'79 SC turns over but won't start

[jons911]

I have a '79 911 sc, stock motor, stock ignition, stock CIS. I recently returned from a long business trip where the car sat for about 5 weeks. It was in a garage that stays pretty consistent between 60 and 70 degrees year round. It started up fine and after filling it up, I took it for a drive. The next day I drove it a short distance (~5mi) and when I came back to the car it would not start. It turns over, but won't catch.

Observations:
-Spark plug wires are all plugged in and in good shape
-Spark plugs are relatively new (<3000mi) but the tips are coated white
-Spark test with separate testing piece showed what I would think is a pretty good spark
-Checked air flow sensor plate and it moves freely and has constant resistance when pushed up
-With the car on, not cranking, there is a quiet, high pitched whine coming from the engine compartment

Conclusions:
I had read in Bruce Anderson's book that if the spark plug ends are white then the car is running lean, which I had been leaning to for a little while but wasn't sure. I checked the fuel distributor, but without a pressure gauge, that didn't yield very much. Either way, hardly any fuel seeped, dripped or sprayed out of the line, so I'm leaning towards a fuel issue, not a spark/ignition issue. Also, I thought I read on here somewhere that with the car on, if you push up on the air flow sensor plate then that should force the fuel pump on. I did that but couldn't hear it working.

After pouring through Bentley's, Anderson's, and Wayne's books in conjunction with this site, it seems like the issue is fuel pump or fuel accumulator/filter or an ignition coil issue. Any advice on what may be the issue or other things to try to further narrow down the problem would be much appreciated. Thanks.

The Answer: Fuse 16, the fuel pump fuse, had a bad contact and was not allowing enough power to the fuel pump. I scraped the contact to clean it off and the car started right up.

[ischmitz]

I quick test to confirm your issue is fuel-related (lack thereof). Spray some starter fluid or brake cleaner into the air intake and then try to start. If that works and the engine runs for a couple of seconds you know you are missing fuel.

From there is it systematic checks:

- Is the fuel pump running when you crank?
- check fuel pump fuse and relay

Next, once you hear the pump running you need to get a hold of a pressure gauge and check for fuel pressure. And then for control pressure. There are tons of threads that explain how the control pressure is responsible for the mixture strength in a CIS car. Read up and buy a pressure tester setup for your CIS.

Cheers,
Ingo

[jons911]

Ingo,

Thanks. I'll try the starter fluid tomorrow. Just to clarify, should the pump run when the ignition is on but the car hasn't been started? I couldn't find the answer to that.

Thanks

[ischmitz]

It'd been a long time since I dealt with CIS. I believe with your car and the ignition ON you need to lift the sensor plate. This will trigger the safety switch and the fuel pump needs to come on. If not something isn't right.

[Bill Douglas]

I might get flamed for how irrespossible this is... But I had a similar problem and I disconnected the fuel line after the filter, put a plastic bag over it and turned the key to start for a moment or two.

If the fuel supply is working up to that point, haha, a surprising amount of fuel should have come through.

Good luck, Bill.

[jons911]

Update: I sprayed some starter fluid into the intake and when I turned it over the tach bounced and was holding at 1000 rpm. It didn't fully start, but that is better than before when the tach stayed flat at 0. I think my plugs are fouled from running so lean and that is not producing as strong of a spark. Stupid me only used the spark tester and didn't try it when I actually pulled the plug out to look at it.

New coil and fuel pump are on the way, so hopefully soon I can get somewhere.

Bill, I'll have to give that one a try.

[JJ 911SC]

Originally Posted by Bill Douglas

I might get flamed for how irrespossible this is...

Let us know when you are a good distance away from the car as we don't really want to flame the car...

[ischmitz]

Originally Posted by Bill Douglas

I might get flamed for how irrespossible this is... But I had a similar problem and I disconnected the fuel line after the filter, put a plastic bag over it and turned the key to start for a moment or two.

If the fuel supply is working up to that point, haha, a surprising amount of fuel should have come through.

Good luck, Bill.

OMG, he revealed a sacred portion of how to do a fuel delivery test. Shame on you


What you really want to do is check the amount of fuel from the fuel return line. The Porsche workshop manual specifies it to be a minimum of 850ml/30 seconds. The key here is that the pump has to deliver this while creating pressure. Checking the output from the pump in front of the fuel filter essentially lets the pump work against zero pressure and thus it might show lots of fuel. But once the pump has to work against back-pressure from the regulator it might not deliver enough fuel.

Ingo

[boyt911sc]

Originally Posted by jons911

Update: I sprayed some starter fluid into the intake and when I turned it over the tach bounced and was holding at 1000 rpm. It didn't fully start, but that is better than before when the tach stayed flat at 0. I think my plugs are fouled from running so lean and that is not producing as strong of a spark. Stupid me only used the spark tester and didn't try it when I actually pulled the plug out to look at it.

New coil and fuel pump are on the way, so hopefully soon I can get somewhere.

Bill, I'll have to give that one a try.

Jonathan,

Why do you think you need a new coil and FP? Have you tested and confirmed they were defective? What happens next after installing new CIS components and still would not start or run? Replace more parts?

To test your FP, you need to understand how the FP operates. The FP relay socket method (terminals #30 & #87a) is a good way to do it. You need a fuel pressure gauge kit and this is a mandatory tool for fuel injection troubleshooting. Unless you want replace parts after parts and hope to get lucky. And this could be expensive too.

Tony

[jons911]

The coil is old and should have been replaced when I replaced the wires, plugs, cap, and rotor, I just wasn't sure what to replace it with as I had only just got the car. I only had a chance to do the quick test today, so tomorrow I'll grab a multimeter and check the pump specifically.

My car is stranded in a non too convenient spot right now, so towing it back to the house or to a shop would be a huge pain, but also it's my only ride so I'd like to get it on the road as soon as possible. So getting certain parts that I'll need eventually ahead of time isn't so bad. But no, I am not going to just keep buying new parts. If it isn't the pump and/or its wiring or the plugs/coil, then I'm going to just bite the bullet and get it to the shop.

[boyt911sc]

Originally Posted by jons911

The coil is old and should have been replaced when I replaced the wires, plugs, cap, and rotor, I just wasn't sure what to replace it with as I had only just got the car. I only had a chance to do the quick test today, so tomorrow I'll grab a multimeter and check the pump specifically.

My car is stranded in a non too convenient spot right now, so towing it back to the house or to a shop would be a huge pain, but also it's my only ride so I'd like to get it on the road as soon as possible. So getting certain parts that I'll need eventually ahead of time isn't so bad. But no, I am not going to just keep buying new parts. If it isn't the pump and/or its wiring or the plugs/coil, then I'm going to just bite the bullet and get it to the shop.

Jonathan,

If you are familiar with CIS troubleshooting and have the right tools, you could do the work by the road side or parking lot. How far are you from home? I rather have the car sitting in my driveway than leaving it unattended in an isolated area. This is a judgement call. Even if you are able to make the FP run, it won't give enough information about the fuel pressures (control, system, and residual).

Do you have a spare FP relay? Test the relay and the relay socket. Read DKLever48's thread about testing the FP relay and socket. I will put my money on 'unmetered air'. And if you decide to bring the car to a shop, make sure they have someone there who knows about CIS. Not all good mechanics know this old and antiquated system. Good luck.

Tony

[SCadaddle]

Originally Posted by jons911

I have a '79 911 sc, stock motor, stock ignition, stock CIS. I recently returned from a long business trip where the car sat for about 5 weeks. It was in a garage that stays pretty consistent between 60 and 70 degrees year round. It started up fine and after filling it up, I took it for a drive. The next day I drove it a short distance (~5mi) and when I came back to the car it would not start. It turns over, but won't catch.

Observations:
-Spark plug wires are all plugged in and in good shape
-Spark plugs are relatively new (<3000mi) but the tips are coated white
-Spark test with separate testing piece showed what I would think is a pretty good spark
-Checked air flow sensor plate and it moves freely and has constant resistance when pushed up
-With the car on, not cranking, there is a quiet, high pitched whine coming from the engine compartment

Conclusions:
I had read in Bruce Anderson's book that if the spark plug ends are white then the car is running lean, which I had been leaning to for a little while but wasn't sure. I checked the fuel distributor, but without a pressure gauge, that didn't yield very much. Either way, hardly any fuel seeped, dripped or sprayed out of the line, so I'm leaning towards a fuel issue, not a spark/ignition issue. Also, I thought I read on here somewhere that with the car on, if you push up on the air flow sensor plate then that should force the fuel pump on. I did that but couldn't hear it working.

After pouring through Bentley's, Anderson's, and Wayne's books in conjunction with this site, it seems like the issue is fuel pump or fuel accumulator/filter or an ignition coil issue. Any advice on what may be the issue or other things to try to further narrow down the problem would be much appreciated. Thanks.

I'm certainly no "Pro" but this can't be too hard to diagnose with very basic procedures. You say "With the car on, not cranking, there is a quiet, high pitched whine coming from the engine compartment"....yes, that noise is probably coming from the ignition "box" located to the left side of the engine in the rear fender area. It's making that noise because it is working. So:

1) Hand me your beer. I'll hold it for you.
2) Remove the airbox cover and air filter
3) With the ignition ON, reach in and lift the plate inside the airbox ONLY for a second or so. Do you hear the injectors making a noise? No?
4) Turn the ignition OFF
5) Open front trunk
6) Remove the fuse/relay panel cover. It is on the drivers side fender.
7) Find the RED relay at the top of the panel. Remove it. Are the pins clean? If not, clean them up and you can even use a knife or the sorts to slip between the "+" in the pins to spread them out just a bit if they are really close together.
8) Re install RED relay. Go to step 3. Are the injectors making noise now? Yes? Great! No?
9) Go to step 4
10) Remove the RED relay once again. Look at the other end of the line of round relays. Find one that doesn't matter, like the one marked "air conditioning". Snatch it out and put it where the RED relay was. Go to step 3 once again. Hear anything? Yes? Great! No? Find the fuel pump fuse and clean it up.
11) See step 3 again! Got noise? Yes? Great! No? Can't help ya further!

[jons911]

boyt911sc,

The car is safe where it is. The lot is on a military base and this specific lot is used for longer term parking, so it always has cars in it. The downside is that the roads are very narrow, so more than likely I'd have to push it a least a little to get a tow truck to it. But there is enough room to work, so there's that. Ideally, I get it up and running and drop it off at a porsche mechanic to have the CIS checked thoroughly and properly tuned. Way more focused of a project for them than me saying it doesn't work, please fix it.

SCadaddle,

Thanks for the checklist. I will also run through that. Last I checked, the injectors were not making any noise when I lifted the air sensor, so I will start checking the relays.

[jons911]

She runs!

Turns out my fuse had a bad contact. I scraped it clean and started right up. I turned it off and started it again and let it run for a few minutes and gave it a few revs. The engine seems to be running just like before. Although I will say that I was not technically wrong when I said I thought it was the fuel pump as the pump was just straight up not running, however it was not the fuel pumps fault. So now I think I will get some replacement fuses for later. Aside from the fuel pump fuse, does anyone have suggestions for other rating fuses that would be a good idea to have on hand?

Thanks to everyone. As much as I had read I was still having trouble understanding how the electrical side was configured and you guys helped a lot.

[SCadaddle]

GLORY BE!

Glad it was something simple. Now go drive it!

Always good to have a handful of spare fuses, both a spare black and red "round relay"----but get the good ones as the Uro branded ones don't get much love around here---and if you've got the Lamda CIS box under the passengers seat you will find a square relay next to it referred to as the "oxygen sensor relay" definitely have a spare one of those handy!

[jons911]

You and me both. I was away for a while and now I've had to watch it sit there. I'll be taking it for a nice drive for sure. Plus, now I have some handy spare parts for later. The '78 and '79 didn't have the oxygen sensor, so I don't have to worry about the square relay.

For others that may stumble upon this thread, Parts Klassik has a fuse assortment pack of 5A, 8A, 16A, and 25A fuses. Five of each for really cheap.

[Rusty 356]

Jonathan, sometimes the fuse holder can weaken or melt down a bit. I've had to replace a couple fuse holders over the years.

[OsoMoore]

Congrats on figuring it out! I have a 79 SC as well. Over the first few years I had corroding fuse contacts cause several issues. Eventually I removed the old fuse box and put in a new one made with $40 worth of parts. (I kept the old parts in case a future owner wants them.)

If you have some time and want to eliminate a common source of problems, doing a fuse box overhaul is a good thing.