More Mopar troubles....

[Toastedlightly]

My mopar (1974 Dodge D100) w/ a 318 V8 is having problems once again. I am getting really weak spark. When checking voltages, I only have 8.5 volts at the positive on the coil. Is this normal? And if it isn't, how can I fix it?

[dwc43]

Balast resistor going bad most likely. Replace it and if it's still weak you'll need a new coil.

[Toastedlightly]

sooo, my question.... whats the ballast resistor? (I am kinda new to this, and thanks for the help). And I just got a new coil, so that couldn't be the problem....

[custom880]

Ballast resistor is the white ceramic bar with at least two leads on it, one on each end and possibly two on each end. Most likely it is bolted to your firewall, or inner fender. A new one runs just a few dollars and you would be smart to get two. Replace the bad one and keep one extra for emergencies in the glove box.

[Toastedlightly]

Yea, I know the part now. Is there any way to test the resitance of it (to see if it is correct) as I buying another part w/o needing it right now is hard (very little extra cash to spend on this vehicle)

One of the resitances is 1.7 ohms, but I can't tell the other one (not getting continuity from it... gonna try again after I clean the contacts more)

OH yea, is this also known as a coil resitor? (I have electronic ignition if it matters..)

[custom880]

The ballast should be 0.5-0.6 OHMS at 70-80% F

[Toastedlightly]

then that would explain the problems I am having if I get 1.7 ohms on one half, the other I have to try again after I clean the contacts even more.

[Ray Bell]

Try (temporarily) taking the positive straight to the coil... bypass the resister...

Or fit an old 12V coil and toss the lot.

[Toastedlightly]

Originally Posted by Ray Bell

Try (temporarily) taking the positive straight to the coil... bypass the resister...

Or fit an old 12V coil and toss the lot.

but since I have electronic ignition.. wouldn't it not fire at all?

[dave571]

It will still fire.

Bypassing the ballast with a jumper wire, or running straight battery voltage to the coil will have the same effect on the vehicle with either points or electronic.

The ignition system is controlled on the ground side. Done with either breaker points or an ECU.

The positive side is reduced by a ballast resistor. The system doesn't run full voltage in the run position. Normally 10 to 11 is seen on a voltmeter, at the coil positive of a running car.

The ballast is bypassed in the "start" position, due to the system voltage drop caused by the starter draw.

[Toastedlightly]

ahh, alright. For some reason I was under the impression of the positive was ECU controlled. Thanks for clearing that up. I'm still new to this car stuff (going from comptuers -> cars). Ill keep you guys informed. Thanks!

Well, I need a new one anyway. Between two of the points, I have no continuity. (one w/ the gree wire that goes to the ECU and some other wire).

[Toastedlightly]

I love you guys. That is waht it was. I now fire up on the first or second crank. Been having this probelm since day one. I owe you guys one.

[custom880]

nah you don't owe anyone anything. Everyone on this board has had that problem sooner or later. In fact lets see if you can come up with something we havent seen. I dare ya. Try to trip these guys up. I bet you can't do it.

[Ray Bell]

Despite the distance, we might do each other some good...

[73scamp318]

And never believe that a part isn't bad because you just bought it. You will chase your tail for awhile. And espcially if the problem happend after you bought it.

Steve

[3276/A-Body/71]

You can get a lot of troubleshooting done free by talking to people on boards,mechanics(some of them) ,some auto parts guys,etc. Have fun!

I bought a new coil once only to later find that I had an open in the wire to the neg side of the coil. Yes,shotgunning can be expensive and unsatisfying but with cheap parts (like the resistor) it doesn't matter as much.