Pelican Parts Forums - 911 SC cold start issue

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911 SC cold start issue

Hello! I have a cold start issue that I’d love some help diagnosing.

The car:

1979 911 SC
3.0
72,000 Miles
Brand new tune up – wires, plugs, rotor, distro
Clean fresh gas

When I start the car with a cold engine it fires right up, but immediately drops RPMs and behaves as if it will stall – but so far it hasn’t stalled out. After a few seconds the RPMs rise to ~900rpm, then up to ~2000rpm a few seconds later. The car stays at this RPM range for about minute before it drops to ~1000rpm and is ready to go. Once the car is warm this problem does not occur on restart.

Video of a cold start: https://youtu.be/t4ccCql7o-8

I suspect the WUR but was hoping that maybe someone here had experienced and diagnosed a similar problem before I throw a $400 part at it.

Thanks!

Quote:

Originally Posted by Lar911sc (Post 9819911)

Hello! I have a cold start issue that I’d love some help diagnosing.

The car:

1979 911 SC
3.0
72,000 Miles
Brand new tune up – wires, plugs, rotor, distro
Clean fresh gas

The issue could very well be the WUR, but you do not necessarily have to replace it. You do need to invest in a fuel gauge pressue set, however. You need to establish if your system, cold control, warm control, and residual pressures are in spec--assuming all else, like timing, ignition, and valve clearances are good. Your symptoms are consistent with a too high cold control pressure, but you need fuel gauges to check. If so, it is easily remedied without buying a whole new WUR.

The key to your issue is to eliminate possibilities, of which the WUR is but one. You need a fuel pressure gauge to verify its proper function.

Ossi speaks the truth.

Location........

Where are you located? Thanks.

Tony

My 81 has lagged longer than that with WUR within pressure specifications. At least it's livable before remedied. Just an annoyance.

Here is a cheater procedure you can do for fun. It may start better but does not fix the root cause(s). Plug the distributor retard hose with a golf tee. Don't worry about plugging the metal tube on the distributor. It advances your timing 5-10 degrees but only at idle. It compensates for little tired things in the CIS. It may also be a tiny bit zippier off idle.

That said, every part on the CIS is testable. If you are new to the car, I cannot think of a better learning curve to go through than to read up, buy a few tools and perform due diligence work on your existing components.

I would start with a pressure test as ossi noted. Get a decent set of gauges.

I just had a similar issue with a 83 SC. Went through the CIS pressure testing and found my rebuilt WUR was a little out of cold spec. (to rich) But the big problem was actually my base timing. I had engine work done and the car was returned to me with the base timing set to 5 ATDC instead of 5 BTDC:eek:. Reset timing and now have perfect cold starts. Your issue may not be timing, but it is a quick thing to check and remedy. Tony and Bob will not steer you wrong with CIS issues.