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Roland Wagner said:
I have a question for everyone have an 85 Chevy half-ton with a 305 and the HEI is not giving off spark I'v checked everything and wonder what you have done in my case.
I always check wires too coil for voltage while being cranked..
if voltage, i pull coil high tension wire from dizzy and crank to see if it sparks, if that sparks and you work your way to the module you have found the problem ..
 

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HEI troubleshoot

Doc here:pimp:

To troubleshoot HEI no Spark,

Check to see you have 12 volts on the cap, at the terminal marked "BATT" If not trace the wire down to a fuse or burned or broken wire, fusible link...

Be sure the TACH wire is not shorted to ground.

Check to be sure the Carbon Contact piece on the cap from the rotor hasn't broken off or worn away.

Pull the Coil Cover and Coil, Check for Debris inside the coil that could short it out. (carbon Spray, or New Lifeforms..)Clean as required.

To test the Coil, Get an Ohm meter Set to RX1 Scale, and place your test leads Between The Rotor button contact piece, and The "Batt" Terminal on the cap.

It should read, 6,000 to 30,000 Ohms...Same applies between The TACH and rotor Button.

Remove the cap and check to see the rotor "Tang" didn't break off..or the Spring contact didnt recesses.

Crank it a bit to insure the Distributor is still turning.

Test the ECM . You can have an auto parts superstore Do it for free if you have one in your area. If not , Just replace it. (Photo)

Test the magnetic Pick up & pole piece on the inside of the distributor.(photo)

With An Ohm Meter set on RX1 Scale, It should read Between 500 Ohms, and 1500 Ohms.

This requires removal and disassembly of the Distributor to replace The pole piece..

If you Have a Crank sensor, Check or replace that.

At this point you may also want to consider, New Cap, Rotor, Wires And plugs...So as to start off with a fresh Electrical tune up.

This should get you going again.

Like Tom said, the most likely suspect is the ECM or the Magnetic pickup & pole piece.

Keep us posted!

Doc :pimp:
 

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King of my Man-cave.
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You can check the pole piece with an ohmmeter. It should have continuity through the attachment leads. Activate the vac advance with the ohmmeter attached to the pole piece leads. The wires can break inside the insulation and be a bugger to diagnose.

QUOTE]Originally posted by Simo
Tom ,, .pheww , I could have confused roland if it wasnt for you, poor bugger would have been lookin for the wire every where. [/QUOTE]

In the OLD days, I used to replace my friends' coil wire with vacuum tubing with some coil wire boots on it. Take them a while to catch on.:D

tom
 

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Discussion Starter · #7 ·
thanks for the help but I did all that you guys said
I have 12 volts going into the cap, the tach wire is not grounded, the carbon contact piece is perfect, no debris in the coil cap, the ohms running through the coil is fine, the twag was fine, the distributer is turning and the timing belt is fine.

I have one question though, what is the ECM, I think your talking the modgule. I replace cap wires and plugs.I also don't know if this engine has a crank sensor or were it would be at.
 

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ECM

Doc here :pimp:

The ECM is located under the CAP, Where all the wires go to.

It is a Semi Curved Epoxy Module That Controls the Spark, and bolts on to the Base plate just inside of the distributor. AND it Fails often!

If the ECM went out, you will have no spark.

If you remove or replace it, BE SURE to clean off all the old silicone Grease, and apply Generous amounts to the new module, they are very heat sensitive , and will fail prematurely without the grease.

Also the Pole piece and Magnetic pick up which supplies pulses to the ECM can fail and kill spark.

If you had a Crank sensor, It would be located at the front of the engine, right next to the crankshaft harmonic balancer. It works like the pole piece and Magnetic pick up and will kill spark also.

SEE ATTACHED PHOTO FOR LOCATIONS.

Doc :pimp:
 

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Discussion Starter · #9 ·
I'v tried everything that you've said and even went to the extent of replacing the distributer. The pickup still is not running thanks for the help the only thing I think the only thing left is to replace the is to replace the sensor under the dash or maybe a broke wire some were.
 

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To clarify a few points:
ECM is the computer, (electronic control module) and is not located in the distributor. It is under the dash. The module is inside the dist, and that is the part Doc was talking about.

The ecm on your truck should not have any effect on the HEI at all. That is a pretty dumb computer, mostly it will control the fuel solenoid on the carb.

Your truck probably has EST or Electronic spark control. Sort of a super module, external to the dist. It is usually mounted on the firewall, and would have a 4 wire connector from the dist . to it.
Try unplugging it and starting the engine.

Finally, if you have replaced the dist, and you do have 12 volts at the BATT connection on the cap. and you still have no spark, then the coil must be bad. The HEI only has 3 componets that create the spark - pick up coil, Module and Ignition coil.

Ground cable in good condition?
 
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