'78 SC: cranking but not firing

[Procul]

First 911, '78 SC Targa. About 20k on rebuilt 3.0 and rebuilt 915 transmission. Cosmetically she shows her age but a beautiful driver.

Put about 500 miles on it on twisty, hilly country roads the first week and loved every second. Then I managed to run out of fuel - the gas gauge bottoms out at 1/4 which is good to know now but would have been nice to know earlier. A couple gallons from a can and vrooom she started right up and off we went. Next morning started fine, ran a few errands and filled the tank with premium.

Next morning she cranks and won't fire.
CDI comes on (can hear the high pitched whine). I figured maybe the fuel filter sucked up crud when I'd run it dry (even though it restarted and ran the next day) so I put in a new fuel filter - much easier than I'd been led to expect and took about 15 minutes. But she still cranks and doesn't fire. Put a battery booster on to make sure there's plenty of juice.

When I push up on the plunger in the air box I hear the pump come on - it sort of shrieks after a few seconds and that makes me wonder if it's pumping dry? The first morning trying to start I thought I'd flooded the engine because I could smell fuel and there were a few drips from the muffler, but I'm not smelling gas now. So I also lifted the popoff valve and sprayed starter fluid while my wife tried to start it - but still just cranking and not firing. I know: "don't do that again!"

I've read related post replies saying to "pull out one of the injector lines and check the spray in a glass jar," but they never say how exactly you just "pull out" an injector line.... or from which end... the only injectors I've worked with were on old diesel tractors.

There's spark - or at least juice to the plugs; I used an in-line tester because I didn't want to pull the plugs yet as just getting the leads back on the recessed plugs is such a pain for a first time 911 owner. But I'm guessing pulling plugs is next.

One of the mechanics at the shop where I bought the car (1,500 miles away) says his gut feeling is that I have a stuck cold start injector. He told me to pull the electrical connector at the back of the throttle body and push up on the plunger for 15 seconds with the ignition on and see if it starts.

With a mirror I found 2 connectors: green one behind the Mixture Control Unit and blue one lower down - is this blue one the CSV? Is that what I should disconnect?

I can get my hand on these connectors (barely) but I don't want to just yank on one and risk breaking it or the housing. Can anyone tell me how to get either of these connectors to release?

Last thing: when I pulled the fuel filter I discovered this ground strap (2nd & 3rd pics) just lying there behind the accumulator. Traced it back to the bottom of the CDI. Not the two brown ground wires from the sleeved bundle - they're tied to a bolt on the sidewall - but a separate strap just lying there. I can't see anywhere this might have come loose, nor any logical place to attach it. Bentley book hasn't been any help so far but maybe I don't know where to look.

Suggestions and ideas? New to the air-cooled world but not a complete novice and willing to try what I can. And a long way from a Porsche mechanic. I've been looking at this old thread
911SC, starter fluid
but I can use all the help I can get.

Thanks!
procul

[Schulisco]

I suppose due to old detoriated fuel there's rust inside the fuel tank which clogs now the fuel pump. It's the first device suffering from rust inside the tank. Probably there's more rust and dirt within the fuel lines, the fuel filter, fuel accumuloator and the rest of the system. You have no other choice than pulling out the fuel sensor on top of the tank and have a look inside the tank to prove if there's rust or dirt or not. Then - if rust/dirt is there, which I expect - renew the tank at best and fuel pump, clean out the fuel lines and inspect all the rest of system. Flush the whole system with fresh fuel to assure that there's no more rust or dirt. Check the tiny sieve in the warm up regulator.
Pulling the injectors mean tearing the injecting nozzles out of the intake runners. The injectors sit with rubber bearings in plastic injector sleeves, there's no other holder. You can pull them by hand pretty easy.
Normally the engine should start with start spray when it has a spark...
That greenish connector in the mirror is a security switch on the sensor plate. It prevents flooding the engine with fuel in case of an accident and engine fire. It's being lifted and switches on the fuel pump when engine cranks and sucks air. When you pull the connector the fuel pump starts running as you switch on the ignition, do this only for testing purposes.
To get familiar I strongly recommend to watch the video series about the 2.7 CIS 911 from Curts fabulous YT Channel "Klassikats": https://www.youtube.com/playlist?list=PLkWFofpgz2OgF9FdliKnlzuY0pygqRkMj
After that you can consult more literature about CIS linked here in the forum as well...

To prevent this trouble again I recommend to use a fuel stabilizer on every fillup. This guarantees that the stabilizer is always in the system preventing rust because the ethanol attracts water which causes the fuel detoriate again. And drive it more often...also using fuel without ethanol might be a good idea, but could you be pretty sure that the fuel is without ethanol for sure? Here in germany we only habe only one brand of premium high octance fuel "guaranteeing" to be without ethanol for an ridiculous high price...

Thomas

[Procul]

Thank you, Thomas!
I'm pretty confident that I have an ethanol-free fuel, but I will be adding a fuel stabilizer from now on.
I'm going to verify that I have fuel flowing first of all, and then more thoroughly check for spark.
And then see about pulling the blue CSV connector.

It's a drag that the car was running so beautifully and now isn't starting, but I'm enjoying the opportunity to learn the engine and systems.

[Procul]

found this picture in another thread, I guess this answers my question about where that earth strap is supposed to go.

[Schulisco]

Originally Posted by Procul

And then see about pulling the blue CSV connector.

Looked at the mirror picture again. I cannot surely identify if the connector is the CSV or the security switch connector.

See in this thread posting #2 a better pictur identifying both:
https://forums.pelicanparts.com/porsche-911-technical-forum/897745-cold-start-csv-location.html

See this page for more details on the fuel pump security mechanism:
https://nineelevenheaven.wordpress.com/the-protection-circuit-of-the-fuel-pump/

Your strategy sounds good. But I doubt that you will success unless you proved if the fuel tank and the pump are rust free...otherwise you're chasing many other problems without getting the car back running. CIS troubleshooting means testing and proving everything step by step and following the logic of the system. That's why it is so important to understand the whole system...

Thomas

[David Inc.]

The injectors are only held in the ports with a peened tab. This may have been cut out in the past, maybe not, but will need to be bent or otherwise smoothed out of the way to pull the injector housing out as a whole.

Edit: Did it fire anything at all while spraying starter fluid or absolutely nothing?

[Schulisco]

Originally Posted by David Inc.

The injectors are only held in the ports with a peened tab. This may have been cut out in the past, maybe not, but will need to be bent or otherwise smoothed out of the way to pull the injector housing out as a whole.

This can be seen in Curts video of rebuilding the CIS:
https://www.youtube.com/watch?v=K-OvjlkrgNo

Thomas

[Procul]

Yes, the mirror picture I posted is the air flow sensor connector. I'm looking for the blue CSV connector right now. Not easy to locate!

[Procul]

Thanks David.

When spraying starting fluid the engine did not fire at all - I was spraying into the pop-off valve, which I'm not sure was the right place.

[Schulisco]

Originally Posted by Procul

Thanks David.

When spraying starting fluid the engine did not fire at all - I was spraying into the pop-off valve, which I'm not sure was the right place.

It's not.
Opening the pop off valve you create a massive vacuum leak. This prevents starting the engine...Instead spray in the airfilter box from underneath the sensor plate, this is the normal way the air takes. Or let the air filter mounted and spray into the intake pipe of the air filter.

Thomas

[Procul]

Thanks again, David!
I was just now able to pull the blue CSV connector and will see if it fires after lifting the plunger a few seconds. If it still doesn't fire I'll try starter fluid in the right place.
Trying not to imagine how fun it will be getting the connector back in place.

[Procul]

The bad news is, disconnecting the blue CSV control switch made no difference, and neither did spraying in the right place: cranking but not firing.
The good news is I was able to reconnect the plug without much trouble. That's not much to celebrate but I'll take it.

[andino]

I would verify you’re getting fuel pressure to the injectors if you haven’t already by using some cis gauges. You mentioned that you’ve got spark so fuel would be next on my checklist.

[pmax]

Originally Posted by Procul

procul

That's the green connector for the safety shutoff.

[Procul]

Pulled one injector - I believe it's cylinder #4 (near right as looking into the engine compartment from the rear) and there appears to be a nice spray.

Wondering if this is the right kit I need to test pressures:
https://www.pelicanparts.com/More_Info/TOLSGT33865.htm?pn=TOL-SGT-33865&bc=c&q=cis%20pressure%20gaug

Meanwhile I'm going to look into spark a bit more thoroughly.

[Procul]

The "safety shutoff" and ASC are the same thing?

[Schulisco]

Originally Posted by Procul

Pulled one injector - I believe it's cylinder #4 (near right as looking into the engine compartment from the rear) and there appears to be a nice spray.

This is the numbering of the cylinders and the firing order, the SC fires CCW:


When did the injector spray exactly? While cranking? Or even with ignition on? The normal way is as follows: Fuel must not be sprayed with ignition on. When cranking the air sensor plate get's lifted and the security switch engages the fuel pump to pump gas. In the same moment the csv (cold start valve) has to be engaged by the termo time switch (switch mounted on the left side of the left chain cover) in parallel to the starter motor (max. 8secs to prevent flooding the engine). Normally the engine start then right away if the control pressure by the WUR is in spec depending on ambient temps.

Originally Posted by Procul

Wondering if this is the right kit I need to test pressures:
https://www.pelicanparts.com/More_Info/TOLSGT33865.htm?pn=TOL-SGT-33865&bc=c&q=cis%20pressure%20gaug

Correct.

Originally Posted by Procul

The "safety shutoff" and ASC are the same thing?

What do you mean with ASC?
The Air Flow Switch and the safety cut off are the same thing...

Thomas

[boyt911sc]

Originally Posted by andino

I would verify you’re getting fuel pressure to the injectors if you haven’t already by using some cis gauges. You mentioned that you’ve got spark so fuel would be next on my checklist.

Procul,

Follow the above suggestion and hope you did not follow your mechanic’s advise “lifting the sensor plate and pulling the AFS plug (with ignition switch @ ON for 15 seconds” to get the motor running. This was an ill conceived suggestion. And if you have done the “15 seconds” advise, it would make your motor more difficult to start. So did you follow the advice of your mechanic? Keep us posted.

Tony

[Procul]

Hi Tony,
Yeah I did and he was dead wrong, I got no change, just crank and no fire, so I reconnected the CSV connector.
For what it's worth, his dad rebuilt the engine and he rebuilt the transmission (which feels amazing). They are a reputable Porsche shop and he's an air-cooled guy but he was off the mark on this guess.

I pulled the plug from #4 and I have strong blue spark.

So I have good spark, I seem to have fuel, but I have no ignition.

Next test fuel pressure?

Thanks to everybody who's guiding me here!

[pmax]

Originally Posted by Procul

the ASC connector.

What's that ?