911 SC No Spark
07-13-2021 | 08:16 PM
#1
Thread Starter
Intermediate
911 SC No Spark
Hello Rennlist,
I "have" (dad's) a 78 SC that seems to refuse to spark. She cranks very strongly, though. I've verified no spark with a timing light on both the coil to dizzy and dizzy to cylinder one wires.
I followed this guide:
From the Pelican forums.
I went ahead and replaced the spark plugs since they were not square and pretty nasty looking. I did smell fuel on the plugs, and I do smell fuel when I crank the car. When I hold the metering plate open, the pump makes its whine. (Side note - any tips on getting into cylinder six? I found that the hard fuel line is right in the way and I'm worried that the plug isn't torqued down all the way. Had this problem with my Miata recently and I do not want to deal with getting a Porsche's head re-tapped. I made it pretty tight with a single click at a time with a wrench but I'm a bit paranoid.)
Anyhow, that of course didn't do anything.
I have tried swapping the coil with the other 911 we have, a 77 S. That of course did not do anything either. I did not however use a multimeter on the coil to check resistance as it seems dangerous to do so.
The CDI box makes its high pitched whine, and I have confirmed that the dizzy to CDI box cable/green wire does pulse power between 1.5 and 2 volts when cranking. I have confirmed there is continuity on the green wire of about 600 ohms. The resistance on the plug wires, should that matter, is about 4100 ohms when measured from the dizzy end to the spark plug end.
I'm at a loss as to what the problem could be. The first Porsche mechanic I mentioned this to said it was most likely the CDI box. The second who I talked to today said that since the CDI box is whining, I should go ahead and replace the green wire since that is most likely the problem, but that small wire isn't cheap - and I really don't want to throw parts at the car without an idea as to what to do.
What should I look for next/what should I do next? I'd love to be able to take the car to Werks in a month, but I can't do that if she won't start!
Thank you so much for reading.
PS: The fuel in the car is old, yes, and I'll definitely replace the old fuel - to confirm it was not a fueling issue, though, I sprayed carb cleaner onto the throttle plate itself while cranking and still nothing happened.
I "have" (dad's) a 78 SC that seems to refuse to spark. She cranks very strongly, though. I've verified no spark with a timing light on both the coil to dizzy and dizzy to cylinder one wires.
I followed this guide:
1. Check for spark by inserting a known good plug in the end of one of your spark plug leads attach jumper wire with alligator ends to spark plug threads and a good engine compartment ground. Get a helper to crank over the engine, bright blue spark all good. If no spark go to step 2
2. Disconnect the coil lead from the distributor and using a spark tester look for a spark when the engine is cranked. If you haven’t got a spark tester you could use a spark and jumper wire with alligator clips. Holding the lead with insulated pliers close to an earth point would be risky as the voltages here can be very high and if the gap is too wide the charge building up in the coil will be too great and may damage the coil or CDI box.
If you have a spark from the coil the problem could be in your distributor, distributor cap, rotor points (or pick up if you have breakerless ignition) or leads. If you don't have a spark the problem could be in one of 4 places: the coil, the green wire that goes from the distributor to the CDI box, the CDI box or the pulse generator in your distributor .
3. Check the coi for obvious damage and with your multimeter look for resistance across the two small connections ( marked 1 and A ), this is the primary coil and resistance should be very low, less than 1 ohm, 0.6 or so ( remember to zero your multimeter or deduct the resistance across your test wires) check for resistance across the high tension center connection and terminal 1 this should be much higher 600 - 800. If test is out replace the coil if test ok go to step 4
4. Turn the ignition on and if the CDI box makes a squealing noise you are getting power to the box. If there is no noise pull the plug at the bottom of the CDI box and check for power at terminal 15 which is the middle terminal on the outboard side of the six pin plug ( see a manual if you have got one) . If there is no power check the supply wire or your ignition switch, if there is power and your CDI box is silent the CDI box is most likely caput.
My CDI box was making a noise however this alone does not prove that it is working so I went to steP 5
5. With the engine cranking check for a 1 to 1.5 volts pulse across terminal 31D and 7 in the plug (these are the two end terminals side by side at the fwd end of the six pin plug.) If you have a pulse then the problem is in your CDI box as it was in mine so replace the Box. if you have no pulse go to 6.
6. Check for continuity in the wires inside the green shielded twin core wire that goes from the six pin plug (terminal 31D and 7) to the distributor, these are probably the most troublesome part of the system as they deteriorate and chafe inside the shield. The pulse generator very rarely fails . If green wire test faulty replace it.
There you have it a more or less complete ignition test for non geniuses.
2. Disconnect the coil lead from the distributor and using a spark tester look for a spark when the engine is cranked. If you haven’t got a spark tester you could use a spark and jumper wire with alligator clips. Holding the lead with insulated pliers close to an earth point would be risky as the voltages here can be very high and if the gap is too wide the charge building up in the coil will be too great and may damage the coil or CDI box.
If you have a spark from the coil the problem could be in your distributor, distributor cap, rotor points (or pick up if you have breakerless ignition) or leads. If you don't have a spark the problem could be in one of 4 places: the coil, the green wire that goes from the distributor to the CDI box, the CDI box or the pulse generator in your distributor .
3. Check the coi for obvious damage and with your multimeter look for resistance across the two small connections ( marked 1 and A ), this is the primary coil and resistance should be very low, less than 1 ohm, 0.6 or so ( remember to zero your multimeter or deduct the resistance across your test wires) check for resistance across the high tension center connection and terminal 1 this should be much higher 600 - 800. If test is out replace the coil if test ok go to step 4
4. Turn the ignition on and if the CDI box makes a squealing noise you are getting power to the box. If there is no noise pull the plug at the bottom of the CDI box and check for power at terminal 15 which is the middle terminal on the outboard side of the six pin plug ( see a manual if you have got one) . If there is no power check the supply wire or your ignition switch, if there is power and your CDI box is silent the CDI box is most likely caput.
My CDI box was making a noise however this alone does not prove that it is working so I went to steP 5
5. With the engine cranking check for a 1 to 1.5 volts pulse across terminal 31D and 7 in the plug (these are the two end terminals side by side at the fwd end of the six pin plug.) If you have a pulse then the problem is in your CDI box as it was in mine so replace the Box. if you have no pulse go to 6.
6. Check for continuity in the wires inside the green shielded twin core wire that goes from the six pin plug (terminal 31D and 7) to the distributor, these are probably the most troublesome part of the system as they deteriorate and chafe inside the shield. The pulse generator very rarely fails . If green wire test faulty replace it.
There you have it a more or less complete ignition test for non geniuses.
I went ahead and replaced the spark plugs since they were not square and pretty nasty looking. I did smell fuel on the plugs, and I do smell fuel when I crank the car. When I hold the metering plate open, the pump makes its whine. (Side note - any tips on getting into cylinder six? I found that the hard fuel line is right in the way and I'm worried that the plug isn't torqued down all the way. Had this problem with my Miata recently and I do not want to deal with getting a Porsche's head re-tapped. I made it pretty tight with a single click at a time with a wrench but I'm a bit paranoid.)
Anyhow, that of course didn't do anything.
I have tried swapping the coil with the other 911 we have, a 77 S. That of course did not do anything either. I did not however use a multimeter on the coil to check resistance as it seems dangerous to do so.
The CDI box makes its high pitched whine, and I have confirmed that the dizzy to CDI box cable/green wire does pulse power between 1.5 and 2 volts when cranking. I have confirmed there is continuity on the green wire of about 600 ohms. The resistance on the plug wires, should that matter, is about 4100 ohms when measured from the dizzy end to the spark plug end.
I'm at a loss as to what the problem could be. The first Porsche mechanic I mentioned this to said it was most likely the CDI box. The second who I talked to today said that since the CDI box is whining, I should go ahead and replace the green wire since that is most likely the problem, but that small wire isn't cheap - and I really don't want to throw parts at the car without an idea as to what to do.
What should I look for next/what should I do next? I'd love to be able to take the car to Werks in a month, but I can't do that if she won't start!
Thank you so much for reading.
PS: The fuel in the car is old, yes, and I'll definitely replace the old fuel - to confirm it was not a fueling issue, though, I sprayed carb cleaner onto the throttle plate itself while cranking and still nothing happened.
07-13-2021 | 09:29 PM
#2
07-14-2021 | 09:49 AM
#3
Team Owner
yup i helped a buddy recently that shorted out his 12v trying to put a lighting strip on his decl lid .. car no start after that but a whine....
took my box over and it fired right up. ( expensive mistake for him )
thing is like 30 seconds to change, know of anyone with an SC who lives close by ?
07-14-2021 | 03:44 PM
#4
Thread Starter
Intermediate
I can't seem to figure out how to quote you guys, annoyingly. Is there a button that I'm missing?
Fair enough, I'm kind of annoyed they swapped to the six pin in 78 as the 77 S has a three pin box that I was going to just cut and paste over.
Boiiiiii - now that's an expensive f*** up! I sadly do know people here but I've not actually interacted with them and I do not think calling people out of the blue to ask to swap CDI boxes is appropriate...
Have you guys used Ashlock Tech before? I'm going to give him a ring and see/pray he can get this rebuilt soon.
I'd like to take the SC (with its M491 bodykit) to Werks - if I have to take the S, it'll be fine, I guess, but there would be no point buying a Werks spot since everyone and their mother more or less has a narrow body 911S.
That car has its own set of expensive issues, but that's a forum post for another time...
ninja edit: I see the multi quote button now, I'm going to guess that's the answer to my first question.
Thanks again!
Just because the CDI whines, don't assume that the CDI is fully functional. You need to either find a tester CDI or put yours in a running car.
yup i helped a buddy recently that shorted out his 12v trying to put a lighting strip on his decl lid .. car no start after that but a whine....
took my box over and it fired right up. ( expensive mistake for him )
thing is like 30 seconds to change, know of anyone with an SC who lives close by ?
took my box over and it fired right up. ( expensive mistake for him )
thing is like 30 seconds to change, know of anyone with an SC who lives close by ?
Have you guys used Ashlock Tech before? I'm going to give him a ring and see/pray he can get this rebuilt soon.
I'd like to take the SC (with its M491 bodykit) to Werks - if I have to take the S, it'll be fine, I guess, but there would be no point buying a Werks spot since everyone and their mother more or less has a narrow body 911S.
That car has its own set of expensive issues, but that's a forum post for another time...
ninja edit: I see the multi quote button now, I'm going to guess that's the answer to my first question.
Thanks again!
Last edited by gtfhercules; 07-14-2021 at 03:45 PM. Reason: added a ps
07-14-2021 | 05:09 PM
#7
Thread Starter
Intermediate
True, but what else could it possibly be? I'm getting power from the plug to the CDI unit itself, and the dizzy is giving me a signal...
Either way, until Mr. Ashlock calls me back, I'll def see if I can borrow someone elses to test.
If you're the Bay Area, I'm asking for your help - I really want to make it to Car Week this year.
Trending Topics
07-14-2021 | 05:52 PM
#8
Ask if he can provide a "loaner";
1. You send your CDI in.
2. He provides a rebuilt for testing (one week). You pay the exchange CDI rebuilding cost. He waits for your test and just holds your CDI.
3. Within one week of testing, you can return the rebuilt CDI and get a credit/refund and your original CDI returned.
4. Or you just keep the rebuilt CDI.
1. You send your CDI in.
2. He provides a rebuilt for testing (one week). You pay the exchange CDI rebuilding cost. He waits for your test and just holds your CDI.
3. Within one week of testing, you can return the rebuilt CDI and get a credit/refund and your original CDI returned.
4. Or you just keep the rebuilt CDI.
Last edited by Lorenfb; 07-15-2021 at 12:20 AM.
07-15-2021 | 01:32 AM
#9
Thread Starter
Intermediate
Ask if he can provide a "loaner";
1. You send your CDI in.
2. He provides a rebuilt for testing (one week). You pay the exchange CDI rebuilding cost. He waits for your test and just holds your CDI.
3. Within one week of testing, you can return the rebuilt CDI and get a credit/refund and your original CDI returned.
4. Or you just keep the rebuilt CDI.
1. You send your CDI in.
2. He provides a rebuilt for testing (one week). You pay the exchange CDI rebuilding cost. He waits for your test and just holds your CDI.
3. Within one week of testing, you can return the rebuilt CDI and get a credit/refund and your original CDI returned.
4. Or you just keep the rebuilt CDI.
Emailed him - he said that he moved recently and has a 2-3 week backlog, which is cutting it awfully close...
I asked about a loaner and will update you if I get a reply.
Sierra Madre seems to have a repair/exchange service that costs a bit more; I'll call them tomorrow to see if they have a six pin unit in stock. If Ashton can't get anything faster, I may go with them.
The other choice is a Permatune system; my local wholesaler has the unit and the new coil needed to run it, but it'll set me back $700 or so and that's...expensive. I know these are expensive cars, but I have to worry about tyres and other expensive maintenance items, plus lodging.
I mean, I guess I could just work on the S instead and just not enter a car in Werks...
07-15-2021 | 01:35 PM
#11
Emailed him - he said that he moved recently and has a 2-3 week backlog, which is cutting it awfully close...
I asked about a loaner and will update you if I get a reply.
Sierra Madre seems to have a repair/exchange service that costs a bit more; I'll call them tomorrow to see if they have a six pin unit in stock. If Ashton can't get anything faster, I may go with them.
The other choice is a Permatune system; my local wholesaler has the unit and the new coil needed to run it, but it'll set me back $700 or so and that's...expensive. I know these are expensive cars, but I have to worry about tyres and other expensive maintenance items, plus lodging.
I mean, I guess I could just work on the S instead and just not enter a car in Werks...
I asked about a loaner and will update you if I get a reply.
Sierra Madre seems to have a repair/exchange service that costs a bit more; I'll call them tomorrow to see if they have a six pin unit in stock. If Ashton can't get anything faster, I may go with them.
The other choice is a Permatune system; my local wholesaler has the unit and the new coil needed to run it, but it'll set me back $700 or so and that's...expensive. I know these are expensive cars, but I have to worry about tyres and other expensive maintenance items, plus lodging.
I mean, I guess I could just work on the S instead and just not enter a car in Werks...
07-15-2021 | 04:18 PM
#12
Thread Starter
Intermediate
Are they bad? I've not looked into the system myself.
Good news! Mr. Ashlock agreed to send me a loaner unit while mine is getting repaired; I saw he put it in the post this morning, so now I need to give him a ring to figure out a few payment details and get my busted unit in the post.
I do need to get myself some allen key sockets/drivers - all of my stuff is mainly regular bolts and Torx since that's what my BMWs use (I borrowed a set of allen drivers from dad to get this sucker out, which worked well enough).
I'll update this thread when I get the loaner unit, and hopefully I can get her to start!
I do need to get myself some allen key sockets/drivers - all of my stuff is mainly regular bolts and Torx since that's what my BMWs use (I borrowed a set of allen drivers from dad to get this sucker out, which worked well enough).
I'll update this thread when I get the loaner unit, and hopefully I can get her to start!
07-15-2021 | 05:12 PM
#13
you get a partial refund of what you paid, right?
07-16-2021 | 03:01 PM
#14
Thread Starter
Intermediate
If it doesn't start I will hit my head against my desk and start this whole troubleshooting process all over again, as the car seems to have everything else in working order.
07-16-2021 | 06:37 PM
#15
I didn't ask for more details... my reasoning here is that it's a 40 year old electronics box that's known to fail, so getting it rebuilt either way is a good idea.
If it doesn't start I will hit my head against my desk and start this whole troubleshooting process all over again, as the car seems to have everything else in working order.
If it doesn't start I will hit my head against my desk and start this whole troubleshooting process all over again, as the car seems to have everything else in working order.