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Old 02-01-2011, 03:49 PM
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Replacing a 1986 GM HEI with an early model

I have a 1986 Chevy pickup I just bought and I would like to replace the present Ignition system with an earlier model HEI. (75-80) I know the earlier models have a four wire plug on the distributor. What would be the right way to hook it up when replacing the 1986?

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Old 02-01-2011, 04:56 PM
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The Non-computer HEI's only need one 12V+ wire for operation and one wire for Tach. Has 2 spade Terminal connection.
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Old 02-01-2011, 06:26 PM
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ss sedan is correct. One thing to consider would be where to hook up the vacuum advance. You probably have a ported source somewhere on the carb you can hook it to. You will need to reset the timing. Set the base timing at about 12 degrees , then reconnect the vacuum advance and open the throttle slightly so you can see if the advance is working by watching the timing mark move towards a more advanced posisiton.
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Old 02-01-2011, 07:16 PM
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The power wire for the original HEI plugs right into the new one - the caps are the same. Ignore the four wire plug. Be aware that the electronic carb won't work without the distributor signal.
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Old 02-01-2011, 07:23 PM
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Quote:
Originally Posted by joe_padavano
The power wire for the original HEI plugs right into the new one - the caps are the same. Ignore the four wire plug. Be aware that the electronic carb won't work without the distributor signal.
Hey thats right joe. good lookin out. I missed that. I am thinking that you could tie the tach signal to one of the pins in the four wire connector to keep the carb in the loop. I dont have a schematic in front of me, nor do I remember wich one to use. Got any Ideas?
I wonder which trans he has.

Last edited by latech; 02-01-2011 at 07:37 PM.
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Old 02-03-2011, 07:28 PM
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Changing to early Gm HEI distributor

sorry I was so long getting back but I couldn't get my password to work and had to change it twice. Thanks for the info.
I was looking in my Hanes book on the 67-86 Chevy pickup and it has the wiring for the early Distributor. It shows the hot wire coming from the ignition switch start/run. The 86 has two start/run wires but think I can get them straightened out.
This pickup is a one owner was under coated when bought and has no rust, dents or scratches. Needs some TLC here and there. My Nephew said he could get me a 305 bore out to 355 with aluminum heads that has never been run and won't cost me anything. Will I go that way or just get the original engine running well. Guess we will see.
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Old 02-03-2011, 07:37 PM
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Someone has put a Holly 2 barrel on and I am going back to a Qudra Jet just to get close to original. All the pollution crap will be removed. If I do change the Intake going with an Edelbrock Preformer and a 600 CFM Preformer.
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Old 02-03-2011, 07:41 PM
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Transmission on 1986

Don't know just what the auto trans is as I haven't had a chance to look at it. Been to cold and I have a 1994 that I am getting everything off before I junk it in the garage right now. As soon as the weather gets warmer I am going to check everything out.
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Old 02-03-2011, 08:14 PM
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Can't bore a 305 out to 355. A 400 Crank can be used for 335ci.
Most likely the truck has a TH350C Trans with Lockup Torque Converter.
They also came with TH350, TH700R4 & TH400.
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Old 02-03-2011, 08:42 PM
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For what its worth my 86 chevy truck 2wd, 305 came with a 700r4.
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Old 02-04-2011, 08:07 AM
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Are you sure this truck has an ECU? Only California emissions trucks came with the computer controlled distributor. 49 state trucks DID come with the knock sensor (ESC - electronic spark control). These distributors have a normal vacuum advance canister - the electronic ones do not - but have the four wire electrical connector that looks the same as the one on the computer controlled distributors. If you have an ESC distributor, there's no good reason to eliminate the knock sensor.
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Old 02-04-2011, 06:54 PM
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700r4

Checked the trans in the 86 and it is a 700R4.
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Old 02-04-2011, 07:04 PM
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Spark box

Mostly want to eliminate the spark box control on the 86 that is tied in to the emission controls. Some say they have hooked the A and D wires together and it works OK but one person told me his didn't run right until he replaced the distributor with an early model HEI. About all I have dealt with on the HEI is putting one from a 1978 Olds 350 into a 68 455 after rebuilding it when I changed from a 350 to a 455. But when it gets warmer I will find out what is what and as usual get it fixed just fine. You know it is amazing how many people tell you that something can't be done when you have already did several times. But there are some good people out there that really want to help and I am getting a bit older and haven't worked on to much in a few years. But it will come back. Thanks for the help.
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Old 02-05-2011, 08:44 AM
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Quote:
Originally Posted by atomiccat44
Mostly want to eliminate the spark box control on the 86 that is tied in to the emission controls. Some say they have hooked the A and D wires together and it works OK but one person told me his didn't run right until he replaced the distributor with an early model HEI. About all I have dealt with on the HEI is putting one from a 1978 Olds 350 into a 68 455 after rebuilding it when I changed from a 350 to a 455. But when it gets warmer I will find out what is what and as usual get it fixed just fine. You know it is amazing how many people tell you that something can't be done when you have already did several times. But there are some good people out there that really want to help and I am getting a bit older and haven't worked on to much in a few years. But it will come back. Thanks for the help.
If you are talking about the ETC system (the knock sensor), it is a standalone unit that has nothing to do with emissions controls. Again, does the HEI have a vacuum advance or not?
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