Coil resistance

[413Polara]

Hey guys, I’ve been chasing a backfire issue the last couple of weeks. Recently installed a new intake manifold, my first time doing it. Was convinced I had a vacuum leak but after spraying a can of carb cleaner around the intake I think I’m ok. The car was converted to a Petronix igniter part# 1381a before I bought it. I’m getting a resistance reading of 1 ohm on the primary and 4.6k ohm on the secondary of the coil. When I check pertronix website they have these kits with a suggested coil of 1.5 ohm primary and 9k ohm secondary. Any chance my coil could be causing my issue? Sorry for the rookie post, trying to learn as much as I can.

 

[steve340]

Did the backfire start after the intake was fitted?

 

[413Polara]

Did the backfire start after the intake was fitted?

It started a week or two after the intake change. Ran great after I put it on and did a couple triple trips to some out of town shows.

 

[steve340]

In that case it may be something new or you have introduced a problem when you changed the manifold - hard to say.
Maybe you damaged an ignition lead when you did the change????
Maybe the manifold is sealed OK but something else around it is the problem.
Not to hard to try another coil or perhaps borrow a known good coil.
If the car was running good before the resistance thing is probably not going to be a factor. Half an ohm is a fart skin.

 

[413Polara]

In that case it may be something new or you have introduced a problem when you changed the manifold - hard to say.
Maybe you damaged an ignition lead when you did the change????
Maybe the manifold is sealed OK but something else around it is the problem.
Not to hard to try another coil or perhaps borrow a known good coil.
If the car was running good before the resistance thing is probably not going to be a factor. Half an ohm is a fart skin.

Would the difference in the secondary resistance make any difference?

 

[steve340]

I don't know for sure .. Remember this is talking thousands of ohms. It is pretty easy to get false readings with high resistance measuring.
I have only bothered to measure the primary winding resistance to ensure compatibility.
Best plan is try another good coil - that will put it to bed.
I keep a couple of coils in my garage just for this type of problem.

 

[413Polara]

I don't know for sure .. Remember this is talking thousands of ohms. It is pretty easy to get false readings with high resistance measuring.
I have only bothered to measure the primary winding resistance to ensure compatibility.
Best plan is try another good coil - that will put it to bed.
I keep a couple of coils in my garage just for this type of problem.

Ok I’ll give that a shot. Appreciate it!

 

[steve340]

No problem - good luck.
Do an update if you can.

 

[413Polara]

No problem - good luck.
Do an update if you can.

Will do.

 

[Canadian1968]

When does the back fire happen? Idle , cruise, accelerating ?

 

[413Polara]

When does the back fire happen? Idle , cruise, accelerating ?

Accelerating seems to be when it happens, I ended up testing the ballast resistor. It was reading zero resistance so I swapped it out and since then I haven’t had a backfire. Maybe a coincidence since I’ve only had it out a couple times and it seemed intermittent. I ordered a new internally ballasted coil, so I plan to bypass the resistor all together and put in the new coil and see how that does.

 

[steve340]

I understand the Pertronix unit does not use a ballast resister - so a bit odd there.
I assumed from your first poste it was gone or bypassed.