Another TI Ignition Issue

[Lawrence S.]

65 L78 TI Ignition:

Have a restored distributor that tested out well with curve notes from restorer, Mike Zamora.
Installed distributor rotor pointing to number 1 plug wire, point window facing forward. Car will not fire off.
Install distributor advanced, rotor pointing between number 1 plug tower and number 8 plug tower car fires off. But can't get static timing close to spec, too advanced. Let car come up to temp turn the car off and won't fire back up until it cools down.
While distributor is installed what I believe is correctly, car fires for a second when turn key off. But do not have this issue when distributor is advance one tooth?
I don't know the history of the TI amp, looks old and likely original. Probably needs the solid state conversion, but seems if so would be a constant problem regardless of distributor installation.
Plug wires installed correctly.
I am at a loss. Thought for sure once the distributor was installed correctly would fire right off, but it does not like something.
Any suggestions are appreciated, before I pull all my gray hair out!
Lawrence

[Richard M.]

Lawrence,

Double check grounds.

Also check distributor 2-wire connector polarity.
See this thread, post #7 for a photo.
https://www.forums.ncrs.org/forum/te...irewal-harness

Yes if a original Delco AMP, it could be faulty. That one pulse you get from key START To RUN, or RUN to OFF, is a artifact of the AMP circuit when a subtle fault exists.

Rich

[Mark M.]

It sounds like it may be off a tooth or so. Between #1 and #8 tower is retarding timing. You need to cold time engine. Get timing mark at 0 degrees on the damper mark to tab with # 1 cylinder on compression stroke. Adjust oil drive shaft with long screwdriver so when housing is lowered and turns rotor, it points at #1 tower ( mark on housing #1 position so cap can be off) while distributor housing vacuum advance canister is near clock position as shown in the assembly manual L78 top view . #1 cap tower is also shown in assembly manual. I would first double check dimple on bottom gear that it lines up with rotor tip.

[Mark M.]

Don't do what I've done once. Fixed issue quickly but these large carbs dump much fuel fast and when it fired, boom. One muffler was ruined. Luck nothing else.

[Richard M.]

Mark, Good ideas. That's right... he's setting the timing retarded going between 1 and 8.

He may want to set damper to 6 degrees advanced, then install distributor with rotor tip at #1. Duke taught me this years ago. It gets timing close to ideal for first start.

Rich

[Duke W.]

I strongly suspect that your distributor assembly and/or installation is wrong. Distributor assembly/installations get screwed up all the time, and I've been helping guys deal with this issue as best as I can for 60 years, but it's tough to fight all the misinformation on the internet. I've made numerous posts, both here and on the CF, of how to properly do this.

Check to see if there is spark. If so and the engine won't start there is a very good chance the above is true.

Like Rich said start by setting the balancer notch on the timing tab to whatever value initial timing you want BTC BEFORE you remove a properly installed distributor or if there is a potential problem with distributor assembly or installation. Most advice is to set the engine at TDC #1. This is DEAD-ASS WRONG as you should understand shortly .

If you aren't absolutely positively CERTAIN that you are BTC #1 rather than #6, pull the #1 spark plug and rotate the engine until you feel compression, then continue until the balancer notch aligns with the proper timing point on the tab. This should take no more than an additional 90 degrees of crankshaft rotation. I've dealt with guys that wrestled with this problem for days only to find out that they were at or near TDC #6. Yes, that can happen!

Once you have the crankshaft properly indexed remove the distributor. Verify that the dimple on the side of the gear is pointing the same direction as the rotor tip. If not, rotate it 180 degrees. (Some aftermarket cams do not have properly indexed lobes to the gear like OE cams and may require the rotor tip to point 180 degrees away from a dimple, and some drive gears don't even have a dimple.)

Also verify that the #1 plug wire is installed in the proper cap terminal. It's the one next to the PASSENGER side edge of the cap window, and this is illustrated in numerous requisite shop manuals and AIMs.

Once distributor assembly and wire indexing is verified to be correct, hold the distributor above the hole with the rotor pointed about 20 degrees to the passenger side from engine centerline. Drop it in, and as the gears engage the rotor will rotate CCW. If the base of the distributor doesn't seat on the manifold, remove the distributor. Check the orientation of the slot in the intermediate oil pump drive shaft and tweak it as necessary. I use a paint mixing stick. If you have never done this before be patient and take your time. It might take several tries to get it right. With experience it's easy.

Once seated rotate the distributor base CW to the limit then rotate CCW until the rotating pole pieces line up with the stationary pole pieces. (if a single point distributor rotate CCW until the points just begin to open either visually or with an ohmmeter). Now the engine should be within a degree or two of where you set the balancer notch on the timing tab. If you're careful and with a little experience it should be dead on.

This is called "static timing" the engine, and it's the way it's done on light aircraft reciprocating engines because it's kind of tough and definitely unsafe to time a light aircraft engine while the propeller spinning

Snug down the distributor hold down bolt, but not so much that you can't rotate the distributor base. Start the engine. If cold let it warm enough get down to normal hot idle and check initial timing if the centrifugal does not start until above normal idle speed. If not use the total WOT method to set timing (VAC hose disconnected and plugged as with setting initial timing) and set at 36-40 a few hundred revs above the point of max centrifugal. (If you don't know the start and stop points of the centrifugal you need to measure and DOCUMENT them. The OE specs are in the applicable service manuals, but many, if not most, have been modified over the years, sometimes for the better, but not always.)

As a final check the plane of the cap window shoule be near perpendicular to engine centerline, not exactly, but close considering that normal initial timing for most vintage Corvette engines is in the range of 4 to 16 degrees. If it's noticeably cocked off to one side or another, something's wrong.

There are distributor installation threads I've started both here and on the CF. This site is difficult to search, so If you want a more thorough step by step explanation search the CF C2 section for threads started by SWCDuke. The detailed step by step explanation thread I started late last year was the last thread I ever started over there. When some "technical advisor" chimed in and said it didn't make any difference how the wires are indexed, that was it for me. I quit the CF the third and final time.

Understand that the above distributor installation procedure is for '57 to '67 small and big block single point and TI distributors. I'm not sure about about earlier small block distributors or small block dual point distributors.

C3 small blocks have DIFFERENT wire indexing and installation orientation. I believe C3 big blocks are also different than C2 big blocks, but I'm not sure.

Duke

[Richard M.]

Duke, and others,
Here is your CF thread.

https://www.corvetteforum.com/forums...sb-and-bb.html

Great reference!

Rich

[Lawrence S.]

Thank you very much guys really appreciate it.

Duke, thank you for the step by step procedute.

I will give this a shot in the morning, and report back.

I have not taken all of these steps but will. Hopefully I can get the car to fire off.

[Curt R.]

I was working on the same issue this weekend, not on one my Vettes , but my ‘69 Z-28 with a factory TI , basically the same system and with the same problem where it will fire when I just start cranking and when I let off the ignition, after many hours on Saturday I found that the connection that goes to the distributor had a loose wire which also connects to the yellow solenoid that allows it to get a full 12 volts to the coil while cranking, not it fires up after securing the loose connection, you might want to check them out first before replacing any parts. PS I had taken my amplifier to Mike Zamora’s shop and tested it on one of his vettes which ruled out a bad Amplifier.

[Lawrence S.]

I was working on the same issue this weekend, not on one my Vettes , but my ‘69 Z-28 with a factory TI , basically the same system and with the same problem where it will fire when I just start cranking and when I let off the ignition, after many hours on Saturday I found that the connection that goes to the distributor had a loose wire which also connects to the yellow solenoid that allows it to get a full 12 volts to the coil while cranking, not it fires up after securing the loose connection, you might want to check them out first before replacing any parts. PS I had taken my amplifier to Mike Zamora’s shop and tested it on one of his vettes which ruled out a bad Amplifier.

Thanks Curt. Will confirm I don't have any loose connections.
Just sold my 69 Z28 RS, enjoy yours.
Lawrence

[Richard M.]

I was working on the same issue this weekend, not on one my Vettes , but my ‘69 Z-28 with a factory TI , basically the same system and with the same problem where it will fire when I just start cranking and when I let off the ignition, after many hours on Saturday I found that the connection that goes to the distributor had a loose wire which also connects to the yellow solenoid that allows it to get a full 12 volts to the coil while cranking, not it fires up after securing the loose connection, you might want to check them out first before replacing any parts. PS I had taken my amplifier to Mike Zamora’s shop and tested it on one of his vettes which ruled out a bad Amplifier.

Curt, to clarify what's highlighted above....

In the TI circuit, Solenoid R does not provide full battery to Coil+ during Crank.

It provides full battery to the Distributor Pickup Coil and the AMP during Crank.

Screenshot_20250602_071338_Chrome.jpg

Also note that in 1964/1965, Coil- is connected via a resistor wire from chassis/AMP ground. Coil+ is driven directly from the AMP output. This is opposite from the 1966-1968 TI circuit wiring.

This is also why there are unique TI Harnesses for the two versions.

Rich

[Lawrence S.]

I have completed the distributor installation per Duke's instructions.
My crank timing at the tab was 6* (decided to start there vs. 12*)
When I pulled the cap off the rotor button was left of the number 1 plug tower. I am assuming I had the timing too retarded.
I reset the distributor per Duke's instruction, with 6* degrees BTDC, and adjusted the distributor housing per Duke's instructions.
When I first tried to fire the car it fired slightly but nothing with confidence. I feel like I have the distributor close enough to fire, the rotor is pointing to number 1 plug, and other instructions followed. I will revisit the connections.
Lawrence

[Richard M.]

If you're confident the distributor is installed properly at #1 reference....

Here's the diagnostic flowchart for 1965.
Screenshot_20250602_090213_Chrome.jpg

First thing I'd check is 5-7 volts at Coil+ with key to RUN.

If good, check Dist PU coil. Disconnect dist plug. Check for 500-700 ohms at the 2 dist terminals. Wiggle wire when testing. Also check each terminal to engine ground to verify there is no hard short, again while wiggling wires.

Rich
P.S. I saw the L78 static timing spec is 4* BTDC. 6*(it was a guess on my part earlier), is close but unsure where you saw 12*.

[Lawrence S.]

One other note, when I turn the ignition to on I can hear a slight buzz coming from somewhere forward of the firewall. Sounds like a faint key buzzer.
When I try to start the car as if it were flooded, accelerator pedal to the floor, it tries to start but wont fire all the way.
I do smell gas as if the car is flooded, but not pumping the pedal at all.
I looked down the carb and it is moist, no drips down the intake.

[Richard M.]

Lawrence and I spoke on the phone and we feel we found the problem. He measured 0 volts at Coil+ with key to RUN.

He'll report back later with the results after he does more tests.

It seems like it was a intermittent fault which led to some confusing results.

Rich