1988 911 won't start warm

[jamiebussell]

hey my 88 911 has the same problem until i spray a touch of eather in the breather box then i can drive it again ...I know what the hell ???but when you're stranded at the gas station i got desperate but it was a only a hit or mis problem for a while but now its a constant , wont start at all now if its warm...i have a fluke multimeter where is the sensor that everyone is talking about and does this cause the pump to cut on ?

[JeremyD]

Usually cylinder head temp sender located on cylinder #3 (driver's side front of engine towards flywheel)

How old is your DME relay? That's located right next to the motronic box under the driver's seat.

[ischmitz]

This could be caused by a bad fuel pump check valve. The check valve maintains pressure in the fuel rails after you shut the engine down. Without pressure the fuel starts to boil due to heat-soaking and creates fuel vapor in the fuel rails. This will make hot-start almost impossibe. Try and get a pressure gauge to measure fuel pressure after engine shutdown.

The sensors (speed and reference) are on the flywheel side of the crankcase. The can be tested by measuring resistance. However, if the car starts fine cold and start fine hot with starter fluid I assume you are missing fuel but got spark. Malfunctioning sensors or DME relay would kill spark and fuel.

Cheers,
Ingo

[jlex]

I had a similar problem on my '85 3.2. Figured it was either a leaky injector or like Ingo says, a bad check valve on the fuel pump. I measured the fuel pressure after shut down... it's supposed to hold 14 lbs after shutdown, but mine went down to 0 almost immediately. Pulled the injectors & had them tested & rebuilt. Rechecked pressure after reinstallation & "residual" pressure is good w/ no hard starting. Yours may be fuel related, but you'll need a fuel pressure guage to make sure. Good luck.

regards,

jlex.