1971 Transistorized Ignition Problem

[Paul C.]

Re: 1971 Transistorized Ignition Problem

Question: What happens if the condensor/capacitor that is attached to the coil + terminal is bad??? Could this cause the misfiring???

Anser I found:Any external condenser should be connected to the coil (+) terminal only. As already pointed out, it is there for radio interference suppression only and plays no part in engine operation. For engine testing purposes it would be best to leave it disconnected.

[Timothy B.]

Re: 1971 Transistorized Ignition Problem

Are you sure the engine and amplifier grounds are good back to the battery, I would suggest checking them with a ohm meter.

A bad ground could create a low voltage condition causing the system to not work properly.

[Paul C.]

Re: 1971 Transistorized Ignition Problem

How many grounds are there associated with TI system?
1. Battery to frame
2. starter bracket to frame
3. amplifier box to radiator to TI harness
4. engine harness to wiper motor
5. ground to bell housing

Did I get them all?

[Duke W.]

Re: 1971 Transistorized Ignition Problem

Does the problem occur with the dist. shield both on and off? Many have had problems with the shield causing shorts due to the inside clear plastic insulator sheet not doing the job.

Have you gone through the entire troubleshooting procedure in the CSM?

You mentioned two different sets of wires on the car, different than what was used during the dyno test. What are they? There are many reports of problems with the repro OE-type RFI suppression wires. Nominal resistance should be no more than 5K ohms per foot and the wire should be twisted and bent during the test.

Duke

[Paul C.]

Re: 1971 Transistorized Ignition Problem

First thank you for your input Duke--it is greatly appreciated. This is occuring with the distributor shield NOT on the car.

The first set of wires are Lectric Limited reproduction NCRS correct ignition wires. Removed that set and installed a new set of copper core (I think) wires. No difference--car still misfires--not the plug wires. Sparks at all cylinders.

The mechanic I'm working with said he has checked all the voltages.

If I can't get the problem figured out in the next couple of weeks and going to trailer it home. I have a friend who an electrical expert and has an osilloscope. Will hook that up to the engine and seen if there is a constant electrical output.

I'm going through the steering coming (for another reason) and replacing the ignition switch (not to be confused with the ignition lock cylinder) and checking the connections--so that eliminates that as a possible problem.

I know it's something simple-just need to find it.

Agains thanks Duke

[Ed H.]

Re: 1971 Transistorized Ignition Problem

Going back to my previous 'troubleshooting' post. Break the system into the two binary parts. One consists of all the very basic ignition related pieces, the other consists of the installation and the complexities thereof.

This is photo taken of the 'minimal' installation, confirming that everything 'worked'. (The TI amplifier is 'attached' to the shielding bracket by the distributor.) The next step would not take place until all the components were installed and wired. If there was a problem then (thankfully, there wasn't), it would, most likely, relate to the installation itself, not the components.

[Paul C.]

Re: 1971 Transistorized Ignition Problem

Sorry to go back to the capacitor on the positive side of the ignition coil but here's a comment I received.

"It shows no capacitor on the + side of the coil in the 1971 Chassis service manual--page6y-20, figure 3i--breakerless ignition system

Installing a capacitor on the + side of the TI coil slows down the shutoff (the high voltage rise time), causing a loss of energy in the coil, and promoting misfires."

It doesn't show one in the 1971 Assembly Manual for TI system page L362, L56. A7.

Can someone please clear this point up for me. Thank You!!!

[Jim D.]

Re: 1971 Transistorized Ignition Problem

John H. posted that 67's with T.I. don't have the capacitor, neither does my 65. Maybe that's where the problem lies.

[Ed H.]

Re: 1971 Transistorized Ignition Problem

John H. posted that 67's with T.I. don't have the capacitor, neither does my 65. Maybe that's where the problem lies.

No capacitor. As for the thumbnails, no idea...

[Terry M.]

Re: 1971 Transistorized Ignition Problem

My 1970 /w TI has a capacitor and many original 1971 to 1972 /w TI that I have seen have it as well. BTW: Those cars will run fine without it. I am not sure the purpose it serves since there are no points involved here. And yes, I know the AIMs don't show one for those 1970-72 engines equipped with TI.

If the OP has a capacitor connected to the coil; remove it. It is not needed. In this case it is just one more part that could be bad.

[Duke W.]

Re: 1971 Transistorized Ignition Problem

Terry - any voltage transients can cause RFI, especially on high current circuits, so whether coil on/off voltage is triggered by points or an electronic system makes no difference. Other examples are the brake light circuit and HVAC blower motor.

The OE-type electrolytic caps are not the greatest in the world, which is why on point ignitions general practice is to always replace the "condenser" ( which is an archaic term for a cap that is still used for that application) whenever points are replaced, but we tend to ignore all the others.

If the RFI cap connected to the plus side of the coil gets leaky or shorts it will definitely affect the ignition system, possibly causing misfires or a complete shutdown.

Back in the sixties I opened up a replaced ignition capacity out of curiosity. It consisted of alternating layers of what looked like thin aluminum foil and thin clear mylar wrapped into a tight roll. The "capacitance" in Farads (Microfarads in the case of ignition caps) is a function of conductor surface area, and the tightly rolled alternating layers of foil and mylar create a lot of surface area in a small package.

Electrical stress can eventually cause micro-shorts in the thin mylar making the cap "leaky", and this will cause circuit problems as above and eventually the cap can dead short, which will cause the ignition to quit operating completely.

I have a ten year old 32" HDTV that began losing audio volume a couple of years ago, and it's now almost silent. Talking to a couple of EEs I know, they both said leaky capacitors, so I opened it up and saw at least a dozen. I considered replacing them, but then figured for $125 I could replace the TV. I still haven't done so because I rarely actually watch broadcast television, and my DVD player is wired into my stereo system, which has four 1974-vintage Pioneer CS-901 big box speaker mounted at the four corners of my "great room" and still sounds great.

Duke

[Terry M.]

Re: 1971 Transistorized Ignition Problem

Terry - any voltage transients can cause RFI. So whether coil on/off voltage is triggered by points or an electronic system makes no difference.

Duke

Well, I learned something today.

[Ed H.]

Re: 1971 Transistorized Ignition Problem

Well this has been fun! I am no EE, but my Father worked in the Raytheon Research Group, and I 'learned' a few things from him along the way. There sure doesn't seem to be a singular opinion as to the role of a capacitor on a breaker-point ignition system! However, based upon what I recollect my Father saying, it's role was to limit arcing across the breaker points as they opened and closed. I am not making a BOLD statement here, but I will ask about my various EE level types and see if there is a consensus on its function. Based upon my limited knowledge of capacitors and their functions, it's hard to believe that they are important with respect to the level of energy that the coil can deliver. I can imagine that they would be effective in matters of RFI. They certainly were fun to charge up and then use to zap unsuspecting people!

[Paul C.]

Re: 1971 Transistorized Ignition Problem

Ed--the person who sent me the comments on the capacitor is an Automotive electronics design engineer. That's why I posted his comments because he obviously knows more about this than I do and so I had to ask again about the capacitor.

[Duke W.]

Re: 1971 Transistorized Ignition Problem

Well this has been fun! I am no EE, but my Father worked in the Raytheon Research Group, and I 'learned' a few things from him along the way. There sure doesn't seem to be a singular opinion as to the role of a capacitor on a breaker-point ignition system! However, based upon what I recollect my Father saying, it's role was to limit arcing across the breaker points as they opened and closed. I am not making a BOLD statement here, but I will ask about my various EE level types and see if there is a consensus on its function. Based upon my limited knowledge of capacitors and their functions, it's hard to believe that they are important with respect to the level of energy that the coil can deliver. I can imagine that they would be effective in matters of RFI. They certainly were fun to charge up and then use to zap unsuspecting people!

Your father is correct. Without the cap breaker points would not last long.

It may be easier to think of the mechanical-electrical analog

Cap = spring
Resistor = damper
Inductor = mass.

When the points open the "inertia" from the inductor (coil) tends to keep current flowing, and this causes high voltage transients and arcing, which is absorbed by the "spring" (cap), which is an energy storage device, and when the points close again, this energy is restored to the circuit and helps overcome the "inertia" from the coil to more rapidly achieve steady state DC current.

RFI caps basically do the same. When a high current circuit is initially closed or opened, high voltage transients occur, which can cause RFI. The cap will absorb some of this energy and "smooth out" these high voltage transients, reducing RFI, and this is why you typically see them on the + side of the coil, brake light switch, and HVAC fan.

Before the advent of digital computers there were analog "computers" that could be used to evaluate various mechanical systems like an automotive suspension that consists of a mass, spring, and damper. They had large patch panels - like on old manual telephone switch board- that allowed rapid configuration of various circuits with various component values that represented the electrical analog of the mechanical system. The circuit would then be energized and its behavior viewed on an oscilloscope, which allowed rapid evaluation of various masses, springs, and dampers electrically rather than building the actual suspension and trying different real masses, springs, and dampers.

Duke