CDI/Tachometer disconnect now starts

[tfulmer1]

Hello all,

I had a few questions I thought you could help with.

My 89 930 had an intermit start problem. This was both hot and cold and happened at random times.

I listened for the whining sound at the CDI, however, there was none. I read at www.permatune.com (this is the unit that is there) that they do not whine.

I had no spark at the plug..dist...etc...

The harness going to the CDI had a voltage of 7.5V. The car had 12V at the battery.

Anyways, I disconnected the tach plug by the o2 sensor....AND IT STARTED! plugged it back....and no start.

THIS is the problem, but I am not sure from here. Is this a problem with the Tachometer itself or the wire leaving the distributor to the CDI? The car will run now but I have no tach.

If anyone has been there...done that... please let me know. I did not see anything with my search.

Thanks.

[RandyF]

I had a conversation a few days ago with a mechanic (Jim) at Performance Plus in Canoga Park, CA, and he mentioned that a bad tach could cause problems with the ignition. This was in reference to problems I'm having with my 78 911 SC blowing CDI units. So this sort of thing isn't unheard of.

[tfulmer1]

thanks....

I learned that this start ...no start...was random luck.

the 86-89 930 has a relay next to the cdi that gives an extra 5 seconds of spark after the key is turned off. I changed the relay and now the car starts with no problem.......

HOWEVER> the tach is now dead. Do you know how to test the tach?

I am not sure if my cdi box is not sending a signal to the tach....or if the tach is toast.

why cant these cars be as bullet proof as a ferrari? they must have sourced the electrical work to the brits.

[RandyF]

"...they must have sourced the electrical work to the brits"

I'd always assumed Bosch was more dependable than Lucas, but you might be right! At any rate my SC seems to burn out about any CDI unit thrown at it, from rebuilt Bosch units, to MSI's to PermaTunes. Both the CDI's and ignition coils get very hot and eventually fail. Actually most of the PermaTunes cool off, then work again (about the time the car's towed home).

I figured I'd try disconnecting the tach to see if it makes a difference. I can pretty much tell the car's RPM by ear at this point anyway. If there's a mechanic in the Los Angeles area that thinks they can trouble shoot my SC's ignition before it blows another CDI, I'm interested, cause this is getting to be a real waste of my time and money.

As far as testing a tach goes, I'm obviously no electrician, does someone else out there know the procedure?

[930LDR]

":the 86-89 930 has a relay next to the cdi that gives an extra 5 seconds of spark after the key is turned off. I changed the relay and now the car starts with no problem....."

Anyone have a pic or diagram shoing this relay? I have some odd starting / tach problems at times and figured changing out the relay may be a quick and cheap way to eliminate one possibility.

Thanks

[A930Rocket]

It's number one on the bottom right hand page.

Originally Posted by 930LDR

":the 86-89 930 has a relay next to the cdi that gives an extra 5 seconds of spark after the key is turned off. I changed the relay and now the car starts with no problem....."

Anyone have a pic or diagram shoing this relay? I have some odd starting / tach problems at times and figured changing out the relay may be a quick and cheap way to eliminate one possibility.

Thanks