Have to jumper ballast resister for car to rev past 4.5 K RMP

[landmizzle]

Hi all,

After a long trouble-shooting session (literally over a year...) I've determined that the high rpm (4.5 K + ) hesitation issue I've had is ignition based (weak spark or too much resistance?). I can make the symptom disappear (or nearly so) by jumpering the ballast resister next to my coil.

My '72 240Z currently has a Petronix ignition on it with the stock coil (1.5 Ohm) and ballast resister. I've gone through a long session of replacing the dizzy, fuel pump, coil, adjusting a/f ratios, and carb float levels in an attempt to resolve the high RPM hesitation. What it has finally come down to is that if I jumper the resister, I get much better performance, if I live it unjumpered, the hesitation returns and non of the aforementioned adjustments and replacements make any difference. See this thread for all the gory details : http://www.classiczcars.com/forums/showthread.php?41414-Mid-Range-RPM-Hesitation

I believe just running the resister jumpered is not the best thing for the car. I understand that the Pertronix unit might be ok, but the coil might ultimately fry. If that's the case, I really would like to trace the problem down.

I'm assuming that by removing the resistance of the ballast (by jumpering it) , I've removed enough resistance in the ignition circuit to allow it to function normally. Therefore, there must be additional, unintended resistance in the circuit. Unfortunately, I'm not much of electrician and don't know where to be begin in tracing this down. Any suggestions?

I'm also guessing that installing a 3.0 Ohm coil and bypassing the ballast resister will not solve anything since the same amount of "coil based" resistance will be introduced into the circuit. Does that seem correct?

I do have a multi-meter as a tool, but, I'm far from an expert in using it. Any suggestions would be greatly appreciated in it's use and how to resolve my ignition issue.

Best Regards,

Landmizzle

[Zed Head]

Search Pertronix under username Arne, if you haven't already read it. I looked through your other thread but didn't see a reference to his long thread on a similar issue with the Pertronix setup.

[landmizzle]

I am familiar with that thread. I don't believe that I have the same situation since replacing the Pertronix unit with points makes no difference. It really comes down to jumpering the ballast resister. That is the only thing that seems to make any impact. As I mentioned in my other tread, I've gone back and forth between points and the Pertronix unit, replaced the coil, replaced the ballast resister, replaced dizzy, replaced fuel pump, etc.

The car actually runs great except for the 4.5K + RPM hesitation. Jumper the resister and it shoots right on past that mark and will rev to nearly 7k pulling pretty nicely through 6K. Unjumper the resister and you're back to square one.

[cygnusx1]

I hate to ask but have you tried another set of plug wires and plugs?

[tlorber]

I'm not understanding why you need the resistor. I thought the purpose of it was so that the points don't get fried. Since you are no longer running points this should not be an issue.

[landmizzle]

I'm not understanding why you need the resistor. I thought the purpose of it was so that the points don't get fried. Since you are no longer running points this should not be an issue.

Since I'm still running the stock coil that is rated at 1.5 Ohms, I believe that I'm supposed to run the resister which also is rated at 1.5 Ohms. This gives a total of 3 Ohms on the ignition circuit. Removing or jumpering the ballast resister removes it's 1.5 Ohms from the ignition circuit. To prevent premature point wear, 3.0 Ohms are required for the ignition circuit. You're correct that I currently don't have points so I don't have to worry about frying them. But, with only 1.5 Ohms in the ignition circuit (from the coil itself), it's my understanding that I could ultimately fry the stock coil too. Of course I could install a 3.0 Ohm coil and jumper (or remove) the ballast resister so that I would not fry the coil. However, I suspect (but haven't confirmed) that doing so, would reintroduce 3.0 Ohms to the ignition circuit and consequently the hesitation issue.

If running only 1.5 Ohms resistance in the ignition circuit won't do harm to the stock coil, than my current configuration is fine. However, it's still a band-aid for the symptom and I would prefer to figure out what's going on. That way I could go back to points if I so choose.

[cygnusx1]

Plugs and wires? You might have the wrong spec in the car.

[landmizzle]

Plugs and wires are in good shape. However, just to be sure, I put brand new NGK plug wires and NGK B7ES plugs in today. No difference. The NGK B7ES plugs are a step cooler than the NGK6ES that I had in before. These plugs were recommended by Rebello Racing whom did the rebuild on the engine.

Plugs and wires? You might have the wrong spec in the car.

[cygnusx1]

I have seen weak spark from two things in my experience. If the 12volt power wire to the coil (or to the ballast in this case) has some resistance in it, it will choke down voltage when the demand for spark rises with RPM. I had this recently in a turbo car I built. When I ran a temporary wire directly from the battery, the spark got much stronger.

Another reason I have seen is that plug wires with too much resistance were used. They are great for radio noise reduction but they can quench the spark at the plugs. I am not sure about the mix and matching of resistor wires with non-resistor plugs or vice versa. Maybe someone else can chime in on this subject.

Those are directly from my experiences. I am sure there could be more reasons. Good luck.

http://www.auroraelectronics.com/Understanding%20Spark%20Plug%20Wires.htm

Edited March 25, 2012 by cygnusx1

[doradox]

Hi all,

I do have a multi-meter as a tool, but, I'm far from an expert in using it. Any suggestions would be greatly appreciated in it's use and how to resolve my ignition issue.

Best Regards,

Landmizzle

Have you checked the voltage on both sides of the ballast resistor? I think madkaw already asked that in the thread you linked to. You should have full charging voltage ( about 13.5-14.5 , check the fsm if you want "exact" numbers) on the side away from the coil while the engine is running at ALL rpm. This is one of the first things, if not the first, to check when diagnosing a running problem. Have you checked the resistance of the ballast?

Steve