911 start problems when warm??

Guest · Apr 14, 2005

Having problems starting a 1986 911ss

It will start when cold and will keep starting until it gets up to temperature
when its run for approx 10 mins and then switched off by the ignition key it will not start again...until it has cooled down.

have check the DME relay...seems to be working fine and have disconected the No 3 temperature sensor and this cause the same problem ....when the car is cold

could it be this....is there anyway of checking it???

oh by the way when it is running, it runs fine and does not miss a beat

initially thought it was the fuel pump...hence checking the DME relay

would be most grateful for any responses
cheers!!

plhorner · Apr 14, 2005

Garry,
Try posting this in the 3.2 area rather than the Turbo, you might be a little more sucessful.
CD burned!!

Laurence Gibbs · Apr 14, 2005

Anything that effects warm start conditions is worth a try. Don't have info to hand so can't help further in that department. you might be losing residual pressure but this is less likely in a pulsed injection system. Don't immediately condemn the injection the ignition side should be checked out too.
The NTC sensor is what I assume your are refering to as a temp sensor(it's an ntc resistor in later motronics anyway). This is a negative temperature co-efficent resistor , basically it's resistance changes with temperature. so if you have a meter that measures resitance you can check for a change in value from completely cold to warm / hot. They tend to go open circuit or high resistance when faulty and stay that way. So a sensor that reads the same hot or cold will likely be knackered. From distant memory i "think" (don't hold me to this) 250 ohms cold to 1k+ ohm when hot is about right/though i may have it the wrong way round.
Hope this helps a little.

Guest · Apr 17, 2005

Mine had exactly the same symptons as yours. Turned out to be the crank sensor. I'd tried the DME and Fuel pressure before I tried the crank sensor. My specialist didn't have a 911 one to try initially so put in a 944 one. This solved the problem. The 911 one cost about Gbp 70.00 plus fitting. Hope this helps.

Guest · Apr 17, 2005

just checked the resistace and it reads:
....when cold 3.28 ohms, and 0.01ohms when hot

does this sound right
also.....
exactly where is the NTC sensor its difficult to see I can only see where the wire goes it goes into a harnes near number 3 cylinder and I can only test it at the end of the wire where it goes into the multiblock also above number 3 cylinder

cheers!