A different cold start problem????

[Guest]

[FONT=Tahoma"]Hi all,

I have recently bought a 1981 911 SC and so far have been very impressed, I can see why everyone loves them so much!

Anyway, I have read through the posts and seen a couple of cold start problems, however, I seem to have slightly different symptoms and was wondering if anyone had any ideas as to the cause?

Essentially, the car starts first time even when cold or unused for a while but the revs will fluctuate between around 10 and 1500 rpm for three to four minutes before finally settling down to the normal 950 rpm mark. It usually doesn't stall and holding the revs up with the throttle only hides the symptoms which return when the car returns to idle.

Don't know if the cold satrt unit is just dying, broken or set badly?

Thanks in adavance

LJ

 

[bones]

Welcome Paul, great choice of car you've made. I've owned my SC since '85 and it has always 'hunted' from cold starts for the first few minutes. As far as I know all SCs do it , maybe not the later ones '82/3 I'm not sure . Most SC owners I've spoken to have this startup procedure , I just live with it , it's not a problem. You could try putting in a new Warm Up Regulator but I think you would be wasting your money. The hunting is worse and lasts longer in winter.
On earlier cars a pipe is fed from the left heat exchanger to the inlet at warm up to heat the mixture at start up , It was discontinued on the SC .
The other possibilities are the 'cold start enrichment valve' and leaks in the vacuum side of things. I live with it and just wait the minute it takes for the engine to settle down , the engine is obviously seeking the correct mixture strength for proper running so just be patient. I'm putting a different gearbox in my car soon and while the engine is out I am going to take the opportunity to replace hoses and other hard to service parts , so I'll see how things run in a few months with the new bits on and post the results for start up.
You will need a manual if you want to remove the WUR and you will need to bleed the fuel injection when re-fitting the new one.

 

[Guest]

Hello fellow new member!

My '83 SC does exatly the same but only for a period of about 20- 30 secs. A friend of mine had a '80 SC which also did the same trick, but for about 2 mins when cold. Come on all you experts, whats the cause?

 

[Guest]

Sorry Bones, I posted before i realised you had answered the question! Cold start enrichment valve sounds like a likely culprit.

 

[bones]

I'm willing to bet it's the normal cold start regime for an SC.

 

[Guest]

Thanks bones for your advice, as you suggest it isn't really a problem, but I was unsure as to whether it was normal..... Thanks for clearing it up!

The SC is in pretty good condition I think, but she does suffer from a few little electrical niggles so when my expertise fails expect to see me back on the forum.

Thanks again,

LJ

 

[Guest]

I bet every sc does it too, I know my does when its cold!!!

 

[911 Turbo]

My first post on this forum so "Hello" to everyone! []

I own a `79 SC and my car does exactly the same thing on initial cold startup.

I remember reading about this in a book many years ago and if memory serves me correct it was explained as follows.

It happens because of the cold running cycle of the fuel injection. When the SC was first made there was a cold running problem whereby if the engine was started from cold and driven straight away with an idle of 900 rpm you could find yourself stalling at junctions etc. until a certain engine temperature had been reached. In other words the injection mechanism ran too lean when cold. This was solved by modifying the warm up regulator which controls the warm up period of the engine. This enabled a richer mixture to be used which causes the hunting action of the engine and gives enough fuel to prevent the stalling from happening. After two to three minutes the fuel pressure increases and drops the rich mixture to a normal operating fuel mixture.

I`m not sure if [8|] is definitely the answer to this but thought I`d add it to this thread anyway. I always think of the hunting action as being the engine "having a stretch and yawn" after being idle for a little while.

(By the way, I also own a 911 Turbo hence my forum name, just in case you were wondering!)

 

[bones]

That sounds about right , I've always thought the engine was searching for the correct temperature to be established but the fuel pressure level sounds like a correct explanation of what is occuring in the SCs start up procedure , you just wait till it stops hunting.

 

[Guest]

Similar problems on start up - four attempts usually before catching and then a minute to run smoothly. I was living quite comfortably with this until two days ago when I had a backfire and suddenly got a terrible loss of power after a couple of miles. Seems fine on initial start up but then quickly fades. Now just limps along and I'm staring at a problem! Anyone any ideas!!

 

[bones]

Sounds like an airbox problem . Have a look in there and se if the air filter box is in anyway damaged. Look for cracks. If the problem persists take it to a specialist and ask them to look at the intake side of things. Most SC owners fit pop-off valves to counyeract this very nasty cold start problem. Once you have the car fixed you should fit a pop-off valve. Doit yourself kits are available or get your mecahnic to fit one.
It could be something else but if the problem started after a load backfire at cold start look to fix this problem first it's common.

 

[grant_goulding]

Adrian - Just noticed your post on this. I can understand the problem you are having - I should add at this point for everyone elses benefit that I used to own Adrian's car and got to know the differing ways it would behave when cold and warm at different times of the year. One of the difficulties with the SC is when starting from cold at this time of year - the mixture is particulary rich and I found it was always best to let the engine idle on its own accord just until it was ready to pick up - ignore this and it would respond with a backfire. The backfire you experienced is the unburnt fuel mixture blowing back through the air box. There was I recall a pop off valve fitted to it - check this is still in place. Also there are a number of tubes attached to the intake at the back of the engine (Very hard to get to) but if these are lose or split they will leak air into the system and prevent it from having any power. Can I ask - is it ok when you first start up at the moment but then it lacks power as it warms up? If so then it is an air issue if not it could be more serious. There is also on the inlet/throttle thingy an opening that should be blocked off with a bolt - if this is now missing it will give the symptoms you describe. I beleive it is by the throttle actuator area - I am sorry I can't be more descriptive about its location but you will hear air hissing in if it is missing (Use a 2fit tub - one end against your ear and the other placed arround the throttle area) to locate it. If you find it then place your finger over it and it then engine will suddenly run a lot smoother. I can't beleive it would be anything more serious otherwise it would surely manifest itself in other ways.