Sudden Weird No Start on '80SC

[rockryno]

I've exhausted my resources and need some help before I tow this thing to the shop. Any assistance is greatly appreciated!

1980 911SC Targa. Unknown mileage. Full service done within the last 1000 miles including oil change, fuel filter, plugs, etc.

Has been driving great. On cold mornings it takes a couple tries to start before it cranks over, then idles rough for a little bit, then after 5 minutes of driving it smooths out and drives great.

Yesterday - filled up on my way to work with 91. Started great at the pump, but developed a clutch groan (by the pedals) every time I pushed the clutch in. Parked at work.

Lunch time - started it, normal rough idle, ran for maybe a minute while I pulled it onto a rack at my shop. Lifted it up, had my buddy listen for new clutch groan under car, confirmed it's from the pedal area. While it was up, figured I'd clean up some oil leaks on the bottom of the engine. Sprayed some brake cleaner, wiped some areas down. Put a wrench on some of the engine case nuts to snug up any that may have been less than tight.

Lowered car and went to start it to put it back on the street. Very weird extended crank when key turned to start, engine sputters, smoke puffs out of the exhaust, tachometer is going nuts from zero to pinned, engine sputtering, any throttle input does nothing, tach pins again, and it dies. Emergency brake light on, even with brake not engaged. This was the first time anything like this happened. Subsequently tried and tried again. Tried a jumper box in case the battery started to drain. Extended crank, even after turning the key back to off. Smoking exhaust, sputtering attempt to run, crazy tach, dies. Had to uber home after work.

After some research, we tried again this morning. No change. We jumped the fuel pump relay and can definitely hear the fuel pump running when car is on. No change. Disconnected rev limiter, no change. Extended crank seemed to calm down and reacted once again to the key's position. Engine will rough idle very low for a few seconds, tach still going crazy, and it dies. Lots of smoke from exhaust.

Called local Porsche shop, stumped him. Was told to tow it in.

Has anyone had any experience like this? Any suggestions? We're going to disconnect the battery after posting this to see if that resets anything. I'm thinking I got brake cleaner somewhere it shouldn't be, but it was a minimal amount and it all should have evaporated by now. OR I snugged up a bolt on the engine case that I wasn't supposed to, but most bolts I touched were already tight so nothing really even moved.

Thank for any insight! I'll try to take a video and post it up if that helps.

[ahh911]

CDI box whirring in back?

[jjeffries]

CDI box is my question too.

John

[rockryno]

The CDI box is silent with key on.

[mysocal911]

Originally Posted by ahh911

CDI box whirring in back?

Not always a viable indication as to a functioning CDI, i.e. some emit a very very low sound.
Always better to check the 12V input and the ,60 ACV trigger signal.
Hopefully the coil is not a silver one!

[pmax]

Check the voltage.

Tach bouncing could be your alternator.

[Walt Fricke]

The tach gets its signal from the CD box, so that is the usual suspect.

Since the fuel pump runs, chances are this isn't a major fuel issue out of the blue.

Have you pulled spark plugs, attached their wires, grounded them, and watched to see if you are getting regular sparks?

If a shop or buddy has one of the oscilloscope deals you can use to check for spark pattern, especially for all six at once, that should also tell you if the CD box is acting up.

The most straight forward way to check CDI function is to borrow one from a car which is running right, and swap them. If the problem follows the box, there is your answer.

Happily, there are places which can redo a bad box - they claim to use better, more modern innards, and I believe them. Electrical engineering never sleeps.

[rockryno]

Thanks for all the help guys. Everything we've checked is coming back fine. We're limited on time and knowledge here, so it's getting towed to the shop tomorrow. I'll report back once we get a resolution!

[mysocal911]

Originally Posted by Walt Fricke

The tach gets its signal from the CD box, so that is the usual suspect.

Since the fuel pump runs, chances are this isn't a major fuel issue out of the blue.

Have you pulled spark plugs, attached their wires, grounded them, and watched to see if you are getting regular sparks?

If a shop or buddy has one of the oscilloscope deals you can use to check for spark pattern, especially for all six at once, that should also tell you if the CD box is acting up.

The most straight forward way to check CDI function is to borrow one from a car which is running right, and swap them. If the problem follows the box, there is your answer.

Happily, there are places which can redo a bad box - they claim to use better, more modern innards, and I believe them. Electrical engineering never sleeps.

Not necessarily! The pressure may be too low to allow the injectors to open. Try spraying carb cleaner into the intake (air filter).

[targa80]

You need to verify fuel, spark without either one you are going nowhere.
Check fuel flow by lifting throttle body plate with ignition on.
Use a timing light or hold ignition wire close to ground and look for spark.
No spark requires fault isolating to failed ignition component I.e. timing, distributor, coil, CDI.
As stated earlier, injectors need a certain fuel pressure to open when fuel pump is running. This would require a fuel pressure gauge set to test fuel pressure and residual pressure.

If all of this is confusing or foreign to you then having it repaired at a reputable shop would be the easiest but not the cheapest.

[ahh911]

If the RPM gets pinned on crank, for whatever reason as you've first stated, isn't the over-rev fuel cuttoff then engaged?

[theiceman]

does the air box have a pop off valve ? is that seated properly ?

[schoward]

My bet is CDI or alternator/voltage regulator. With CDI going bad, car can run intermittently, weird or not at all. Simply age of the cars at this point but sadly it will strand you. The E-Brake light could indicate voltage issue (alt. or volt reg.)...

If one of the above, a good shop should be able to pinpoint it quickly and easily via procedure. Sometimes better to have a fresh set of eyes with a methodical procedure give it a shot.

[ischmitz]

Originally Posted by rockryno

The CDI box is silent with key on.

If this is a standard Bosch (silver aluminum) 6-pin box it must make noise with the ignition ON. While this is not a 100% proof of health it is a pre-requisite for it to function.

If you cannot hear the typical whine unplug the 6-pin connector and verify presence of +12V and GND according to the sticker on the box. If both are present your CDI box most likely needs repair. If your CDI is a Permatune or other aftermarket version then there might be no noise.