911sc stalling problem

[Bob Kontak]

Originally Posted by et cetera

Took it to the smog shop and it passed, but it was only because the guys were cool about it stalling a few times.

You passed because your car was blowing "clean".

The emission requirements on your 78 vs that water cooled devil are night and day. Far less stringent on the 78.

If you are hell bent on not springing for pressure gauges, the absolute core of CIS functionality, I would focus on air leaks.

There is one thing I will throw out here for grins. The deceleration valve on my 81 is designed to bleed air into the air box if you lift throttle at high rpm. The high vacuum opens the diaphragm. As rpm's decrease the diaphragm should close. I can put a golf tee in the small hose that feeds the unit and eliminate it from the system. Not sure if it's that simple on the 78. Your's is a little different.

[T77911S]

do you have the CO reading?

[et cetera]

These were the results from the test.

[Discseven]

Minor hijack

.

[et cetera]

Good news, its running great now. I replaced plugs, wires, dist cap, rotor and coil. Most seemed near original and well past their useful life.

Next up is the vacuum lines. I picked up a bunch of 3.5mm line but it looks like there are a few other sizes in there. I searched but couldn’t find a definitive chart of what else I’ll need. Does anyone know the other sizes?

[Bill Douglas]

Vacuum lines. I snip 10mm of the ends and refit. It seems to work well. Another thing to do sometime is to replace the fuel filter.

I'm pleased the car is running well and you can get out there and enjoy it. It's a great looking car.

[et cetera]

False hope. Took it for a longer drive on the freeway this morning and the problem came back.

Time to pick up a fuel pressure gauge. Which one do you guys recommend?

[Guardsred911]

I am not sure if the '78 SC has this, but I had an issue with my O2 relay under the passenger seat going bad and exhibiting same symptoms on my '80 SC.

Here's a thread on it... with the part number that worked for me. (although if your relay has that plastic tab on it, you might want to order the other one on the page)

Rough running and the green wire

[mysocal911]

Originally Posted by et cetera

Confirmed, black coil. Blue Perma-tune CD.

Not reliable! They are intermittent. Porsche factory only used a 3 pin unit (points ignition)
for one year and NOT for a 911SC.

[rwest]

Originally Posted by et cetera

False hope. Took it for a longer drive on the freeway this morning and the problem came back.

Time to pick up a fuel pressure gauge. Which one do you guys recommend?

There's several types, but most seem to be about the same- Pelican sells this one CIS K-Jet F.I Tester w/ Case - PelicanParts.com

Intermittent problems that involve heat seem more like an electrical or ignition issue. The Permatunes are notorious for intermittent failures, although usually they require a bit of time to cool before they restart.

If you crank and it doesn't start right away, get a timing light on it to see if you're getting spark.

[pmax]

Decel valve and O2 relay not present in the 78 CIS.

[et cetera]

Originally Posted by mysocal911

Not reliable! They are intermittent. Porsche factory only used a 3 pin unit (points ignition)
for one year and NOT for a 911SC.

I was reading up on replacements for the permatune, it sounds like some people have had success with the MSD Streetfire. I’ve also read a bunch of complaints on the MSD, so I’m not sure if that’s the best route.

[et cetera]

Originally Posted by rwest

There's several types, but most seem to be about the same- Pelican sells this one CIS K-Jet F.I Tester w/ Case - PelicanParts.com

Intermittent problems that involve heat seem more like an electrical or ignition issue. The Permatunes are notorious for intermittent failures, although usually they require a bit of time to cool before they restart.

If you crank and it doesn't start right away, get a timing light on it to see if you're getting spark.

It fires right up when cold and settles in to a good idle. It’s only after extended use, 20+ mins, that it starts to have a problem.

When it does die it’s when the clutch is in as I pull to a stop. From there it fires right back up and will run as long as I keep some throttle on it.

I also noticed that it’s blowing a pretty large cloud when I first start it cold. Not sure if that’s related or normal. I know a little smoke is typical but this is like a solid 10ft radius. Blew it straight across the street this evening.

[emcon5]

Ignition components doesn't seem like the right direction to me. I would expect if there really was a problem with the ignition, that there would be other symptoms.

What is your idle speed?
Where is your timing set?
Does your distributor have one vacuum line or two? I think the early SC only had one, for vacuum advance.

[et cetera]

Originally Posted by emcon5

Ignition components doesn't seem like the right direction to me. I would expect if there really was a problem with the ignition, that there would be other symptoms.

What is your idle speed?
Where is your timing set?
Does your distributor have one vacuum line or two? I think the early SC only had one, for vacuum advance.

I'm starting to feel like it is a mixture issue. The more I go over the car the more I suspect the POs mechanic was a bit lazy. I've found a few vac line "repairs" (splicing lines that had broken rather than entirely replacing) that still had large cracks.

I plugged the vac line that ran from the throttle body to the smog pump control (Diverter Valve?) because it was cracked and leaking. Ever since then it has a huge cloud of white smoke when I cold start. Makes me think that the mixture was rich to cover up for some of these vacuum leaks.

Much of the parts on the motor are original. Is it crazy to consider just dropping the motor so I can easily replace all of the vac and fuel lines?

Oh and your question about the idle, it seems a little high, hovers just above 1000 and occasionally will drop to 950.
Distributor does only have one line.
I'll have to check on the timing.

[universeman]

You have got to get all the vacuum / air leaks out of the system before you start doing anything else. Sounds like you have a lot of old rubber; old rubber splits and leaks, and with the sheer number of vacuum-controlled bits on these SC engines, you're chasing ghosts until you get real certain that all the air leaks are gone. Unmetered air can cause you to run lean, and if you adjust mixture while you have unmetered air, you'll be off again as soon as you fix the leaks.

There are some tricky leaks in hoses that run behind the CIS and fuel distributor. Also, check the rubber boot on your CIS and your airbox itself - those can leak too. Good luck! A smoke machine or a cigar can really be of assistance with this.

[universeman]

Haven't seen this asked/answered here - does RPM drop when you remove the oil filler cap with engine running?

[et cetera]

Originally Posted by universeman

Haven't seen this asked/answered here - does RPM drop when you remove the oil filler cap with engine running?

It does drop 100-200 rpms, which made me think I dont have a major leak. But ask you also pointed out, there are so many components in the CIS that are dependent on vacuum that it only takes one leak to really mess things up.

My goal is to replace all of the lines. I purchased a bunch of 3.5mm line but it appears there are a bunch of different sizes. I couldnt find a straight answer on what I need to order.

The next challenge becomes, how do I get to all the lines on the back side of the motor.

[TibetanT]

Hello There:

You can get to most of the smaller lines in the back of your CIS system by doing a partial engine drop.

Hope this helps and Good Luck!