69 TI Spark Plug wire location on distributor

[Lawrence S.]

Is the plug wire location on the distributor cap different for a TI car than on a points distributor? I got my car running finally and it was running rough. I checked the plug wires they seemed to be off so I made some changes per my Chilton book and now it is back firing while trying to start. Something simple is wrong...Any ideas?

Thanks

Lawrence

[Keith B.]

Re: 69 TI Spark Plug wire location on distributor

TI or points it makes no diffreance in the firing order

[Terry M.]

Re: 69 TI Spark Plug wire location on distributor

Is the plug wire location on the distributor cap different for a TI car than on a points distributor? I got my car running finally and it was running rough. I checked the plug wires they seemed to be off so I made some changes per my Chilton book and now it is back firing while trying to start. Something simple is wrong...Any ideas?

Thanks

Lawrence

Larry

In the latest edition of the 1968-1969 TIM&JG, among the pages at the back, there is a page from Chevrolet Service News showing both the C2 & C3 Corvette distributor orientation with the spark plug wires enumerated. The orientation changed from C2 to C3 and we often see the distributor and/or wires improperly oriented in judging. Sadly those pages at the back of the 1968-69 TIM&JG are not numbered and I have seen their order different in different manuals. Whoever bound them paid no attention to the order of those pages. The next edition of that manual will correct that so that I can give you a page number to find that article. I know a lot of people think those pages at the back of the manuals are "fluff," but there is important information in them. One simply has to take the time to look at them.
There is a description in the Chevrolet Service Manual of how to properly install the distributor so it is indexed to Top Dead Center of number 1 cylinder on the firing cycle. I don't have my CSM here with me in Ontario, or I would cite the relevant page for you. Sorry about that, but perhaps someone with their Corvette Library at hand can do that for me..

[Duke W.]

Re: 69 TI Spark Plug wire location on distributor

There should be photos of proper wire indexing in the CSM. Big block may be different than small block. I'm not sure, but be sure you use the proper sequence for a big block. TI and single point are indexed the same for each engine family.

Check each wire end to end with an ohmmeter to ensure proper wire indexing and verify that resistance is no more than 5K ohms per foot assuming you are using OE type RFI wires. Check that the terminals are properly crimped to the wires and seat fully in the cap. Wiggle the wires while you check.

Set the engine at the initial timing point #1, NOT TDC. Snug the dist. hold down bolt just a bit, so you can still rotate the dist. Then rotate the dist. base so the stationary and rotating pole pieces line up. This is called static timing and will place the initial timing within a degree or two of spec. I believe the OE spec is 4, which is very conservative. I recommend about 8.

The engine should now start and run smoothly, and you can check timing with a light. The problem you are reporting can be due to a couple of wires being swapped out of proper sequence.

The above assumes that the dist. has not been recently removed or disassembled. If it has it should be removed to verify that the dimple in the gear is in line with the rotor tip and then reseat the dist. to proper indexing with the cam gear..

Duke

[Michael W.]

Re: 69 TI Spark Plug wire location on distributor

Is the plug wire location on the distributor cap different for a TI car than on a points distributor? I got my car running finally and it was running rough. I checked the plug wires they seemed to be off so I made some changes per my Chilton book and now it is back firing while trying to start. Something simple is wrong...Any ideas?

Thanks

Lawrence

The OEM location of the wires in the book will only work if the distributor rotor is also in the correct OEM position. Sounds like it's not.

[Richard M.]

Re: 69 TI Spark Plug wire location on distributor

Terry, Here is a post with photo of the document by Wayne Midkiff that shows the 1968+ 327 only orientation change. Lawrence has a 427 so it won't apply in his case. His #1 wire should face front as normal and close to the VAC. However, his wiring may have been indexed by one with the VAC in the normal position by someone before.

https://www.forums.ncrs.org/showthread.php?104768-Which-terminal-do-you-have-your-number-1-spark-plug-wire-at&p=696763#post696763

Also the Lars' distributor document attached for reference which shows the altered configuration for the 327 and basic steps.

Lawrence, if you recorded and marked the plug wire positions before you removed them, set them back where they were. Obviously you re-configuration is not right. If the engine started and ran after the new TI harness was installed(as I read in your other post) you may have other issues. Your present backfiring is a mistiming condition and best to go through the steps Duke has outlined to get back to a basline configuration. His recommendation to set the balancer mark at the timing tab static timing spec then verify the rotor tip points to the #1 at the cap, is the preferred method. I use that always. This way the engine will run immediately and can be easily timed with the timing light. If it's running rough it could be other problems.

If the VAC is originally configured (iirc MS201 15) with ported vacuum then iirc static timing is 4*.

If you have VAC configured for manifold vacuum using a different VAC I suggest 8* static.

If you're not sure, that will be a different discussion once you get the engine running better.

Rich

[Lawrence S.]

Re: 69 TI Spark Plug wire location on distributor

Nope the distributor location was not in the OEM location. I went to TDC, pulled the cap noted where the button was pointing (way off from OEM). Assembled the wires based on #1 and the car started right up and ran like a top.
Thanks guys

Lawrence

[Terry M.]

Re: 69 TI Spark Plug wire location on distributor

Terry, Here is a post with photo of the document by Wayne Midkiff that shows the 1968+ 327 only orientation change. Lawrence has a 427 so it won't apply in his case. His #1 wire should face front as normal and close to the VAC. However, his wiring may have been indexed by one with the VAC in the normal position by someone before.

https://www.forums.ncrs.org/showthread.php?104768-Which-terminal-do-you-have-your-number-1-spark-plug-wire-at&p=696763#post696763

Also the Lars' distributor document attached for reference which shows the altered configuration for the 327 and basic steps.

Lawrence, if you recorded and marked the plug wire positions before you removed them, set them back where they were. Obviously you re-configuration is not right. If the engine started and ran after the new TI harness was installed(as I read in your other post) you may have other issues. Your present backfiring is a mistiming condition and best to go through the steps Duke has outlined to get back to a basline configuration. His recommendation to set the balancer mark at the timing tab static timing spec then verify the rotor tip points to the #1 at the cap, is the preferred method. I use that always. This way the engine will run immediately and can be easily timed with the timing light. If it's running rough it could be other problems.

If the VAC is originally configured (iirc MS201 15) with ported vacuum then iirc static timing is 4*.

If you have VAC configured for manifold vacuum using a different VAC I suggest 8* static.

If you're not sure, that will be a different discussion once you get the engine running better.

Rich

Rich

Good catch. Reading comprehension is not my strong suit late in the evening. Wayne's post is exactly the illustration I was referencing, but I failed to note that Larry has a fat motor. DUH!! Looks like you and Duke are pointing him to the right path, so I will go back to lurking.

[Richard M.]

Re: 69 TI Spark Plug wire location on distributor

Nope the distributor location was not in the OEM location. I went to TDC, pulled the cap noted where the button was pointing (way off from OEM). Assembled the wires based on #1 and the car started right up and ran like a top.
Thanks guys

Lawrence

Good diagnosis. Glad you fixed it.

However, Just for the sake of correct configuration, is your #1 cap position in the right place, ie as shown in the photo in the pic/pdf above? If not, it will work fine as you've witnessed but may be confusing the next time you or someone else works on it. It seems it may be off one plug wire position and when you tried to correct it by "the book", it was then off one position. Or you may have been looking in the book at the '68 up 327 unique configuration.

If you want it right you'll have to pull the distributor and re-clock it properly, but I understand that you may not want to as it's now running fine. Glad that the TI worked out with that new harness. TI works great, except when it's broke.

Rich

Good catch. Reading comprehension is not my strong suit late in the evening. Wayne's post is exactly the illustration I was referencing, but I failed to note that Larry has a fat motor. DUH!! Looks like you and Duke are pointing him to the right path, so I will go back to lurking.

Terry, I wish I knew a % of what you've forgotten about the C3's. They are my weakest generation. I always lurk your C3 posts to help me learn, along with all the other C3 guys posts.

Rich

[Lawrence S.]

Re: 69 TI Spark Plug wire location on distributor

Before I had the issues I had the timing set at 4* per spec. Car runs fine with no detonation, but if it would take a little more timing I will do so.

Duke, I did not read your post prior to finding the number one plug location on the distributor and installing wires accordingly. I would had gone to 4* and started there if I would had known. But I don't understand what the stationary and rotating pole pieces are? I know little about TI ignition. Can you help me out here?
Thanks
Lawrence

[Duke W.]

Re: 69 TI Spark Plug wire location on distributor

The rotating pole piece (on the mainshaft) and the stationary pole piece (mounted on the dist. housing) have eight projections. You can clearly see them if you remove the rotor.

As these magnetized projections pass each other they generate a small voltage in the pickup coil that surrounds the stationary pole piece. This is the timing signal to cut current to the coil, which generates the spark.

The pole pieces/pickup coil are essentially a set of "electro-magnetic points".

The four degree initial timing is a very conservative, emission control oriented value. When combined with the 30 degrees centrifugal it only yields 34 degrees total WOT advance, which is below the optimum range of 36-40, so you should advance it to up to 10 degrees or the detonation limit.

The engine will also run better, cooler, and use less fuel if you convert the ported vacuum advance (which is also an emission control oriented configuration) to full time, and you will have to replace the OE 210 15 15.5" VAC with a 12" B26 if you do. This simple modification has been discussed and explained many times on the TDB, so a search should yield several threads on how to do it.

Duke

[Richard M.]

Re: 69 TI Spark Plug wire location on distributor

A few photos to enhance Duke's explanations....











A few photos of the pole piece and pickup coil/magnet assembly from the internet for reference






Note position of the pickup coil terminals and their wire color code positions in the plastic connector housing. Polarity is important.

[Lawrence S.]

Re: 69 TI Spark Plug wire location on distributor

The rotating pole piece (on the mainshaft) and the stationary pole piece (mounted on the dist. housing) have eight projections. You can clearly see them if you remove the rotor.

As these magnetized projections pass each other they generate a small voltage in the pickup coil that surrounds the stationary pole piece. This is the timing signal to cut current to the coil, which generates the spark.

The pole pieces/pickup coil are essentially a set of "electro-magnetic points".

The four degree initial timing is a very conservative, emission control oriented value. When combined with the 30 degrees centrifugal it only yields 34 degrees total WOT advance, which is below the optimum range of 36-40, so you should advance it to up to 10 degrees or the detonation limit.

The engine will also run better, cooler, and use less fuel if you convert the ported vacuum advance (which is also an emission control oriented configuration) to full time, and you will have to replace the OE 210 15 15.5" VAC with a 12" B26 if you do. This simple modification has been discussed and explained many times on the TDB, so a search should yield several threads on how to do it.

Duke

Thanks Duke.
I understand the full time manifold vacuum. I have converted such on my 69 Z28. I will confirm the manifold vacuum on the this car. I do believe the vac is a B26 but again will confirm.
Thanks for the explanation of the TI distributor. Along with Richard's pictures I have a better understanding of system.
Lawrence

[Lawrence S.]

Re: 69 TI Spark Plug wire location on distributor

A few photos to enhance Duke's explanations....











A few photos of the pole piece and pickup coil/magnet assembly from the internet for reference






Note position of the pickup coil terminals and their wire color code positions in the plastic connector housing. Polarity is important.

Great pictures. Thanks Rich

[Duke W.]

Re: 69 TI Spark Plug wire location on distributor

Thanks Duke.
I understand the full time manifold vacuum. I have converted such on my 69 Z28. I will confirm the manifold vacuum on the this car. I do believe the vac is a B26 but again will confirm.
Thanks for the explanation of the TI distributor. Along with Richard's pictures I have a better understanding of system.
Lawrence

30-30 cam idle behavior is typically 10" @ 900, so a 8" VAC (B28) is required to pass the Two-Inch Rule when converting the DZ engine to full time vacuum advance. The SHP big block cam has less overlap, so it pulls more vacuum, typically 14" @ 900, and a 12" VAC passes the Two-Inch Rule.

It's always a good idea to measure manifold vacuum before deciding which VAC is necessary for full time vacuum advance because a different cam could have been installed sometime in the last 50 years.

Duke