weak spark some backfire

[Dave WM]

yep, that's the same as mine. I got and aftermarket unit of ebay for 50$ IIRC, pulled my OE off to test it, left the aftermarket unit in place so I carry the hitachi as a spare. The aftermarket unit seemed to have fewer parts IIRC. I can see several electros in there that prob should be checked at least of not just shot gun replaced. I can't believe the engineers ever expected this kind of long term life.

[Captain Obvious]

Wow. Lot of changes from that unit to 77.

My 77 only has one electrolytic cap. Everything else is film.

 

[zclocks]

FOUND SMOKING GUN!!!!

I finally found the source of my miss and sometimes backfire thru AFM.

With all the things I had done I didn't look at the spark at the plugs. So...... I removed the spark wire at each plug, plugged in a spare spark plug and started the motor.  Each plug was firing, but VERY weak. To cut to the chase the ignition coil was the problem. Let me rephrase that....I was the problem.  I remove and replaced the coil many years ago for whatever reason. The Primary side coil resistance  is supposed to be 0.40---0.55 ohms, per service manual for the 75. The Fire  ball I put in there many years ago was 1.6 ohms. This might not seem to be a big change , but when I replace the coil with a "Flame-thrower -2" what a difference.

The new coil has a primary resistance of 0.6 ohms , but try and find a coil today which is 0.4 ohms is not possible.  I know I have my OEM coil , but at the moment I can't locate it .BTW this new coil is used with the OEM ballast resistor.

This is a good day!!!

 

PS : I should give credit to a u-tube guy with a site called "Restoration for beginners". He seems to have good understanding of basic mechanics

and after watching his segment on ignition systems, which covered coil replacement, he ran into the same problem with selecting coils. Oh yea his

car is  a 78 280z. 

Edited July 19, 2019 by zclocks
addditional info

[dutchzcarguy]

On ‎6‎/‎13‎/‎2019 at 8:54 PM, zclocks said:

What I am going to do is remove and clean all connections on the distributor, transistor ignition unit, and  injectors.

Good to hear you found the problem.. only thing i wanted to ad is clean your injectors with injectorcleaner.. you put it in the tank with some new gas and just let it run. most times these old injectors don't give the same amount of fuel each time they fire..  it's just an extra.. maybe it will run even better after a good clean.