Distributor Cap leaking?

[slowcpa]

While searching for the reason behind an inconsistent idle, I sprayed starting fluid around various vacuum hoses. As i sprayed near the distributor advance mechanism the truck made a tiny fwump sound. i wasnt able to replicate it consistently even after several attempts spraying directly at the distributor cap. not letting common sense deter me, I really layed on the starting fluid...as you can imagine the next fwump included a large ball of flame and then a small fire on the intake/carb base/dist. i beat the flames with some rags. those caught fire for a second but then fortunately everything that was on fire went out almost immediately. is there any way to check to see (not involving flammables) if my wires or cap are indeed "leaking" spark? Darwin will have to wait for another day.

 

[JB Fab]

Well done!
Or maybe medium-well done......

My guess is that your vacuum advance has a vac leak, the fact that you achieved ignition does not surprise me (but it does make me smile).

 

[.94 OR]

I'd take the distributor cap loose, turn it over and kind of pull it apart to see if you can see a vertical crack anywhere.
I had one on an EFI 302 in a pickup and it would short out in the rain when the fan blew water back at it. Replaced the cap and all was good again.

 

[DirtDonk]

You could isolate the vacuum from the mechanical, by clamping the vacuum hose shut.
Or simply disconnecting the vacuum hose from the distributor and plugging it.
Then when you spray around the distributor advance, if it doesn’t change the idle, you’ll know the problem is within the advance mechanism or hose attachment.
If it’s still gives you trouble, then it is indeed getting past the cap.

But keep in mind that caps are not perfectly sealed. Depends on how precise you were with your spraying, but there is not only a vent in the top of the cap, but the mating surface between the cap and distributor body is imperfect at best.

 

[ba123]

Yeah, don't spray starter fluid anywhere near anything that generates a big spark!

You might just have old spark plug wires that might have cracks too.

Certainly will never hurt to change all that stuff (assuming you replace them with good new parts).

Maybe try something like water next time and also around the vacuum hoses...and just replace the one to the dizzy.

 

[ared77]

You'd be amazed if you look very close around your distributor cap, plug wires etc on a dark night or in the garage w the lights off. It's a great way to see if you are "leaking" spark energy.

 

[ba123]

You'd be amazed if you look very close around your distributor cap, plug wires etc on a dark night or in the garage w the lights off. It's a great way to see if you are "leaking" spark energy.

Safer too!

 

[slowcpa]

You'd be amazed if you look very close around your distributor cap, plug wires etc on a dark night or in the garage w the lights off. It's a great way to see if you are "leaking" spark energy.

this is a great idea. thank you.

 

[ared77]

^^^Just be sure if you are in your garage you don't stare too long at the little "lightning bolts" jumping around unless you have adequate exhaust ventilation ... or you may be seeing stars pretty soon to go along with the lightning!

 

[ssray]

You'd be amazed if you look very close around your distributor cap, plug wires etc on a dark night or in the garage w the lights off. It's a great way to see if you are "leaking" spark energy.

I was gonna mention something similar. When you have short distance arcs probably with more current those are visible in daylight, but arcs that can travel on the surface of wires or caps have more resistance following a path and can be thin and faint but easy to see in the dark. Caps that have a lot of hours on them or have been used in dirty environments like dirt or gravel roads can develop carbon tracking on the inside especially in combination with humid conditions. It can be hard to see but sometimes will look like a crack as well. l used to see that on deep well engines that are exposed to the weather. Usually time for a new caps at that point.