Background: 81 911 SC, 12K miles on rebuilt engine. WAS starting immediately, cold, warm and hot. Cold, warm or hot, runs excellent, pulling fabulously. -Was at Porsche Palooza in Arkansas in November. February is my oil & filter change, but since it had been about 10K miles, I adjusted the valves (they were all still about .004). I installed new spark plugs too, although the Bosch I pulled out looked nice and evenly tan.
In January, I installed a new fuel filter and new accumulator - was having questionable 60 minute park warm start extra cranking required. I believe the accumulator solved that issue as it fires immediately upon cranking if warm or hot.
Trouble - no longer starts/fires during cold cranking. To get it to fire, I have to give it about 1/2 throttle pedal travel and then it catches and runs great with no drive-off hesitation, pops, etc. So once running, the idle goes to 1250rpm or so and after about 30 seconds, it drops to 1000. No drive away troubles, pulling normally.
So, went to the checklist found elsewhere in these forum pages.
WUR - I rebuilt and properly configured my WUR a few years ago. But I tested the cold pressure just in case: (‘81, US delivered, WUR p/n …090..)
Valve closed - fuel pump pressure - 74psi.
Valve open - 57F, vacuum pump at 14psi on intake port, fuel pressure is 26psi, which is basically in the middle of the range for 57F and this model WUR
Maybe a vacuum leak? - did a smoke leak test - no leaks.
Engine fully warm - very steady vacuum of 15 in hg at idle of 1,000.
Thought maybe the NGK plugs were the trouble - so I pulled them back out and reinstalled the tan Bosch but no help.
Further note: I had my hands around backside of throttle assembly checking connections hoses, etc. and didn’t find anything amiss.
Thoughts: It takes opening the throttle to get it to fire so the engine wants more air. Could my cold start injector be injecting for some reason (this morning it was 65 so the cold start injector should not be operating)? One thing I will try is to disable that injector.
Could a weak spark be not igniting the cold start fuel? (The plug wires are not new but recently cleaned light corrosion off the contacts of the rotor and dist cap, but again it runs so well once running.
More: A few years ago, I had the engine out to replace the intake manifold so I also tested the auxillary air flow and other cold start devices and they were working well.
Where to go from here? Thanks in advance for your ideas.
Charles in Dallaas.
