SC does not start when warm. Why?

911sc79 · 08-03-2006, 11:41 AM

My SC starts just fine when cold.

When warm, it will start if I start it within a few minutes.

If I wait more than 15 minutes, it will not start.

What do you think is the problem?

vash · vash's Garage

fuel accumulator or fuel pump check valve.

only way to be sure it to test your "at rest system pressure" with the CIS tester guages.

anthony · 08-03-2006, 11:58 AM

Could be a bad starter too.

Does it do it every time or just from time to time.

Purkinjefibre · 08-03-2006, 12:04 PM

I agree with Vash,
fuel acc

vash · vash's Garage

good point. does it not crank over, or not fire up?

ruf-porsche · ruf-porsche's Garage

Could be the thermoswitch for the coldstart or the cold start injector.

sfoster13 · 08-03-2006, 01:09 PM

Seems like there have been a couple of threads on this recently. For me it was the starter.

Sean

Purkinjefibre · 08-03-2006, 01:29 PM

If it's a hot start issue and NOT cold start, my money would be on the fuel acc.
If it's a starting issue, i would inspect the tranny ground strap...

911sc79 · 04:50 PM

The starter is not the problem, it turns the engine fine. The problen is that eventough the engine is turning it does not start

I just tried to start it again and this time it did start. It took 5 hours before it would start again.

ruf-porsche · ruf-porsche's Garage

Get the prssure test gauge for the CIS system and see what the pressure are in the lines when you have a no start situation. As they mentioned previously could be the accumulator or the fuel pump check valve. If the fuel pressure us within spec check the thermo switch and cold start injector.

Purkinjefibre · 08-04-2006, 05:45 AM

911sc79, If your car runs normally it suggests that CIS is working and WUR is good (i think). For your problem i can suggest a quick and dirty test of fuel pressure which is the following. Drive around and get you car hot. Stop and make sure you induced your non-hot start phenotype. Now with the ignition on, go to the engine bay, loosen the airbox straps (kinky black rubber) take off the airbox. Now this is where all your previous escapades with the opposite sex come in- put your hand up inside the airbox (ooh err) and push up the cis air metering deflection plate (gently, we don't won't to cause discomfort). What you should hear is the wailing banshee semi-scream of six injectors- singing away as they inject fuel. I suspect that you will more likely hear a dull moan (like an old man might make as he is shot in the face by his hunting buddy). This would suggest that when your motor is HOT there is a fuel pressure issue- a lack of stored pressure e.g. fuel acc or pump or whatever. Does your fuel pump sound OK. Listen under the front of the car- is it noisy- it could be dirty. Our gas tanks after some many years are full of ***** and soemtimes the screens break letting dirt into the pump= noise + low pressure

With a cold start issue you can do the same thing, except from cold, this is how i had to start my 79 sc from cold (bad cold start injector, turned out).

If you want to borrow some working CIS components to test your car, just let me know,
cheers
Brett

donstevens · donstevens's Garage

I had this problem on my old SC too it was very annoying. It wa s the Fuel Pressure Accumulator. Solved for <$50 and 1/2 hour of do it yourself install labor.

Don