Help me understand voltage readings '69 L71 TI

[James N.]

Re: Help me understand voltage readings '69 L71 TI

Jim, Now would be good time to state the history of the TI.

Was it working before or is this a re-installation after a long time using other ignition system?

If so, which TI Circuit board was installed? Was it good? If so, reinstall that for a baseline test.

I DON'T DRIVE THIS CAR TOO MUCH...AROUND 100 MILES A YEAR. AND IT WILL SIT WITHOUT BEING DRIVEN FOR 6 MONTHS AT A TIME. HOWEVER, IT HAS RUN PRETTY GOOD UNTIL THE PAST FEW YEARS WHEN IT HAS BECOME HARDER TO START AND RESTART. SO I DECIDED THAT THIS YEAR I WOULD REPLACE THE STARTER SOLENOID AND THE TI BOARD. THE STARTER IS A REMAN UNIT AND THE MOTOR WORKS FINE. BUT SOME TIMES THE SOLENOID WOULD ACT UP, JUST CLICK. THE TI BOARD I REPLACED IS A GOOD OLD DELCO PIECE, COULD BE THE ORIGINAL I DON'T KNOW. BUT I HAD READ THAT GUYS CLAIM THE NEW BOARD IS SO NICE AND SOME TIMES I HAD TO CRANK THE ENGINE OVER QUITE A BIT TO START IT AND REALLY STRUGGLED TO RESTART IT AT TIMES. AND I READ THE CLAIMS OF INSTANT STARTS WITH THE NEW BOARDS SO I THOUGHT I'D CHANGE IT OUT TO SEE IF IT MADE A DIFFERENCE. IT WAS RUNNING REALLY ROUGH WHEN I LAST DROVE IT THE FIRST WEEK IN DECEMBER, 2016.

As far as the PU coil reading is concerned.....Reading of "1"? What unit? Ohms?

YES, I CHECKED THE RESISTANCE BETWEEN THE TWO WIRES FROM THE MAGNETIC PICK-UP COIL USING A MULTIMETER ON THE OHM SETTING AT SEVERAL DIFFERENT SCALES FROM 200 TO LIKE 20MILLION AND THE READING NEVER BUDGED FROM 1.

Did you disconnect the 2 terminal plug at the distributor to disconnect it from the TI harness before the reading? If you did not, you must. The coil should read apx 500 to 700 ohms separately.

I ATTACHED THE LEADS FROM THE MULTIMETER TO THE PLUG ENDS OF THE TWO WIRES THAT COME FROM THE DISTRIBUTOR WHERE THEY ATTACH TO THE OTHER PLUG THAT IS PART OF THE WIRING HARNESS. THIS IS JUST A FEW INCHES AWAY FROM THE DISTRIBUTOR.

If you did and reading 1 Ohm at the PU coil separately, then there is a short.

Also check your 3 prong plug at the TI Module. A common fault is the terminals dive into the rubber plug and cause a open circuit fault.

Also, are you certain that the K&B circuit board's 3 terminals are not hitting the rear cover?

I DID CHECK THAT TODAY WITH A STRAIGHT EDGE ACROSS THE RAISED RIM OF THE TI CASE. THEY WERE CLOSE, BUT CLEAR, AND I BENT THEM OVER A LITTLE ANYWAY BEFORE I PUT IT BACK TOGETHER.

If all of these simple checks prove negative, it'll probably be time then for a detailed flowchart diagnosis.

Rich

I hope this helps you better understand this problem. Thanks.

[Richard M.]

Re: Help me understand voltage readings '69 L71 TI

Jim,

A reading of 1 Ohm at the disconnected plug of the distributor Pickup Coil is a failure. It's possible the 2 wires at the bottom of the distributor are shorted or internally the coil is shorted. One caveat. If it is shorted, I don't think it would cause a spark to occur at IGN Crank to ON. That is typically caused by a OPEN circuit in the PU Coil. But I've never seen the results of a shorted PU Coil before so I'm unsure.

Also, if it was shorted, it would put (non-pulsed) straight DC BAT+ voltage directly at the input Trigger circuit in the TI module. It would never pulse so I don't see how it could then trigger the power transistors to cause a pulse at the ignition coil.

However, before we do anything, I'd like you to verify your meter is working properly. What brand/type of meter is it and is it a "auto range" type, or can you set it to read different ranges, like 1K ohms, 10K ohms, etc? If you touch the 2 meter leads together what is your reading?

Can you do a baseline test of your meter with a separate resistor that you might have. Ideally, a 500 to 1000 ohm resistor would be best. Even if you had a old junk radio or old electronic device, you could clip one out and do a test.

I'd feel better if we could prove your meter is good before a overhaul of your distributor to change the PU coil.

Rich

[Gary C.]

Re: Help me understand voltage readings '69 L71 TI

Jim,
Could get a resistor from Radio Shack to check the multimeter if old junk resistor is not around.

On my comment, I was mistaken on the failure mode (made comment before I went to work and thinking about it later, remembered that it was opposite), my failure was the pickup coil was reading too low ~300 ohms when hot, then went up to 550 ohms when cold.

On my car, the spark would happen when moving from CRANK to ON and this may happen since the voltage change between the two key positions (terminal R and resistor wire) would simulate the pickup coil voltage change that goes to the amplifier when normally operating.

Thanks,
Gary Craig (54981)

[James N.]

Re: Help me understand voltage readings '69 L71 TI

Jim,

A reading of 1 Ohm at the disconnected plug of the distributor Pickup Coil is a failure. It's possible the 2 wires at the bottom of the distributor are shorted or internally the coil is shorted. One caveat. If it is shorted, I don't think it would cause a spark to occur at IGN Crank to ON. That is typically caused by a OPEN circuit in the PU Coil. But I've never seen the results of a shorted PU Coil before so I'm unsure.

I AM NO LONGER SEEING THAT FAINT SPARK WHEN I TURN THE KEY ON AND OFF. NO SPARK AT ALL NOW.

Also, if it was shorted, it would put (non-pulsed) straight DC BAT+ voltage directly at the input Trigger circuit in the TI module. It would never pulse so I don't see how it could then trigger the power transistors to cause a pulse at the ignition coil.

However, before we do anything, I'd like you to verify your meter is working properly. What brand/type of meter is it and is it a "auto range" type, or can you set it to read different ranges, like 1K ohms, 10K ohms, etc? If you touch the 2 meter leads together what is your reading?

I HAVE 2 MULTIMETERS. AN E-TEK 10709 WITH THE VARIOUS OHM RANGES AND A SOUTHWIRE 400A AC THAT IS A CLAMP TYPE THAT I RECENTLY BOUGHT AND HAVE USED ONCE TO CHECK THE VOLTAGE OF OUTSIDE WIRING THAT I NEEDED A NON-CONTACT VOLTAGE DETECTOR FEATURE FOR. IT IS OHM AUTOMATIC READING. THEY BOTH READ 1 BETWEEN THE WIRES FROM THE MAGNETIC PICK-UP COIL. BOTH METERS READ 1 WHEN THE LEADS ARE TOUCHED TOGETHER.

Can you do a baseline test of your meter with a separate resistor that you might have. Ideally, a 500 to 1000 ohm resistor would be best. Even if you had a old junk radio or old electronic device, you could clip one out and do a test.

I TESTED THEM BOTH ON A NEW 500 OHM RESISTOR AND THE E-TEK READ 490 ON THE 2K SCALE AND THE SOUTHWITH READ 492.

I'd feel better if we could prove your meter is good before a overhaul of your distributor to change the PU coil.

Rich

Rich - I hope this helps. Thanks.

[James N.]

Re: Help me understand voltage readings '69 L71 TI

Jim,
Could get a resistor from Radio Shack to check the multimeter if old junk resistor is not around.

On my comment, I was mistaken on the failure mode (made comment before I went to work and thinking about it later, remembered that it was opposite), my failure was the pickup coil was reading too low ~300 ohms when hot, then went up to 550 ohms when cold.

On my car, the spark would happen when moving from CRANK to ON and this may happen since the voltage change between the two key positions (terminal R and resistor wire) would simulate the pickup coil voltage change that goes to the amplifier when normally operating.

Thanks,
Gary Craig (54981)

Gary I tested my multimeters on a new 500 ohm resistor and they seem to read fine. One read 490 and the other read 492. Now, I'm not getting the faint spark when I tun the key on and off. I would get it occasionally before, but nothing now.

[Richard M.]

Re: Help me understand voltage readings '69 L71 TI

Rich - I hope this helps. Thanks.

Jim, Thanks for the detailed info. Glad you got a good baseline measurement. That eliminates the meter(s).

Sure seems like the PU coil is shorted. One thing you can do is remove the dist cap and check for bare wires inside where the wires come through the grommet. A common fault is a open on the wires as they just dangle there.

Here's a quick grouping of what the coil looks like. Note how close the wires are to the base plate, and also notice the metal wire clamp above the grommet. Maybe it's one of those. Maybe it's a simple fix, but you may want to consider a new PU regardless. K&B makes those too. The new coils are much better.

Rich

[James N.]

Re: Help me understand voltage readings '69 L71 TI

Rich - Thank you for your help. I will order a coil from K & B.

[Richard M.]

Re: Help me understand voltage readings '69 L71 TI

Rich - Thank you for your help. I will order a coil from K & B.

Jim,

Did you get inside the distributor to check it? Just curious if the short is obvious. It's always good to find root cause. Either way, that PU is 48+ years old now and has had it's share of use and movement at the wiring.The coil itself is not typically the problem, it's the junctions of the lead wires to the internal micro-wires inside the bobbin.

When you do get the new part, pay close attention to the connector terminals and their position in the plastic connector housing. The wires are polarized. Also verify proper equal clearance of the stator tips to the pole piece tips when tightening the 3 screws holding the assembly to the rotating baseplate. There should be about a business card thickness clearance between the stator tips during full rotation.

Jim,
Could get a resistor from Radio Shack to check the multimeter if old junk resistor is not around.

On my comment, I was mistaken on the failure mode (made comment before I went to work and thinking about it later, remembered that it was opposite), my failure was the pickup coil was reading too low ~300 ohms when hot, then went up to 550 ohms when cold.

On my car, the spark would happen when moving from CRANK to ON and this may happen since the voltage change between the two key positions (terminal R and resistor wire) would simulate the pickup coil voltage change that goes to the amplifier when normally operating.

Thanks,
Gary Craig (54981)

Gary, Yes that temperature difference was likely caused by the lead wire to micro-wire junctions or even the breakdown of insulation of the internal windings of the coil. I had the exact issue when keying from CRANK to ON on one. Statically, the 500-700 ohm reading was intermittently open circuit while moving the terminal wiring around.

It was a challenge at the time, but I decided to open up the pickup coil. I didn't take photos of that exercise as I was trying to get a BB running to break in the engine. I did that with a points distributor instead.

Later on the bench I took the distributor apart to remove the PU coil. I unwrapped the white adhesive tape from the bobbin and got to the wire junctions. The distributor was like brand new, and probably was removed from a car as it had this problem originally.

I got to the wire junctions and found root cause. The end of one of the wires was properly stripped, and the micro-wire was spiralled around it, but there was basically no solder connecting them together. I separated the wires. I suspected the micro-wire wasn't properly bared, so using a X-Acto blade I removed the insulating coating. I then twisted the micro-wire around the pre-tinned terminal wire and soldered together, re-wrapped new white tape around the bobbin. I tested it and was fine with correct reading of 500-700 ohms and put it all together and back in the distributor, then back in the engine and was all fixed.

Fortunately that repair has lasted ever since with many thousands of miles of use. At that time, about 6 years ago, K&B wasn't making the new coils, or I would have replaced it at that time. NOS PU's were not to be found then, and if so, were extremely expensive.

Rich

[Gary C.]

Re: Help me understand voltage readings '69 L71 TI

Rich,
For my car, I just replace the coil with a K&B version. Running good now. For old coil, will try and diagnose the failure mode and see if I could fix it. When I replace it, did not see anything obvious (chaffed wire, bad terminal, etc)
Thanks,
Gary

[James N.]

Re: Help me understand voltage readings '69 L71 TI

Rich - I have not dug into it yet. I want to wait until the new pick-up coil arrives and then tackle the removal and replacement during the same time frame. Thanks for the advice.

[James N.]

Re: Help me understand voltage readings '69 L71 TI

Removed the distributor and found the pick-up coil wires bare in places....shorted just as Rich suspected. Someone had been in there before and had done a band-aid repair as shown in the photos. I did notice something that is worth mentioning....the grommet in the base of the distributor where the coil wires exit is split so that it can be installed around the wires. On mine, the split in the grommet was facing away from the shaft and in the direction to where the wires lead to the harness connection. The wires had dug into the split in the grommet and were wedged against the distributor body. The grommet needs to be installed with the split facing the distributor shaft so that the wires stay protected by the rubber grommet. Tomorrow's job is reinstallation .

[Richard M.]

Re: Help me understand voltage readings '69 L71 TI

Jim, Glad you got to root cause. That one is certainly nasty.

Good detective work. Great photos of the culprit.

Rich