Heya,

I have a '74 Valiant with the original 225 in it, and been running into some misfire issues. Plugs (NGK ZFR5N without washers), wires, distributor cap and rotor are all new. I've done quick checking with a timing light, and #1 doesn't fire on the electric side. Shortening the gap on the #1 plug helped, but it's still misfiring, just less.

The ignition coil looks old and is probably the original one (the car only has 30k miles on it), so I thought I'd replace that, and get a new spark plug for the #1 just to be sure. I can see that an original replacement from Mopar is still available, so I thought I'd order that. I just thought I'd ask if it's a good choice, or if there's a better one out there?

The MPG is pretty bad as well, roughly in the 13-14 area. The misfiring probably affects that quite a bit, and it'll hopefully be better once I get the misfire to go away. If not, then it's time for more troubleshooting.

For some side notes:

The car runs quite well, once warmed up there's maybe a misfire every 3-5 seconds. However, starting cold, it feels like not all the cylinders are firing, but it gets better once the car has run for a minute or two.

I recently (a few weeks ago) rebuilt the carburetor myself with a kit, cleaned it up well and took care in doing so.

It seems like it's also rather hard to start cold (cold being 20 F here at the moment) now, not sure why. Possibly it is misfiring like I think it is. Did all the adjustments carefully and accurately, and it seems to be working well, so I don't think that's creating any issues. The accelerator pump's stream of gas when pumping the pedal is quite visible, and the choke is working. I wrapped the fuel line in heat insulating tape with a reflective surface. Not quite the fuel line mod, but it seems to keep the fuel cool enough so it doesn't start boiling.

Read my post on coils in the Electrical Forum "EI conversion minus ballast resistor"

How much voltage are you showing at the coil at idle? I show 10 volts on my 74 using a .85 ohm MSD Blaster resistor.
The voltage at the resistor output should be identical to the voltage at the coil.
A full 12Volts should be coming into the resistor.

I also run a .045 gap on NGK plugs with a MOPAR Orange box and stock chrome Pertronix coils or MSD Blaster coils.

Let us know what voltages you have at all three points.

You may have a bad plug even though it's new.......

_________________
Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

well, the mopar coil is ok. There are others that have more output but for a 100% stock application, you should have no problems with the mopar coil. With the ignition system it is imperitive that you use good components in regards with cap, rotor and wires. Some caps that are "discount" are more trouble than they're worth. I'm leaning towards a bad cap even though you have changed it. If the rest of the plugs are getting good spark (this must be verified) this kinda narrows down the possibilities.
Other questions; have you adjusted the valves?
have you checked for vacuum leaks?
have you checked the voltage to the resistor?
have you checked the voltage out of the resistor?
have you checked all connection of plug wires?
The only other thing that I can think of would be related to some kind of oil fouling but you did not mention this. Distributor pick-up star wheel could have one bad "spike" but this would be slim odds as a possibility.
(I assume that this is an electronic ignition)

_________________
1979 W150 Shortbox
225, NP435, 9 1/4, Dana 44

The Good Life.

Thanks for the replies, and thanks for pointing out the post about EI minus resistors.

I haven't checked voltages yet, I'll do that this week. I actually noticed today that the control module is an unmarked replacement part. It looks fairly new (I bought the car in '08 from its first owner), any chance that cheaper control modules would create issues?

I went back to look, and the cap & rotor kit I got from Summit are Accel, this one: http://www.summitracing.com/parts/ACC-8326/ - any way to check the cap?

I ordered some more plugs, so I can switch the bad one. It may not be the plug, but they're only $2, and it may have gotten fouled with all the misfires anyway.

Also:

I have not adjusted the valves yet, I'm waiting for warmer weather.

I have checked for vacuum leaks, vacuum is good.

I've checked the plug wires and their connections, and they're all good.

Good point about the distributor pickup, I'll have a peek at it just in case.

Not really...

I followed SL6 Dan's advice and went with the BlueStreak cap and the NAPA MO-3000 rotor. It has a longer tip and the cap is ground close tolerance. Using them along with 8mm wires allows for the wider plug gap and the light tan plug color. There has been allot written about the lower quality ECU's. You may want to upgrade.

Click on the red link below to view pictures of my set up. Once the picture comes up double click on it for full screen slide show mode.

_________________
Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

Heya,

First off, let me thank everyone again for the assistance.

I got some readings, and here's what I found:

With the engine off, the resistance from primary terminals to the output terminal is roughly 12k ohms.

With the engine at normal idle, voltage coming to the resistor is 14.4, and out of the resistor is 9.8. One of the primary terminals is getting the same 9.8, and the other 3.2 volts. Should both terminals be getting the same voltage?

Right now I'm planning to get the Mopar coil, the orange mopar controller (seems like I can get that for cheaper than the black one), and a few extra plugs to switch out.

Your #s sound fine (the - coil w/ the car running is hard to say - w/ ign on, car not running it ought to be <1V). I've seen many, many old coils start to arc internally as the insulation breaks down from age and use - it is very hard to test them properly, and even then their problems can come and go.

I've had flaky coil-to-dist wires cause me very intermittent severe problems too.

Also, reversed connections to the pickup or coil will give odd problems.

Finally got the new coil today - the online store took its sweet time sending it.

Have a new orange box, the new coil, and switched the #1 plug to a new one. I did them one at a time, in that order, to see the difference.

Wow! The coil made an enormous difference. Started running like never before. Along with the orange box, I can no longer even visually see the engine shaking at all, and I can barely tell that it's running with my finger on the block. Much better throttle response, especially with low throttle and rpm, and of course the misfire went away with the new coil.

Now it just remains to be seen what will happen to the fuel economy. Since it seems to accelerate and run on much lighter gas now, I'm guessing it should be better.

Once it gets a little warmer, I'll do the valve lashes just to be sure. Thanks for all the tips!