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Help! No spark on HEI ignition

Started by _jklumpp_ , Aug 17 2019 08:39 PM

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12 replies to this topic

#1 _jklumpp_

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Posted 17 August 2019 - 08:39 PM

After 3 years, I was hoping to finally fire up the LJ today.

Engine was removed from car 3 years ago, and has just gone back in after a full rebuild - nothing changed in the ignition system though.

Cranked it over, but no spark....

I'm running the HEI ignitiion, but basically put straight back in as it was removed, and was working when the engine was pulled out.

I'm fairly certain all wiring is connected correctly, as I followed a photo I took before removing it.

If I measure the voltage across the coil with everything connected, I get 3.9 volts. If I removed the red wire from the coil, it measures 12.8 volts.

I've tried swapping the coil out with another I had, but no change (can't be sure either coil is working, though both were when removed from car)

Not sure what to do next?

Any suggestions on what to check, and how to do it?

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#2 S pack

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Name:Dave
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Posted 17 August 2019 - 09:11 PM

I notice you don't have the cover on the module. Install the cover and retaining screws. I believe one of the screws grounds the electronic module to the distributor housing.

Failure of the electronic module will result in no spark.

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#3 rodomo

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Posted 17 August 2019 - 10:11 PM

I notice you don't have the cover on the module. Install the cover and retaining screws. I believe one of the screws grounds the electronic module to the distributor housing.

+1

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#4 LJ RB30

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Posted 18 August 2019 - 10:34 AM

And put heat transfer paste under the module or it will get hot & cut out.

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#5 RallyRed

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Posted 18 August 2019 - 10:46 AM

main earth cable on block to frame? ( guessing)

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#6 Rockoz

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Posted 18 August 2019 - 12:39 PM

Dont measure the voltage across the coil.

It will give you funny readings and cause you to pull your hair out.

Measure the voltage from the positive side to ground.

You should get the same voltage as the battery with the ignition turned on.

Making sure the module is grounded is a must.

Without it grounded it too will give you silly readings.

Voltage measurements with an electronic system need to be done better than with straight points.

Across the coil with points would have given a good indication, but with electronics it can add to confusion.

You should as a matter of course make all voltage measurements against the ground.

Cheers

Rob

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#7 _jklumpp_

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Posted 18 August 2019 - 07:23 PM

Thanks Guys.

Cover was only off the module when I was trouble shooting - trying to follow testing instructions I didn't understand!

Module is glued to dizzy....

I have a feeling the module is the problem, but unsure how to test...

Voltage was tested to earth, as well as across coil.... only 3.9v with everything connected, but positive wire disconnected from coil provided 12.8v...

earth cable to block is good - earth is dizzy is good

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#8 fuzzypumper

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Posted 19 August 2019 - 12:01 AM

You could try some basic testing of the module and coil in this guide:

http://www.gmh-toran...ei-distributor/

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#9 Rockoz

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Posted 19 August 2019 - 02:31 PM

Im not sure of the make up of the electronic module.

But if it has a metal chopper type assembly attached to the rotor, you could remove the rotor and pass a metallic object passed the sensor.

Check the readings as you do so.

It seems that the module may be giving a sensed reading, similar to points closed given the voltage readings you are getting.

Activating the sensor manually will tell you if it has any smoke left in it or not.

Cheers

Rob

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#10 _jklumpp_

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Posted 21 August 2019 - 08:00 PM

Found the problem today... the tacho cable was earthing the coil negative!

Tested battery positive to coil negative with a test light, and found that I had full time negative on coil.... with tacho lead disconnected, only pulsing on the test light as the engine cranks over.

must be something funny happening under the dash, but with tacho lead disconnected, she fired up.... only to show me she had an oil leak from the front main seal.... :-(

one step forward,...

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#11 Rockoz

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Posted 22 August 2019 - 11:07 AM

Old cars can be a bit of a lucky dip with wiring.

The more owners its had, the more likelihood of dramas.

The trick to finding electrical faults is to break the circuit down into individual sections, and test each one progressively.

In your case, if each wire had been taken off individually from the circuit, you would have likely found the problem earlier.

There is a knack to electrical wizardry.

I am a master of it.

But diagnosing over a chat type page makes it increasingly difficult.

But I have had successes.

For anyone else reading with interest, you need the following 2 items before trying to tackle it yourself.

A good multimeter and the ability to use it properly

A good schematic diagram of what you are working on.

Cheers

Rob

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#12 _jklumpp_

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Posted 22 August 2019 - 04:28 PM

Old cars can be a bit of a lucky dip with wiring.

The more owners its had, the more likelihood of dramas.

The trick to finding electrical faults is to break the circuit down into individual sections, and test each one progressively.

In your case, if each wire had been taken off individually from the circuit, you would have likely found the problem earlier.

There is a knack to electrical wizardry.

I am a master of it.

But diagnosing over a chat type page makes it increasingly difficult.

But I have had successes.

For anyone else reading with interest, you need the following 2 items before trying to tackle it yourself.

A good multimeter and the ability to use it properly

A good schematic diagram of what you are working on.

Cheers

Rob

And an understanding of what you're testing, and what results you should get & why....

Once I understood (or maybe 'remembered') that coil negative is used to 'fire' the HT output, I understood what I was testing, and that if I had a permanent earth there, the coil would not fire....