No spark! Tried a new coil, still no spark

[Captkaos]

If it was a factory 84, it has ESC, it was standard on all trucks.  Not a 400 didn't come it in though, so you would think the ESC was gone.  How may wires does your distributor have on it for the coil plug?  That is an easy way to tell if it has ESC.  If you find it does have it, and it is possible based on the way it is acting, you should just bypass it completely.

Read this for reference:
http://73-87.com/7387garage/drivetrain/escrepl.htm

[buddy84GMC]

Thanks a lot.  Thats good to know since my 400 should not have an ESC and I know my distributor has wires going to the computer above the glove box.  I traced those wires to see if they were broken before I took the control module out of the dist.  If I am not mistaken, the ESC should be the 'computer' above the glove box and it has a long parallel port similar to what you see on computers; right??? 

The only thing I can say is that there were no signs of the truck ever going to stall or the pick up wires being broken since I was told the truck would have seemed to miss as the distributor rotated which would have been the wires being snapped off when the engine was accelerated.  The truck shut down when I accelerated, but there was no signs of hesitation before that.  So, if the pick ups are ok, then I can lean towards this ESC issue.  What are the chances the ESC worked before with my 400 and all of a sudden does not anymore?  Could it have shorted out?  I can bypass it and this seems to be my last resort if the pick up wires are not broken.  I have not pulled the distributor yet, but hope to in the next day or 2.  Thanks for all the help again.

[Captkaos]

The box above the glovebox is the ESC on carb'd vehicles.  the likelyhood of it dying all of the sudden it not out of the ordinary.

[buddy84GMC]

I did what the article Chris posted said and still no good.  I bypassed the ESC and soldered the 2 wires that needed put together and plugged the pink ignition wire directly to the BAT terminal.  Gave it a try and still no start.  I will have to have the coil checked and the control module again.  Could it be the pink ignition wire gone bad?  Maybe snapped off somewhere, but not sure if that would cause all this.  Thanks for any more pointers. 

[VileZambonie]

If the engine sounds normal during cranking and you have B+ at the ignition coil then check the ignition module and the pick up coil. Disconnect the pigtail at the module and measure the resistance of the pick up coil. spec is 500-1500 Ω typically you'll find 800Ω on a good one. If the pick up coil is good replace the module.

did you do this?

[buddy84GMC]

I tried to that a few days ago after trying a new coil.  I do have a voltmeter but am not sure how to read it well since there is no 800 on the Ohms scale, but I have to figure out how to convert the reading I guess.  The manual sucks and does not explain a thing.  It does sounds normal when cranking though.  I will try to read the meter again but I know I am missing how to multiply something to get the actual reading I need.  Its an old one and a crappy one at that.  Thanks

[blast]

The wire connections on the magnetic pickup wires inside the HEI distributor of my 1990 c1500 are intermittent.  I occasionally lose spark, and have to remove distributor cap, and wiggle the two yellow wires that connect to back of the ignition module under the distributor cap.  Then I'm good for a few months to a year.  Then it does it again.  Really irritating.  I have another distributor to put in when I get the chance.  Maybe give those wires a wiggle and see what happens.

[VileZambonie]

Why not just replace the pick up coil rather than wiggling the wires and hoping it doesn't fail you again? It's a $12 part.

Buddy:
You can't read ohms scale on the volts scale. Select the 2KΩ scale if it's not auto ranging and measure across the two leads when you disconnect them from the module. Post your results.

[blast]

Why not just replace the pick up coil rather than wiggling the wires and hoping it doesn't fail you again? It's a $12 part.

Everything under the cap is a big ball of rust, truck has 250K miles on it now, was waiting for another distributer to swap the whole thing out.  I just picked up a good used one last weekend for free. 

[buddy84GMC]

I did what I could and it did not give me a reading.  I know it worked 2 days ago, but I was in a hurry to get down to the store have the control module tested again and it passed 5 times.  I bought a pick up coil in case since the only thing left to do is take the distributor off since I cannot find a way to get the voltmeter to give me a reading. 

One other comes to mind...I did bypassed the ESC by following the article and I know it did it right, but the one thing he never mentioned was about plugging anything back in or cutting the blue wire that goes in front of the started on the knock sensor.  Thats the only one thats still conected to the truck, but disconnected at the computer ESC.  There is still the vacuum line for from the ESC vacuum switch that is still connected as well to the carb.  Should I block this off???  What about that blue wire to the sensor?  Still having no spark and I am pretty sure the pick up coil wires are in tact since I have wiggled them before and they did not pull out or seem damaged, I have a few more questions.  What about my control module...It had 5 prongs 2 on one side and 3 on the other.  The yellow wire is the middle prong but thats part of the connector I disabled coming from the ESC.  Should I replace the control module with a 2 and 2 prong one???  I have no clue, but I did disconnect that harness from the ESC.  I put the 2 wire green and black together like I was supposed to as well as part of bypassing the ESC.  I just hope I did not miss anything.  I bought the pick up coil and it has only 2 prongs to plug into and my old was has 3 since the control module has 3 prongs...I might have to take a picture to show you what I mean.  let me know if you need a photos of my setup.  Seems to me like its a little different than others. Thanks

[buddy84GMC]

I was on the 73-87 site and found out that if I get no reading from the pick up...might be the culprit.  I mean there was no reading at all, but I ran the meter on my control module and it gave no reading but did 2 days ago...I will replace the batteries and give it a try again.  Still puzzled on how I am going to plug the new pick up coil with 2 inlets into the control module with 3 prongs? 

[Blue 82]

pictures please

[Blue 82]

There are two color codes for the in-cap ignition coils:

Red and Yellow wires  Used on vehicles that use the Yellow coded pickup coil.
Red and White wires  Used on vehicles that use the Blue/Black, or Clear pickup coils

These coils may have different color codes, but NONE OF THEM is a HIGH PERFORMANCE/BETTER/FASTER/MORE POWERFUL version of another.  You don't get stronger sparks with a yellow-coded set than the others.  The ONLY difference is that when you pass an electric current through them, they produce a magnetic field in opposite directions.  Note that for the Blue/Black and the Clear color coded pickup coils, the lead wires and the plastic connector (if used) are arranged in such a way that the wires must be crossed in order to connect them to the module.  The Yellow-coded pickup coil wires plug in without crossing.  This maintains proper ELECTRICAL polarity, while allowing reversed MAGNETIC polarity.  And magnetic polarity is only important at low engine speeds, (especially cranking) because of electrical interference from the starter or perhaps the alternator--If the interference is "just right", the module gets a false trigger signal.  Using the correct magnetic polarity pickup coil can eliminate the interference, and the correct magnetic polarity ignition coil is needed to match the pickup coil.  You "can" mis-match the parts, but don't complain if the engine takes longer to crank or misfires during cranking.


Look at the wires for the pickup coil
on a vacuum advance disty they move back and forth millions of times because the coil is connected to the vac advance. (the one in the pic is locked in place)







The thin pickup coil lead wires have had a history of failure due to the motion of the vacuum advance.  The problem often starts showing itself as the engine dying, then running, then dying, then running, etc.  When the vacuum advance moves the pickup coil to a certain position, the broken conductor inside the insulation of the wire disconnects, and the engine dies.  When the engine dies, vacuum is reduced, the vacuum advance relaxes--and the broken wire re-connects and the engine runs again.

the plug should be disconnected from the module to test
mine read 830 ohms

[Blue 82]

Try this test
hook up a wire to the disty
using a female spade connector
connect to your battery

now try it

[buddy84GMC]

Here is my set up.  I would have to think that the pick up coil they gave me was wrong even though I had the control module right there with me.  I almost need an double ended pick up coil to make this work.  The pick up coil connector is located between the control module and the wires that came from the ESC that I modified by cutting and crimping the 2 cut wires together like I was supposed to.  Let me know what you think.  Thanks a lot.