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Random misfire multiple cylinders - 997.1 C4S

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Chach65

New member
Joined
3 Dec 2016
Messages
27
Hi All,
This is my first ever post about my first ever 2005 911 997.1 C4S.
(Actually just re-posting this from the Newbie forum)
Have owned the car for about 18 months now with no issues.
Recently have experienced random misfires in multiple cylinders.
Diagnostic readings have been P0300, P0301, P0303.
All 6 coils have been replaced and now considering changing the MAF.
Spent time today trying to establish what sets off the misfire as well as what cures it albeit temporarily.
Things that set off the misfire
When starting from cold the car runs fine and idles around 1,200 rpm
When the choke cuts out then the engine idles below 800 rpm and begins to misfire
Switching the engine off then on again settles the idle and cures the misfire
When the engine is warm and running smoothly, if the throttle is blipped VERY gently then the engine continues to run smoothly.
If the throttle is blipped normally (not gently) up to say 3,000 rpm and allowed to drop to idle then the car runs below normal idle and goes into misfire again.
Switching the engine off and on allows the car to idle normally once again.
Wondering if anyone else has experienced these symptons and whether they found a solution to this.
Thanks and sorry for the long first post!
 
I had something similar on mine a wee while ago. I kept getting misfires/revs dropping below 800 after cold starting (and the yellow warning light appearing) after replacing all of the coils. Turned out it was a faulty camshaft actuator/solenoid so had them all replaced and the car's been fine since.

That's the height of my tech knowledge I'm afraid but there's plenty of knowledgable folks on here (Demort etc) who will hopefully have more to offer diagnostic wise.
 
your fault codes are random misfire and cyls 1 and 3 misfireing .

I would have liked to see all of the same bank for it to be cam / hi lift solinoids .

Also would have been good to see a lambda sensors swopped fault code .. thats another indicator for faulty hi lift solinoid.

I would normally be looking at other cylinder rough running to see if it is in fact all on the same bank but 1 is slightly under the thresh hold for generateing a misfire code.

That would lead me down the solinoid route .

You can also run a test on the cam solinoid with a tester , although that wont help if its intermitant .

I would also be looking at the Rkat etc figures .. basically how the car is running and adapting .. fuel trims .

As it is and with out further testing we would be guessing at what to replace and basically possibly be wasteing money.

If your tester can look at these items then please do and post results .. if not it might be cheaper to get a garage to have a look .

My guess atm though is as FRZ 911 has said but changeing all 4 when it might only be one might be a little over kill :)

Ive only seen a Boxster have a single bank misfire which turned out to be a maf sensor .. need to look at the fuel trims and actual values for this before just changeing it i feel .
 
Thanks FRZ 911 and Demort.
Will try to obtain some more readings from my diagnostic tool and re-post.
Your advice is much appreciated!
 
As already said but have you also considered plugs :?:
 
Thanks.
I have considered the plugs but, if I can create and resolve a misfire via blipping the throttle and then switching the engine on/off to reset the idle then (although not an expert by any means) I guess it isn't plugs although I could be wrong. With hindsight I doubt it was the coils now. Will try to get some more data from my diagnostic tool to help with establishing what this might be and as a last resort will have to take it ito Porsche or an Independent and take a hit on labour costs!!
Thank you for your post!
 
Hi all,
Managed to check the car out again today and below is a summary of what I found.
15.45 Engine started and running smoothly at 1,100rpm, CEL is off and outside temperature is 3.5C
15.47 Choke cuts out and engine starts to misfire. CEL lights up and is flashing.
15.47 Engine switched off then on. CEL on but not flashing.Engine running smoothly again. Idle seems to reset each time engine is re-started.
Live diagnostic data as follows.
DTC_CNT 2
FUELSYS1 CL
FUELSYS2 CL
LOAD_PCT (%) 26.3
ETC (oC) 46
SHRTFT1 (%) 0.0, -0.8, -2.3, 1.6 (Variable result)
LONGFT1 (%) -0.8
SHRTFT2 (%) 0.0, 0.8, -0.8, 1.6
LONGFT2 (%) -0.8
RPM 732
SPARKADV (o) 8, 9, 10, 11, 12 (Variable result)
IAT (oC) 13
MAF (g/s) 5.66
TP (%) 12.5
AIR_STAT OFF G
O2S B1S12--B2S12
O2 B1S1 (V) 0.120, 0.720, 0.695 (Variable result)
SHRTFTB1S1 (%) -0.8, 0, -2.3 (Variable result)
O2B1S2 (V) 0.715
O2B2S1 (V) 0.130, 0.245, 0.745 (Variable result)
SHRTFTB2S1 (%) -1.6, 0.8, 1.6 G (Variable result)
O2B2S2 (V) 0.705

16.03 Oil temp 70C, Water Temp 80C, Oil pressure 3
16.04 Error codes erased, CEL Off, Engine running smoothly at 750 rpm
16.05 Throttle blipped, sets engine into misfire, CEL comes on and is flashing
16.06 Error Codes now showing P0300, P0301, P0302, P0303
16.10 Live data checked again with following results
SHRTFT1 (%) 0
LONGFT1 (%) 0
SHRTFT2 (%) 0
LONGFT2 (%) 0
SPARKADV (o) 24
All other readings were similar to those given above

16.20 Engine switched off then on again. Engine resets and is running smoothly!!

In summary, the engine will start smoothly and will only begin to misfire when (A) the choke cuts out
(B) the throttle is blipped

When the engine is misfiring it can be reset by switching the engine off then on again. This state can only be maintained as long as the throttle is not blipped. That means it's going to be hard to get the car to a garage. Any guidance would be greatly appreciated!!
 
Your problem starts when the lambda become active , they need a warm up when first started so the car initially runs on default settings.

Once the car starts to see these readings its reacting to them and running rough.

I assume from your description you mean REALLY rough and not just its lumpy .

You now have all of bank 1 misfireing ..

From your readings and now these fault codes i would go with its cam solinoid thats sticking / failing ..

I would have liked to see 1 other code with this but my guess would be bank 1 Hi lift solinoid ..

It can be proved pretty easily .. swop it bank to bank .. if it is this you will then get codes for the other bank ..

You will see p0304 , p0305 , p0306 and p0300 .

The solinoid is the one in the middle , couple of bolts and it pulls out .
 
Thanks Demort for your prompt reply.
I can confirm that the car is really rough when misfiring to the point of almost stalling.
I don't know where to locate the solenoids so will try to find a youtube video on that. If you have a link that shows me how to replace the solenoid that would be very helpful.
Once again, thank you so much for your help. I am really missing driving my C4S!
Once I figure out how to swap the solenoids I will have a go at the weekend and let you know the results.
Fingers crossed it's that and I can get it back on the road!
 
Are the solenoids next to the coils?
 
right I'm officially very interested in this thread now!

Ive got the same problem car is misfiring and running very rough on idle with yellow CEL flashing.

I have read the fault codes and I am getting the same 4 fault codes the P0300 and the cylinder specific P0301, P0302 & P0303.

Demort this is the same misfire problem I pm'd you about a few weeks ago, not driven the car since and been away. Do you reckon its the same issue as Chach65?

should I also swap over the cam solenoids? - If so can you pm the info you pm'd Chach65 showing where they are located?

cheers
 
Chach65 said:
Are the solenoids next to the coils?
Click to expand...

Check your PM box .. top right on the screen , theres some info in it.

You want section 15 55 19 .


Monster .. PM sent but you can always phone me if you wish .
 
Thanks for the link Captain Lockheed unfortunately I don't have a Durametric or PIWIS to actuate the solenoids.

Demort, excuse my ignorance, but what is a PM and where would I see what you have sent?

The only work I've undertaken myself on this car is to replace the coils, whilst I found it tricky due to the very limited space, after 5-6 hours I managed to get them done. Is changing the solenoids a similar job albeit 2 instead of 6 components?

Aiming to have a go at this at the weekend.

Monster hopefully this helps you out too!!
 
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