1983 911sc wont start

[alange]

Hi-

Hoping that people may be able to help a novice out with some troubleshooting. After putting ~100 miles on my car last weekend, I went to start this weekend and it wouldn't The engine turns, but doesn't catch. I tested the battery and it's reading ~12.6 so I've ruled that out as an issue.

I haven't had this issue in the past (although only have had the car for 7-8 months), other than one or two times the car fires on a second try. Now it's just turning and not catching.

I've ready a handful of other posts, and it appears the likely issues or ones to rule out are that the engine isn't sparking or getting fuel. What is the best way to test one vs. the other to rule out? I have Dempsey's book, but didn't quite find it helpful (again - I'm a total novice here).

Thanks,

[targa80]

Originally Posted by alange

Hi-

I tested the battery and it's reading ~12.6 so I've ruled that out

I've ready a handful of other posts, and it appears the likely issues or ones to rule out are that the engine isn't sparking or getting fuel. What is the best way to test one vs. the other to rule out? I have Dempsey's book, but didn't quite find it helpful (again - I'm a total novice here).

Thanks,

You need to be more specific on the battery voltage and symptom.

1. Is the 12.6 volts a static voltage without cranking the starter?
2. Monitor the 12.6 volts and crank the starter does the voltage drop off?
3. Does the engine crank fast or very slowly or does it just click?
4. If it cranks fast does it try to start i.e. fires once and then just cranks, stumbles multiple times and but does not start.

You need to ask yourself these question and any other questions you can think of.

Put the battery on a charge overnight so it is fully charged. A static voltage of 12.6 volts will drop dramatically under load if it has a bad cell.

[alange]

Originally Posted by targa80

You need to be more specific on the battery voltage and symptom.

1. Is the 12.6 volts a static voltage without cranking the starter?
2. Monitor the 12.6 volts and crank the starter does the voltage drop off?
3. Does the engine crank fast or very slowly or does it just click?
4. If it cranks fast does it try to start i.e. fires once and then just cranks, stumbles multiple times and but does not start.

You need to ask yourself these question and any other questions you can think of.

Put the battery on a charge overnight so it is fully charged. A static voltage of 12.6 volts will drop dramatically under load if it has a bad cell.

Thanks for this response. I went back to check the battery tonight and it was 12.6 static, but when I tried to to start the engine, the voltage dropped to ~10 or while cranking. Based on this, I'm going to try and charge the battery and give it another shot. Electronics (radio / lights) also come on so I felt the battery may be fine, but I may be wrong here.

It cranks pretty normal just doesn't fire - not slow or clicking or stumbling. Thanks for the guidance on this.

[motorstereo]

did you ever get your car started?

[alange]

Originally Posted by motorstereo

did you ever get your car started?

It didn't unfortunately. Checked the battery and then fuse relay. Could smell fuel when trying to start so fuel was flowing. Had to call in some help and believe the issue is the CDI box. Mechanic has a spare, so going try swapping out to confirm that's it. Thanks for checking in and everyone with some thoughts.

[mysocal911]

Originally Posted by alange

It didn't unfortunately. Checked the battery and then fuse relay. Could smell fuel when trying to start so fuel was flowing. Had to call in some help and believe the issue is the CDI box. Mechanic has a spare, so going try swapping out to confirm that's it. Thanks for checking in and everyone with some thoughts.

Check here under No-Start; https://www.systemsc.com/diagnostic.htm

[GAJon]

Originally Posted by alange

It didn't unfortunately. Checked the battery and then fuse relay. Could smell fuel when trying to start so fuel was flowing. Had to call in some help and believe the issue is the CDI box. Mechanic has a spare, so going try swapping out to confirm that's it. Thanks for checking in and everyone with some thoughts.

For CIS cars, fuel will always run as long as the pump works. That doesn't 100% mean that fuel is making it to the cylinders.

Just a few points as I went from a start to no start car similar to you:

Checked for good spark by removing the king wire from the distributor and plugging it into a good spark plug. I was getting a weak spark (faulty CDI box), but still some spark. At least verified that the CDI was getting power. I think the spark voltage was very low though. I ended up replacing mine.

Checked the CIS system connections. Found the thermo-time switch had a loose connection. This will affect the cold start behavior of the car. Since you're in NC, you might be running into the limit where it's cold enough now that this is a problem. The CIS system is a bit confusing, so need to read up on that if you intend to trouble shoot it.

Fixing these two items got me back to cranking, however it still struggles a little if it's been sitting for a few days now that it's chilly in ATL. I plan on diagnosing the CIS system some more, but it's not extremely straightforward. Happy to have a running car and don't want to press my luck right now..

[JSV798]

So looks like you have no spark; check as above or remove one plug lead, insert spare plug and with a helper turning the key to crank the engine, look for spark when plug is grounded on the engine. Most likely you have a dead green wire to the distributor if it has never been changed; much cheaper than new CDI box. This check for a spark is always the first thing to do on no start.

[stlrj]

If your engine has a pop off valve, try spraying some carb cleaner inside and see if it fires up. That should tell you if you have a fuel problem.

[ischmitz]

A simple timing light with the trigger clamp on the spark plug wire will tell you if you have spark. Depending on what CDI box you have (stock or aftermarket) you should verify if you can hear the distinctive whining noise with the ignition ON. If not is is definitely suspect.

Swapping in a known good one is a great way to get certainty. Let us know what you find,

Ingo

[mikesarge]

I'd do as follows: the old-school ground a plug to the block test, as JSV798 suggested. that's quick. Alternately, just use your timing light.

Then,

CDI box is easy to test –this thread has good info
Next,

Check your green wire too. This thread has the same CDI test, as well as info on the green wire test.

If it's your green wire, verify your alternator output. My voltage regulator died, causing wild voltage spikes, nuking my green wire.

There's not much else to the system here for spark. Then you've just got timing and fuel to track down. I'm no expert in CIS yet, but timing should be very easy to verify as well. Just be methodical.

[997at]

Don’t trust a simple visual spark. A weak spark can be seen at the plug but may not cause ignition. I had a time where the car would not start. Everything checked out but I thought the spark looked a bit weak. Changed the coil out with a new one and the engine fired instantly and ran beautifully.

[G450X]

If the airbox has a pop-off valve, check for a leak. I had a no start issue (engine turned over fine) on my stock CIS ‘82 SC and it was the pop-off valve.

The whole pop-off assembly “popped out” of the mount in the airbox. The old epoxy had given up when I had a very mild backfire - just a little pop, all it takes. The fix was new epoxy and all has been well for 7 years...

[alange]

I was able to check the car with a good CDI this weekend and the car fired up instantly, so that’s definitely an (if not the) issue. It appears to be the stock box so we’re going to repair and go from there, but believe that should do the trick. Thanks for the input from everyone - helpful insights.

[AFB24911S]

I had a guy in SoCal named Bob Ashlock go through my CDI box when I was having starting issues, and he found a connection that hadn't been grounded properly that was causing a fault. Charged me $50 for the work and returned the box in a few days. Stellar service, expert wizard technician. Give him a look at TACH-ADAPT if you need someone to rebuild your box.

[G450X]

Please let us know where the fault lies - it could help others in chasing a similar problem.