Help me understand voltage readings '69 L71 TI
I'm confused. Voltage at the battery and at the power supply cable connection at the starter are both 12.95. Voltage at the S terminal at the starter is zero with the key off and 6.92 with the key in the on position. But, voltage at the S terminal at the starter when cranking the starter is 10.63 at the highest. Shouldn't it be 12.95 or close to it? New starter solenoid.
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Re: Help me understand voltage readings '69 L71 TI
Keep in mind that while cranking the battery voltage will drop significantly. What issues are you experiencing? As far as I know there should be no voltage at the S terminal with ignition on but not in the "crank" position, you may have the resistor bypass wire on the S terminal rather than the R terminal. -
Re: Help me understand voltage readings '69 L71 TI
Sorry, I should have said from the R terminal instead of the S terminal. I have the purple wire on the S terminal and the yellowish wire on the R terminal. I am taking those voltage readings on the R terminal. My issue is that I'm not getting spark when the motor is cranking. I have the number 1 plug pulled, hooked up to the plug wire and have the spark end just off a grounded bolt to watch for a spark as I crank. I got one spark once during a series of cranking the motor over several times. Other than that, nothing. Except a few times just when I turn the key on prior to cranking and also when I turn the key off after cranking there is a small, very light spark. Weird......I don't understand that. Anyway, I had changed out the starter solenoid and replaced the TI board with a K&B replacement and now no spark
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Re: Help me understand voltage readings '69 L71 TI
Jim,Sorry, I should have said from the R terminal instead of the S terminal. I have the purple wire on the S terminal and the yellowish wire on the R terminal. I am taking those voltage readings on the R terminal. My issue is that I'm not getting spark when the motor is cranking. I have the number 1 plug pulled, hooked up to the plug wire and have the spark end just off a grounded bolt to watch for a spark as I crank. I got one spark once during a series of cranking the motor over several times. Other than that, nothing. Except a few times just when I turn the key on prior to cranking and also when I turn the key off after cranking there is a small, very light spark. Weird......I don't understand that. Anyway, I had changed out the starter solenoid and replaced the TI board with a K&B replacement and now no spark.
During crank, the load is very high and the voltage will drop to what you're seeing that is normal. That's not your TI problem.
The faint spark you see with key to ON, or to OFF is also normal.
I suspect your problem is a bad ground either inside the module or at the mount of the case.
When you mounted the TI circuit board, did you use the original screws? If you did, they're too long. Cut apx 3/16" off of the ends, or get shorter screws. Then, very important, use toothed lockwashers under each screw.
On the outside case, make sure you scrape some paint away from where the ground terminal mounts, and I highly recommend you add a toothed lockwasher between the case and the terminal before you bolt it in.
Rich
PS Attached below.....Some of the details of the conversion to the new boards. Pg 6 talks about the 3 screws. Pg 9 about the mount ground.Comment
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Re: Help me understand voltage readings '69 L71 TI
Okay makes more sense now. My concern is that those readings are what you'd expect to see on a non TI car with the ballast wire still in play. As far as I know the TI specific harness bypasses the ballast wire, is this a factory TI car?Sorry, I should have said from the R terminal instead of the S terminal. I have the purple wire on the S terminal and the yellowish wire on the R terminal. I am taking those voltage readings on the R terminal.Comment
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Re: Help me understand voltage readings '69 L71 TI
Thats how I understood it, does that mean that the TI module feeds/switches power to the coil rather than the points switching ground to the constantly powered coil as in a standard set up?Doug, on a TI system the R terminal during crank puts full Bat+ on the Dist PU coil input and TI module.
I guess what has me confused is the 6.92v reading at the R terminal with the key in the run position. That is what you would expect to see in a non-TI car as the power got back fed to the R terminal through the resistor and resistor bypass wire from the coil+ terminal fed via the ignition switch. As I understand it, when TI was installed, the original coil+ wire(along with resistor wire) was abandoned and full battery power was fed to the TI module and pick-up via the TI harness via the ignition switch.Comment
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Re: Help me understand voltage readings '69 L71 TI
Jim, Try not to be intimidated by it. One other important ground at the TI module I didn't mention....also from that same terminal is another wire terminal which connects to the radiator support via a screw or bolt. I'm not sure which on a C3. Make sure that is clean and solid and if not there, I recommend adding a toothed lockwasher there also.
Conventional ignition uses the points(a switch) activated by the rotating 8 sided cam in the distributor. TI uses a mini generator inside the distributor as it's switch. It's made up of a 8 tip rotating "gear", called the Pole Piece, connected to the main shaft, in conjunction with a mating 8 tip stationary "gear", called the Stator.
Thats how I understood it, does that mean that the TI module feeds/switches power to the coil rather than the points switching ground to the constantly powered coil as in a standard set up?
Yes. TI applies the power then drops it via the power transistors in similar principle to the points system. They both turn the coil on and off at specific times. In the TI system, the Ignition Coil(-) is hard grounded. This comes from the TI harness via the TI Module case ground terminal, which is sourced and connected to the Radiator Core Support via a screw. This ground is most important for both the TI module and the coil.
I guess what has me confused is the 6.92v reading at the R terminal with the key in the run position. That is what you would expect to see in a non-TI car as the power got back fed to the R terminal through the resistor and resistor bypass wire from the coil+ terminal fed via the ignition switch.
With IGN ON, yes, the R terminal is not the source of BAT+. A reading here with IGN ON is seeing the voltage through the TI Harness dropping resistor paths. During Crank, the power from the IGN ON feed gets diverted from the IGN switch. It now comes from the R terminal to get increased voltage to both the Distributor AND the TI Module. The increased voltage results from a bypass, similar to the Ballast bypass in a points system.
With TI, normally during RUN, the IGN ON voltage goes through the TI harness which has built in resistors. These are made up of resistor wire, wire that has a specific amount of resistance per inch or foot. There are 2 of these wires in a TI harness. One for the PU coil, one for the TI module. The R terminal takes over and provides Bat+ higher voltage to increase PU coil pulse generation and to provide a higher voltage to the power transistors in the module for higher spark voltage during crank.
As I understand it, when TI was installed, the original coil+ wire(along with resistor wire) was abandoned and full battery power was fed to the TI module and pick-up via the TI harness via the ignition switch.
Yes, via the ignition switch, but only during Crank, which activates the R Terminal to override the TI Harness resistor wire paths.
See this diagram from the Corvette CSM. Note the R terminal wire and where it's connected to the Dist, then through that resistor back to the IGN switch.
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Surrounding this Stator is a wire-wound "Pickup" coil with 2 wires coming out of it which connect to the TI harness and Main harness. One wire is the coils input which gets it's voltage from the IGN switch Battery feed when IGN ON, which goes through a small resistor built into the TI harness. The other wire is the Output of the PU Coil "generator" which connects to the TI Module circuit board Input.
When the rotating Piece tips pass by the stationary Stator tips, it generates small voltage pulses, a rising and falling signal. These pulses act just like a switch, pulsing rapidly up and down and varies it's duration(frequency) based on engine speed. The small pulses, on the order of just a few volts, are input to the TI module. Inside that is a device called a trigger transistor, which converts those small pulses into a much bigger pulse, which then triggers large amplifier switches(transistors). Thess higher power transistors are the output of the TI module which then directly drive the Ignition Coil.
Those high powered pulses then turn the Ignition Coil+ terminal, on and off, at specific duration to the distributor to be sent to each spark plug at the right time within their 8 cap positions, in general sync with the 8 Pole Piece rotating tips and 8 Stator tips.
Rich
ps much discussion in other posts with more diagrams...advanced search for more info:
String:" TI " AND module
User: Richard Mozzetta (13499)Comment
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Re: Help me understand voltage readings '69 L71 TI
Jim,
Your problem could also be a problem with the pickup coil. I had same issue as your where I would only get a spark when I released the key from the cranking position. While cranking, no spark. Check the pickup coil for resistance across the two leads, should be 550-750 ohms.
The strange thing with mine was that the resistance was fine (within 550-750) when cold but when hot, the resistance was bad (>750 ohms) and I would get this one spark when releasing key from cranking position. It was frustrating where I could start the car, drive it a bit and park in a different location, then try to restart it to move back to original spot and have this trouble on restarting. Finally found it when I could get to the two pickup coil leads with the ohm meter when engine was hot and saw the ohms slowly go from high toward 750 when it cooled off. Replaced the pickup coil and solved the issue. This was after checking all grounds.
Gary CraigComment
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Re: Help me understand voltage readings '69 L71 TI
Gary is spot on, could be that too. My first TI experience had the same problem......Engine got a poop of spark only when key turned to back to ON from CRANK. Bad PU coil, but I actually repaired it.
https://www.forums.ncrs.org/showthre...249#post535249
If Jim had a running engine before with the old Delco TI board and just did the K&B upgrade, I'd not suspect that. But anything is possible.
The CSM has a good flowchart to help too. Attached below.
RichComment
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Re: Help me understand voltage readings '69 L71 TI
Richard, makes sense now, I guess I just assumed that there were no resistors in the TI harness. Strange that GM chose to switch the power supply rather than the ground for the coil, pretty much unheard of nowadays.With IGN ON, yes, the R terminal is not the source of BAT+. A reading here with IGN ON is seeing the voltage through the TI Harness dropping resistor paths. During Crank, the power from the IGN ON feed gets diverted from the IGN switch. It now comes from the R terminal to get increased voltage to both the Distributor AND the TI Module. The increased voltage results from a bypass, similar to the Ballast bypass in a points system.
With TI, normally during RUN, the IGN ON voltage goes through the TI harness which has built in resistors. These are made up of resistor wire, wire that has a specific amount of resistance per inch or foot. There are 2 of these wires in a TI harness. One for the PU coil, one for the TI module. The R terminal takes over and provides Bat+ higher voltage to increase PU coil pulse generation and to provide a higher voltage to the power transistors in the module for higher spark voltage during crank.Comment
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Re: Help me understand voltage readings '69 L71 TI
I removed the TI amp, removed and replaced the board using toothed lock washers, checked the resistance in each wire in the pigtail harness, reconnected ground using toothed lock washer, added a ground wire from the TI amp case to the ground at the case of the alternator for good luck. No spark. Checked the resistance between the two wires from the magnetic coil and the reading is 1. Stays at 1 regardless of the meter scale or movement of wires or pick-up coil. Does this point to a bad pick-up coil?Comment
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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.
As far as the PU coil reading is concerned.....Reading of "1"? What unit? Ohms?
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.
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?
If all of these simple checks prove negative, it'll probably be time then for a detailed flowchart diagnosis.
RichComment
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