1983 720 No Spark

[TheMrFlippers]

Truck recently has a no spark issue, oddly enough it happened after the carb was rebuilt and replaced. Have replaced the ICM, and the Ignition Relay, as well as the Rotor. Truck will sometimes start cold, sometimes not. Will shutoff once it gets warm, and not restart. When it refuses to start, there is no spark at either coil (tested with a coil tester.)

 

I appreciate any help.

[datzenmike]

When it quits, get a volt meter and measure the voltage on the + positive terminals of the coils.

 

If you have 12 v or so try measuring it again when trying to start it.

 

If you still have 12v when using the starter, take the rotor off and check for voltage on the middle of the three terminals of the ignition module.

 

 

See what results you get....

[TheMrFlippers]

I will test that while I’m at the shop tomorrow. It has new coils as of today (keeping all original parts.) Another symptom, there is a definite misfire, thought it doesn’t cause any shaking. You can hear it from the exhaust, and see a slight shudder from the engine. RPM’s are staying high for quite a bit longer then normal as well, took quite awhile on this last start for me to get it to drop below 2k.

[datzenmike]

Fast idle...

 

Carburetor has to be open slightly to let in more gas and air. After warm up, about 10 minutes, check that the choke plate is fully open and in the vertical position. Part of the choke circuit is a fast idle cam that prevents the throttle from closing fully. The higher revs warm the engine faster. When the choke warms up and slowly turns off the fast idle cam is released and the throttle can close to it's warm idle speed setting. The fast idle cam may have stuck.

 

Plugs, cap, wires and rotor do wear out or go bad with age but seldom do the coils cause a problem. Never replace them unless you have proven positively that they are not working. The chance of one bad coil is unlikely in the extreme, two coils bad is impossible. Unless you replaced with a genuine Nissan part there is a good chance that the 'new' coil is inferior to the original.

[TheMrFlippers]

Carb was just completely gone through and rebuilt, by about the only decent shop I personally know of in AZ. However I will definitely check the choke plate as well, once I get it to actually warm up. She may run for 3 minutes max before shutting off. This ignition module has 4 terminals, wires from top to bottom are (Blue, Black w/ Yellow Stripe, Orange, and Red.) 
 

The truck sat for quite some time (father bought it brand new in 83 off the California coast.) Occasionally I would head over and run it for 30 minutes to an hour just drive it and keep it going. The entire issue started when the accelerator pump started spraying fuel, the carb was also in need of a rebuild as it had never been off the truck and it sat consistently (only 125,000 miles.) Put the carb back on and then the random no starts/shut offs started. 
 

Only reason I swapped coils was due to ease of access with parts (shop’s dime, easily returnable) and crossing things off the list. Coils are Delco’s, probably not as good as OEM, but certainly better then Standard which are the only other options.

[TheMrFlippers]

Problem solved, definitely a face palm moment. Went through the system again, tested voltage, tested key on power, tested the ignition switch during warm and cold cranking. Tested voltage in hot and cold conditions at the coils and ignition module. Found no issues, only that it wasn’t starting. Followed the wires on the bottom of the distributor up to the junction box next to the vapor canister on the driver fender well. It has 3 studs and 3 nuts holding the connections in place, found the third nut (one closest to the firewall to be loose and for some strange reason missing the washer. Repaired connection with a new washer and tightened down. Ran truck for an extended period of time, no issues whatsoever. Now to swap back all the old ignition pieces, new module is causing the misfire (only happened once replaced) and the old coils are obviously good. 
 

Now on to the next steps in getting her DD worthy.