Lately, I"ve been having what feels like a cross fire issue at idle with my 78 Magnum w/318.

Only does this at idle. If i don't hold the pedal down a tad, it'll die. But starts back up OK. Changed cap, wires, & plugs. Still does it. It has been elect. ign. converted from leanburn. I have no idea how long ago. I bought this from an estate.

Why do you think it's ignition related ? Sounds like it could just as well be a carb issue. I would also avise verifying your grounds, voltages and bulkhead connections. Going to need a bit more info

BTW: I did have a pickup coil wire break internally years ago, I assume it was from the constant flexing it was subjected to by the vacuum advance. It was a fun one to find
Another was an elect Ign conversion that had the control box mis-wired to the wrong side of the ballast so it was only seeing about 8V. it was an intermittent that drove several shops into giving up. The owner paid me and said he wasn't convinced it was fixed. That was 20 years ago. I still ask him how's the AAR starting LOL

I thought carburator at first, but if you've ever had a cross fire experience, you'd understand what I'm saying. It "bumps" when it occurs.

Definitely not the carb, at least I'm 99% sure on that. Too hard a miss. I lightly cleaned the reluctor and changed the rotor. We'll see.

if you were closer I might have you bring it by and throw it on the scope to confirm your suspicions. And yes I still have a working one

Silly question, what are your voltages doing at idle. I ask because if they drop below a given level with electronic ignition it can wreak havoc. You're mentioning that slightly raising the idle makes it stop could indicate a ground, alternator or connection issue

Do keep us posted

OK, tonight. it ran great till I got it home, idled horribly and kept dying but immediately starts back up. Can't say I notice a voltage drop, but will check that out.

I went out and started it, turned on the headlights and no change. Starts immediately and runs fine when cold. This roughness is after it's warmed up at highway speeds. Almost feels like crossfiring.

Thanks.

Might try a ballast resiistor as they are cheap. And Check the V's and G's

Sure it's not vapor lock? Put a timing light on the coil wire and look at it. Does it ever stop flashing when the engine is running?

Sure it's not vapor lock? Starts right back up. Almost instantly.

Plugged carb. When it wants to die try partially choking it to see if it smooths out.

I will try that.

I'm getting confused In your original post you said:

Quote

Lately, I"ve been having what feels like a cross fire issue at idle with my 78 Magnum w/318.

Only does this at idle. If i don't hold the pedal down a tad, it'll die.

but now your saying its also "after it's warmed up at highway speeds?

The misfiring at hiqhway speeds could be due to a number of things including too much advance.
Please clarify

I always treated Misfires/CrossFires as follows:
At Idle/Low Speed: focus on primary side of ignition,
At High Speed: focus on the secondary side.
Also #5 & #7 plugs wire routing.

Funny responses.

Which? Care to elaborate?

You need to figure out if it's ignition or fuel related! Put a timing light on the coil wire and watch it. If it doesn't act up(not fire/flash the light) when it runs bad it's probably not ignition. Does the distributor have a vac advance? Also what carb is on it?

Is the EGR still hooked up? Sticking open at idle?

No.

It only does this at idle after it's been ran awhile. I started it to move it today and ran smooth as snot off a doorknob.

Someone locally suggested the ballast resistor. It has a dual one as it was converted to elect. ign. years ago. Long before I got it

The electronic ballast resistors are cheap, buy a new one and put it on. If it doesn't make any difference (I'd be surprised if it does) you have a known good spare to put in the glove box. I carried one in the glove box for years (never used it though).

How old are the plugs, wires, cap & rotor? All will show signs of failure first when hot, or wet. I'd look inside of the cap first, then look at the wires where they contact stuff for hot spots. Gene

I suggested that earlier as well, the ballast is cheap and worth a shot, they can be intermittent when getting ready to fail and they do get hot after the car runs a short time.
Raising the idle which increases the Alternators output could compensate for a flakey ballast by making more current / voltage available. Worth a shot IMO

Did you try to slightly choke it when it is acting up to see if it wants to smooth out???????

Oddly, I did change the ballast, and it seems to have solved the problem.

I had to use an old one I had found as all my other Magnums have a single ballast. So....... I think problem may be solved.

I did bump up the idle oh so slightly.

Thanks gang!!

Bad connection (intermittent breakup) or high resistance (low power to module) ??.

what did the ballast connectors look/feel like when disconnected ? did the "new" one feel like the connectors were tighter to plug on ?

If the fix stays,
I'm going to guess the one or both of Ballast resistors ( assuming it was a 4 pin) were breaking down internally. Raising the idle speed the alternator produce more current to compensate. It also coincides with it being OK when cold and starting right back up as the ballast is bypassed> Time will tell

One on the car was only a few weeks old. Both were tight. The one on the car when I got it was from the conversion kit the original owner used, which went bad recently. Only Jesus knows how old it was. New one was a Carquest? piece I picked up.

I ordered 2 MoPar OEM's from Ehrenberg today.

Thanks to everyone who helped out diagnosing this. I only thought ballasts went totally out when bad.

They can do that, but also have a poor connection between terminal & coil inside.
Term. are brass, coil wire (nichrome maybe) & are just crimped together.
They get hot & that connection can degrade over time.