Misfire and rough engine run

[Lemon_Belve]

First of all, I have to say that it always proves true: never touch a running system.

But now to my problem

It's a 69 440hp engine.
Electric ignition (no name to identify on distributor), Orange mopar performance box, Taylor ignition wires.

It ran fine before, started maybe a little bad but otherwise really top running and performance.

Now I started to change the spark plugs.
Before Autolite 85, now NGK xr5 3332

One plug was really shitty to tighten (second from the front, driver's side), because everything is in the way.

Well, I took the plugs off and put them on one by one so as not to mix up anything.

It starts noticeably better now, is right there.

However, it now misfires on mass under load. In addition, the warmer it gets, the crappier and more jerky it runs. It's really bad, I can't
I can only let it roll.

If you gently increase the revs at idle, it does that, but if you only give it a light burst of throttle power, there's a direct pop in the exhaust under the car.

I suspect the distributor cap because the carbon pin no longer looks good to me.

Maybe it broke off somehow when I plugged it on and off?

Do you have any other ideas what it could be?

The distributor will hopefully arrive from the Part shop in the next two weeks.
Then I will change the ignition cables to MSD 8.5mm Super conductor, as the spark plug connectors engage much better.

Attached are pictures of the old plugs and the distributor.

 

[SlinktRR]

You can clean up and put the old plugs in, or pull wires to check if there is a specific cylinder causing the misfire. If this is a stock iron head build I would just stick with the autolites.

 

[pnora]

Well you did not have that problem before so you did something. Double check your firing order. If ok pull one wire at a time and see if it changes anything. It might help pinpoint it to one cylinder. If nothing is found pull the plugs and inspect them. Start with the one you had troubles with. You could of cracked the porcelain.

 

[khryslerkid]

Looks like the carbon contact in the center of the dizzy cap is broke off. Need a clearer picture.

 

[pnora]

Looks like the carbon contact in the center of the dizzy cap is broke off. Need a clearer picture.

It looks to be there but has some wear. If the rotor is ok and still hitting it ok I doubt that is the problem.

 

[Carcinogen]

Sounds like a bad new plug/wire or 2. Been a lot of problems with new parts lately. Try another set or clean old ones.

Check resistance in new plug wires with multi-meter, might have a bad one.

Does it rev ok without a load and only misfire when under load, might be too wide plug gap or coil is getting weak, also check for proper voltage at coil, might be ballast going bad (if using one).

Also, If you drop a plug you are not supposed to use it.

 

[Lemon_Belve]

I dont know anymore, but it can be possible that I dropped one. The Spark plugs are the old ones

I will test the old plugs on monday
But from this I also dropped one...

New ignition coil, Spark plugs and Distributor Cap are also on the way. But for the fact I live in Germany, summit is not the fastest way to get new parts

 

[glenns hc]

That cap looks fine , you could have cracked the porcelain on a plug , damaged a wire pulling the boot off the plug now you have spark either jumping to ground , or no longer connected to the electrode . Or when you screwed the plug in , gunked it up with old dirt and oil near the holes.

 

[glenns hc]

I’d double check the firing order just to do as well , never know

 

[Don Frelier]

It's not clear which parts you replaced.

I have had bad plugs right out of the box and they were usually autolites.

Get some rubber gloves and pull one plug wire at a time. Then try replacing that spark plug.

 

[dan juhasz]

i agree with glenns hc, most likely you cracked a spark plug insulator on the install or in handling the plug wires created an open. take out all the plugs and looked for cracks, ohm out all the wires.

 

[Skytrooper]

It's not clear which parts you replaced.

I have had bad plugs right out of the box and they were usually autolites.

Get some rubber gloves and pull one plug wire at a time. Then try replacing that spark plug.

Don, is on the mark with this ! I was pulling my hair out when mine wouldn't idle or accelerate without back firing. We (ok..Don) discovered that 4 of the 8 brand new, out of the box Autolites were garbage. Switched to Champions and it fixed the issue.

 

[Lemon_Belve]

Also one guy talked to me in our German mopar Forum, that the Gap of the NGK are bigger as of the autolite.
I get in tuesday or wednesday 10 new and 20 good used autolites to Test

 

[Lemon_Belve]

I found the Problem After Installation of the old Autolite 85 everything is fine

 

[Skytrooper]

ouch ! Glad you found the issue !!

 

[Lemon_Belve]

It's very interesting.
One of my old Autolite were dropped and I need to open the gap. But also with this issue it's run so good.

The new Autolite will come tomorrow so I will Change the one

 

[SlinktRR]

I would send that one to NGK quality control...

 

[Lemon_Belve]

I worked in the past at Automotive supplier. It make no Sense if there not more than 10.000 fails per Million produced items