Intermittent loss of power 997S
Discussion
Advice appreciated. MY06 997S owned by me from new. FPSH, 75k miles with v little gone wrong over the years. Recently sudden transient loss of power at low revs when cold, usually on accelerating away from stationary. No warning lights and sudden restoration of power within a couple of seconds. Idles normally. It's happened 3 times today. Car is used daily for 15 mile commute on motorway/town roads. Doesn;t seem to happen when engine fully warmed up and performance otherwise unchanged. Clutch master cylinder went on Monday so it's been in the OPC for repairs and new clutch (under warranty - result!). It feels like fuel starvation but could be more sinister? Big service in Jan 14 with no problems picked up.
Thanks for any advice.
Thanks for any advice.
ocd said:
Just been to OPC Bournemouth (thanks Richard). Happened once accelerating out of roundabout coming off motorway. Nothing on the diagnostics. Gave it a bit of an Italian tune up on the way home. If it happens again it will have to go back....
997S.1s can be running fairly poorly long before fault codes are generated by the ECU. This is particularly true of lambda sensors and MAF sensors (formerly known as air flow meters). A good tech at a proper independent will be able to look at real time values in the diagnostics to see if any of the above are on their way out, but haven't quite got bad enough to throw a code - yet!Other items that could be responsible:
1) Coil packs, as said above. Just because they're new doesn't mean they were fitted properly or that one isn't faulty.
2) Main battery/alternator cable. There was an issue on the mk1 997s where the main cable that runs from the back of the alternator to the battery at the front of the car started to fail at a joint (where a connector was attached to the end of the cable). The resistance of the wire increased to the point where all sorts of issues started to happen. From memory, I think the connection is made-up of 2 physical cables that join in a junction box on/near the side of the gearbox (can't remember exactly). Replacement is the only cure.
3) The 2 large, circular multi-plugs at the right-hand side of the engine bay - make sure they're done-up correctly (rotate clockwise) and none of the pins/sockets inside have corroded.
4) Ignition switch. These are known to fail and can cause the car to cut out.
5) Multi-block plugs on the ECU and other control units - under the insulation behind the back seats. The ECU is attached to a metal plate that's held down by 4 (I think) fasteners. Undo them, lift the plate and make sure all the plugs are secure in the tops of the control units. They all have locking levers that that should be fully in the down position - if any aren't, there could be an intermittent connection.
6) This may be unique to the 997S.1 I used to own as I've not heard of the same problem elsewhere, but it could cause the symptoms you describe. The main wiring loom behind the dashboard had chafed on a bracket near the glovebox and had shorted a couple of the cables. Nothing worked properly and it took the local OPC days to find the problem. (And several more days for an electrician to mend everything)!
There are other possibilities - such as engine/cam position sensors, variocam units etc. - but these would typically throw a code, so are unlikely if the diagnostics are clear. There will also probably be several I haven't thought of - hopefully others will chip-in.
Hope you find the problem. My instinct would be ignition switch or the alternator-to-battery cable(s), but it's difficult to know at a distance.
Thanks very much for such a detailed reply. The abruptness of the loss/recovery of power feels like someone has switched off the ignition so I wonder if ignition switch intermittent failure is the problem. I will feed this back to OPC and let you know what happens. The car is in the last year of its warranty so it should be covered.
You I think hit upon the problem: fuel starvation. Fuel pump then most likely. Intermittent failure. Eventually it will fail outright but in the mean time the car is not much fun to drive.
Would I replace the fuel pump on just the above? No.
Let's consider some other explanations...
No CEL so it is unlikely it is coils.
You observe nothing untoward at the dash so I would eliminate the ignition switch, unless you are the type of owner who has every key he ever owned on a keychain and this dangles from the Porsche key in the ignition…
There are more esoteric explanations. A converter brick loose and intermittently moving out of position and blocking exhaust gas flow. Check for any abnormal noises/rattles/buzzing from the exhaust system.
The throttle body butterfly valve is being interfered with. One possible scenario has the valve out of position due to wear or some kind of mechanical failure and binding upon giving the engine some gas. But if the drop off in power comes with no throttle action on your part, on steady application of throttle, then no.
This leaves the fuel pump or something amiss in the fuel system. The fuel lines could have a crack or be loose and upon high g-force situations could move and allow fuel pressure to drop. The crack/split closes when the g-force goes away. If this is happening it will get worse over time but you are still faced with living with a car with drivability issues which is not fun.
Would I replace the fuel pump on just the above? No.
Let's consider some other explanations...
No CEL so it is unlikely it is coils.
You observe nothing untoward at the dash so I would eliminate the ignition switch, unless you are the type of owner who has every key he ever owned on a keychain and this dangles from the Porsche key in the ignition…
There are more esoteric explanations. A converter brick loose and intermittently moving out of position and blocking exhaust gas flow. Check for any abnormal noises/rattles/buzzing from the exhaust system.
The throttle body butterfly valve is being interfered with. One possible scenario has the valve out of position due to wear or some kind of mechanical failure and binding upon giving the engine some gas. But if the drop off in power comes with no throttle action on your part, on steady application of throttle, then no.
This leaves the fuel pump or something amiss in the fuel system. The fuel lines could have a crack or be loose and upon high g-force situations could move and allow fuel pressure to drop. The crack/split closes when the g-force goes away. If this is happening it will get worse over time but you are still faced with living with a car with drivability issues which is not fun.
David W. said:
Trev450 said:
There is indeed. I found this out the first time I left foot braked mine. 
As a left foot braker in any auto,tip,pdk that is the reason I like a manual 911. I didn't get on well with pdk test drive at Milbrook a few years ago, it took a while to work out why.dw
Elliott-xpb6a said:
I am having the same problem following some left foot breaking on my tip 997.
What is the part called that was replaced by the OPC? I think I need this switch!
I routinely heel & toe my 987 without problems - there's no difference in throttle when I'm under braking. It doesn't make sense to me that Porsche would fit a switch to cut the throttle when brakes are applied - many drivers will either left foot brake or heel & toe?What is the part called that was replaced by the OPC? I think I need this switch!
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