One of our members was dealing with a Datsun 411 J13 engine issue where it runs well until it warms up, then begins to misfire, especially in cylinder four.
Here’s a summary of potential causes and solutions based on the details shared:
Possible Causes:
Ballast Resistor Issue
Without a ballast resistor, the coil may receive too much voltage, causing it to overheat and fail. A failing coil could lead to misfiring, particularly when the engine is warm.
Ignition System Components
Even though ignition system parts (cap, rotor, wires, plugs, etc.) may have been replaced, if any of these parts are faulty or not properly installed, it could cause issues as the engine warms up. The absence of the ballast resistor (if needed) could have also damaged the new coil, leading to further problems.
Cylinder Four Specific Issue
If cylinder four consistently misfires when warm, that tells us there’s a specific issue related to that cylinder. As long as the compression is fine (within 10% of the other three cylinders), other factors like a faulty spark plug, wire, or even a problem with the cylinder’s fuel delivery could be at play.
Suggestions:
Check Ballast Resistor Setup
Ensure the ballast resistor is present and properly wired if required by your setup. Verify the ignition switch and wiring as well.
Double-Check All Connections
Re-inspect all connections in the ignition system, ensuring nothing is loose, corroded, or improperly installed.
Test Coil Resistance
Confirm the coil resistance values. For a non-internal resistor coil, 1.5-3 ohms sounds correct, but verify it matches your setup’s requirements. You can reference the Datsun 411 Factory Service Manual here.
Examine Cylinder Four
Swap spark plugs and wires with another cylinder to see if the problem moves. If it does, the issue is likely with the spark plug or wire. Don’t forget to check resistance (ohms) of all four wires. If one is significantly different than the others, there’s your issue.
Fuel System Check
Consider checking the fuel system related to cylinder four. Although a carbureted engine isn’t going to present the issues that an injected engine may have, a fuel delivery issue (such as vapor lock, clogged filter, or a blockage in the intake runner might only become apparent when the engine is warm.
By systematically addressing these areas, our J13 friend (or you) should be able to pinpoint the issue.