911SC electrical problem

07-25-2002, 03:33 PM

MY cousin has a 911 with a major electrical problem we cannot figure out. A while ago, his SC would intermittedly stop running and would not re-start until the next day. Now It's not starting at all. It's getting plenty of fuel, but no spark. For some reason as well, the CDI unit was burned out. He replaced this, and it did the exact same thing, burned out the CDI. Someone told him it could be the wire going from the distributor to the CDI , so he replaced that. No such luck. SO now we were told by a shop to replace the whole engine wiring harness. Does anyone have any idea what this might be? While cranking the car, there is no voltage at the coil. It was weird, the car would start up fine before, run for like 5 minutes, then just stop, no sputtering or anything. Does anyone have any ideas?

RazorRacer · 07-25-2002, 04:03 PM

You've come to the right place. These guys will figure it out. If your thread drops off, bump it up on Monday morning.

07-26-2002, 08:49 AM

bump, we have to figure ths thing out

RoninLB · 07-26-2002, 08:59 AM

not an expert, but the wires are simple to replace from the CDI ..also I change the CD and coil at the same time..to my understanding a bad/crazy coil will destroy a CD box..also I added an extra ground strap from base of CD box to chassis ground..I used the ground where the engine lid ground is grounded.I assume the transmission ground is good.......Ron

07-26-2002, 09:14 AM

Quote:

Originally posted by RoninLB
not an expert, but the wires are simple to replace from the CDI ..also I change the CD and coil at the same time..to my understanding a bad/crazy coil will destroy a CD box..also I added an extra ground strap from base of CD box to chassis ground..I used the ground where the engine lid ground is grounded.I assume the transmission ground is good.......Ron

If there is no voltage reaching the coil during cranking, could this be a bad coil, or is it a wiring problem?

Targa77 · Targa77's Garage

My car had the same sympstoms and my coil had gone bad and fried my CD Box. Went to Permatune's site and ordered a new box and coil. No problems since. Go to http://www.permatune.com/Technical%20Support/Porsche/911.htm for more info. Hope this helps.

07-26-2002, 10:57 AM

Quote:

Originally posted by Targa77
My car had the same sympstoms and my coil had gone bad and fried my CD Box. Went to Permatune's site and ordered a new box and coil. No problems since. Go to http://www.permatune.com/Technical%20Support/Porsche/911.htm for more info. Hope this helps.

Whatever the problem is, it's already burned thru two Permatunes

Roland Kunz · 07-27-2002, 07:10 PM

Hello

Maybe the engine wireloom has a bad connection and uses the ignition wireloom ?

Hell thats hard to figure out what causes the CDI box to burn up ?

I don´t see that replacing the harneses will help, removing them partially to check and repair makes sense as you can use the saved money in worktime.

Well is the story longer ? did it came suddenly or after some other things ?

Grüsse

RoninLB · 07-27-2002, 07:28 PM

Hello

Maybe the engine wireloom has a bad connection and uses the ignition wireloom ?

I think the bad connection MAY be an unknown grounded system that is using the ignition system ground, due to its own poor ground...not an expert here, an easy answer can be boring .......Ron

Targa77 · Targa77's Garage

Did you perform the troubleshooting checklist on their site? I would suspect the coil at this point. Also, perform the ground check on the site.

Kevin Stewart · 07-28-2002, 08:40 AM

Widebody bump in, he had the loom lead to the cdi box go bad this would cause a short, Kevin

Early_S_Man · 07-28-2002, 09:14 AM

I'm not sure whether you understand that the CDI-system only puts out narrow pulses of 350 Volts to 460 Volt pulses to the coil, or not??? For certain ... it isn't a steady 12 Volts, if that is what you or your cousin were looking for! An oscilloscope is the appropriate tool to be looking at coil Voltage during cranking. The 'B' coil terminal is ground, and the 'A' terminal gets the 460 Volt pulses!

Have you checked the coil winding resistances lately? Less than 1 Ohm [0.4 Ohm to 0.6 Ohm, to be precise] for the primary, and 650 Ohms to 790 Ohms for the secondary. The secondary winding is usually what shorts out when the coils fail. Also, most inexpensive DMM's don't make accurate measurements below 1 Ohm, so don't be surprized if you can't get readings in the 'proper' range!

Were there any problems with the alternator, battery, or Voltage regulator ... just prior to the CDI-unit burning out the first time? High system Voltages of 16 Volts to 20 Volts can burn out the CDI-unit!

On final note ... it might be helpful if you just got your cousin to login here ... so info didn't have to be passed on/translated thru a third party.

07-30-2002, 10:00 AM

bump, surely someone has had this problem?

Early_S_Man · 07-30-2002, 10:42 AM

You have already been given several suggestions, and asked for more info ... which you evidently chose to ignore!

It is not likely that you will get any answers until you provide more info on the past incidents and do the basic checks at the Permatune site. If you or your cousin can't even attempt to communicate what the situation is, and what attempts you have made to check for grounding problems ... then asking 'why' is pointless!

How did you determine a Permatune unit was 'burned out' ... when a grounding problem can prevent a working CDI-unit from operating?

I suggest that you read the following thread VERY CAREFULLY! There is a lesson for you in there ... about feedback!

need help debugging total instantaneous cutouts while driving

Do the checks at the Permatune site, paying particular attention to corroded connections and grounds, and the green cable and 600 Ohm pickup coil in the distributor. Do a search of the Pelican site on 'SC green wire' ...

ferrari2porsche · 07-30-2002, 10:55 AM

Warren, Great info, I can sure use it myself