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Discussion Starter #1
does my oem HEI distributor require the tach wire to be connected to the distributor in order to crank the engine?what is the TACH terminal/wire for on an oem distributor if there is no factory (or any at all) tachometer in the vehicle? is the BAT wire enough to do the job? thanks. :confused:
 

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Originally posted by bowtie455:
does my oem HEI distributor require the tach wire to be connected to the distributor in order to crank the engine?

No.

what is the TACH terminal/wire for on an oem distributor if there is no factory (or any at all) tachometer in the vehicle?


It is there to attach a hand held tach in order to do tune-up work.

is the BAT wire enough to do the job?
Yep, that's all you need. ;)

BL
 

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Originally posted by bowtie455:
is the BAT wire enough to do the job? thanks. :confused:
The BAT wire is enough (providing the distributor it is bolted onto the engine) but do not wire it to the battery unless you want to shut off the motor by stopping the fuel or air intake. If it is wired to the battery or a constant 12V there is no way shut off the engine with the key switch. Wire the BAT terminal to an ignition 12V source to where that terminal will have power when the ignition switch is in the run position AND the crank position. Also the distibutor takes a full 12V so do not use the resistance wire or a dropping resistor if the car was that way originally.
Jim
 

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Discussion Starter #5
thanks a heap,guys!i'll trace the tach wire off the distributor to find out what the heck it is connected to.i don't understand what its being used for.the engine died at 30 miles per hour the other day.it cranked again and got me home after sitting a few minutes so i'm troubleshooting the half-assed wiring job some jack-legged moron did.i've got a feeling the old ignition module is near death from someone previously monkeying around with the wiring connections.i've never seen so many splices with electrical tape and bare wires showing through.oh well,$250.00 for a 1985 silverado with little rust..i can't complain.i just wish i was working on my chevelle project instead!
 

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Originally posted by bowtie455:
thanks a heap,guys!i'll trace the tach wire off the distributor to find out what the heck it is connected to.i don't understand what its being used for.the engine died at 30 miles per hour the other day.it cranked again and got me home after sitting a few minutes so i'm troubleshooting the half-assed wiring job some jack-legged moron did.i've got a feeling the old ignition module is near death from someone previously monkeying around with the wiring connections.i've never seen so many splices with electrical tape and bare wires showing through.oh well,$250.00 for a 1985 silverado with little rust..i can't complain.i just wish i was working on my chevelle project instead!
85 silverado, that's important. Need to let people know what you're working on. On a Chevelle you don't need it at all. Not positive on that car but the tach wire may feed an ECM. Maybe someone else knows that vehicle.
 

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It will run without the tach hooked up. Auto Zone should be able to check the module for you.
 

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Originally posted by John_Muha:
It will run without the tach hooked up. Auto Zone should be able to check the module for you.
John, there is no tach in this vehicle and it's not a Chevelle. I was suggesting the tach feed may be going to an ECM since this is an 85. I don't know for sure, are you saying it's not needed on an 85 pickup either?
 

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Originally posted by Finally:
</font><blockquote>quote:</font><hr />Originally posted by John_Muha:
It will run without the tach hooked up. Auto Zone should be able to check the module for you.
John, there is no tach in this vehicle and it's not a Chevelle. I was suggesting the tach feed may be going to an ECM since this is an 85. I don't know for sure, are you saying it's not needed on an 85 pickup either? </font>[/QUOTE]A stock HEI distributor will operate without a tach. The tach is an output from the distributor.
 

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Discussion Starter #11
i just straightened out the mess of spaghetti the "mechanic" left behind.i removed 3 poorly wrapped(electrical tape)and poorly connected splices out of the "tach" wire and installed a new connector on it and cut off the worn,exposed "bat" wire end and replaced the connector on it also.there must have been a shortage of wire available.maybe tomorrow i'll have time to swap the module and the rotor button out to see if she'll crank.i'll be sure and have the old one tested before i throw it away.i've been cleaning and re-connecting all the battery cables and grounds to eliminate any possible electrical bugs.i hope i can remove and clean all the starter wires before the rain gets here tomorrow afternoon.what a poor,neglected chevy! but thats okay,i'm having fun!
 

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Originally posted by John_Muha:
A stock HEI distributor will operate without a tach. The tach is an output from the distributor.
John, As I said I'm not familiar with a 85 'stock' HEI distributor. I also wasn't clear from the post that it was like the HEIs we all know and love, 12v source and tach output, use or not use, your choice. They did evolve and some did receive feedback from an ECM to control timimg. I know you're basically always right but sometimes your answers don't always clear everything up for me. Guess I'll have to get use to that since I do trust you to provide the correct info.
 

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I'm hardly ever right. If the module inside the distributor isn't providing an output pulse to the coil, then there won't be a pulse to the tach output. Check and see where the tach output comes from. It's another winding on the coil (transformer).
On later distributor modules, ECM type, there is an extra terminal to control advance. Unplugging the tach output won't change things. Cars were built with tachs as an option.
 

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Even though the truck has no tach in the dash the wire to it will still be in the harness,the tach wire is always provided just not used.If the vehicle comes from the factory without a tach it is just taped into the harness and not connected to the HEI tach terminal.
If the stock HEI in your truck has a vacuum advance the ECM does not need a tach signal to provide spark.
If it has a "4 wire" connecter and no vacuum advance then the ECM controls spark timing and is a different story.
What is the 8th digit of the vin?
 

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IIRC that is a 305 V8 with feedback carb.The HEI only needs the 12 volt bat wire for it to provide spark.
Check the 2 small wires (1 yellow 1 white)from the pickup coil going to the module.Very common for them to break where they attach to the pickup coil.
Also check the bottom side of the rotor,look for a small pinhead size burn through at the very center.
 

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Discussion Starter #18
thanks for the great info! i'll check all this stuff out tomorrow when the weather hits a balmy 37 degrees.it probably won't make it above freezing today. :rolleyes:
 

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Discussion Starter #19
well,i decided to just replace the ignition coil, rotor button and distributor cap with a used set i knew were good.i had the module tested and it checked out fine.my truck is now running!next up is a new set of plugs and wires.thanks a heap for all the great advice guys!if it dies again i'm gonna replace the pick-up coil. :D
 
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