, didn't do a very good job of it... <can of worms opened here...>

The best person to shed some light on this is probably APIDave... Dave are you about?!...

drb5

iTrader: (4)

I reckon there's a few things that add to the engines blowing up. Oil, fuel, servicing, etc. My own P1's engine hasn't given up yet and has 47500 miles on it(which is for sale at the moment ) and quite a few other guys have engines which are yet to let go with over 60-70k miles on them.

drb5

iTrader: (4)

As stated in a small P1 brochure i have, they say to use at least 97 ron fuel when available.

joz8968

iTrader: (13)

Unfortunately, my WRX's (c. 90k miles) has just let go - dreaded rattle on start up the other day (spun big end shell, I reckon) .


<Sorry, back to original thread starter...>

joz8968

iTrader: (13)

Sorry, it may have been for 97 RON anyway.

+Doc+

I think the choice of fuel has a lot to do with it, The cars are getting on for 7 years + and I bet a fair few that have gone bang have had low ron put in from time to time.
Stupid modifications dont help, nasty dump valves and performance mods without having a re map.
Mine has done 50k, I`ll let you know when it goes pop :x

scoobynutta555

The truth is that even the 'experts' have conflicting views of why P1 engines, indeed classic engines go. My take from this is no-one really knows and just push forward their best guess as to why it happens. The vast magority of P1s will have been run on Optimax or V-power so a theory based of RON levels alone seems a bit dubious to me. I would just say there was an inheriant fault thoughout the whole range with the engine and it rears it's head more frequently with higher tuned Imprezas.

How many new shape engines do you hear this about on Imprezas?

joz8968

iTrader: (13)

I totally agree with the above. The engine's boxer configuration must have something to do with its inherent weakness on Classic Impreza's (quite apart from other contributing factors)...

p1mark

The P1 under the shell is pretty much pure STI5, including the ECU. It has not been remapped by prodrive, the base fuel and ignition maps etc. are identical. There is however a little bit of extra knock correction in there.

As for fuel broquets, even if they are in there, these things have been proven in the past to have little effect.

There is a an awful lot of crap talked on this forum at P1's blowing up. They are not the most reliable of Imprezas for sure but i have seen figures of anywhere from 50% to 80% of them have popped. Where they get there info from i don't know.

If you look over on P1woc there is a poll that will give you the best indication of the facts (how many percentage wise) and reasons why (according to the owners and not some idiot who likes the sound of his own voice on here).


I personally blew my own up by holding it at 150mph+ for miles on end with oil temps at 120 degrees+. I.E hardly a fault of the car, more my own for being a complete idiot.

The reasons for the majority of failures are two fold and the same as any other Subaru - 1) detonation related (pistons nibbled/holed etc) 2) big end failure.

What causes these are many and varied, some proven, some internet heresay, some a load of crap.

Some definites are these:-

Oil pressure loss due to oil pump cover retaining screws loosening.
MAF failure causing lean running and subsequent detonation.
Top speed runs for anything more than a short distance.
Poor rebuilds - the amount of cars that have gone for a second time shortly after a rebuild (normally at a dealers) is shocking.
Caning it on low spec petrol.

Some distinct possibles:

Oil pressure relief plunger sticking.
excess oil temp affecting lower spec oils.
Poor servicing techniques (there are a number that have gone shortly after a service. could be coincedence, could not be?)
Detonation shocks down rods (caused by MAF/petrol etc) knocking out big ends.

Then there is the stuff like you mention above (instability in crank cases) that is impossible to prove and more likely than not a load of bollox.

New_scooby_04

iTrader: (4)

What are these weaknesses?

I know three "common" for want of a better term inherent causes of engine failure on the Subaru flat four (please forgive my crap layman's descriptions): one is the OEM Oil pump, which on rare occassion gets stuck open, another relates to the layout of the fuel rail, which has been known to cause problems on occassion, then you have the good old high speed airflow to the TMIC issue. That said, Subaru never saw fit amend the cars spec, with the exception of the latter issue untill very recently, with the front end re-shape. So they can't all be the villians they're made out to be under all circumstances. None of the above are weaknesses in the flat four configuration itself though (except maybe the fuel rail issue, but its not like the flat four won't accept a parallel fuel rail mod if I understand it correctly): it's the supporting bits that let the engine down.

If it's true that the P1 runs an STI 5 map, then it should be getting 100RON fuel, if owners have been running it hard on 97 RON as the handbook says (98 and 99 RON availability is more recent) then that would account for why they can let go suddenly at different mileage. These cars will be driven hard at some point, so any such deficiences could spell expensive trouble!

It is hard to believe that prodrive didn't account for this though!

Edit: forgot about the good ole MAF sensor weakness, a known killer of 99/00 engines! Hardly a problem inherent in the flat four design though.

The biggest problem is probably the people who drive em for the most part, to be honest How many people do you know that drive these cars with no mechanical sympathy! Some of the meets I used to attend made me wince! Couple that with the fact that classics are getting on now and some are falling into hands of people who don't look after them properly.

We seem to forget about the amount of examples (mine included) that run about 50% more power than Subaru released the car with and have no reliability problems whatsoever!

Andy.F

Good summary Mark

Vampire

Yup, that's basically what Bob Rawle told me when I had mine too.

Andy.F

What ? that Mark was good at summarising

exvaux

iTrader: (1)

but its not just p1's my sti5 type R is awaiting a new engine as we speak

joz8968

iTrader: (13)

I agree that the major problem would, obviously, be lack of mechanical sympathy, etc. but, just as an example, on a pro rata/percentage basis, what's the ratio of Lancer Evo engines letting go compared to the Impreza? (There's certainly one engine builder that'll be able to enlighten you...)

So I'm convinced that there is ultimately a weak link/s to the motor which kick off the 'problems'... [just my, albeit considered, opinion, of course]

New_scooby_04

iTrader: (4)

I'm not entirely sure that's a fair comparison mate. One problem is that Subaru do std and STi spec engines, the latter having tougher internals as std. There is no such division with Evo engines as fas a I know - they all get the tougher stuff as std (?)

Also, I'm not sure about the evos mapping for RON, was the equivalent year to the P1 mapped for 100RON, or with more tolerance? What about relative numbers of cars in the UK? At that point Evos were grey import only, the P1 was a "UK car". More UK cars brought by joe "it's just a car" Blogs, more failures than imports brought by Calvin "my car is my pride and joy" McLovin!

exvaux

iTrader: (1)

every car has its quirks withregards to engine problems,for imprezas with piston damage/big ends away same can be said for evo 1-4 and crank walk

joz8968

iTrader: (13)

Of course, there certainly appears to be a lot more Imps than Evos - that's why I qualified my statement with 'pro rata/percentage'.

I see what you mean by STi internals being stonger than WRX's but don't more STi variant motors let go compared to WRX's (or at least a similar number)? Perversely, perhaps the tighter STi tolerances do them no favours?

Vampire

Heh, good one.

joz8968

iTrader: (13)

Of course, I understand that... It just seems to me that, unfortunately, for us, the Imp's motor - in comparison to a lot of other similarly high performance turbo'd engines - seems to be particularly weak - for whatever reason/s. After all, the evidence is all around us!

New_scooby_04

iTrader: (4)

Pro rata percetnage is confounded by the type of owner who would import as opposed to buy a UK car, I'd argue.

Again, there is a problem comparing STI engines per se with Evos, as untill the bugeye all STis were JDM market (they have caused problems over here on pooer fuel) after that we started getting UK market STis and instances of failures declined very rapidly.

Ns04

New_scooby_04

iTrader: (4)

I reckon if you compare instances of failures in UK spec STis with UK Spec Evos running comparable power (that's the fairest comparison), there would be no significant differences in instances of engine failures......if only we could equate driver competence and inclination to look after the car properly

It's my understanding the evo is more amenable to higher levels of tune though. Stand to be corrected!

joz8968

iTrader: (13)

For sure - but there's the crux... All genuine STi badged Classics are JDM cars (same with Evos 1 to 6). So there is a direct like for like comparison, based on the 'wrong' UK fuel for these cars...

New_scooby_04

iTrader: (4)

Assuming that the evos are also mapped for 100 RON with the same limited capacity to retard ignition etc.. for lower RON fuel, then yes, I guess so!

I suspect they're not equal in that respect. Perhaps scoobies are more sensitive to factors relating to fuel other than RON. I recall hearing Bob Rawle talk about what a P1 ECU does when you put BP ultimate in the car compared to Optimax (both were 98 RON at the time). Evos didn't seem to mind it though! Suspect that has more to do with mapping that the engine configuration per se???

I wish I wasn't such a technical ludite!!

joz8968

iTrader: (13)

Yes, I'm pretty certain Evos 1 to 6 were designed to run on 100 RON, like the JDM Classics (but don't know how far their ECUs can retard their ignition for lower quality fuel, compared to the Impreza).


What happens? I'm intrigued...

New_scooby_04

iTrader: (4)

I don't think I can do Bob's description justice mate, but it was something to the effect of the ECU pulling all the car's ignition advance out of the map etc...

He refererred to it as the worst SUL available for Imprezas and horrible for tuned cars generally IIRC I'll see if I can dig up the post for you!

NS04

stoneface

iTrader: (6)

[quote=p1mark;7427514]

I personally blew my own up by holding it at 150mph+ for miles on end (on a private test track)