TI system questions

[Gary S.]

A neighbor has a 1967 originally with a 435 hp but now a 400 hp due to a blown engine. He has owned this car since 1979 in its current condition. Last fall he put his car to bed for the winter and it was running well. He went to start it two days ago and it will turn over but will not light off. I pulled a spark plug out and grounded it but got a single spark before it failed to spark anymore. My searching here tells me that these TI amps are finicky and tend to lose a good ground. i don't have the knowledge or skills to do more than the basic tests that Dave Fiedler has on his site. Fwiw, his car has a 207 coil whereas Dave says it should be a 263 but he has been running this 207 for years and hasn't changed it in the past. I did swap out his 207 coil and put in a spare 270 coil but I can only guess at its condition. the 270 has 2.7 ohms resistance between the + and - posts and 11.1 between the + and the center terminal. Again, googling says that this should be a good coil.

So my questions are: is it normal for an ignition system to just not work without anything being done to it? Secondly, how much of a difference would the proper coil be to its operation once his no-start condition is fixed? I need to sort through Dave Fiedler's schematics but are the grounding wires obvious? I plan on pulling the amp out tomorrow to look for obvious corrosion but this will be as far as I can go. Any help? The worst-case scenario is to ship it off to TI Specialty since i am way out of my league here.

thank you in advance,
Gary

[Jack C.]

Re: TI system questions

Gary, as it apparently failed while sitting over the winter you could be on to the problem suspecting a ground issue. A 207 coil is a TI coil, and while I don't have my ohm readings right at hand at the moment, you swapped the coil so I doubt your failure is the coil. I believe that anyone with a car with TI should have a spare amp module, and from what you have described, you have all the skill needed to swap this out and try it. If it doesn't fix it no harm no foul as having one for a spare is a good thing. Maybe take off the ground wire at the amp module and ensure it is clean and getting a good ground to the box and to the core support first. Check other basics like ensuring he has a strong battery.

Does he have the original style amplifier in the car? There are two after-market replacements. While I believe it is a bit of a religious argument which one is better, I have one of each and both work fine for me. One is made by Lectric-Limited and for this one they say you do not have to run a TI coil, any standard coil will work. It is fully encased in resin with no visible components other than the terminal leads. The other is Delco Products P/N 1115005-M. It is a circuit card with the components on the board and it must be more specifically electronically similar to the original because it does require a TI coil.

By the way, testing it with a grounded plug is the correct way. I read somewhere that testing by having it arc from a plug wire to a ground area on the engine can damage the module.

Delco Products version
https://www.corvettecentral.com/sear...gnition+module

Lectric Limited version

https://www.lectriclimited.com/transistor-ignition-amplifier-box-module-87585

[Duke W.]

Re: TI system questions

It can get very expensive to repair a TI system, and since the car does not have its original engine... I assume the car is not being judged.

Keep in mind that the single point and TI system use the EXACT same finished machined dist. housing, and it's easy to convert to single point operation. You'll need a breaker plate to replace the stationary pole piece and the little "wavy c-clip to retain it to the housing. I'm not aware that new breaker plates are available, but there are plenty from used parts dealers.

You'll also need a cam assembly to replace the rotating pole piece, plus points, condenser, ballast resistor and associated single point wiring. Since the 400 HP redline is 5300 the common 19-23 oz. points are adequate.

The 1967 CSM has a good troubleshooting procedure for the TI. Connectors, particularly at the amp, and grounds are common problems.'

Duke

[Gary S.]

Re: TI system questions

Thank you both for your comments. While the car isn't being judged, it looks like it would do well enough. That said, I am toying with the idea of making a jumper to go from ground at the amp and to a chassis section to see if the problem lies there. Another link online suggesting testing cranking volts at the coil and we have none. Our next task will be to pull the amp and clean all of its contacts and see if that helps.
Gary

[Jack C.]

Re: TI system questions

Reference this schematic and note that the 12v goes through the amplifier before the coil. Remember also that there are two sources for 12v to the distributor - one from the R terminal on the starter solenoid (provides 12v while cranking); and one from the key (provides 12v while key is in the run position). You can check for 12v at the pink wires at the distributor plug.

https://www.corvetteforum.com/forums...rts-ti_mod.jpg

[Richard M.]

Re: TI system questions

Gary,

See pdf HERE. It's the GM TI diagnosis Procedure. Always a good idea to check grounds, especially at the AMP. Common problem. Also common is the 3 terminal plug at the AMP gets loose or corroded.

If you get 0 volts at Coil+ with Key at RUN, then no power is getting to the AMP. You should get 2.5V to 4.5V.

Try this.....

Key OFF, Remove 3 terminal connector at AMP. Make it accessible for meter readings later. Put a 1/4" bolt in the hood support joint for safety when reaching down in there.

Then Key to RUN. (Note NOT Crank)

Check voltage at #14G Pink-to-White resistor wire connector coming from Ignition switch. This powers the PU Coil AND the AMP when in RUN. If not there, bad Ignition switch or wiring fault.

Also check the #18G Pink(pair) at the Dist connector.

If 12V is there at both places, then probe the TI harness at the AMP power terminal. Which one? Explained next.....

With the connector terminals facing you and the 2 side-by-side terminals at the top, single terminal below them, 12V should be on the upper right terminal. This becomes the Brown wire inside the AMP to power the circuit board.

Rich
PS
Since you don't know if the AMP is original Delco, or Repro(K&B or M&H), you may want to open it up to check connections.

The 207 Coil was the service replacement for the factory supplied 263, so it's the correct TI coil. A TI coil should read about 0.7 ohms at the primary, and around 15K ohms or so at the secondary.....IIRC from memory.

When reading low ohms, remember to short your 2 meter leads together to then subtract that error from actual readings.

No idea what a 270 is, likely a points coil based on the primary reading, but I think your 11.1 secondary reading on it was really 11.1 K ohms, simply a mis-read "K" on the meter display.

[Gary S.]

Re: TI system questions

Richard and all,
You are all so helpful and we are making progress. In addition I have been to Dave Fiedler's site and used his troubleshooting guide.

Richard we got 3.3 volts at the coil key on, engine off and I put a temporary wire from the amp to chassis ground hoping to bypass any bad ground.

The 207 coil, while a TI coil, is not the one called for on Fiedler's site. Thus the comment. I got approximately . 7 ohms at the primary and the secondary was 11.1 K, simply a proofing error on my part. And of course I did subtract the lead error to come up with those values. His amp is indeed a DR amp and my comment on the 270 coil was that it was a quick substitute. It is a 1972 LT-1 coil I had extra. We have an offer of a used DR amp, if the gent can find it, to swap in and see if there is any improvement. I will definitely check for 12 V at the pink wires too as well as other suggestions.

I will check all other suggestions and see where we go. I really wasn't intending to get this deep into someone else's car but he has zero skills. I'm only marginally better. To save me some searching does anyone know where the chassis ground is for the amp? I suspect it's on the radiator support. It wasn't isn't obvious with a cursory glance. That's wht I substituted an add-on quick ground.

Once again, thanks.
Gary

[Richard M.]

Re: TI system questions

Richard and all,
You are all so helpful and we are making progress. In addition I have been to Dave Fiedler's site and used his troubleshooting guide.

Richard we got 3.3 volts at the coil key on, engine off and I put a temporary wire from the amp to chassis ground hoping to bypass any bad ground.

The 207 coil, while a TI coil, is not the one called for on Fiedler's site. Thus the comment. I got approximately . 7 ohms at the primary and the secondary was 11.1 K, simply a proofing error on my part. And of course I did subtract the lead error to come up with those values. His amp is indeed a DR amp and my comment on the 270 coil was that it was a quick substitute. It is a 1972 LT-1 coil I had extra. We have an offer of a used DR amp, if the gent can find it, to swap in and see if there is any improvement. I will definitely check for 12 V at the pink wires too as well as other suggestions.

I will check all other suggestions and see where we go. I really wasn't intending to get this deep into someone else's car but he has zero skills. I'm only marginally better. To save me some searching does anyone know where the chassis ground is for the amp? I suspect it's on the radiator support. It wasn't isn't obvious with a cursory glance. That's wht I substituted an add-on quick ground.

Once again, thanks.
Gary

Gary,

AMP/Coil-

Yes, Ground is sourced from the Core Support, a separate sheet metal hex-head screw at about 11:00 up from the AMP, facing forward. Follow the Blk jumper wire to it. Also note Core support gets an additional ground at the Horn Relay mount screw, which comes from ALT ground and under dash on the crossbar under the Inst Cluster. Ensure a toothed lockwasher is there at all mount bolts. Make sure all connections are clean and free of paint, particularly at the AMP mount bolt. Not factory, but I always suggest toothed lockwashers at all ground points, particularly the AMP ground. For such corrosion susceptible areas, I could never understand why the factory didn't add a few cents of lockwasher security at these points.

207 vs 263 Coil

Yes Dave's sheet says 263, but ignore that. 207 is made for TI. The 263 was a factory installed coil, never available in service depts. His original 263 likely died years ago and he or someone before him replaced it. Your readings on the 207 are good.

Spark Plug Test

Docs warn about pulling more than one plug to check spark and never to just use the plug wire to ground or the dist cap coil wire either. Another way is to use a series spark tester between a wire and plug, or a inductive timing light to see if there's any life from the coil.

Continued Diagnosis:

Key RUN 3.3V at Coil+

It appears your 0V reading earlier was not valid. So, yes, 3.3V is within spec per Diag Proc, so your 12V Ignition source appears to be working. Still worthwhile to check 12V source at Pink(s) to verify proper voltage there at #14G Pink/White IGN wire connector and #18G Pink at distributor connector(this wire powers the PU Coil.

Keep in mind that TI relies on a fully charged battery with high current capability during CRANK.

Next Step

Since Coil+ is within Key RUN spec, it's time to check resistance at the PU Coil. Unplug connector and measure 500-700 ohms at distributor plug. Polarity independent. While ohm meter is connected, wiggle the wires up and under the distributor for intermittency, a common failure point. I believe this is why the Diag Proc wants you to rotate it also to check wires inside the dist. Also check each terminal to ground to verify both are open circuit, infinite ohms.

If the above checks are good, it points to the AMP, but other faults like bad grounds and bad harness connections can be relevant too. Based on your findings we can go from there.

It's good of you to help your friend with this. Hopefully it's something simple.

Rich

[Ray K.]

Re: TI system questions

Gary, In response to your question:
"To save me some searching does anyone know where the chassis ground is for the amp? I suspect it's on the radiator support. It wasn't isn't obvious with a cursory glance. That's wht I substituted an add-on quick ground."

The TI power amp module's jumper wire ground is located on the driver's side radiator support. According to my AIM, it's held in place by a 1/4" - 14 x 1/2" (GM #9422404) plain hex head screw. It's location is about 1 1/2" above the middle radiator support mount bolt asm, GM #3847758

Below is a picture of my '71's amp ground . . . .
Ray K (#43777)


71 Vette - TI Power Amp Rad Support Ground_1 - 09May23.jpg

[Gary S.]

Re: TI system questions

Perfect Ray. Thank you. And Richard, that PDF you sent is the same one that Dave Fiedler has on his website. I will look at this tomorrow and see where we are.

You guys are great
Thank you

[Richard M.]

Re: TI system questions

Perfect Ray. Thank you. And Richard, that PDF you sent is the same one that Dave Fiedler has on his website. I will look at this tomorrow and see where we are.

You guys are great
Thank you

Yes, That's where I got it but it's actually a original GM document published in the Chevy Service News Jan 1968. Note top line.

We'll be waiting and hopefully you find the smoking gun along the way.

Rich

[Gary S.]

Re: TI system questions

PROBLEM SOLVED!

Thank you all. It was a bad ground like some of you commented on and is all over the internet as a very likely source. The problem is fixed but should have been fixed days ago. It was the GROUND to the TI amp. The original ground had a splice with heat shrink on it so I knew it had been messed with. There was an additional ground that looked good but obviously wasn't. The added ground was a black with green stripe wire and a ring connector that was taped to the wiring bundle and ran to the back of the alternator. It looked very well done. There wasn't any ground going to the core support at all and the bolts appeared to have never been off. Ray K's photo helped confirm visually where it should have been originally. Several days ago I tried a temporary ground by holding the wire to the TI amp and the brake master cylinder. Nothing. Then, over the course of the last few days I had tried just about everything with so many good comments here. So, back to basics, I rigged up a real ground under the amp hold down bolt, like it should have been and tied the other end to the proper bolt on the core support. After a proper grounding, it lit off immediately.

My friend has owned the car since 1979 and somewhere before or after his acquisition its blown 435 hp was replaced with a 390 hp. Regardless, I speculate that in the course of the engine replacement some of the wires were messed with. For instance, the TI amp has standard 7/16" nut and bolts and, since I don't have an 67 AIM, I will guess that they aren't original and look like hardware store bolts with no typical head stamps. In addition, the car has been restored and I suspect that any witness marks on the core support were obscured. Again, without the AIM, I assume that the original ground wire was in the wire bundle under GM wire tape and exited to join the core support?

I am suggesting to him that he purchase Dave Fiedler's solid-state board and put that worry behind us.

Thank you. My friend is happy and I am happy.

Gary

[Richard M.]

Re: TI system questions

PROBLEM SOLVED!
.
.
Again, without the AIM, I assume that the original ground wire was in the wire bundle under GM wire tape and exited to join the core support?
.
.
Gary

Gary, great news, glad you solved it. Good work.

Yes the AMP ground wires are part of the TI Harness. It is sourced at the core support terminal at the hex screw, then to a terminal at the AMP mount bolt, that terminal being doubled wired then into the TI Harness back to Coil-.

1967 shown. The bolts are typically "TR" headmark, 1/4x20.
P1130035.jpg P1130036.jpg P1130037.jpg

AIM K66 A2 - The AIM is actually wrong as it doesn't show the double wired black terminal at the AMP as shown above. Electrically identical, physically different.
1967_K66_A2.jpg

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[Gary S.]

Re: TI system questions

Great photos and they clear up the remaining questions.

Thank you