Posted by Clint Dixon [172.71.255.79] on Friday, September 25, 2026 at 19:18:28 :
Hey Tom. I was going to call you directly but I thought if we talked about it here that I may benefit others as well.
Two trucks. The '47 WDX is running great. The '51 B3PW is having electrical issues. First I will list known conditions, my diagnosis, and then I will share the backstory.
Both trucks are 6-volt Positive Ground. All components are original Auto-Lite and/or NOS replacements. All conditions were checked with fully charged fairly new batteries with new battery cables hooked up tightly. I used only a test light to check and results are below.
Conditions:
1) Ignition key turned to "off" and both distributors clocked so that points are open.
- Result for both trucks - no power to coil
on the battery (negative) side. No power
from the coil on the distributor
(positive) side.
2) Ignition key turned to "on" and both distributors clocked so that the points are open.
- Result for both trucks - power to the coil
on the battery (negative) side and power
from the coil on the distributor
(positive) side.
3) Ignition key turned to "off" and both distributors clocked so that the points are closed.
- Result for both trucks - no power to coil
on the battery (negative) side. No power
from the coil on the distributor (positive)
side.
4) Ignition key turned "on" and both distributors clocked so that the points are closed.
- Result for WDX - power to the coil on the
battery (negative) side and no power from
the coil on the distributor (positive)
side.
- Result for B3PW - power to the coil on the
battery (negative) side and also power from
the coil on the distributor (positive)
side.
Diagnosis:
Because there is power at both sides of the coil (+ & -) on the B3PW when the points are closed and the key is on, this is telling me that the coil is the problem of why it is getting no spark when trying to start the engine.
At first I thought it may be the condenser, but I have tried three new condensers (one modern and two NOS) and there is no change. I failed to do my checks above when the original condenser was in the truck as the problem began.
I also changed the old points out for a new set - still no change.
So the problem really started two years ago on the first trip during springtime. We were taking it out for a 60 mile trip on a road with a lot of hills and semi truck traffic. I was really pushing it against a strong head wind. She started missing. I could hear it pinging. And an odd smell filled the cab. When we got to a place where I could pull over I found the fuel in both sediment bowls boiling. I chalked it up to vapor lock. After it cooled down we headed back home with wind behind us an no problems.
Then last year it happened again on flat ground against the wind. I was almost to a T-intersection so I slowed down and turned perpendicular to the wind to continue home. She quickly started running normal. Again I blamed vapor lock but I did not stop to look at the sediment bowls. Martie blamed sparkplugs which I found had not been changed in 10 years. I installed new ones.
A month ago we headed out on an 80 mile trip one way. The first 30 miles she ran perfect and we were cruising at 55. We stopped for gas and about 3 miles after the station was the bluff hill. It started vapor locking again up the hill and kept doing it after we got to the flat after the crest even though I slowed way down. Stopped and the gas was boiling again. Drove the remaining 50 miles at a lower speed with no problems.
At the show we were attending I replaced the fuel pump with a used one I thought was good. It would fill its own sediment bowl but would not pump gas to the carburetor sediment bowl. I then replaced this with a new (Chinese) pump. The truck ran fine most of the way home until we stopped for gas again.
Leaving the gas station the truck abruptly stopped running. There was no gas in either sediment bowl or the carb. Multiple tries at cranking the engine failed to fill either bowl. We finally took the carb apart and filled the float bowl with gas, put it back together, and she ran long enough to start pumping again. The 30 miles home I really pushed it to see if anything would happen again. No issues. She ran fine.
This past weekend I started her and she was running perfectly. Eased down the drive to head to another show and as soon as I put a load on the engine, she started acting like she was running on only two cylinders. No power at all. Let off the gas and she ran fine.
Martie noticed that there was gas leaking from the output fitting on the new pump. Replaced the fitting and pump with new ones. Leak cured. Started off for a test drive and same thing again. Truck would barely run with a load on the engine but would idle perfectly.
Yesterday. Changed out the condenser. Tried to start it and no spark. I actually knew it would not start because when I turned the key there was no drop below 0 from the needle in the ammeter. Changed the condenser two more times. Still no spark.
That is when I got out the test light and found the results above.
As I said, it looks like a bad coil to me, but I have never had a coil go bad so I do not have any experience in that area.
If it is a bad coil could it have been going bad over the past few years? Could this have been causing an erratic misfire that caused it to start running hot which in turn cause vapor lock?
Ideas?
Thanks Clint
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