Porsche Enthusiasts Club Forum

Not a new topic I know, but I'd appreciate a bit of advice.

Bought a 90 951 two years ago with only 25,000 miles on it, FSH by Porsche from new, and having been recently extensively 'refreshed' and maintained by Porsche Reading (no expense spared sort of thing).
Since then I have done 7,000 miles including 3 European trips, had a JMG wastegate and manual boost controller fitted (max 1 barg) and a 'Superchip'. All has been good apart from two things and I want to know what (if anything) you'd recommend:

1. Oil consumption. I have never owned a turbo before, so I was unprepared for the technical booklet saying 1 -1.5litres every 1000 km was to be expected. When I first bought the car the consumption was at the lower end of this range, but this has been increasing and on the latest trip of 1250 miles (2000km) I used 4 litres of Mobil 2000 10w-40 - so 2l/1000km. Virtually all of these 2000km were on French autoroutes at 80-85mph (3-3500 rpm). There is no blue smoke on start up or hard acceleration and no oil in the water. It is a white car and there is minimal/no soot visible around the exhaust. So where is it going ....? And what are the possible causes if it's an issue.

It was just serviced by a Porsche specialist (Parr) before departure and needed new plugs as it had started to falter on acceleration. Other than this no issues were noted.

2. With my old (72) 911 when you blip the throttle the response is instantaneous, with the turbo there has always a bit of 'hesitancy' before the revs pick up. I don't think this is turbo lag, as this comes later! Mind when the turbo wakes up she goes off like rocket-ship! Again just wanted to know if this was a characteristic of these engines, or whether there is anything else I could check.

Any help appreciated. I am new to turbo-charged cars in general and 951's in particular, so please don't assume I am aware of the basics! Fuel consumption was about 30mpg

Thanks
Mick

I should perhaps add there are no oil leaks of any kind - not a drop on the garage floor.

Mick

How does your coolant look? Also if you get the chance, pop the intake hose of to the turbo and see if there's oil in there. The seals on the AOS system can go and kick oil into the inlet as can the seal on the turbo.

Thanks Darryl,

Coolant looked good when I last looked (before this trip), and nothing was mentioned at the service.
I will look in the turbo intake as you suggest.
All I have read to date about the Air Oil Separator seals is that if they are u/s, or the pipe is split, they leak out onto the engine. If so then there is no sign of external oil leaks anywhere.
If there is oil in the turbo intake what does that mean re repair?

Mick

If you had bits fitted at JMG than I suggest you give Jon a ring for some advise on the oil consumption.
Don't do many miles in my Turbo, only covered 17,000miles in 8 years but never had to top up annually. 2l/1000km seems a bit excessive to me.
Clive

I would say that's pretty excessive, how hard are you driving it? 80/85 mph shouldn't sweat it, are you off boost at that speed. It can be quite hard to keep that speed on a hill and keep the boost needle below 1 bar.

What's you mpg during that mileage?

I would expect an oil leak somewhere. Leave it running over a wet ground. Will be easier to spot

As I said above I think the mpg was about 30 - just an estimate, but certainly it was pretty good.
Maintaining the speed did cause the turbo to boost to about +0.5bar quite often as there are quite a few hills on the route and the car was pretty laden, and I enjoy driving it! - but as you say the motor was coping easily and if it wasn't for the oil consumption I'd have said it ran smoothly and easily.
I'm sure there is no oil leak. The garage floor is clean dry concrete and even a drip would show clearly.

But as you say it does seem excessive, and it does seem to be slowly increasing over time, so I do think something is not right. Just looking for things to check out I suppose.

Oh and JMG didn't fit the wastegate - I just bought it there. It was fitted by Parr Porsche in Crawley.

Thanks
Mick

Might be worth getting a compression test done + a call to Jon at JMG he will give you some advice/suggestions on what to look for.
HTH
Clive

Mpg would suggest a light foot. Mostly off boost.

I would say to try a different oil 15/60 Mobil is what I use.

Are you filling from dip stick? Maybe keep it around half way and see if the consumption is less

Have you had anybody follow you whilst you are giving beans to check if anything is coming out of the exhaust? mine uses about half litre per 1000miles.

No, not had anybody following - just me looking in the mirror, and the lack of any soot/oily mess around the exhaust. It's a white car as I said and pretty much anything shows!

I'm going to have a poke around into the intercooler pipes and the turbo intake and see what I find. Might also remove the intake manifold and see if I can see any oil pooled around the closed exhaust valve that might indicate valve seals are going/gone. I understand you can change these without removing the head??

Mick

Ok I have time for a bit of exploration, and the results to date are:

1. Had a good look over the engine with flashlight and endoscope. There are no external oil leaks of any size, anywhere.

2. Removed the intercooler pipes, and the air intake for the turbo. While there is the faintest smear of oil on the surfaces there is no evidence of any liquid in any of the pipes, the turbo intake, the throttle body and inside the turbo.
I infer from this there is no evidence of turbo bearing leakage or any oil consumption issues related to the turbo. Is this correct or do I need to check anything else? This would fit with operation as the turbo boost is superb - when it arrives!

3. I pulled all the spark plugs. These are Bosch WR7DC+ plugs and were new at the service immediately before this trip, so they have done ~1300 miles, predominantly at 80-85mph, with good fuel consumption.
To me they look black for relatively new plugs 1-3 not excessively so, but No.4 has evident significant carbon buildup.
Also car was starting to miss/run on 3 just before the service and the new plugs sorted that, but I now wonder if they (or just No.4) were badly coked. Asked the garage, but the service manager said it wasn't noted - not to say they weren't though!

So I'm thinking my issue is most likely valve seal or piston ring related, most likely the former given the overall performance of the car.

Next step is compression/leak down test on Friday when my mate arrives with his tester kit.

Oh and I might have found my throttle response issue. The cable is slack - it moves about ⅛" before being tight enough to move the throttle. I assume this should not be the case. Again if someone could confirm it should be tight please.

Any comments or observations on this appreciated.

Mick

Cable should have a slightly play. There should be a click from the tps black box on side off throttle when cam is slightly moved. To tight and there be no click

Won't that trigger the engine oil light? In both of my 944s 1/2 way was when the light tended to illuminate.

I have readjusted the cable such that when you press down on it slightly the 'click' can be heard. This has moved the adjustment bolts by at least ⅛", so I cannot but think this will be noticeable.
Anyway I hope to do the compression/leakdown tests later today and will report those.

Mick