crusader 270 1987 , cutting spark after 20 minutes of running

[Wilsi]

Hi there ,
I hope that someone here, with more knowledge and experience than me , can help me , please.
I have been chasing this problem for over a year , so any ideas how to solve it are very much appreciated .
I have a Silverton 1987 with a pair of crusaders 270 350 8 cylinder engines.
Starboard engine started to cut off after 20 minutes of running ,after a minute will start no problem , but will run only for a minute before quitting again.
Before dying rps will start to drop down for 5 seconds or so, is not like a switch cut off .
After isolating the problem to electrical ,there is fuel on carb after cut off ,and test light at spark plug confirms that spark cuts off and misses sparks before dying completlly.

I replaced :
-Distributor cap
-Ignition Coil , Petronix flamethrower 1.5 ohm, oil filled
- Electronic Ignition, Igniter 1 Petronix ( for mallory 25/26 distributor)
-switch carbs with port engine ( both rebuilted recentlly), just in case .

Same results after this changes , spark cuts off after 20 minutes or so

Then
-Tested negative on petronix base plate at ditributor, same resistance from battery to base plate , as negative on battery to negative pole at engine
-Tested positive coming to coil , 12.8 volts
- just in case I replace the ignition switch , also running a new wire from ignition to coil to eliminate any resistance on positive after runing for the 20 minutes

Same results after this was done

Then
-I realized that the alternator was putting out 16 volts , way too much , so I replaced the alternator , now doing 14.3 v, prior messurements where done with the ignition switch on , not with engine running , my bad .
-Reconected the ballast resitor that I had disconected a while back , so now I have 12.2 volts on positive terminal at coil
-Petronix module still at 14.3 , petronix says is ok.

Still cutting off spark after 20 minutes of running
If I go now and start the engine it will start without any problem and run for 20 minutes
Any ideas ?
Thanks so much in advance
Wil

 

[makomark]

assuming your swap of the ignitor module was AFTER replacing the alternator, I'd say you can monitor the +12VDC feed to the coil and ignitor module and see if it disappears when the engine dies. You can also delete the ballast resistor if the flamethrower coil is still installed. the other option is to run the tests pertronix has - https://pertronixbrands.com/pages/ignitor-12v-troubleshooting.

Another thing to check is the harness connector between the engine harness and the dash harness...separate the two halves and check for corrosion. Clean as necessary and then reassemble...NYOGEL is an excellent lubicant for electrical connectors.

 

[Wilsi]

Hi Makomark !
I appreciate your response very much .
No , I didn’t replace the module after I found the alternator problem ,I did that before I knew of the overcharging situation.
It went through 4 or 5 ,20 minutes shutting down episodes with the new module ,and new coil before the new alternator .
I have read that the modules either work or not work , maybe wrong ?
Didn’t know there was a harness connector !
Is it near the engine ? I will look and clean
Do you think that the new module and coil are compromised?
Thank you Again
Wil

 

[Wilsi]

The Petronix test was done and everything checked ok , but with cold engine
The engine runs super smooth when starts from cold , maybe I should do those test when shuts off, no?

 

[Droid]

You have a good running engine 3' away. So swap parts 1 at a time until you discover your problem.
I would start with the ignition coil. Sounds typical of overheating coil. The 16 volts didn't go you any favors.