Starting problem when hot

[Guest]

Can anyone help please, engine refuses to fire when hot but only when left for a few mins. When engine cools after about an hour it starts up ok. I read somewhere about fuel evaporation but can't remember any details of the cure.

 

[bones]

If it's only on hot starts Ray , I'd replace the fuel accumulator and see how things are then. It sounds like fuel evaporation for sure.

 

[John_Ward]

There's another - associated - possibility. There is a non return valve in the fuel system which keeps it pressurised - if it fails, the problem you describe occurs.
I seem to recollect that there is an in depth description of the hot start problem and what to do about in "101 Projects for your Porsche 911"
John

 

[bones]

The non-return valve or 'check valve' is in the fuel pump and on ealier pumps is replaceable (in fact my low pressure cold start problem could be exactly related to that if I could be bothered to check it out) but the accumulator is much easier to get to as a starting point.

 

[Guest]

I have the (classic SC) hot start problem on mine. Tuthills changed the fuel pump valve last year as it is a cheaper fix than the accumulator (if it solves the prob) but had no effect. They then played with the FP regulator last service to try and sort it but again no go. Gonna have to bite the bullet now and change the accumulator as driving me nuts. Wayne Dempsey does point out the check valve, but recommends the accumulator as first port of call for a hot start prob fix.

Some interim solutions are keep the fuel tank full or as close as poss; the tank acts as a fridge for the fuel system and minimises vapourisation, which is what is happening on the hot start; the pump trying to cycle what has become a gas. Also reputedly helps to run your fuel pump for about 30 seconds after you knock the car off when hot, so the fuel line will fill with cooler fuel and there will be less chance of it boiling off. I have tried both solutions and the full tank thing definitely effective - up to a point. My engine cover was almost too hot to touch yesterday afternoon after a day spent parked in direct sun at Walton Hall, took three 10 second cranks to get it to fire. Not good for starter, fuel pump, engine or driver, so new accumulator ordered today []

 

[Guest]

Here's what the bently manual says about "Hot start - engine starts hard or fails to start when warm"

Air flow sensor plate rest postion incorrect - inspect and adjust
Fuel Pressure incorrect - test (i assume you need the gauges etc)
Cold start valve leaking or operating continuosly - test cold start and thermo time switch
Vacuum leaks (intake manifold) - inspect intake air coponent for leaking hoses and hose connections
Control plunger in fuel distributor binding or fuel distributor faulty -check air flow sensor plate. if necessary replace fuel distributor(arggg!!!!)
Control pressure regulator faulty - check control pressure regulator full load function

Tests for each are covered in the manual. If you want I can photo copy them and post them over to you. The airflow sensor and cold start valve are really easy to check.
Rats

 

[geoff Ives]

About 10 years ago I ahd the same problem with my 2.7 911. Ok it is a different car but the system (k-jetronic) is much the same. All I did was replace the 'One way' valve. It took less than seven minutes and I lost about half a pint of petrol. It cost less that £10 and today, nearly 10 years on it is fine.