Ignition problem(?)

[aris64]

Hi to all! My engine is 1608 cc and few days ago I installed my new 123 distributor using my existing BOSCH Blue Coil. I don't know how old is but its colour is fade and certainly should be on the car the last 30+ years. Primary winding resistance 3 Ω as expected. When starting the engine everything was fine and current draw (as per 123 BT interface) is 3.8 Amp. After half an hour of normal driving in ambient temperature 30+ deg. Celcius, I felt small hesitations from the engine like misfiring, I kept going to complete my journey (about 4 hours driving on the highway) with RPM about 3500-4500 the problem became more distinct. I stopped to check, the coil was hot, I could touch it but not to keep my hand on for more than 2-3 secs and the current was now less 2.6-2.8 Amp (increase of primary winding resistance?). Misfiring was there clear and obvious, but the engine was responding well in the acceleration even in high speeds but misfiring was there all the times. Next day, when coil was cool the current was again 3.8 Amp, no misfiring but now driving was much more cool in the city. All other parts are new, plugs, wires everything as the car restored few months ago. The engine without load runs fantastic in the whole RPM range like a charm. Fuel pump is electric and new as well. All symptoms are saying that coil is tired and very old so a replacement already ordered. But I would like to hear your opinions, am I missing something?

[18Fiatsandcounting]

I don't have any experience with the 123 ignition, but yes, a failing coil could cause misfiring. Is the coil on the exhaust side of the engine, or on the intake side? Normally, the coil shouldn't get any hotter than anything else around the outer edge of the engine compartment, but on the other hand, 3500 to 4500 for 4 hours is going to heat things up pretty good. Plus, an ambient temperature of 30 oC is fairly hot, maybe not excessively so, but coupled with the sustained engine speed, an old coil might start showing issues.

-Bryan