SC cold starting

Having trouble with my SC - starts fine the first time, but then impossibly to start again a few minutes later.

A friend who is into Audi Quattros came up with the following:

Had a chat to some friends about you starting problem and another lightly
> culprit could be the temperature sensor. This is the one that plugs into the
> coolant and decides weather to use the cold start value. It works something
> along the lines of:
>
> if it's 10 degrees then operate the cold-start value for 4 seconds
> if it's 5 degrees then operate the cold-start value for 1 second
> if it's above 2 degrees the don't operate it at all.
>
> It's all done with a bi-metaic strip so it's easy to see how it might get a
> tad confused.
>
> if we assume that the bi-metaic strip heats up too slowly it seems to follow
> that if the engine is started again after being run for 5 minutes then the
> temp sensor could cause the cold-start injector to flood then engine.
>
> If the temp. sensor is the same as on my audi (given Bosh /K-Jettronic
> injection it seem lightly) it's about 70 mm long (most - 60mm of the length
> will be in the (a) head) with a ~ 19mm dia nut on the end for removal. On
> the other hand it may be totally different ! (sod's law and all that).

Does this ring a bell with any SC owners (yes, I know my engine doesn't have any coolant!).

Thermotime switch is located on the driver's side chain cover on my '83 SC. Sounds more like a fuel pressure problem. If engine has been running, the thermal switch should most likely be open and engine warm, thus no need for cold start valve.

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Robert Stoll
83 SC
83 944

I think the car would start, even if the cold start valve were operating despite engine temp.

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'83 SC

My mechanic noted that my car idles lower on a warm restart and reckons it is a fuel pressure issue. Mine is minor , always starts , just a lower idle than norm for a minute.

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Bob
1982 911SC Targa

I am a novice compared to most who contribute to this forum but with all the threads I am getting better at fixing my problems and diagnosing with good results. It would appear to me that if indeed it is a fuel pressure problem then the accumulator should be replaced. I had the same problem and replaced my old original accumulator ('73T - CIS) and it solved the problem. It was cheap and easy....Good Luck

Sailor

replace your fuel pump check valve along with the accumulator. 81'SC

I can't see why the fuel pump is at fault. The car starts well from cold, and then starts again fine once the engine is warm. It's just between starting from cold and the engine warming up that it is not possible to start the engine again.

Here's what I think is going on.

You've run the car just long enough that all of the cold start components (i.e. the warm up regulator, theromvalve, aux air regulator) that have an internal heater element have gotten warm, but not long enough to warm up the engine. Therefore, when you go to restart, you don't get any cold start enrichment of the mixture, or a higher idle.

I wouldn't think that the thermotime switch would have warmed up enough not to give you a bit of gas while cranking. Does the car fire up and die, or just not fire up at all?



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Bill Krause
'79 911SC Euro

Doesn't fire up at all. I suspect flooding. I tried pulling out the fuel pump relay to stop the supply of petrol while turning over the engine and it did then start.

Flooding? Maybe you've got a leaky cold start injector.

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Bill Krause
'79 911SC Euro

I suspect the cold starter injector, but what do you mean by leaky?

It might be leaking fuel into the intake manifold. The cold start injector stays under pressure with the engine off, whereas the other injectors are not under pressure. So the only place for fuel to get into the engine is through a leaky cold start injector.

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Bill Krause
'79 911SC Euro

Phil,

I'm sure the time-temperature plot of the Thermo-Time switch action is a bit more complex than what your friend with the Audi said, but those MAY be valid data points on the curve ...

It should be easy enough to test the cold-start valve on a hot engine to see if is still squirting fuel, both with and without the solenoid lead attached. And, the Thermo-Time Switch can be tested off the engine, too, in a pan of boiling water and cup of ice water.


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Warren Hall
1973 911S Targa