Then all of a sudden, it just wouldn’t start.

[atnorman]

I’ll try to keep this as brief as possible. 1973 911T, mostly stock and original. Took it out of winter storage this week. Had a couple of beautiful days taking the scenic route into work. Yesterday, ran some errands in the car then home to tinker with it. The car was running pretty good, but a little rough and some backfiring. My intention was to adjust the carbs (original MFI was replaced with Webers years ago, long before I acquired it). I went about setting the idle, checking the timing and dwell, before adjusting and balancing the carbs. Prior to putting the car away for winter, I put in new plugs, wires, distributor cap, rotor, and points. All was well at that time.

So, prior to making the adjustments, I hooked up a multimeter to measure engine speed and dwell (never used a dwell meter before). Initially, I got a dwell reading on the meter of like .50, but I couldn’t get any RPM reading on it. So, using the tach in the dash, I adjusted idle speed up to 900 (engine was warm). It was bugging me that I couldn't get RPMs on the meter. I turned the car off, checked the manual. Restarted, still nothing. Off and on a few times checking different things online and such. Then, I found this part in Wayne’s tech article, Setting Timing, Dwell, and Idle Speed: “Don’t hook up the dwell meter to the coil, or you may damage your capacitive discharge system and your meter. Instead, hook the signal wire to the dwell meter directly to the points wire that is coming off the distributor.” I had followed the instructions in the multimeter manual and indeed had hooked up the leads to the positive and negative terminals on the coil. Never mind that the coil has this very helpful warning label that would make sense to anyone familiar with IKEA instructions as I most certainly am.


I rectified the hookup for the meter and proceeded. Bingo, RPM on the meter worked. And dwell was now showing .30 (a bit low). That all made sense as Wayne’s article also said that hooking the meter to the coil wouldn't give an accurate signal. Checked timing with the light and it was a bit off at about 10 degrees ATDC. I reset timing to 5 degrees ATDC. I checked the advance at 6,000 rpm—well, 5,000 and change before getting a shotgun level backfire. The advance appeared to be close to the 32-38 degree marks. Throughout this process I had turned the car off then restarted it two or three times. Car was still starting and running. At this point, I turned the car off to adjust the gap in the points. Did so. Then went to restart the car. It cranked and cranked, but no sign of turning over. I could smell the fuel, so I assumed something was wrong with the spark. I checked the points, reset them. Tried again. Nothing. Checked the points again, they were dead on--.35 mm.

I checked all the wires and connections to the coil and such just to make sure I hadn’t knocked something off. Then, I checked the spark at the coil with one of those gap testers. Upon turning the key on, one single faint spark. But upon cranking, nothing. I took the coil out and did a bench test with the multimeter. Primary winding came back 0.5 (0.4 to 0.6 is the range). Secondary winding came back .697 on the 20k setting. I’m no Ohm meter pro, but by every interpretation I could find, that’s 697 Ohms, within range of “near 600” (and now I can’t remember where I saw these resistances).

So it would seem the coil is good. Did I damage the capacitive discharge system as Wayne’s article suggests? Mine is a blue Perma-tune, not the stock Bosch unit. How can I test this? Any other ideas as to what went wrong? Sorry for the long post, but I wanted to provide all the info. Any help is appreciated.

[atnorman]

After posting my initial thread, I found the key to my issue in the search function. “No start.” This lead me down a very informative, rewarding, albeit head-spinning path—that of troubleshooting and diagnosing the entire 911 ignition system. Thanks go out to two individuals who seem to have made the bulk of the contributions to this particular area: Warren Hall, Jr. (Early-S-Man) and HarryD. The beautiful thing about forums like this is, even after passing on, Warren continues to serve the Pelican community and keep these old 911s alive. I followed their instructions (pulled from multiple threads). Here’s what I did.

• Tested trigger wire coming off distributor = 10.85 volts. Close to 12v, probably close enough.
  
• Tested ground on Perma-tune CD box = One lead to box, one lead to ground. 0.3 Ohms (should be 0.5ish)
  
• Tested top of three fuses in engine electrical panel = 12.2v
  
• Telegraph test = Spark plug wire in center coil terminal to grounded spark tester. Done both ways, using black distributor trigger wire to ground and opening and closing the points manually. Both produced blue spark at spark plug tester each time contact was made.

So, those tests checked out. At this point, I was suspecting the CD box. Then I came across Warren’s petition for folks to stop throwing out and replacing good parts without properly diagnosing the problem. He suggested starting by removing the engine electrical panel and ground straps and cleaning all connections. I don’t know if he intended to go as far as I did. But I got going and couldn’t stop. About 12 hours later, I had removed and cleaned every connection in the ignition system. I removed plastic connectors, soaked contacts in vinegar/salt solution, cleaned with wire brush, neutralized with baking soda/water solution, rinsed, dried with compressed air, and rubbed down with silicone dialectic grease. I mean everything, even BOTH 14-pin connectors, removing all 14 wires on both halves of each (warning: if you do this, document, document, document, with pictures and notes. I did. It went fine). I found a lot of oxidation, corrosion, and even two critical wires that were so loose as to be barely hanging on. The system shines line new throughout. Then, I went to start it. Plenty of crank, no fire. Nada. Just like before my 12-hour exercise. Now, I could have put something back wrong. But I had triple checked along the way and was confident it was all done right. No regrets. It needed to be done, it was therapeutic, and now I know this system. So, back to the series of tests.

• Voltage at CD box = 12.05v center red wire on 3-pin connector (perfect).
  
• Distributor test = 12v test light w/one lead at top of the three fuses, other on distributor trigger wire. No light upon cranking.
  
• Coil test #1 = spark plug wire in center coil terminal to grounded spark tester. On crank, nothing (should show spark). When turn key off, one single spark.
  
• Coil test #2 = Disconnected CD box. Disconnected wire from small ungrounded terminal on coil. Spark plug wire in center coil terminal to grounded spark tester. Wire from #3 fuse touched to unused coil terminal. Spark on terminal itself each time it is touched. No spark at the spark plug tester.
  
• Spark plug test = everything connected, grounded spark plug tester in plug wire to cylinder #3 coming off distributor. Same as coil test. On crank, nothing. When turn key off, one single spark. Sometimes single spark upon turning key on.
  
• Points test = with CD box disconnected and cap and rotor off, connected Ohm meter across points. Manually opened points. Ohm meter should read 0 with points open, infinity with points closed. I got no change, the meter stayed at infinity. I made sure the connections were all good, rotated engine by hand. Nothing. Pulled the points and did this same thing holding the points. Bingo, it worked. Open points, 0 resistance. Closed points, infinity.
  
• At this point, the reality of what all transpired hit me. The problem started after I adjusted the points. I tripled checked that gap. None-the-less, somehow, I had adjusted the points such that they weren’t closing. Thus, no signal sent to CD box. No signal from CD box to coil. No spark. Then something my father taught me years ago as a youth hit me: “Always start with the simplest things first.” I did, I just didn’t do it right.
  
• Reset the points. Did it right this time. Double-checked by doing the Ohm meter test. That checked out.
  
• 2:30 a.m. on night #4, car started. Life is good.

 

[RSTarga]

The backfires are common with the wrong point gap.
At least you cleaned it all up. Congrats!

[Discseven]

Originally Posted by atnorman

The beautiful thing about forums like this is, even after passing on, Warren continues to serve the Pelican community and keep these old 911s alive.

Damm fine point AT. And way to dig and get it done!

[steely]

Bravo - and welcome

[RSBob]

Great problem solving. Your tenacity really came through.

One suggestion for the future so you will never have to deal with points is Pertonix. I installed it in my 73 and never had to touch it again.

Again, well done sir.

[Quicksilver]

It may seem weird that the points would cause an abrupt failure to start but keep this truism in mind...

"Things work right up to the point where they don't."


It may be a bit trite but it brings into perspective why to check the basics and work your way through a system step by step.

[atnorman]

Thanks for the props guys. Pertronix is already on my list.

[dicklague]

I have had my 1973 for 17 years....the first 5 with points....what a pain.

Installed pertronix and have never touched the points in 12 years.

Just remember that all the installation needs is switched +12 vdc to the red wire on the Pertronix and the black wire is the points signal same as the old points wire to the CDI.