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Mis-fires on Cold Start-up

Pamela Rimmer

Pamela Rimmer

PCGB Member
Member
Hello everyone, does anyone know why my 968 might be mis-firing on 1 or 2 cylinders on cold-start up? It has just started this since the engine was steam-cleaned about a week ago. It mis-fires for about 3 minutes after cold start-up and once it has started to warm up it behaves impeccably, running smoothly. The plugs, leads and coil have been changed so far, but to no avail. It has done 86K miles. Any ideas please?
 
Maybee your dizzy cap + rotor arm are old..Poss condensation...
I was going to say the spark plug recesses may be full of water, but you say youve changed the plugs + leads,,, since.???
Lessons to be learnt,,,
Dont steam clean your engine bay.
I only ever did it once, on another car...I had the same problems + have NEVER been near my engine bay with one since....[8|][8|][8|]
 
Hello Dave
Many thanks for your reply. The leads, plugs and coil have been changed since the steam-cleaning but to no avail.
Tell me the worst - what happened to you other car ....did it survive?
 
To be honest. i cant remember as it was a long time ago..
I just remember it being a real pain .....
 
Thank you for your reply anyway. Hopefully over time whatever has got wet will get dry. Someone has suggested it might be the thermal sensor / switch putting in too much/too little petrol.
 
Hi
Dont know if you noticed Daves suggestion re distributor cap and rotor arm, I had an HPEie Lancia 25 years ago with same problem and same as Dave, I have never used a power washer under the bonnet since!

The cap was cracked, it looked perfect until you took it off and pulled it about a bit.

Mike
 
Hello Mike

Many thanks to you and Dave for your suggestions - we will try this. It's got to be something electrical, I am sure, as the fuel is definitely getting through as you can smell unburnt fuel coming out of the exhaust. I am reading up but haven't found anything conclusive yet. It runs perfectly once it gets warm, so I still suspect that it might be some sort of fault with whatever tells it the engine is cold - thermal sensor / or switch or whatever they have, but of course if it has a cracked distributor cap then each time it gets cold it may be getting condensation in there as you and dave say ... I will let my mechanic know.
 
Hi Scotty, thanks for your reply.
I think they have - I'm not doing this work myself, the professionals have the car. It was started today and ran perfectly from cold until the accelerator was pressed to give it a rev, then it dropped a couple of cylinders out again! So it's changed a bit in it's behaviour .... very odd. (Thanks for the info re the gaps - I think I had a set of what they called "feeler gauges" if they are the same thing (?) a very long time ago when I had a very old Morris Minor that my dad taught me some basic car mechanics on - I have to admit that taking a Porsche to bits is too daunting a project for me!) I will report back as soon as I have any news ... at the moment there are a lot of men peering in under the bonnet looking very confused....!

 
Hi defenlety check the cap and rota they do burn and crack and often get left on service! It could also be the first sign of a head gasket blowing and nothing to do with the steam clean! Do take it to a good Porsche indy. Berny.
 
Hi Berny & A9XXC, many thanks for the suggestions. It is with the experts but they are very busy there at present so I expect it might be next week before we see any progress now. I will certainly suggest the cylinder head gasket and see what they say. It could very well be something completely unconnected with the steam clean! They reckon they've done the "cheaper" things like plugs, leads etc, and are about to move onto the more expensive stuff like the Mass Airflow Meter, hopefully they will have one somewhere they can try before having to order one in before they know it is definitely that, but I will certainly suggest the cylinder head gasket before they embark on the MAM.

I'll let you know as soon as there is some progress. Many thanks to you all. P
 
Hi everyone. The mystery is solved! It was the Oil Pressure Release Valve (or quoted on the bill as "Relief Valve") - all fixed now. Nothing to do with the steam cleaning in the end. Thank you to all for your help and suggestions. Looking forward to getting back to driving her tomorrow! [:)][:)][:)]
 
Hi
Glad to know its all sorted.

Not sure how the oil pressure relief valve would affect the engine like that, however the fuel pressure relief valve (or regulator) could.

Hope you have a good long time to the next visit to the garage (I still wouldn't have it steam cleaned again!)

Mike
 
Hello Mike

Thanks for your reply. I can't profess to know how it works, but it does seem to have! And you are quite right - no more steam cleaning - ever!! Many thanks for our interest and help. Pamela[:)]
 
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