Sanity check on dual points conversion

[z3beemer]

Have not checked the coil but it's cheap enough to just replace it to eliminate the possibility.

[Yarb]

Check the ohm rating in the FSM for your car. Amazon has a good selection including Bosch. One of the 240 guys here could probably advise.

[Captain Obvious]

The symptoms of breaking up worse under load do make me think of an ignition related issue. Your different colors on the plugs might be a tuning issue as well, but load dependent misfires would have me looking at ignition stuff first.

Plug wires arcing to ground somewhere, or coil wire arcing over to someplace it should not be going.

Have you put in new cap/rotor/wires? 

[zKars]

We had a case here recently with high RPM misfires that turned out to be a poor fitting distributor cap that must have been moving around at higher vibration levels at high RPM’s. You could wiggle it with your hand, wouldn’t seat square and tight.  Replaced it with a new cap and viola as they say, revs to the moon with no mis-fire.   Ignition systems rely on a in-spec gaps and fitment, any “Extra” energy lost with a too large gap (or inconsistent gap) and resulting spark, results in a weak plug spark and mis fire. 

[SteveJ]

2 hours ago, zKars said:

We had a case here recently with high RPM misfires that turned out to be a poor fitting distributor cap that must have been moving around at higher vibration levels at high RPM’s. You could wiggle it with your hand, wouldn’t seat square and tight.  Replaced it with a new cap and viola as they say, revs to the moon with no mis-fire.   Ignition systems rely on a in-spec gaps and fitment, any “Extra” energy lost with a too large gap (or inconsistent gap) and resulting spark, results in a weak plug spark and mis fire. 

This goes back to a thread somewhere on here about using an oscilloscope to diagnose ignition issues. I need to play around with that some more. You need an attenuator on your voltage input. That gets connected to the negative terminal of the coil.  It helps to use an inductive probe to put on the plug wire for #1. That will serve as the trigger for the scope, and you can trace the signal from the coil voltage to a cylinder.

Larger spikes on the coil voltage trace when the ignition is firing is indicative of having to overcome a larger gap. That gap could be at the rotor button, coil HV wire, or plug wire. There are videos on YouTube that explain this better than my quick summary.

[Mark Maras]

 The only time (in twenty plus years of spirited driving) I ever experienced an erratic misfire at high RPMs was cured with a new set of BP6ESs. My experience with a partially plugged fuel filter resulted in the car refusing to go above 45 mph in any gear but would freely rev to 6000 rpms under no load.

[zKars]

I thought of another mis-fire problem and the solution. Like Mark, it was related to the plugs. 

I used, and still use, NGK BPR6ES plugs. The issue I routinely run into with them, is that the end of the plug where wire snaps on, is threaded on to the plug, and is often loose. 

Several years ago (2015), a random issue with mis-fire throughout the range dogged me for a year or better, and when I finally discovered that one of the end caps was loose on a couple of plugs. Tightened them up, and the mis-fire went away. 

The BPR6ES-11 plugs that also spec'ed for 280's with EFI, don't have the threaded end cap. 

I described this WAY back in 2015. The thread lionk is below if you want to see pics.

 

EDIT EDIT : just doing a bit of a good search. NGK plugs BPR6ES  #7131  have the threaded caps, #4008 have solid caps! Jim, stop buying #7131 BPR6ES plugs you old idiot!

 

BTW, Don’t order the Denso #4008 plugs by mistake. They are NOT the same….. Just saying…..

Edited September 26, 2023 by zKars

[Mark Maras]

@jalexquijano Have you checked this?

[z3beemer]

Well, it appears that the problem was the coil.  I replaced it, and took several rides and problem appears to be gone.  I also took your advice and ordered new NGK one piece plugs, but haven't got them yet.  The finish line is in sight.  Thanks guys.

[Yarb]

Fantastic, start with the spark!! Cheap fix and good for the long haul.

 

[Captain Obvious]

Glad you got it running well.

However, just to make my little brain good with the whole ordeal... That same coil ran just fine with the original dual point distributor? Some ideas?

Been a long time since it ran at all and anything could have happened between then and now.
The coil was borderline before and your moving stuff around and angered the electrons in the coil.
Your car runs fine now and it just doesn't matter why changing the coil fixed it.

[z3beemer]

Never really ran it much with the dual points.  It did start but it was intended to be a restoration project since I purchased it.  All I can say is that it ran, not well but It had so many other issues I didn't worry about it too much. Thanks again to all for your help.  I have a few more minor gremlins to deal with but close to the finish line.