More questions on running of a 964

[NormalNorm]

Call me a clutts, but these are the new experiences of running a 964 daily!

1.When starting the car from cold on ignition. it has a noise like my 912 1600 on carbs use to sound. Not like a backfire but a metallicy sound, which I raised with Dave at Strasse, he said it was I think the valves?!?yes?no? cant remember but like as I said my 912 when the carbs arent in tune, like a splutter. Is this common?

2. When shes started up, and about to warm up, you hear the sounds of water rushing at the back, is that the sound of the fuel or water circulaing in the system?

3.Not sure if it happens in your car. But when driving off from cold, the car seems to splutter a little bit for a mile, obviously me not pushing her from cold, but driving slow until warmed up. Anyway, after a couple of minutes when the car is warming up whilst on the run the car is fine. Can you explain why?

4. The clutch as been great after this week. But im not sure if the car has feelings!haha Mainly because my first long outing with her, we drove about 150 miles to Wales, and at the end of our destination the car was obviously very warm. Anyway, the problem was that 1st gear was very hard to select, even when pressing the clutch to the very bottom. A few attempts were made until finally 1st gear was in, but very frustrating.

The next day, I decided to return to the dealers in Leeds to show them the problem, and guess what! She was fine from start to when we got to the garage. Since then shes been fine...so can this be explained?

I know problems can be raised when the car is cold and the clutch may have problems, but this was when warm, after a long end run.

How do you know when a clutch is on its way out?

 

[Dave Wilkinson]

Norm,

I think it's pretty normal to find lots of questions on your mind - particularly with a 964!! I'll do my best to answer your points:

1. This one is difficult to tie down from just a description but it's possible the noise you hear COULD be the Idle Stablisation Valve (usually just called ISV) which controls the air flow at tickover. It's an electrically controlled valve (drven by the DME) and constantly varies the amount of air allowed into the induction tract in order to control the idle speed. This valve is often a casualty of an oil overfill as it can get "gummed up" with oil residue and cause stalling issues.

2. I sincerely hope it's not water you hear - unless you've mistakenly bought a 996 in disguise!!! The sound you hear is actial OIL being returned to the oil tank. It seems to be more apparent in some cars than others - and then often will not happen for a while. It can be related to which oil and/or which oil filter is used. It can also be something to do with how much oil is left in the engine when you leave the car parked. If, for example, you leave the car parked on your drive for a while - long enough for the engine to cool down - and then, later, start the car to put it into the garage, the oil thermostat will have closed and the engine will take a huge amount of oil from the tank in starting. If it takes a few seconds to put the car into the garage, when you stop the engine the scavenge pump will have had little time to collect that oil to return it to the tank. As soon as you start the engine next time, the scavenge pump will then return the oil to the tank - hence the noise. It seems that cold oil makes more noise than hot oil,

3. This sounds like a possible problem with the Cylinder Head Temperature sensor. The DME is programmed to ignore the input from the O2 sensor until it reaches working temperature. Until that point the DME over-fuels the engine (like a choke) to ensure it runs. A problem with the CHT sensor would prevent the DME realising that the engine is cold and it would therefore not over-fuel as designed. Once the engine wamrs sufficiently to cope with normal fuelling it runs fine.

4. The clutch on a 964 is operated hydraulically. The hydraulic fluid is drawn from the same reservior as the brakes, the master cylinder attached to the clutch pedal forces the fluid down the pipe to operate a slave cylinder attached to the bell housing which pushes the operating arm to the clutch itself. The slave cylinder is quite close to some exhaust components and can get quite hot - particularly on a long journey. The effect of the heat on any water absorbed into the hygroscopic fluid, as well as any air in the system, is to (a) lower the boiling point of the fluid (in the case of the water) and (b) reduce it's compressibility (in the case of the air). Both will drastically reduce the efficiency of the operating mechanics. There is also a chance that the slave cylinder itself may have seen better days, but a first approach should probably be a complete change of the hydraulic fluid (unless you have evidence of it being done within the last 2 years) and a complete system bleed (including brakes).

Typical signs of impending clutch failure are (a) a heavy pedal and (b) obvious clutch slip - often in a high gear. Difficulty in putting the car into gear is probably a sign of the clutch being good rather than bad.

Hope that hekps.

Regards

Dave

 

[NormalNorm]

Thanks again Dave, well executed and shall we say very technically answered.

Are any of these described to be a concern, and is it a common thing? and can we live with it or does it neeed attention? as the car is still under warranty.

1.The ISV on point one sounds about right, because ive had issues with the ISV being just clogged up on a Audi S3, and it needed to be cleaned.

What you pointed out about the car stalling, can at times. For example, when the car is started from cold, if you rev the car, she tends not to hold on and goes back to idle, she drops and stalls. Also whats weird is when say you stall by accident, and you start her up, she cuts off if you press any of the gas pedal. So I tend to leave her to idle first before I engage and move on. Is this common?

2.hahah Yeah I would certainly be a clutts if I mistaking owned a 996! The sounds of the running water is definately apparent when you start the car from cold, as you say it could be cold oil rushing back to the tank, is this common? and should I move or let her warm up and the sounds to go before the setting off?

Theres another point, is it always best to let an old car such as this to warmup 1st before she moves from cold?How long do you guys tend to warm her up first before making a move(hmmmmm sounds like foreplay!) Obviously I dont push her until shes warm on the temp needle.

3. Yes she runs fine when shes warm I guess. Not annoying for me, as I rather shes warmed up before I move a bit quicker. Is this a problem I should get sorted? And is this a big and expensive job to replace the Cylinder head sensor? Guess this isnt normal then, and you guys dont have it?

4. Clutch slip(is that a sign of judder), only a sign of judder when setting off from cold on 1st gear, when your intially not putting much gas at 1st.

Guess i worry to much, Mucho Gracias Dave!

 

[appletonn]

Norm, I too get the 'running water' noise on first starting her up, but none of your other symptoms so can't help you with those.

Did clean out the ISV on my previous 944 turbo and that definitely made a positive difference.

 

[NormalNorm]

Thanks Nick for the reply anyway, as helpful as always.

Wheres Dave?

 

[Dave Wilkinson]

ORIGINAL: NormalNorm
Wheres Dave?

Sorry - I have been known to leave my desk occasionally!!

I think we concluded that the ISV has got to be worth a clean before you start to look for more complicated problems.

The warm up issue I think is pretty much a case of drive it, but don't cane it, until the oil gets warm. Personally, with a C4 I always wait for the hydraulic pump to stop before I start the engine and then just drive, but don't exceed 4,000 rpm until I see the drop in oil temp once the thermostat opens. The more I think about it the more perturbed I'm getting about the experiences related by Colin and Nick Applton about their thermostat operation. There are obviously differences between individual cars.

I don't think the CHT sensor is a big job but some amount of dismantling is necessary to get to it.

I wouldn't say clutch judder was normal. Clutch slip is how I would describe a rise in revs while trying to accelerate in a high gear.

Regards

Dave

 

[Steve Brookes]

In response to your questions:

3. No spluttering on mine. She drives as smooth as silk from the first turn of the key.

4. When hot mine was difficult to engage first gear yet the clutch was only about 25,000 miles old at the time. Bleeding the slave cylinder cured the problem.

 

[NormalNorm]

Thank you 2 amigos!

Ive noticed the car doesnt splutter when 1st driving off when from cold, when the car is warmed up before setting off. think that helps!

And Dave, when you say with it being a C4, wait till the hydraulic pump to stop before starting, do you mean when I start the engine, i would hear the Hydraulic pump then wait for the noise to stop? Yes I think I have learnt that, because not only do I wait for the noise to stop, but also the light on the dash showing the 4wheel drive light i think with the 4 wheels and the diff. As it sometimes comes on then goes off in a few seconds if not longer at times.

 

[Dave Wilkinson]

ORIGINAL: NormalNorm

And Dave, when you say with it being a C4, wait till the hydraulic pump to stop before starting, do you mean when I start the engine, i would hear the Hydraulic pump then wait for the noise to stop? Yes I think I have learnt that, because not only do I wait for the noise to stop, but also the light on the dash showing the 4wheel drive light i think with the 4 wheels and the diff. As it sometimes comes on then goes off in a few seconds if not longer at times.

Norm,

There have been lots of discussions over the years about this pump. On the C4 (and the RS, WTL cabs and the Turbo) you'll hear the pump run as soon as you turn on the ignition. It pumps up the hydraulic pressure in the pressure accumulator (aka "the bomb") which s used for the braking system (and the PDAS on the C4). If you drive off before the pump stops the C4 will potentially give you the PDAS warning alarm if the pressure isn't sufficient. It doesn't affect the non-C4 cars in the same way since they don't have PDAS.

It's a useful exercise to time how long it takes for the pump to stop as it can tell you a lot about the state of the hydraulics. From a cold start with the car having been left overnight, turn on the ignition, but DON'T start the engine. Take a note of the time taken for the pump to stop. Something around 20-25 seconds is perfect. Much longer than that is a sure sign that your primary hydraulic circuit needs bleeding. Any longer than 2 minutes and you are in real trouble.

You should be aware that PDAS is the C4's traction control - it's NOT the 4WD. 4WD on a C4 is permanently engaged and the PDAS engages the centre and rear diff locks as required to redirect traction as determined by the wheel speed sensors and the accelerometers.

Regards

Dave

 

[Steve Brookes]

ORIGINAL: NormalNorm

Thank you 2 amigos!

Ive noticed the car doesnt splutter when 1st driving off when from cold, when the car is warmed up before setting off. think that helps!

It might be developing a slight vacuum leak on the inlet manifold when it's warmed up. It's worth going around all the hose clamps on the manifold and give them a tweek up. A screwdriver socket with 7 mm socket is the ideal tool for this.

 

[NormalNorm]

ORIGINAL: Steve Brookes

ORIGINAL: NormalNorm

Thank you 2 amigos!

Ive noticed the car doesnt splutter when 1st driving off when from cold, when the car is warmed up before setting off. think that helps!

It might be developing a slight vacuum leak on the inlet manifold when it's warmed up. It's worth going around all the hose clamps on the manifold and give them a tweek up. A screwdriver socket with 7 mm socket is the ideal tool for this.

Steve, tell me where u live, then I can come round and you can check it for me![] dont want my hands dirty!hehehe

 

[mcgc0]

Yep, I too get the 'oil rush' on start up - some days hardly at all, other days a bit longer. Either way I wait for the sound to disappear before moving off (usually not much more than 5 secs).

The brake/PDAS pump motor for me doesn't take long before turning off. Although if I move out of the garage pretty much straight away I do get the warning tone, but by the time I'm out the garage all is fine.

I too used to wait a while before driving off thinking a little warm up would benefit. However, the drivers handbook actually says to drive off (immediately) after starting - maybe it's the air-cooled thing. But, as Dave mentioned, until the oil temp needle lifts off and reaches the first mark, I tend to change gear @3k rpm and don't push it.

Dave, a couple of questions re your comment pointing out that the clutch and brakes share the same fluid reservoir; a) what's the standard (Porsche) spec for the oil? and b) for track use, moving up to a higher temp fuild is also going to affect the clutch slave cylinder performance in some way?

 

[Dave Wilkinson]

ORIGINAL: mcgc0

Dave, a couple of questions re your comment pointing out that the clutch and brakes share the same fluid reservoir; a) what's the standard (Porsche) spec for the oil? and b) for track use, moving up to a higher temp fuild is also going to affect the clutch slave cylinder performance in some way?

Marcus,

By "oil" I presume you mean "brake fluid"?? The spec according to the manual is SAE J1703, DOT 3 or DOT4. The purpose of a "higher temp" fluid, as you put it, is to raise the boiling point of the fluid such that heat transfer from the brakes will have less impact on the functionality of the fluid. It will have no impact on the performance o fthe clutch other than to improve it in the same way. There is some potential for the clutch slave cylinder to suffer from heat transfer from the exhaust so something like SRF can only help matters.

Regards

Dave

 

[mcgc0]

Thanks Dave, interesting thought though; suggests that it pays to opt for a higher spec/temp fluid in the next service or flush. Any downsides to a higher spec fluid (e.g. price?).

Cheers