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968 Sport Track Car - Misfire

rbignell

rbignell

New member
Hi There

I live and work in Dubai and lucky to attend track days at Yas Marina and Dubai Autodrome in my LHD 968 Sport that I purchased from Strasse and imported here. All has been going really well but I have had a problem recently when going round corners say in 2nd gear and trailing throttle. When I try to accelerate the engine dies then pops and bangs and then accelerates without a problem up to the next corner and the same thing happens.

Has anybody suffered this themselves and any suggestions what has to be looked at?

Many Thanks

Ray
 
There is a baffle system in the fuel tank (I've seen it called a swell pot also) which can come loose. So if your running the tank fairly low and pushing on you can get fuel starvation, I remember it being especially mentioned on RH corners.

There is a guy called 'Paul Follett' who races 968s and he had to fix the baffle pot inside his car. (I think he may have used a young boy and some cable ties :))

He lurks here and hopefully will be along to give you the full story. I've seen him document it on Porsche968uk but not here.
 
Ray.
Its sounds very much like the fuel swirl pot in the tank that at fault, as Ken has said.
Yes the man to explain it all is Mr Follet, as he had a few challenges just like you..
 
Ray -- just spotted your post -- yes it is me Mr F here (just lurking quietly in the background!!)

Firstly, you did not tell us whether it happens going round right handers or left handers or both.

So, two things to check first. If it is the swirl pot problem it will only happen when going around right handers. Another thing to do is fill the tank up well over half full, say 40 to 50 ltrs and drive it again on track. If you still get the problem then you are going to have to look elsewhere for a solution as it is not the swirl pot.

eg blocked breather system, old/choked fuel filter (over the RR drive shaft), dodgy fuel pump (under fuel tank) or even an intermittent DME relay

a few things to go on there, pls report back your findings asap

 
Hi Paul

Many thanks for your reply.

The first hesitation that I had when I was on a fairly full tank on a right hair pin before the long straight at Yas Marina but it went away. On the second track day again on full tank the problem returned but slightly worse but it was on Friday with only half tank at Dubai Autodrome that I had real problems and I would say that is was mosty on right handers but on left handers as well.

I have asked about the DME relay and sent them the correct number for the 968 but it is worth checking the filters and breathers etc as I feel it is definitely fuel related.

The car is at my local porsche independent so I am forwarding all posts to him. I can do little myself here in Dubai as I live in an apartment and car space is underground and baking hot !

Will keep you updated

Thanks

Ray
 
Ray - hi

Sounds quite strange that you had the 'apparent' starvation problem on a fairly full tank -- confirmed by the fact that you said it also happened on left handers (nb could happen then if it was soon after a right hander as it can take a few seconds to clear starvation) Another quick thought are you sure your fuel gauge is accurate -- it may be you think you have more fuel in the car than you have in reality.

For now I would check through a few things, my thoughts are tending towards fuel starvation from sources other than the tank: (you could give Strasse a ring as they know the car and are race engineers - they may just have the insight you need)

-- have you got the proper fuel filler cap and does it seal correctly?
-- find the end of the fuel breasther pipe and make sure it is not blocked
-- check the fuel pressure regulator, it is on the injector rail at the back end of the engine -- it should give 4.8 bar pressure when running AND it must have a good vacuum pipe connected to it -- common problem is that the pipe may fall off or be perished so no vacuum! Also, if all OK it might be a good time to check that the fuel pump draws the correct current -- any variation from std would suggest that it might be about to fail.
-- then if the above does not cure it, take out the fuel sender from the access hatch in the boot floor area -- peer in side with a small torch and see if the lid of the swirl pot is in place NB it looks like a normal flat Tupperware type lid and if you poke about a bit with some strong wire from something like a coat hanger it should stay firmly in place over the pot. (fix described elsewhere -- a teenager and nylon cable ties are required !!)
-- then if swirl pot lid OK, it is time to drain the fuel out of the tank, and from the underside of the tank remove and clean/check the fuel filter sock that screws into the tank, also replace the canister fuel filter, assuming the pump is OK re-assemble and test.

if you get through all of that and you still have a problem -- 2 things a) contemplate getting some stress counselling b) find a decent Bosch trained auto electrician to dig a bit deeper
 
Hi Paul

I really appreciate your help. I will pass on to the guys here.

I have been following your exploits in your race 968 and will be getting a set of new suspension arms that you developed when I come home at the beginning of May to hand carry back and bring the old ones back when I return in July.

Thanks again

Ray
 
Hi Paul

The 968 is now being readied for the UAE GT Championship. Regarding the Alternator do you run with standard pulley and regulator? I presume that my alternator is the same age as the car so suspect inconsistent voltage could be affecting performance?

Thanks

Ray
 
Other similar problem areas I have encountered on my S2 due to racing are fuel pump going weak, in that particular case the pump was only 2 years old as well, and the other was a dodgy crank sensor causing the ignition to start to drop out after about 30 mins on track that gradually got worse.
 
Ray - hi

As I read our regs we have to stay with the std pulley - a larger one might be advantageous ie it runs slower and thus less drag on the engine. Never heard of anyone using a different voltage regulator - as long as the std one checks out OK keep with it.

 
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