'83 911SC Distributor Pulse Generator Voltage...
 

Does anyone know what the voltage spec is supposed to be for the distributor pulse generator (measured at the CDI harness connector). I measured 1.36VAC during cranking and I have no idea if that is sufficient voltage or not. The test was listed in the Bentley manual and all the manual indicates is to make sure that it is generating a voltage...

Thats plenty. Those things RARELY ever go bad unless they have been destroyed by bad bushings.

If you hook it up to an analog volt meter you can see it pulse while you crank. If it's pulsing it's working. The failure mode is an open circuit so no voltage, no pulsing.

-Andy

Thanks for the info. I have a freshly rebuilt Bosch CDI box (whines with the ignition key on) and a brand new Bosch ignition coil. Voltage at pin 15 of the CDI harness with the ignition key on is 12V, with the ignition key in the start position is 10.75V. Green wire at the CDI harness measures 622 ohms resistance and 1.36VAC during cranking. No spark (checked with the coil wire pulled out of the distributor cap). Gremlins perhaps???

Check that the coil wire is on correct + and- Voltage at coil should be around 300v. Use caution around high voltage.

Double checked the coil wire connections and they are correct. White wire connected to terminal A and the brown wire connected to terminal 1. The new ignition coil is the same diameter as the old coil only slightly shorter. The old coil was Made In Spain and the new coil is Made in Brazil. Bosch P/N 0 221 121 001. Decal on the coil specifically warns not to connect a voltmeter across the primary terminals...

If you have 12.0 volts on pin 15 you have a dead battery-- even with the voltage drop from the battery cable from the trunk to the starter through the harness you should still be seeing more than that. What is the exact voltage at the battery with the ignition off? Should be at least 12.5V, at 12.25V the battery is at 25% charge.

Now I'm really confused. Dead battery? The voltage at the battery measures 12.33VDC and I get exactly 12.25VDC at the CDI harness with the ignition key ON. How can the battery be dead and yet spin the engine quite rapidly? Please explain. Is 10.75VDC at the CDI harness during cranking an insufficient voltage to run the CDI box? Does "dead battery" translate to being a weak battery and not a dead battery. Dead battery to me means that the battery will do nothing. The battery is an Optima Red Top 34/78 model. I guess a quick jump to another battery would be a good test.

Ok, 12.33VDC at the battery is too low. Wil Ferch posted in another thread:

12V at battery terminals indicates a nearly dead battery.
full charge...12.6-12.7 volts
75% charge....12.4 V
50% charge....12.2 V
24% charge.... 12.0 V
"Dead"............ < 12V

So as the starting point for going through the electrical system, you should charge the battery. The trouble with Optimas is they sometimes don't charge properly sometimes and you have to use a special procedure.

From one internet source I like their mention of not using the alternator to charge the battery-- jump-starting is only for life-or-death emergencies.

From the manufacturer about fully charged voltages.

Optima Battery FAQ - Frequently Asked Questions

Anyway, once you see the right voltage at the battery you can then start chasing down whether you have a high-resistance connection somewhere, probably caused by the inevitable corrosion.

The Brazilian-made coils are highly suspect and there are many cases here of them being dead right out of the box.

Sounds like the Optima is junk and a normal car can never keep it properly charged. And an expensive battery to boot...

JMHO, but Optima's are excellent batteries; they simply require different charging procedures than non-AGM batteries and thats what most people do not know.

Fault them for less-than-ideal communications about care & feeding, but not for a poor product.

3 of my 4 cars have had Optima's for 25+ years and I really like them. :) :) :)

I stand corrected. I will either need to switch my battery type or invest in a really expensive battery charger. My standard 2amp or 10amp automatic style battery charger is inadequate it would seem. It certainly does not have the 100 amp charging capability that the Optima requires...

Well, I have been running my optima for several years without that fancy charger and it works great with my 55 amp alt.

Well, I jumpered the car to a known good and fully charged "standard" battery and she still won't start. I double checked all of the measurements (both voltage and impedance) at the CDI harness and everything is within spec. The next plan of action is to re-install the old coil and see if that works. I installed the rebuilt Bosch CDI box and the new Bosch coil at the same time. Since there were previous comments that the Bosch coils made in Brazil are highly suspect, maybe I got a "suspect" coil.

Some chargers have a 100 amp "start" feature where you can hammer them for a while to get them charging. As Steve says, they aren't bad batteries. Most batteries last a very long time-- they are usually killed by their operators. I personally like the Sonnenscheins and recommend them.

Anyway back to the coil, you probably searched here for "Brazilian" coil (careful what that brings up in the Off-Topic Forum :)) - you may want to check the primary and secondary resistance of the coil to verify it's within the specs for the old Bosch "black" coil bearing the same part number.

Do you have any photos of your wiring? That is always a help for remote diagnosis.

Good luck, the answer is not far away.

I measured the impedance in the old ignition coil that I removed. It measured 3.1 ohms primary resistance and 9.55K ohms secondary resistance. The Bosch P/N is 0 221 119 027 which is not even listed to be a replacement for my '83 SC(I have no idea how/when that coil was installed). I wonder if this "odd" coil eventually took out the Permatune and/or maybe damaged other components? Sounds like I should not put it the old coil back in the car if the new coil is out of spec after measuring impedance. More details to come after measuring the primary and secondary impedance of the new coil after I remove it.

Wait, you have a Prematune CD box?

I did have a Permatune box. After all of the voltage and impedance tests that I performed were good and from all of the Pelican forum readings about the Permadoom/Permacrap box, I suspected that the Permadoom box was the source of my intermittent ignition problems. I even bench tested the Permadoom box based on information on their website. Everything checked out but there are several posts on the Pelican forums that they can still be bad if they bench test OK. Even if it was not the source of my problems, I wanted to remove it and put a Bosch CDI unit back in the car. I purchased a rebuilt Bosch CDI box from Specialize ECU Repair (Specialized ECU Repair - Rebuilt Porsche DME, BMW ECU, Jaguar ECU, Volvo ECU, Ferrari ECU Bosch Motronic Electronic Control Units) In Fort Lauderdale, FL and the unit came with a 5 year warranty. So since I was replacing the Permadoom with a Bosch CDI box, I decided to also replace the ignition coil (also recommended on the Pelican forums). Now after buying the new Bosch coil (made in Brazil), I discovered that there are potential problems with that coil. Zim's Autotechnik in the Dallas area won't even sell that coil anymore due to manufacturing issues (clearly listed on their website). The coil that was in the car with the Permadoom box was not even the right Bosch coil to begin with. It was a regular Bosch Super Coil (blue) that is not even designed for CD ignition systems.

OK, very good, carry on. I have a coil from my '81 SC looks original, you can use it if you want for troubleshooting.

The new coil checks out. Primary resistance measures 0.7 ohms and secondary resistance measures 746 ohms. I put the old coil back into the car and still no spark. While I had the coils out, I ohmed out the white and brown wires from the coil terminals to the CDI harness. Both wires have continuity. I have not measured voltage at the coil because everything I have read says not to do that. There is a decal on the coil warning not to do that as well. More updates as I know but I'm still at a loss. Does anyone know why it is verboten to measure voltage at the coil?