Cylinder 6 misfire on a 997 GTS

[bobt54]

Hello, I have a misfire on cylinder 6 which now seems to be all the time from starting the engine.
New coil packs fitted, plugs are not that old (swopped around to test)
new injector
new HPFP
AOS changed, inlet ports/valves very gunked up, cleaned up as best I could, looking not to bad at all.
Any help/ideas much appreciated

 

[deMort]

Is it only no.6 that's misfiring ? have there been times you have seen 4 and 5 also ?

If so then X1 bank issues and i would start with the hi lift tappet solenoid .

So if only no. 6 .. plug , coil and injector replaced so what does that leave ..

Compression is one thing so a cylinder leakdown and compression check is next followed by a bore scope to inspect the cylinder .

What else .. well we have the wiring from the dme to the injector / coil and we have the dme itself .

Valves gunked up is common on these engines but doesn't seem to cause any issues .

You changed the AOS .. erm .. why ? smoking when cold perhaps ?

HPFP .. similar question as its an unusual item to replace for a single cylinder misfire .

 

[bobt54]

Thanks for the reply.
A few months ago I changed the hi lift solenoid as there was a radom misfire on cylinders 6,5,4.
While I had all the plenum and such off to do the injector, I thought for the cost of a AOS it was ideal time to do it.
The HPFP was very messy, oil leaking and such, so again I thought while all in bits take the opportunity to change it.
I have had a look at the bore with a camera scope and it looks ok.
When I started it up after doing the injector and such and it was misfiring, I took the plugs and coils off again, the plug out of cylinder 6 was spotless ( I cleaned them all earlier) all the other plugs had evidence of firing, it's as if there is no charge getting to the plug. :?:

 

[deMort]

When you changed the hi lift solenoid did it run ok or did you do other work ?

Inlet manifold off makes me think the gasket might have kinked or not sealed correctly .. at work i would smoke test the inlet system looking for leaks .

AOS is pretty good on these but i can see why you changed it .. any sealing issues and it would either loose coolant or a general misfire .. the same as leaving the oil cap loose .. its not that .

HPFP .. oil leaks is what i think you mean .. again no bearing on this although you should use a tester to do a first start when replacing these .. either way it's not your issue .

borescope .. good call .. it's an outside chance of an issue but needs to be ruled out .

Old school check but you need to be careful here .. remove the coil .. fit a spare plug in it .. wire the plug to the engine as an earth .. in other words a solid connection from the plug to the engine .. if you don't do this the dme might get damaged .. crank or start the car .. is there a spark ?

You could use a spark tester instead of a plug .. as long as it has a good earth you will be fine .

If a spark then we have to lean away from that being the issue .

EDIT .. just to say .. if you had it running ok and then replaced the injector and had a misfire then its injector based .

 

[bobt54]

I did wonder about trying a plug to see if it sparked, reminds me of messing about with Mini's when I was a lad
I will try that at the weekend
I thought I had the manifold seated correctly but will check and see, when I changed the hi lift solenoid that was all at that time.
The misfire was happening before I changed the injector.

 

[deMort]

Ok .. so the misfire was at the beginning and nothing you have worked on and it suddenly started ? that's all i need to know

Old school .. if we can't see it we can't believe it lol .. to see a spark tells us a lot but to be honest .. i've not used this process on these cars so far .. very rare to be a wiring or dme fault .. possible but rare .

 

[bobt54]

I had just been up to Newcastle with my son in law for him to collect his (new to him) 997.1 S and was about 15 miles from home after a journey of around 200 miles and then it started.
It did used to have a misfire sometimes in a morning when first started for a few moments and then it used to clear itself, but recently it had been ok, until now :frustrated:

 

[deMort]

I'm going to sling tappet failure into the mix as well .. i kinda doubt it but it's possible .. more tests with a cold engine .. compression etc are needed .

As you seem to know your way around a car can i just remind you .. don't just check the compression with a gauge but check the first spin of the cylinder versus the others .. a small issue might not show up on a full compression test but that single stroke might .

 

[bobt54]

Good point, I was going to do a compression test over the weekend, I will make a note of the results, and try a plug spark test..
I kind of get the feeling it's a wiring fault or DME with the plug being so clean, it's not attempting to fire, but guessing a bit. :?:

 

[bobt54]

Carried out compression test today
Cyl 6 first crank 150psi then 265 psi
Cyl 5 first crank 160psi then 265 psi
Cyl 4 first crank 160psi then 270 psi
Cyl 1 first crank 155psi then 270 psi
Cyl 2 first crank 170psi then 270 psi
Cyl 3 first crank 170psi then 265 psi

Also tried a spark test on cyl 6 sort of thinking it will not spark, it did....
Tried 5 b& 4 as well all ok.
On my icarsoft diagnostic test it says all ok, no faults, but when you try it on the OBD11 test it comes up with P0306 permanent misfire on cylinder 6.
Not really sure what to do now.
Could it be worth trying another dme ?

Thought about contacting Cartech Electronics, they seem to offer a good sounding replacement trial, if it works fine, if not send it back.

Has anyone had experience of dealing with them?

 

[Newbe]

I was just following this thread out of interest.

If you took the plug out and it sparked then I don't think it would be your DME? As you have a spark? Unless I've missed something and I'm no expert!

Surely that just leaves a fuelling issue?? I know it's on cylinder 6 only but could it be your fuel pump? I'm not sure if cylinder 6 is the end of the rail? Or a blockage before your injector which you replaced?

 

[bobt54]

I was a little surprised when it did spark, sort of expected it not to.
I changed the HPFP, the old one was in quite a state, leaking oil and such, and I wondered if it was making full pressure to that rail, 6 being the furthest away cylinder.
As you say if it's getting a spark, you would think that leaves fuelling.
I am puzzled as to why it comes up 'permanent misfire', what would cause that?
Could it be that cylinder 6 injector is not getting a signal to work?
Think it's getting to the time to ship it off to an Indy or Porsche

 

[deMort]

Can you just confirm the car actually has a misfire and runs rough , especially on idle ?

Spark side seems ok but we havent eliminated the injector side ..wiring or worst way would be a dme issue .. i cant remember if its this model onwards but the injector voltage is higher .. 48 volts .

 

[bobt54]

Yes, its a five cylinder porsche at the moment, constant misfire on cylinder 6.
If you have your hand over the exhaust tip on that bank very lumpy from start and idle and when you increase revs, other bank nice and smooth.
I took it all out again the other day just to double check that I had not made a silly mistake somewhere, and am now kicking myself in that I left the new injector in cylinder 6 instead of swopping it to a different cylinder (just to prove a point)
It just comes up with permanent misfire cylinder 6. When the misfire first started, it used to happen (sometimes not all the time) on first start up for a few moments and then clear itself, now its on all the time.