High RPM Miss 340

[74 340 4speed]

if you upgrad the ECU go to the Chrome box
 might be worth checking the wires , under higher load they can break down especially if the iwre has been pinched or pulled or burnt

What should an acceptable resistance be Chryco?  I have an ohm meter. I can check this out this weekend.  The wires aren't that old, or burnt, but that doesn't mean there couldn't be some sort of factory defect.  What distributor would you recommend me getting?  Is the mopar performance unit any better than a rebuilt stock one?  Should I get a MSD or mallory unit?

If I got this kit,




What would I need to do with my current wiring harness that accepts the four pin ballast, to modify it to accept the two pin ballast?  Is it necessary to run a 2 pin ballast with the chrome box?

[Chryco Psycho]

the new Mopar  Performance dist is a better piece with adjustment to limit both the vacuum & mechanical advance , if you have the Mopar ECU in the car now the Chrome box will just plug in , you should replace the ballast with the lower resistance one in the kit , the side of the dual ballast with the green wire is not used , the Blue wire powers the ECU
 the resistance depends on the type of core used inside the wore , just test to be sure they are all close to equal resisitance
 The Crane , Mallory & Msd are all similar products but the MSD will be 2x the cost , I would upgrade the coil to a high output coil though

[74 340 4speed]

Thanks Chryco!  I've got something to keep me busy over the holidays now. 

[cudabob496]

I think plug wire resistance should not exceed about 10 ohm per foot of wire length, but I'm going on memory. With high performance wires its much better.

[cudabob496]

http://www.moparaction.com/Tech/ques...H_BALLAST.html

http://www.moparaction.com/Tech/ques..._BROOKLYN.html

http://www.moparaction.com/Tech/quest/ROUNDY-ROUND_MIRADA.html
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[Aussie Challenger]

  Missing can be a hard thing to find, going on what you have written I would make sure that the coil is a ballast coil, you may want to upgrade this. Also unless the motor is spending most of its time above 4,500 rpm I would think that the NGK spark plugs BPR7ES is a bit cold and may be fouling. I would use BPR6ES or BPR6EY gapped at no more than .040.   

  David

[74 340 4speed]

http://www.moparaction.com/Tech/ques...H_BALLAST.html

http://www.moparaction.com/Tech/ques..._BROOKLYN.html

http://www.moparaction.com/Tech/quest/ROUNDY-ROUND_MIRADA.html
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first two links don't work for some reason.

[Mt.St.BigBlock]

Hi, I think the best clue is in the very first post. After the vac advance was disabled the problem
moved up the RPM band some. I'm thinking its a reluctor phasing issue in the distributor. I've read
in the rags about it but can't remember which or when to reference you to. They had a test for it
and a fix but don't remember the details. I'll have to look thru my files for it. I keep all the tech-how-to
stuff from all those magazines and throw away the rest when I'm done. If I find it I'll update you.   Jeff

[74 340 4speed]

I bought the mopar performance electronic ignition kit.  The one that contains the distributor, chrome 8000 rpm box,  ballast resistor, and wiring harness.  What should I gap my plugs at with this kit?  I have them gapped at .045" now and I have been told previously in this thread that this was too much for the stock setup.  I want to make sure I have them set properly for this kit.

the new Mopar  Performance dist is a better piece with adjustment to limit both the vacuum & mechanical advance , if you have the Mopar ECU in the car now the Chrome box will just plug in , you should replace the ballast with the lower resistance one in the kit , the side of the dual ballast with the green wire is not used , the Blue wire powers the ECU
 

This is a wiring diagram I found Chryco.  So, I do not use the side of the ballast with the green/red wire and brown wire?  Do I plug the blue wire onto one side of the new 2 pin ballast resistor?  What wire do I plug into the the other side of it? The brown one that goes to the hot side of the coil?  I'm not great with wiring, and I just want to be sure that I get it correct.  I'm taking mechanical engineering in school right now, and I had to take one electrical engineering course back in the summer to meet the one class requirement for my degree.  It wasn't easy to say the least, lol.  I like the mechanical side of things, gears, levers, linkages ect...

[Chryco Psycho]

you have it right , the blue wire & the brown wire to the coil + connect to the ballast
 spark plug gap is determined by the power of the coil , , if the coil is a high output one .045 is fine if you have a good quality ign wire as well , if the coil is still stock set to .035

[hemiken]

Another good way to check the leads is to run the engine at night in total darkness and rev the engine up to break down point, watch the leads and look for any sparks jumping from lead to lead and look at the boot of the leads to see if their is any problem with spark jumping through the boots.

[74 340 4speed]

you have it right , the blue wire & the brown wire to the coil + connect to the ballast
 spark plug gap is determined by the power of the coil , , if the coil is a high output one .045 is fine if you have a good quality ign wire as well , if the coil is still stock set to .035

Thanks for the help!

[Chryco Psycho]

 
Welcome!

[74 340 4speed]

I got the kit installed and the car runs great now!  It has better throttle response, the missing was eliminated and it feels like it has more power.  I took it to about 6500 in 2nd and 3rd on the test drive and it felt awesome!

[Chryco Psycho]