Turbo questions
Discussion
As you may have seen in another thread I am the proud new owner of a 3.3 Turbo (930).
Now that I have lived with it for a weekend I have discovered some of its foibles and potential problems.
I filled it up with LRP on Thursday night (60 quids worth) and having covered 130 miles it is down to 1/4 tank - I make this 10.5 mpg & I assume this is not normal.
The loud noise I noticed (as the boost comes in) when I first drove the car now sounds like a mis-fire (in fact sounds like a Le Mans Porsche GT3), it's also got a burbling, banging, crackling exhaust on overrun. I'm guessing this means it is running rich which ties in with the fuel economy question above.
Finally the generator light comes on (and eventually goes out) when the car starts up, the lights flicker at night and there doesn't seem to be enough juice to drive the stereo. Is it likely that my alternator is kaput or are the alternators on these cars feeble anyway? Is the alternator buried inside the engine like with VW campers? & what sort of price would I have to pay for a new alternator or brushes - assuming I don't want to get my hands dirty.
Any help on the above gratefully received, I guess I will need to find a rolling road to have the mixture set up.
Cheers
Dan
Now that I have lived with it for a weekend I have discovered some of its foibles and potential problems.
I filled it up with LRP on Thursday night (60 quids worth) and having covered 130 miles it is down to 1/4 tank - I make this 10.5 mpg & I assume this is not normal.
The loud noise I noticed (as the boost comes in) when I first drove the car now sounds like a mis-fire (in fact sounds like a Le Mans Porsche GT3), it's also got a burbling, banging, crackling exhaust on overrun. I'm guessing this means it is running rich which ties in with the fuel economy question above.
Finally the generator light comes on (and eventually goes out) when the car starts up, the lights flicker at night and there doesn't seem to be enough juice to drive the stereo. Is it likely that my alternator is kaput or are the alternators on these cars feeble anyway? Is the alternator buried inside the engine like with VW campers? & what sort of price would I have to pay for a new alternator or brushes - assuming I don't want to get my hands dirty.
Any help on the above gratefully received, I guess I will need to find a rolling road to have the mixture set up.
Cheers
Dan
Dan, the altenator is inside the fan on the engine. If you go to www.autofarm.co.uk you will see they're doing a deal on them at the mo. as for the crackling and popping on overrun, do you have an aftermarket exhaust, if so that will be the noise.
You are quite right in needing a rolling road to check the mixture. Im not sure but the 965 3.3 which has the same engine and this has two distributors and twelve spark plugs, the second dizzy is run off a rubber belt from the primary dizzy, this belt can break meaning you only have half the sparks needed especially on full boost. this will cause 'pinking' and can be loud, also will give you crap milage. you can check the belt is intact by removing both dizzy caps and checking the rotor arms dont move indepently from each other. hope this helps.
You are quite right in needing a rolling road to check the mixture. Im not sure but the 965 3.3 which has the same engine and this has two distributors and twelve spark plugs, the second dizzy is run off a rubber belt from the primary dizzy, this belt can break meaning you only have half the sparks needed especially on full boost. this will cause 'pinking' and can be loud, also will give you crap milage. you can check the belt is intact by removing both dizzy caps and checking the rotor arms dont move indepently from each other. hope this helps.
Forget the fuel comsumption figure until you have done at least a couple of tanks, and do a top-up to top-up measurement. Some gauges drop like a rock over the first or last quarter. I would imagine 10mpg hoofing it, low to mid twenties on a cruise. Maybe high teens overall.
No harm checking mixture tho' etc. On a turbo car it is very important to have the fuelling right to prevent detonation etc. This often means running it rich, hence the popping and banging on the overrun. This is OK, just a sign of overfuelling and a less sophisticated injection system than some cars have these days.
Misfires are felt rather than heard, and Le Mans Porsches do not have misfires, so I'm not sure what you are talking about with the misfire thing. If the car hesitates or jolts then you have a misfire, which could be any one of 40 or 50 things on a car like a 930... from a simple spark plug to wastegate actuation problems etc.
AFAIK, the 930 does NOT run the twin dizzy set up. This was a feature that Porsche introduced in 1989 with the 964 C2 and then carried over to other models later. I may be wrong, but check for twin dizzies before checking for twin dizzy problems
The generator light does sound like an alternator problem, and should be changed asap before the car lets you down. In my experience, you have only a day or so of flickering before the battery fully drains and the AA have to come to your rescue. The alternators are good enough when working fine. Dunno about prices as I'm sure it depends on what a main dealer can get away with - probably between 100 GBP up to 250 GBP - have a look at German and Swedish online (google it) for prices as these guys do Bosch factor parts for porsches. Get a Porsche tech to fit it for you - you will need a friendly one with a 930 as things will go wrong, sadly.
Cheers
Dom
>> Edited by domster on Monday 22 September 15:42
No harm checking mixture tho' etc. On a turbo car it is very important to have the fuelling right to prevent detonation etc. This often means running it rich, hence the popping and banging on the overrun. This is OK, just a sign of overfuelling and a less sophisticated injection system than some cars have these days.
Misfires are felt rather than heard, and Le Mans Porsches do not have misfires, so I'm not sure what you are talking about with the misfire thing. If the car hesitates or jolts then you have a misfire, which could be any one of 40 or 50 things on a car like a 930... from a simple spark plug to wastegate actuation problems etc.
AFAIK, the 930 does NOT run the twin dizzy set up. This was a feature that Porsche introduced in 1989 with the 964 C2 and then carried over to other models later. I may be wrong, but check for twin dizzies before checking for twin dizzy problems
The generator light does sound like an alternator problem, and should be changed asap before the car lets you down. In my experience, you have only a day or so of flickering before the battery fully drains and the AA have to come to your rescue. The alternators are good enough when working fine. Dunno about prices as I'm sure it depends on what a main dealer can get away with - probably between 100 GBP up to 250 GBP - have a look at German and Swedish online (google it) for prices as these guys do Bosch factor parts for porsches. Get a Porsche tech to fit it for you - you will need a friendly one with a 930 as things will go wrong, sadly.
Cheers
Dom
>> Edited by domster on Monday 22 September 15:42
Thanks for all that.
AFAIK the exhaust is an OE one, the two tailpipes appear to be welded together (or is that a casting?). Doesn't look boy-racerish.
The 'misfire' I speak of is crackling under power, it's not pinking or detonation - seems to be coming from the exhaust or inlet.
Turning the 'getting ones hands dirty' issue on its head - is there a Haynes manual or equivalent available for this car? I am a chartered engineer so am fairly adept at spanner twirling but prefer to leave the hassle to someone else. Only trouble is, I don't know anyone I can trust yet.
AFAIK the exhaust is an OE one, the two tailpipes appear to be welded together (or is that a casting?). Doesn't look boy-racerish.
The 'misfire' I speak of is crackling under power, it's not pinking or detonation - seems to be coming from the exhaust or inlet.
Turning the 'getting ones hands dirty' issue on its head - is there a Haynes manual or equivalent available for this car? I am a chartered engineer so am fairly adept at spanner twirling but prefer to leave the hassle to someone else. Only trouble is, I don't know anyone I can trust yet.
Could the 'crackling under power' be induction noise? Is it purely noise or does the engine misbehave? I'm not sure we can ehlp unless we can hear it. One for the mechanic, as it could be normal for all I know...
You can get workshop manuals for Porsches (not sure Haynes do the turbo models), I think gmund books do them (google it). These are quite expensive and to be honest, a turbo is not the simplest car to work on and there may be some specialist tools you'll need to invest in. Give it a go if you're brave enough, tho'
If you are based in Essex, JZ Machtech in King's Langley may only be an hour or so away, and they are trustworthy and good value. There may be other Porsche techs nearer to you, but JZ are rare in that I'd recommend a drive to them and am positive that they'll look after you.
You can get workshop manuals for Porsches (not sure Haynes do the turbo models), I think gmund books do them (google it). These are quite expensive and to be honest, a turbo is not the simplest car to work on and there may be some specialist tools you'll need to invest in. Give it a go if you're brave enough, tho'
If you are based in Essex, JZ Machtech in King's Langley may only be an hour or so away, and they are trustworthy and good value. There may be other Porsche techs nearer to you, but JZ are rare in that I'd recommend a drive to them and am positive that they'll look after you.
Your exhaust (or at least the tailpipes sound like the OE system, but could be a modded silencer ? I changed mine from the standard rear box which is pretty muted with no pops and bangs, to a very open one which was very loud and popped and crackled like a good 'un on the overrun. While it was loud under acceleration though, it was a 'clean' roar with no crackling sounds. I liked it, but it's a personal preference thing and definately no good for trackday noise tests.
Fuel consumption I'd agree with the other comments : Up to 25 on a motorway run down to low teens giving it stick.
Fuel consumption I'd agree with the other comments : Up to 25 on a motorway run down to low teens giving it stick.
Thanks for all your tips, this is all very interesting to me, I guessit's not so interesting to everybody else but at least reading this thread is not mandatory 
My alternator problems seems to have gone away (at least temporarily) - could have been sticking brushes I guess.
The comments about fuelling and/or economy have been very useful - in the main I have been hammering it about so the economy is bound to be low and I won't work out exactly how low until I fill up again.
Today I noticed that the heater doesn't work - I drive about 23 miles to work so there should be opportunity for it to warm up. I had the thermostat set to DEF and the sliders on defrost as well but no heat was coming out. Is it likely to be the thermostat or will I have to inspect the hoses?
Finally and potentially more worrying, I do leave the car running for a minute or so after I have been out for a drive (to keep the turbo lubricated). A minute or so after shut down a cloud of oil mist emerges from the OSR wheel arch - presumably this is venting from the dry sump tank and I guess it's not normal! What should I be looking for? Is it a vent hose that's fallen off?
My alternator problems seems to have gone away (at least temporarily) - could have been sticking brushes I guess.
The comments about fuelling and/or economy have been very useful - in the main I have been hammering it about so the economy is bound to be low and I won't work out exactly how low until I fill up again.
Today I noticed that the heater doesn't work - I drive about 23 miles to work so there should be opportunity for it to warm up. I had the thermostat set to DEF and the sliders on defrost as well but no heat was coming out. Is it likely to be the thermostat or will I have to inspect the hoses?
Finally and potentially more worrying, I do leave the car running for a minute or so after I have been out for a drive (to keep the turbo lubricated). A minute or so after shut down a cloud of oil mist emerges from the OSR wheel arch - presumably this is venting from the dry sump tank and I guess it's not normal! What should I be looking for? Is it a vent hose that's fallen off?
Hmmmm, how closely did you look at this potential minefield of a car before you bought it, Dan? FYI it should have a wheel at each corner and a big spoiler on the back I've heard that Ray Charles does very cheap Porsche inspections, but he can miss the odd fault 
OK, enough cheekiness. The heating problem, as mentioned already, is most certainly a heat exchanger problem. Unfortunately, these are not overly cheap to replace (hundreds of pounds each) and a known trouble spot - just one of the things that can go on a 911 that a tech should have spotted in an instant. Hopefully you got it at enough of a bargain price to cover the problem.
Without further inspection it is difficult to say about the oil. Turbo cars always burn a little through the turbo, but it could be a worn seal in the turbo or something. Not sure. I'd advise you get it to a specialist asap just in case, and to check on any other faults that may be there. (Have you checked brakes and steering carefully, as these are the most important bits from a safety point of view...).
Cheers
Dom
FYI it should have a wheel at each corner and a big spoiler on the back I've heard that Ray Charles does very cheap Porsche inspections, but he can miss the odd fault OK, enough cheekiness. The heating problem, as mentioned already, is most certainly a heat exchanger problem. Unfortunately, these are not overly cheap to replace (hundreds of pounds each) and a known trouble spot - just one of the things that can go on a 911 that a tech should have spotted in an instant. Hopefully you got it at enough of a bargain price to cover the problem.
Without further inspection it is difficult to say about the oil. Turbo cars always burn a little through the turbo, but it could be a worn seal in the turbo or something. Not sure. I'd advise you get it to a specialist asap just in case, and to check on any other faults that may be there. (Have you checked brakes and steering carefully, as these are the most important bits from a safety point of view...).
Cheers
Dom
I'll keep my clown face on for the moment.
I just found out (whilst sneaking down to the BMW dealers for a bit for my M5) that the heating works when you operate the 'emergency' heater control. So now I have manual control over the heating but not thermostatic - reading through the owners manual suggests that this manual lever needs presetting somewhere for the thermostat to work. Conclusion - not a heat exchanger (thankfully). However GR4 your mountain of spares has been duly noted and I will get back to you once have found any definite problems.
Domster - the oil is not coming from the exhaust or inlet, it is coming from the dry sump tank, I guess the vent for the tank should be plumbed into the inlet somewhere but it seems to be venting to atmosphere instead. Will have this inspected. (PS - the car is still good vfm in my book at this moment in time).
I'm compiling a list of the problems with the car for when I refer it to the tech for checking. I'm thrifting them off the list when I find the cause of each problem.
List now reads:
1. Oil mist from OSR wheel arch
2. Heater Thermostat NF
3. Check AFR (just filled up - average 12.75 mpg over 180 miles mixed driving)
4. Alternator suspect
5. A/C - check for leaks and recharge if OK.
My pre-purchase inspection confirmed that the car had three wheels was painted grubby yellow and had 'Trotters Independent Traders' written on the side - think it had the spoiler delete option!
Item 6. Search for and locate fourth road wheel........
I just found out (whilst sneaking down to the BMW dealers for a bit for my M5) that the heating works when you operate the 'emergency' heater control. So now I have manual control over the heating but not thermostatic - reading through the owners manual suggests that this manual lever needs presetting somewhere for the thermostat to work. Conclusion - not a heat exchanger (thankfully). However GR4 your mountain of spares has been duly noted and I will get back to you once have found any definite problems.
Domster - the oil is not coming from the exhaust or inlet, it is coming from the dry sump tank, I guess the vent for the tank should be plumbed into the inlet somewhere but it seems to be venting to atmosphere instead. Will have this inspected. (PS - the car is still good vfm in my book at this moment in time).
I'm compiling a list of the problems with the car for when I refer it to the tech for checking. I'm thrifting them off the list when I find the cause of each problem.
List now reads:
1. Oil mist from OSR wheel arch
2. Heater Thermostat NF
3. Check AFR (just filled up - average 12.75 mpg over 180 miles mixed driving)
4. Alternator suspect
5. A/C - check for leaks and recharge if OK.
My pre-purchase inspection confirmed that the car had three wheels was painted grubby yellow and had 'Trotters Independent Traders' written on the side - think it had the spoiler delete option!
Item 6. Search for and locate fourth road wheel........
LOL
Things are getting a little too specific for me to help now, but just check that the 'override' button isn't the 'superblower' windscreen demist feature found on many Porsches. This delivers instant hot air to the screen using an electric heater rather than the air from the heating system, IIRC. This could mean it is still a heat exchanger problem.
Not sure about the dry sump venting problem. Most 911s are dry sumped and I've never seen or heard of similar symptoms before. Strange. One for Mulder and Scully...
Things are getting a little too specific for me to help now, but just check that the 'override' button isn't the 'superblower' windscreen demist feature found on many Porsches. This delivers instant hot air to the screen using an electric heater rather than the air from the heating system, IIRC. This could mean it is still a heat exchanger problem.
Not sure about the dry sump venting problem. Most 911s are dry sumped and I've never seen or heard of similar symptoms before. Strange. One for Mulder and Scully...
domster said:
Hmmmm, how closely did you look at this potential minefield of a car before you bought it, Dan? I've heard that Ray Charles does very cheap Porsche inspections, but he can miss the odd fault
*ahem* pot & kettle Mr C, was ray too busy to look at the BMW for you, so you got Stevie Wonder to give it the once over
ref ya oil mist, the dry sumps do rust out but usualy on older cars, I suspect a cracked/leaky oil line, a decent tech will soon spot it anyway.
I suggest you go to a DECENT specialist & ask 'em to do you a full run through of faults with the car.
The results may scare you £ wise, but at least you will know where you stand & can get the important jobs done first.
iguana said:
*ahem* pot & kettle Mr C, was ray too busy to look at the BMW for you, so you got Stevie Wonder to give it the once over
That is v true - but I thought Andy HAD inspected the sodding thing, as he had seen it before and wanted to buy it. Turns out he hadn't! Live and learn, eh?
Good choice of car! Nice to see another full fat turbo freak to compensate for all the Atkins obsessed lightweight types!
Hard to guess at the misfire noise on full boost from a written description but could be related to a broken or loose head stud or studs, which is quite common on the 930. You can get some strange noises at full boost which are actually related to the head lifting off the barrel or the barrel moving around in the crankcase. Don't actually think it's too serious if they just need torqued down, but in the worst case if one is broken it could need drilling out. (Of course it should really be considered very serious in any circumstance in that it could mean you're losing power!) That being said they're pretty noisy on full boost anyway so you could just be describing the normal state of affairs.
Why not post a question on the JZ Machtech website? I asked them about a problem with mine cutting out randomly. They gave me a list of about five things to check in priority order - got to number two on the list and found the problem which I was able to fix myself for pennies. Wonder how many other Porsche specialists would have told me to bring it in for a look then proceeded to completely strip my engine and charge me thousands! Wouldn't hesitate to recommend them if you need anything looking at.
Your fuel consumption situation is certainly consistent with my experience - trickle round off boost and the petrol gauge needle is quite well behaved, but start using it as it's intended and it quickly takes a dive!
As for popping and banging on a trailing throttle - mine certainly does it, not sure if it ought to but I've always presumed it's because the Bosch K-Jet is pretty notorious for over-fueling. Got to admit I quite like it, all adds to the sense of occassion around driving the car.
One question - you mentioned you are using LRP, I didn't think you needed to on this engine because it's got hardened valve seats? I've always used Super Unleaded Hope I haven't been doing something daft!!!
Good luck with the car anyway!
Chris
Hard to guess at the misfire noise on full boost from a written description but could be related to a broken or loose head stud or studs, which is quite common on the 930. You can get some strange noises at full boost which are actually related to the head lifting off the barrel or the barrel moving around in the crankcase. Don't actually think it's too serious if they just need torqued down, but in the worst case if one is broken it could need drilling out. (Of course it should really be considered very serious in any circumstance in that it could mean you're losing power!) That being said they're pretty noisy on full boost anyway so you could just be describing the normal state of affairs.
Why not post a question on the JZ Machtech website? I asked them about a problem with mine cutting out randomly. They gave me a list of about five things to check in priority order - got to number two on the list and found the problem which I was able to fix myself for pennies. Wonder how many other Porsche specialists would have told me to bring it in for a look then proceeded to completely strip my engine and charge me thousands! Wouldn't hesitate to recommend them if you need anything looking at.
Your fuel consumption situation is certainly consistent with my experience - trickle round off boost and the petrol gauge needle is quite well behaved, but start using it as it's intended and it quickly takes a dive!
As for popping and banging on a trailing throttle - mine certainly does it, not sure if it ought to but I've always presumed it's because the Bosch K-Jet is pretty notorious for over-fueling. Got to admit I quite like it, all adds to the sense of occassion around driving the car.
One question - you mentioned you are using LRP, I didn't think you needed to on this engine because it's got hardened valve seats? I've always used Super Unleaded Hope I haven't been doing something daft!!!
Good luck with the car anyway!
Chris
Gassing Station | Porsche General | Top of Page | What's New | My Stuff