No spark, need suggestions

[kudu]

I just purchased a ‘78 620 that has no spark. I did new coil, wires, and plugs but nothing has changed. I also did a new distributor granted it seemed the same apart from the bottom shaft part of it was a millimeter or two longer than the one i pulled out of it but again still no spark. I had been suggested by someone I know to try bypassing the wiring and going with a hei. Before I do that I was wondering if there’s anything I’m overlooking? (The truck did run about a month ago when I originally looked at it but when I went to pick it up it had no spark and he had only driven it once during that month and it drove fine)

[datzenmike]

I hope to god you didn't throw out the original coil and distributor. Throwing parts at a problem is expensive and most replacements are poorer quality. You probably have a crappy distributor and coil that may also be 'bad in the box'. You may have made fixing this harder than it needs to be. As replacing the coil and the distributor didn't help, and IF you still have them.... put them back on.

 

Now we can trouble shoot this and replace what's really wrong.

 

 

 

Get a test lamp or meter and check the coil positive terminal for power when the ignition is turned on. You have to have power here to power the coil and the electronic ignition. So got power or not?????

 

 

[kudu]

14 hours ago, datzenmike said:

I hope to god you didn't throw out the original coil and distributor. Throwing parts at a problem is expensive and most replacements are poorer quality. You probably have a crappy distributor and coil that may also be 'bad in the box'. You may have made fixing this harder than it needs to be. As replacing the coil and the distributor didn't help, and IF you still have them.... put them back on.

 

Now we can trouble shoot this and replace what's really wrong.

 

 

 

Get a test lamp or meter and check the coil positive terminal for power when the ignition is turned on. You have to have power here to power the coil and the electronic ignition. So got power or not?????

 

 

I do have all of the original parts. Everything apart from the dizzy was done by the previous owner in an attempt to fix it but i did the dizzy myself just because a friend of mine had a reman one. But I just printed out the oem wiring diagrams at work so tonight i’ll be probing wires and seeing what’s going on and hopefully get to the root of the problem. I’ll update when that happens.

[datzenmike]

Check the coil positive terminal for power when the ignition is on. This powers the coil and the electronic ignition. If you don't have one get $5 a 12v test lamp.

 

 

 

[banzai510(hainz)]

your see if spark come out of the center plug wire to ground?

 

I would ck to see if you get 12volts at the + side coil.  this happens when you turn the key ON and the power goes thru fuse box to the ignition coil and on a 78 has a remote EI box I think.  if you have the 12volts then maybe the box went bad. here where the HEI module and drawing (How to section on EI) might help.

 

most coils dont go bad,

Im not famliar with the remote box ignitions but Mike will guide you thru this.

 

I would ck the ignition fuse or fuses where ever they are on a 620

[kudu]

4 hours ago, datzenmike said:

Check the coil positive terminal for power when the ignition is on. This powers the coil and the electronic ignition. If you don't have one get $5 a 12v test lamp.

 

 

 

I forgot my power probe at work but I used a multimeter on the positive and negative on the coil and got 10.49 volts. That’s with all of the original stuff back in except i left the plugs and wires the new ones.

[datzenmike]

Should read closer to battery. What does the battery read???

 

 

This is a remote igniter on the '78 so the coil reading does not power the EI only on the later '79 matchbox type. Still I would expect the coil power to be higher.

[kudu]

2 minutes ago, datzenmike said:

Should read closer to battery. What does the battery read???

 

 

This is a remote igniter on the '78 so the coil reading does not power the EI only on the later '79 matchbox type. Still I would expect the coil power to be higher.

battery is 12.4 and yeah me too i would expect it to be almost the same as the battery voltage

[datzenmike]

Use one jumper cable to apply 12v directly from the battery?

 

 

 

I see that you bought it 'broken' so.... as previous owners are all idiots, there's no telling what damage was done to it. If that does not work then we can assume that (maybe) the voltage is normal. As you tried another distributor we can assume (again) that the pick up coil is ok. This leaves the remote igniter box in the cab beside the glove box. Have a look and see if it is there. It's on the kick panel on the passenger side up out of sight to the right of the glove box.

 

 

If missing this makes it easier and we swap in an HEI module from an older GM product.

[kudu]

21 minutes ago, datzenmike said:

Use one jumper cable to apply 12v directly from the battery?

 

 

 

I see that you bought it 'broken' so.... as previous owners are all idiots, there's no telling what damage was done to it. If that does not work then we can assume that (maybe) the voltage is normal. As you tried another distributor we can assume (again) that the pick up coil is ok. This leaves the remote igniter box in the cab beside the glove box. Have a look and see if it is there. It's on the kick panel on the passenger side up out of sight to the right of the glove box.

 

 

If missing this makes it easier and we swap in an HEI module from an older GM product.

running a jumper wire had the same outcome. and yes it is still there but the previous owner did give me a hei granted not sure if it’s the correct one but I have one. I saw the car running in person about a month ago and it say for about 4 weeks before i picked it up and had no spark when he went to move it the day before i came to pick it up.

[datzenmike]

You tested for spark? or assuming no spark because it didn't start? Stick an old plug in the coil wire and lay on a grounded surface. Turn with starter.

 

I can't see why sitting would cause no spark.

[kudu]

1 hour ago, datzenmike said:

You tested for spark? or assuming no spark because it didn't start? Stick an old plug in the coil wire and lay on a grounded surface. Turn with starter.

 

I can't see why sitting would cause no spark.

yeah i confirmed no spark, that’s the first thing i did when I got the truck to my house. I’m the type where i don’t trust anyone’s work or diagnosis most of the time. I did it with a screw driver in the plug wire resting just slightly off or the valve cover but same concept. Yeah I’m surprised too.

[datzenmike]

Well the HEI can be got very cheap, ($10-$20 or drop one in your pocket at the wrecking yard) so why not wire that in? There are some checks you can do on the remote igniter box but you pretty much need an oscilloscope.

 

 

Module must be well grounded. If fail to spark reverse the red/green wires.

 

Ignore the 1.6 ohm coil resistance. Use your original EI factory coil.

 

 

 

Don't spend more that $20 and don't be fooled by 'Flame Thrower' or 'MSD' or High Output' it's just an on off switch and the coil makes the spark....

 

https://www.amazon.ca/Baosity-Ignition-Distributor-High-Coil-Reliability/dp/B07MFTG7TS/ref=sr_1_13?dchild=1&keywords=HEI+module&qid=1634089785&sr=8-13

 

[kudu]

59 minutes ago, datzenmike said:

Well the HEI can be got very cheap, ($10-$20 or drop one in your pocket at the wrecking yard) so why not wire that in? There are some checks you can do on the remote igniter box but you pretty much need an oscilloscope.

 

 

Module must be well grounded. If fail to spark reverse the red/green wires.

 

Ignore the 1.6 ohm coil resistance. Use your original EI factory coil.

 

 

 

Don't spend more that $20 and don't be fooled by 'Flame Thrower' or 'MSD' or High Output' it's just an on off switch and the coil makes the spark....

 

https://www.amazon.ca/Baosity-Ignition-Distributor-High-Coil-Reliability/dp/B07MFTG7TS/ref=sr_1_13?dchild=1&keywords=HEI+module&qid=1634089785&sr=8-13

 

alright sweet thank you. He grabbed one from Napa that he gave to me that looks the exact same so i’ll hook this up tomorrow after work and see what happens. For the wires going to the “on” and “start” positions i assume those are new wires that have to be ran right or can an existing wire be used(i would think the on one could be an existing since that still seemed to work or am i off in my thinking)? If so which wires on the ignition switch would i need to tap into(obviously i’m new to these cars so i just didn’t want to tap it in wrong and think it doesn’t work)?

[datzenmike]

The coil positive is a switched supply from the ignition and should work fine. There won't be a start wire on an EI set up.

[kudu]

12 hours ago, datzenmike said:

The coil positive is a switched supply from the ignition and should work fine. There won't be a start wire on an EI set up.

So i don’t need to run those two extra wires off of the positive in the diagram(“on” “start” wires)?

[datzenmike]

You will need the one already on the coil positive terminal... that's the ON signal from the ignition switch on your '78. There will be no START wire.

 

This diagram is for replacing an earlier truck or car points system using a '78 EI set up and will have an ON and a START for the ballast resister.

[banzai510(hainz)]

first I would resea the elelctrical plug on the remote box in case its just a corrossion issue right there. If that dont fix then maybe use the GM module.

 

as Mike said just ignor that part of the drawing  for the ON /START.  you have this already set up on your 78  you cust need to know C goes to - side coil B goes to +side coil

 

if that dont work then maybe the pickup in the coil. but I think there is a wasy to ck that also

 

 

if you can post a photo of the coil area under the hood would be nice also if possible

Edited October 13, 2021 by banzai510(hainz)

[datzenmike]

1 hour ago, banzai510(hainz) said:

 

 

if that dont work then maybe the pickup in the coil. but I think there is a wasy to ck that also

 

 

 

The replacement distributor also didn't work so I assumed two pick-up coils wouldn't be bad.

[kudu]

6 hours ago, datzenmike said:

You will need the one already on the coil positive terminal... that's the ON signal from the ignition switch on your '78. There will be no START wire.

 

This diagram is for replacing an earlier truck or car points system using a '78 EI set up and will have an ON and a START for the ballast resister.

So not sure if I’m doing something wrong but there was still no change in the outcome. I followed the diagram exactly

[datzenmike]

1 minute ago, kudu said:

So not sure if I’m doing something wrong but there was still no change in the outcome. I followed the diagram exactly

 

Did you try reversing the red and green wires?

 

 

 

 

Take distributor cap off and turn engine with key. Is rotor turning?

[kudu]

8 minutes ago, datzenmike said:

 

Did you try reversing the red and green wires?

 

 

 

 

Take distributor cap off and turn engine with key. Is rotor turning?

i did reverse the wires and the rotor is turning. I can send pictures of things if need be

[datzenmike]

Make a jumper and briefly ground and then release from the coil negative terminal, with the ignition on. Should spark every time you remove the ground.

 

 

HEI module MUST be grounded!!!

[kudu]

10 minutes ago, datzenmike said:

Make a jumper and briefly ground and then release from the coil negative terminal, with the ignition on. Should spark every time you remove the ground.

 

 

HEI module MUST be grounded!!!

nothing happened with the jumper there was no spark. And the hei is bolted to a piece of aluminum that is then bolted to the chassis.

[datzenmike]

Well from the information supplied Positive is 10 v on the positive terminal then the coil is bad. Check the positive terminal once more for voltage with ignition on.

 

If you have 10-12 v then replace the coil.