03 955 Turbo Bad missfire
 

Hi guys,

Hoping to get some advice on this.

Have recently purchased a 03 955 turbo which is running very rough at idle and on hesitates when accelerating.

Codes read only state multiple misfire on cylinder 5,6 & 8.

I've bought replacement coils and already changed the plugs, new plugs made a slight improvement but not 100%. I'm waiting for the coils to arrive from Pelican parts, however I was thinking shouldn't the codes read that there is a bad coil if that were the case?

I was thinking about the possibility of the timing being out or a scorer cylinder as a potential possibility also. Anyone have any thoughts?

Thanks!

Most likely the coils.
If you have a scored cylinder, the spark plug would be very fouled and there would also be a loud tick from that cylinder.
Less likely but also possible could be bad gas or sticky/dirty injectors

Thanks for your reply, I swapped out the plugs already and the old plugs didn't show anything out of the ordinary.

No loud ticking also, I'm awaiting the parts and will see if that fixes the problem [emoji106]

blocked or dirty injector?

Update:

New plugs, coils and I did the valve cover gaskets.

Cars running better but still has a miss and hesitation under load mainly when boosting. There's also a sound which sounds like a back fire when it hesitates but it picks up and then goes.

that's a relief, from what I understand the turbos are no affected by the nickasil issue they have forged internals

03 955 Turbo Bad missfire
 

I'm getting a Porsche independent mech to check it out in the next few days. Hopefully not a scored cylinder... I'm thinking either a intake leak or timings out

Porsche independent can't figure it out either lol..... I'm going to check ground straps and voltage, also might swap injectors around on cylinders 5 & 6 as that's the only 2 recording a cylinder missfire

How many miles? Did the codes go away after the new coils? If so, and it's just hesitating now, I'd lean towards fuel pumps/filters.
A weak battery can cause all sorts of running issues but usually results in many bizarre fault codes too.
Also, did you go get the coils from Pelican as mentioned? If you changed your mind and went with a generic from someone else, they rarely work.

Lastly, buy a cheap USB borescope from eBay or Amazon (less than $10 bucks) and look into those cylinders...although I doubt that's your problem.


Not true at all. That rumor was started up by a guy on "the other forum" and he stated it so many times, it became internet fact. Fortunately, he and his few followers seem to have disappeared.
A quick Google search will turn up MANY turbos with that issue. Then consider how few were sold compared to S models.

Only 85K miles, all codes went away after new coils however after driving say 30miles, the engine light would display and stay on, codes recorded are multiple cylinder missfire on 5,6 & 8.

Have only checked the injectors so will look at the fuel pumps and pressure, also change out the filters incase they are blocked.

Battery is showing as good and I had another spare that I tested with but no improvement.

I got the Beru coils from pelican parts but the coils didn't seem to ever be a issue as I got a coil tester and all the old ones were still working.

We did a leak down test and all is well, do you still recommend a borescope?

I agree with the Nikasil, they wouldn't only use it in the S and leave out the turbo when the bare bones of the engine is bearly indentical.

Something else is going on here if coils didn't fix it, did you get new gas recently?

If it keeps coming up with those exact cylinders, probably not a fuel filter/pump problem.
I'd scope out those cylinders for the heck of it.

Another problem that plagues these vehicles is water under the carpeting which corrodes electrical connectors. It makes it in from the sunroof or plugged A/C drain.
It's a shot in the dark but a possibility. Pull the carpet up on the driver and passenger side and see how things look under there.

Full tank of fresh gas

True, Good point about the water corroding electrical connectors, I'll have to check that out.

Thanks for the tip, throttle body is another item that's going to be checked out or swapped.

I took it to another Porsche Indy, they did a leak down which came up fine but believe the fault is the Variocam adjusters on the left bank so one bank is slightly out of time or the cams stuck in the high preformance position as the car goes well from 5k rpm onwards. Has anyone done this job before?