Chasing Intermittent Crank - No Start Condition When Hot

[Ron1200]

Hi 

I have a 1979 620, L20B, Matchbox Distributor with MSD Blaster 2 coil. My 620 typically starts easy. Normally, when cold, it starts within 1/4 to 1/2 of a revolution (longer if it sits for more than a week).

 

Within the last couple of months, it has occasionally refused to start (Crank - No Start) when hot and not allowed to cool (Like when you go into the store to by beer, and it won't start when I return to the car).  This condition is intermittent, but has been increasing in frequency.  Saturday took the 620 to the Tacoma Caffeine & Gasoline, drove from Olympia.  It died on Pine St but restarted after about 10 minutes.  Drove it back to Olympia but it died again, this time it refused to start at all.  So called for a tow home.  I couldn't start testing until the next day.  And the truck started immediately when cold. 

 

Originally, I was thinking It was a wiring issue with the connectors at the Ignition Module.  I've changed both connectors and soldered them to the wires. This obviously did not correct the problem.

 

From what I've read on the forums (Ratsun, Zcar, Datsun1200), a bad coil can cause a engine to crank - no start when the coil has not had sufficient time to cool. 

 

I went ahead and changed the coil to a Hitachi I had in my parts stash, but at this point I don't know if it's going to fix the issue as both coils test good when cold. 

 

This is what I found when I tested the coils at room temp:

MSD Blaster 2

                     Test     Spec

Primary        .7        .7  (meter at 200 Ohm)

Secondary   4.5      4.5 (meter at 20K Ohm)

 

Hitachi 22433-H7280

                     Test     Spec

Primary        1.0        .842 - 1.02 (meter at 200 Ohm)

Secondary   10.0      8.2 - 12.4 (meter at 20K Ohm)

 

Can a hot coil fail, but test good when cold?  Am I on the right track with my troubleshooting?  Anything I'm missing?

 

I hate Intermittent problems.....

 

Thanks

 

[Roadster-ka]

Confirmed no spark when it does not start?

[Ron1200]

When it died in Tacoma, there was no spark at the plugs.  I didn't check the coil. At the time I thought it could be Ignition module, coil or switch relay (DZ Start).

Edited July 10, 2018 by Ron1200

[Roadster-ka]

Possible pickup coil. When it fails to start, dump cold water on distributor with cap off. Or, you could swap distributor with known good unit

 

[datzenmike]

The EI definitely needs a SOLID ground. Some even have a terminal on the side for this.

 

The matchbox might be the cause if exposed to exhaust heat. But if not starting when cold this not this. Try unscrewing and cleaning the distributor area around it and put back on. Corrosion and bugs like to set up house behind them and they need air circulating around them. 

 

Take the coil wire of the cap and hold near a ground and crank the engine over.  It should jump the gap but may be jumping from the coil tower to the negative terminal if cracked or carbon tracked. Distributor caps can also be carbon tracked or cracked and the rotor.

[Ron1200]

Update: Had the truck out this morning, noticed a slight miss just before I reached my destination (about 15 min driving time).  On the way back, It started dying  after about 5 minutes. This time I had a multi meter and checked the following with the ignition on:

 

Coil connections

  Ignition/start wire to coil +  = 12v

  Coil + = 12v

  Coil - = 12v

Continuity tested

  Black/white from module to coil = good

  Blue from module to coil = good

Spark Plugs

  No spark

 

A friend suggested using a can of compressed air to cool the module and see if it starts.  Well, not having that but having a can of semi-cool diet coke, I dribbled the coke over the module and this seemed to work... but only for a mile or so. However it was repeatable, touching nothing else, this process worked five times in a row. 

 

I believe I'm here in my trouble shooting: 

  Cap & Rotor Good - Installed new parts

  Coil is good - changing out the coil did not fix the problem

  Ignition switch 12v power is good - When the problem happened, I had 12v at the coil

  Wires between the coil and ICM are good - When the problem happened, I confirmed continuity

  Ignition module is suspect - When cooled with coke, it would start and run for a short while

 

 

I have ordered a replacement ICM (STANDARD MOTOR PRODUCTS LX516).

 

Edited July 10, 2018 by Ron1200

[datzenmike]

Try cleaning the module. They can collect crap like bugs in behind it. The back face is solid metal and needs clearance between it and the distributor body. Most of all the ground might be so so. Just unscrewing it and tightening back on may fix it.

[Ron1200]

Thanks for the help...

I'll check behind the ICM Mike...

[datzenmike]

...and solidly grounded. They very seldom fail Ron and you can use a HEI module from a GM mulletmobile..

[Ron1200]

Just a note to close the loop... I installed a new LX516 and have had no issues since (about two weeks).

Seems that the engine starts easier and idles smoother.  Maybe its just the halo effect :)

 

Sorry Mike, I did not test after I loosened-tightened the screws (there was no crap behind the module).  I didn't want the 'cooling dance' hassle on the drive back if it started acting up again. 

 

Thanks for all the input guys.

[banzai510(hainz)]

next time no start ck the coil wire  to ground test and see if you get spark. If not maybe dist not telling coil to fire or coil is bad. I highly dought coil is  bad.