911SC Ignition Cutting Out

[Davis Montham]

'79 911SC ROW. The ignition cut out on my car at about 4200 RPM tonight accompanied by a puff of black smoke from the exhaust. It has done this before on hard acceleration but usually around 6000 RPM which I have come to live with (and avoid) even though I believe it's not normal. The car runs strong otherwise.

I pulled over and cranked it for a bit but the engine would not start. Stock CD box was whining away. I assumed it was flooded. Luckily I was close to home. I returned 30 minutes later and cranked again but no start. I removed the air filter and lifted the air sensor plate for just a second and the fuel pump engaged. I then tried to start it and it fired right up and ran fine.

Is there something or things I can trouble shoot to track this issue down before I really get stranded? What would cause the ignition to shut down - some feed back loop? My car is a ROW import so I don't believe it has the rpm limiter behind the dash. Any guidance is appreciated. Thank you

[timmy2]

RPM limiting rotor in the distributor ok?

[zelrik911]

Originally Posted by Davis Montham

'79 911SC ROW. The ignition cut out on my car at about 4200 RPM tonight accompanied by a puff of black smoke from the exhaust. It has done this before on hard acceleration but usually around 6000 RPM which I have come to live with (and avoid) even though I believe it's not normal. The car runs strong otherwise.

IMy car is a ROW import so I don't believe it has the rpm limiter behind the dash. Any guidance is appreciated. Thank you

Hi Davis
I am trying to sort out similar problem on my 78 SC -

The CDI & coil connections & especially the GREEN wire to the dizzy should be checked. The units themselves are quite robust but old wiring/Earths brings them down.

Have a good hard look at the red fuel pump relay ( & buy a new spare one). The relay can fall out of its socket &/or just play-up

I think your ROW will have a black box 'sped sensor' module hidden behind the dash (unless it has Lambda ) and this might explain the 6K cutouts.

Good luck

[boyt911sc]

Originally Posted by timmy2

RPM limiting rotor in the distributor ok?

Davis,

I believe the speed switch (rev limiter) in your car is located behind your dash (left most). And double check your ignition distributor too. The '78-'79 USA MY and later models (USA) have them behind the dash. Keep us posted.

Tony

[wolds]

Originally Posted by boyt911sc

Davis,

I believe the speed switch (rev limiter) in your car is located behind your dash (left most). And double check your ignition distributor too. The '78-'79 USA MY and later models (USA) have them behind the dash. Keep us posted.

Tony

Tony,

I think RoW cars use mechanical RPM limiter only. I'm pretty sure my 83 (in stock form) does not have any additional limiter other than the rotor.

[Davis Montham]

Thanks for the replies. The car does not have a speed limiter switch in it, I've looked before behind the dash. Good advice on the distributor. Is the fact that it will start with lifting the air sensor plate up a clue as to why it quit?

[timmy2]

Tony,
No speed limiter box in the dash area for ROW cars. At least not in my '78 ROW.
Only the rpm limiting rotor in the distributor.

[timmy2]

OP,
As to the lifting of the plate and car starting, you should check the fuel pump relay and wiring as mentioned.

[T77911S]

lifting the sensor plate would indicate a residual fuel pressure problem.
use to do it with my 77s.

check the vacuum control on the warm up regulator (WUR),.
pull the hose of the WUR, there should be vacuum on it.
if there is, see if you can tell if it runs differently with the hose on vs off. (just a crude way to see if it works)
the best way to test it is with pressure gauges. you should see about a .8 bar drop with no vacuum.

if it wont strart again, verify spark before lifting the sensor plate.

[Steve@Rennsport]

Did you check for spark while cranking?

This is a basic test and should the very first thing when beginning the troubleshooting process to isolate whether its an ignition or fuel delivery issue.