47 V8 ignition mystery

Terry said:
Does your engine have a heavy battery ground cable bolted to one of the head studs?
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deuce_roadster said:
I would also double check the ground of the engine to insure it was clean and tight clear to the battery. If loose and dirty, it might fail as the engine heats up.
An old timer once told me that all electrical troubleshooting begins with and at the battery.
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Engine is well grounded with webbed ground cable from head bolt to firewall within a foot of the same style ground cable from battery post to firewall. Starter motor works fine so ground not the problem.
 
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Seth Swoboda said:
When you say it stumbles under load, it's when you are hard on the accelerator pedal? How do you know you don't have a problem with your accelerator pump?
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I just rebuilt the carburetor including replacing the accelerator pump. If that was the problem it would hesitate when first pressing the gas pedal. It doesn't do that. It's after pushing the pedal with the pedal still.

On my trip I ran mostly with the throttle holding the gas steady. Still, when under load up an incline it stumbled but not so much when on the level.
 
47topless said:
You could just buy one of those Blue Streak (Flame?) tube coils at NAPA or O'Reilly, depending on your system, with or without built-in resistor, and test that. They are very inexpensive, and you would then have an emergency spare.
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I just ordered a $15.00 6 volt coil from Amazon that will be here Monday to try before laying out $80.00 for the real thing. Hope it fixes the problem. That would be a fix easier than anything I've done so far.

The coil I'm using was rebuilt by Skip Haney in 2015, 70,000 miles ago.
 
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deuce_roadster said:
How many miles are on this engine? I would certainly replace that cap and not write anything inside of it.
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80,000 since engine bearings replaced in 2014.

95,000 since pistons replaced in 2013.

Just replaced the distributor cap if that's the cap you're referring to. Don't understand not writing anything inside of it. Do you mean some other cap?
 
Terry said:
Which cylinders are not firing correctly?
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6,3,7, & 8. 6 the worst, 3 next, then 7 & 8 less than the others.

I switched plugs between 1 and 3 then 2 and 6 in case plugs were bad. It isn't the plugs. It's those cylinder locations.

When I just replaced all of the spark plug wires I confirmed continuity of each one between the distributor cap terminal and the spark plug end.

What else could it be?
 
Old Henry said:
Just replaced the distributor cap if that's the cap you're referring to. Don't understand not writing anything inside of it.
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You should NEVER write anything inside a distributor cap, most especially with a lead pencil. It is extremely likely that a spark will jump to and follow the writing instead of going to where it is supposed to go. It's a phenomenon called carbon arcing.

Coop


.
 
V8COOPMAN said:
You should NEVER write anything inside a distributor cap, most especially with a lead pencil. It is extremely likely that a spark will jump to and follow the writing instead of going to where it is supposed to go. It's a phenomenon called carbon arcing.

Coop


.
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Good thing I've never written anything inside of a distributor cap. I use an engraver to mark each terminal for continuity testing. (See post #33 photos)
 
Old Henry said:
Good thing I've never written anything inside of a distributor cap. I use an engraver to mark each terminal for continuity testing. (See post #33 photos)
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If that is one of those engravers that vibrates, you may be inducing cracks in that plastic that cannot be seen to the naked eye. Cracked caps need to be tossed in the round can immediately. If you're having such a hard time determining which terminal is which, use some masking tape to write on which can be peeled off later.

Coop


.
 
V8COOPMAN said:
If that is one of those engravers that vibrates, you may be inducing cracks in that plastic that cannot be seen to the naked eye. Cracked caps need to be tossed in the round can immediately. If you're having such a hard time determining which terminal is which, use some masking tape to write on which can be peeled off later.

Coop


.
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Good "point".


Next time I'll use my Dremel spinning engraver instead of the jackhammer.


Thanks.
 
Old Henry said:
Good "point".


Next time I'll use my Dremel spinning engraver instead of the jackhammer.


Thanks.
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Why would you NOT use masking tape, for instance? Whether you use a "jackhammer" or spinning engraver, any time you disturb the finished surface on a distributor cap, you introduce POSSIBLE pathways for errant current travel. It's been proven in the past that these pathways or anomalies in the cap's surface don't necessarily need to be visible for them to exist. Electricity only knows to follow whatever path that physics has deemed the easiest way to get back to ground, whether it makes sense to us humans, or not!

Coop


.
 
I just ordered another new distributor cap and will chuck this other new one that I marred up. I'll install the new one without marring it. Hope it solves my ignition mystery. Doesn't seem to be any other ideas to solve it.

I'll also try the new coil when it comes although that doesn't seem like the problem. I've tried everything everyone's suggested so far. Something's got to work.
 
The breaker plate terminals can give issues. We have to check them thoroughly during every rebuild. That usually only causes a random miss. You declined the recommendation of a full rebuild on your distributor and only had us adjust the dwell and timing so there is a lot of still unknowns

Only missing under heavy load only with no relative relation to rpm’s sure sounds like carburetor power valve or accelerator plunger to me
 
I'm afraid that my ignition problem has deteriorated to the point that it is now constant, even at idle. It is just more noticeable under load.

Regarding the distributor, it is my understanding the it has just three simple functions:
1) turn the coil on and off to create spark,
2) distribute that spark through the rotor to the terminals in the inner distributor cap and then out through the spark plug wires to the spark plugs, and
3) advance the timing of the spark as the RPMs rise.

I just tested my coil again to check on the first function, i.e. switching the coil on and off to create spark.

First, I put my timing light sensor on the high tension wire coming out of the bottom of the coil and started the engine. Even at idle the light fluttered consistent with the missing sparks in cylinders 3, 6, 7, & 8.

Then, I pulled the high tension wire from the coil and inserted a short spark plug wire. Of course, I couldn't start the engine because of no spark going to the plugs. So, I just cranked the engine while holding the other end of the spark plug wire near a head bolt enough to cause a spark with the timing light sensor on that wire. As I cranked the engine the spark and the timing light both fired consistently without any misses at all.

That would lead me to believe that the function of the distributor to turn the coil on and off is working just fine with no issues of the points that perform that function. It would also suggest that the coil is working fine although I was not able to test the coil independent of the distributor distribution function at an RPM higher than idle. Any problem with the coil at higher RPM would need to be tested some other way.
 
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35fordtn said:
Only missing under heavy load only with no relative relation to rpm’s sure sounds like carburetor power valve or accelerator plunger to me
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If I still have problems after I get reliable and consistent spark to all plugs I will look to the carburetor. Until then, I'm relying on the fact that I just rebuilt the carburetor and installed new accelerator pump and power valve.
 
I decided that maybe I hadn't pushed all of the spark plug wires all the way into the distributor cap but far enough that each showed continuity with my ohm meter but maybe not far enough to carry a full spark. So I Marked all of the wires at the top of the socket, pulled out the most offending one, number six, measured the depth of the socket to compare the depth that the wire was pushed in and, sure enough, it was only about halfway. I then pulled out the rest of the wires, none of which were pushed all the way in, greased the sockets, and kept pushing each one till it got to the bottom hoping that would fix my problem. Unfortunately, although it eliminated the slight stumbling of #7 & 8, it didn't help number three and six which are still only sparking erratically. Oddly enough, both of those are next to each other in the distributor cap. I'm still waiting for a new cap to replace the one I have engraved terminal numbers on, hoping that will fix it. If not, I have no other ideas.
 
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Craig, my thought was that if you are getting proper voltage to the distributor it has to be something in the distributor. In the last year I've replaced wires on both my 42(has a 59 A-B engine and cap) along with my 48 coupe and know what a difficult job it is. When you get your new cap double check your plug wire locations. If you are still in the same spot, I'd send the distributor to Michael for the full rebuild. You will get it fixed although it can drive you nuts until you do....
 
I got the new distributor cap in and got all of the wires installed and checked continuity between the distributor terminals and the end of the wires. All is well except the center coil wire terminal. There is complete continuity to the outer ring of that terminal but the center rounded part had about 30 ohms resistance. The new cap I just took off had the same. The old cap that new one replaced had no resistance. I checked two other old caps. One had resistance and the other didn't.

Is resistance of that center contact point OK or should I keep buying new caps until I get one without any resistance?
 
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