79 911

[moro mechanic]

i'm working on a customers car, a 79 911 carrera it came in last week with a no start prob and it would start and dies 3 times and then wouldn't start at all. I pulled the cold start injector and cleaned it and replaced a plugged solid fuel filter and it started right up. now it is back with the same prob and i checked the filter first thing and it was clear then i pulled and cleaned the cold start again and still nothing and i'm getting signal to the cold start and lots of fuel through the filter anyway but not much through the return line. any ideas of what i should check next?

[magcuda]

basics - is it getting spark? what are the fuel pressures?

[moro mechanic]

basics - is it getting spark? what are the fuel pressures?

There is good spark and the fuel pressure after the filter is from 25-35 psi while cranking, is it suppose to register with the key on or just when cranking?

we are able to get it to somewhat run if we manually open the air inlet valve but it won't stay running if we let go of the valve.

[wwest]

basics - is it getting spark? what are the fuel pressures?

There is good spark and the fuel pressure after the filter is from 25-35 psi while cranking, is it suppose to register with the key on or just when cranking?

we are able to get it to somewhat run if we manually open the air inlet valve but it won't stay running if we let go of the valve.

The fuel pump power circuit is a little complex. Without the engine started the fuel pump only works in the ignition starting position. Once the engine starts, engine vacuum results in intake airflow, there is a microswitch on the intake airflow fuel metering inlet plate. The microswitch is out of adjustment or you have a blown airbox and the intake airflow has other openings to get to the engine.

[judgejon]

i'm working on a customers car, a 79 911 carrera it came in last week with a no start prob and it would start and dies 3 times and then wouldn't start at all. I pulled the cold start injector and cleaned it and replaced a plugged solid fuel filter and it started right up. now it is back with the same prob and i checked the filter first thing and it was clear then i pulled and cleaned the cold start again and still nothing and i'm getting signal to the cold start and lots of fuel through the filter anyway but not much through the return line. any ideas of what i should check next?

1. check the air box... just to be sure it has an escape valve installed. if not, its probably a cracked box...

2. replace the fuel pump relay.... and/or replace the fuel pump

3. replace the cis unit....

this probably is too basic to help, but I replaced several fuel pumps in my '79 over the years and is all I can think of at the moment. good luck...

[70Sixter]

I can't add to judgejon's comment, but I had weird symptoms in my 911. It would start fine, run for a bit and die. After going nearly nuts I discovered internal fuel pump leak let gas into motor side from pump side.

[topmech0]

there is plenty things that could cause this but as it starts on cold start i would consider possibly the fuel metering head itself as had plenty that simply get gummed up or the metal strip inside has holes once stripped for overhauling. failing that i would check for air leaks on the intake!