1 Attachment(s) Volt meter reading at coil - wire drops and fluctuates. Problem?

Posted this question in another forum but could really use some help so posting here also. Hope that's alright.

Car is 1967 Mustang with 200 six. Stock ignition. Coil, points, condenser, cap, rotor, wires, spark plugs are new. Just rebuilt carb and played with different float settings. Confirmed valve seals are good. Confirmed wires are correct on coil. Cleaned all ground points. Compression test shows 185 to 190 all cylinders. Dwell stays steady at 38. Timing is good.

Issue is car will foul out plugs in about 10 miles of driving. Also have pop pop pop in mufflers on deceleration. Probably from unburned fuel igniting in mufflers.

My car is having a weak spark. When I hold the coil wire off the block and crank engine the spark is a thin line of yellow. I have done this test before while chasing another issue and it was a fat blue spark. I found an old post of mine where I mention that.

I have an Actron dwell / rpm / volt meter.

Followed the instructions and hooked black to chassis ground & green to the - side of the coil terminal that runs to distributor.

When I fired up the car it was cold and showed nearly 7 volts with the needle fluctuating some. As it warmed up the volts dropped to 6 volts and would sometimes go slightly below 6. The needle continued to fluctuating some. The volts increased a lot when I revved the engine.

Should this be a steady number? This is what provides juice to the points right?


Would a bad alternator or voltage regulator cause weak spark? The voltage needle on the dash moves back and forth some and the headlights flicker some (get brighter dimmer over and over) too. Similar to how the volts fluctuate.

Really appreciate any advice. Will do any test that can be recommend right away. Have regular volt meter too.

I have an answer for my main question.

I was measuring voltage drop of the coil. The voltage drop across the coil when added to the voltage drop of the resistor wire will equal the battery voltage. As the RPM increases you will see a higher voltage to a point simply because the alternator is putting out higher voltage then idle.

Can anyone offer any suggestions of other tests I can do to figure out why I have a weak spark?

Thanks!

Bad coil

thanks for the reply. I just replaced the coil with a brand new one. No change. Don't think it is the coil at this point. Wish it was. That's an easy fix!

1.5 ohm coil?

It sounds like your alternator may be weak or a problem with the regulator. But I'm not sure that would effect the spark that much if you have enough juice to run the lights while the engine is running. I would check the ground in the distributor, make sure all the connections are good. If this problem started after the tune up, I would swap in the old condenser or buy a new one, also you should ohm out the wire from the coil to the distributor and see if it has any resistance, if so replace it.

There really isn't much more to it, coil, wire, condenser, points, ground. It's gotta be one of those if it's getting power

Hi, problem was before all of the new parts.

"you should ohm out the wire from the coil to the distributor"

Do you mean the wire hooked up to the coil - side? How do I go about doing that?

Probably disconnect both ends and set meter to ohms I guess. Should read zero resistance?

Thanks

Yes, resistance should read near zero. Touch your leads together beforehand and note any resistance in the leads and subract this from your measurement. While you have the wire disconnected from the condenser make sure the connection contact spot is good. Also check resistance from the breaker points ground connection point to the block and the ground wire connection to the block.

any ele. issues, & ign. are my poorest skills. But…

1) In a car of this age I'm wondering about most of the grounds.
Also -
2) there's a ground inside the distributor.

Keep talkin~

I clarified my post above

"corrected my post"
Yes, I C:
"...the ground in the distributor…"
Thanks Seth.

BTW:
where would I C this tinny lill wire inside there?

Great advice thanks.

I do have a new 1.5 coil. Installed brand new battery - to engine block cable. recently cleaned all the other grounding points. Did not seem to help. Confirmed the ground wire inside distributor is in good shape and connected properly.

Done for today but while do the resistance tests as suggested tomorrow.

I did manage to fix the volt needle on dash moving and headlights flickering. Turned out to be corroded connections where the wires hook up to the voltage regulator. Cleaned the metal parts and used dialectical grease. Now needle is rock steady and no light flicker!

Going to test drive tomorrow to see if by some miracle that improves things.

Hi, I would make sure you have motor craft Bsf82c spark plugs, gapped at .035 . A lot of these engines don't run well with modern platinum or any of that. I would set the points to .026. My guess is that you have a bad condenser. I would get another condenser. The voltage at the coil is ok. Good luck

Have seen plenty of electrical items defective right out of the box.way back in the 60`s even.So much of the tune up stuff is China made anymore,and is junk right out of the box.Try and find a NOS condenser such as Eichlin or other name brand NAPA maybe.That should fix the condenser problem.
Good luck.Have fun.Be safe.
Leo

Thanks for the help!

I have tried 2 different condensers so pretty sure I can rule that out.

I'm running autolite #46 plugs. I set the gap at 32 because I read somewhere that a smaller gap will give a stronger spark?

Took the car for a test drive this morning. Ran absolutely perfect for a while. Great throttle response, no backfiring in mufflers, smooth idle, just really running good. I think fixing the corroded wires on the voltage regulator really made a difference in overall perfomance. Lasted just long enough that I started to get real happy thinking I may have fixed it! But......there's more...

After about 10 minutes of driving it started missing, engine was shaking badly and wanted to stall out. Barely made it home. When I took out some plugs they had a strong gas smell and were a bit wet with fuel.

Pulled off air cleaner and was a lot of vapors coming out of the top of the carb (just rebuilt autolite 1100). Pretty sure it was flooded badly. I think this is a case of two problems at once? I fixed voltage regulator issue but not done yet.

Today I set the float to 1 5/32 (manual says 1 3/32) but that did not seem to help. I do have a plastic float not sure if that makes any difference. By the way carb was new old stock when I got it so is in nice shape and not totally beat like many out there. I made sure the seat is working properly by blowing on it. No crud in there. My main jet is a 67F. I ordered some from Mikes carburetor in smaller sizes to try that. Probably need to check the fuel pressure? I have a gauge. It is a vacuum / fuel pressure gauge.

Can I just remove the hose from the filter at carb and hook my gauge up there? Car will run for a while that way I guess?

Also how much gas should be in the carb when I pull the top off? It only had about 1/2 to maybe 5/8 of am inch so did not seem overly full. Wondering if this is a jet problem. Could a main jet that's to big cause it to run good for a while and then slowly build up to much gas causing it to flood?

Hi, it seems like something craps out when it gets hot. I would still lean towards a condenser or coil. I might try to mount the coil off the engine, away from any heat. Good luck

Sure sounds like coil/ignition problem, gets hot, starts missing, fouled plugs, acts like it's flooded.

After thinking about this for a while I think you guys are right and it is still an ignition issue. Weak spark will act like flooding I guess because the fuel is not being burned properly.

Car has always run a little rich so I will mess with the different jets if I ever get it fixed.

Here is my new plan.

Going to check resistance on coil - wire and to points, breaker plate etc. as suggested. Put in yet another condenser.

Going to drive the car until it starts to run like crap (about 10 minutes of driving). Choke is wired open so not choke related.

Then remove wire from + side of coil and run jumper wire from battery + to coil + and see if it improves things. I'm starting to think that maybe the pink resistance wire is heating up and dropping the voltage to low at the coil + after it gets hot? I did have to change the resistance wire a few years ago after it failed completely.

Wondering how long I can run the car with coil wired directly to battery? This will fry the points and coil at some point right? Maybe I should just wire it up that way and drive it to see if it craps out after a while or not?

Yeah it will burn up the points and the coil before long if the coil is a standard 1.5 ohm coil. Sounds like a good test though. And get the best condenser you can find. I've had good luck with the higher end napa points and condensers, the premium "Echlin" ones. I have a friend who's a Harley guy and he tells me evryone's gone away from points on bikes b/c it's so hard to find good parts and you end up

reweb67":3tewve2i said:

Posted this question in another forum but could really use some help so posting here also. Hope that's alright.

Car is 1967 Mustang with 200 six. Stock ignition. Coil, points, condenser, cap, rotor, wires, spark plugs are new. Just rebuilt carb and played with different float settings. Confirmed valve seals are good. Confirmed wires are correct on coil. Cleaned all ground points. Compression test shows 185 to 190 all cylinders. Dwell stays steady at 38. Timing is good.

Issue is car will foul out plugs in about 10 miles of driving. Also have pop pop pop in mufflers on deceleration. Probably from unburned fuel igniting in mufflers.

My car is having a weak spark. When I hold the coil wire off the block and crank engine the spark is a thin line of yellow. I have done this test before while chasing another issue and it was a fat blue spark. I found an old post of mine where I mention that.

I have an Actron dwell / rpm / volt meter.

Followed the instructions and hooked black to chassis ground & green to the - side of the coil terminal that runs to distributor.

When I fired up the car it was cold and showed nearly 7 volts with the needle fluctuating some. As it warmed up the volts dropped to 6 volts and would sometimes go slightly below 6. The needle continued to fluctuating some. The volts increased a lot when I revved the engine.

Should this be a steady number? This is what provides juice to the points right?


Would a bad alternator or voltage regulator cause weak spark? The voltage needle on the dash moves back and forth some and the headlights flicker some (get brighter dimmer over and over) too. Similar to how the volts fluctuate.

Really appreciate any advice. Will do any test that can be recommend right away. Have regular volt meter too.

Click to expand...

The thin yellow spark is a sign of a weak coil, the resistor wire from the ignistion switch is designed to drop the voltage to the coil and points to the 6 to 8 volt range. Have you tested your battery voltage? When fully charged you should read in the 13.4 to 13.8 volt range at the battery terminals. Next test your voltage at the starter solenoid, then at your ignistion switch too. Are you sure that you have good grounding? Ie the battery's neg. terminal (-) to a very well cleaned of all rust & paint place on the engine block (boss) with at least a 3/8 inch size bolt with washers. The engine is then also grounded to the cars chassis in the same way using at least a 10 gauge wire or better is to use a larger wire that's the same size as your negative battery cable. All your engine and body wiring connections also need to be very clean and tight too. Yes a bad alternator and voltage regulator can cause many problems in running the engine and the cars electrical system because it might not bring the battery back to its full charge. So have them tested out to know if they are working correctly it's free at many auto parts stores. How is the condistion of your ignistion switch? If it is on the sloppy side when it may need to be replaced you could test its output using your volt / ohm meter. Also clean up all the wiring connections on the back of the ignistion switch. I wouldn't run 12 + volts to the coil / points very long (the exception is during starting) unless you don't mind rebuying all your ignistion parts and coil over and over again. Good luck