'78 911SC: No Spark/Start ... then Yes Spark/Start ... Mechanic Turns to Drinking!
 

Quite a baffler this one :rolleyes:

'78 regularly starts instantly, run great. Then (drumroll): no start, nor spark, battery run down in the process, and just the faintest smell of fuel.

This first happened about 3 years ago, (not to the point of running down the battery) and then after 5 days of letting the car sit, the car started.

This time however, onto the flatbed it went and into the mechanics. They said no start for them either for the last 2 days, neither any spark, but can't find why. (And these guys have been doing 911s since before Steve McQueen). And then after letting it sit last night, today it starts just fine. They're baffled. I'm baffled.

So the question to you saavy Pelicanisters is, (in the works of the immortal Vince Lombardi): "What da hell's goin' on out dere?!?!?" :confused:

Your humble fellow driver.

First thought is intermittent electronics failure. When it doesn't start, does it try to turn over?

What kind of CDI box do you have? Bosch? PermaTune other?

When the car won't start do you have spark at the plugs? The smell of fuel would suggest the presence of fuel but no spark. If you lift up on the pressure plate with the ignition ON (not start) do you hear the injectors squeal?

Easy test would be to try swapping the coil with a known good one.

Fuel pump relay should be another easy swap.

Always check grounds for loose or corroded connections.

Battery over charge results bouncing tack, tach bouncing, causes rev limiter latch up, rev limiter opens fuel pump relay circuit.

Car will NOT restart until the ignition key is switched off long enough to release the rev-limiter latch. Very, very frustrating.

2 years of random events before the engine no-start become an issue that had to e addressed.

Early warning was the e-brake warning light latching on. Had to disconnect the each time to clear it. Not worth taking the time to look into, car started and drove just fine.

Then...random engine dying while underway...

New battery seem to fix that.

Car was mostly stored so basically not driven on long enough drives to overcharge the battery.

Then...drove ~200 miles in one leg...Engine died and would not restart.

Flat-bedded to shop in Moscow, Id, were it sat overnight until the shop opened the next AM.

Car started perfectly every time.

Called Squire, ACE 911 GURU. Check the battery voltage said he.

15 volts....

Turn on the lights to discharge the battery, drive ~75 miles, engine dies, pull the VR, discharge the battery overcharge, drive ~75 miles, install the VR, drive another ~75 miles...ah home at last.

Replace the alternator (integral VR)

But now the CDI module overheats underway unless it gets a dose of cool-spray every so many miles, off to Loren it goes.

Analysis: Alternator stater wire support insulators overheated and crumbling.....random shorting inside the alternator beginning years ago, worsens as the months drag by.

My 77 does this at times as well and I traced the problem back to the fuse that controls the fuel pump. If I wiggle the fuse in the holder then the car starts. This only happens sometimes. I really need to clean the fuse panel and spray the terminals.

No spark.........
 

In the 6 pin plug on the CDI, check the rear center wire (small red wire) to see if it is consistantly getting (switched) power when the ignition switch is turned to the start and run positions. The problem could be in the ignition switch, not the ignition system. Hope this helps!

Clean or replace
 

Cleaning is good, replacing is better. What you need is one of my ATO/ATC replacement fuse panels!

Fred C.

My 79 had a similar issue as yours. My mechanic replaced the ignition control unit and told me the problem is fixed(I pick up the SC tomorrow). Coils were also replaced. I hope this fixed the issue.

I hope you find the issue and get your SC running well.

Kenny

for no spark there are only a few things that will cause it:

bad CD- swap with good one is only real test
coil- same thing
power to CD- 14 pin connector and ignition switch. easily checked. cant remember ifit is fused
dist- no output from dist. could also be random.
grounds- you have to have good grounds for the 12v to the CD, the coil back to the CD and spark plugs back to coil.
wiring- the wiring from coil to the CD can get brittle and crack. same with the dist wire. it is a coaxial wire that can get brittle and crack

this is what i love about these cars. very simple and reliable, not much to leave you on the side of the road.

Many thanks to all of you for your quick and sensible responses. I have forwarded your ideas to the mechanic. Best to you all :)

We Have an Update (!)
 

Car towed to mechanic. They cannot find anything wrong as to why there is no spark nor start. Fuel pump is fine. They keep the car overnight and then the next morning it starts for them just fine. They keep the car for two more days just to check it and find nothing wrong. I pick up it and have since driven it successfully starting for five days. All is well. Then yesterday, again no spark/no start. So I checked the fuse box (thanks Newfie911s) and there is just one wire where the copper going into the screw hole atop the fuse appears corroded, green and brittle: that for the fuel pump. Will clean it, perhaps restrip it, (hopefully this morning) and let all y'all know (!) Stay tuned!

Fuel pump relays and CDIs have also been known to fail intermittently. I just recently replaced my Permatune CDI with an intermittent failure. Took my son to his basketball game - car ran fine. Went to leave and the car wouldn't start. Swapped fuel pump relay and it started. Five miles later, the CDI died completely and left me stranded.

Thank you Tirwin Tim for the note of encouragment :rolleyes:

The saga continues...
 

Still no spark after fumbling with fuse(s). Flatbed tow truck en route as we go back to the mechanic's.

Might be that darn CDI box after all...

Case Successfully Solved!
 

Thanks to everyone's learned input. Here is what was found.

A leaky oil line was spewing oil around various "contact" areas behind the distributor cap. (This explains why the problem was intermittent). Due to this and general aging, there was general deterioration in this area. Mechanic replaced the line and replaced broken bits, distributor, et alia. Even stopped drinking.

All-in total cost of the misadventure, (including two tow trips crosstown): $723

Again, thank you fellow Pelicaneers!