Distributor Cap Exploded (1 Viewer)

[sk8salomon]

Went to leave work yesterday, turned the key and "POP", i heard a loud noise that sounded like a .22 rifle. I tried to start it again and all it did was turn over and over. So I popped the hood and found a hole in the side of my distributor cap. WTF??? Why would this happen? I put a new cap and rotor button on and cranked back up and drove home with no problem.

 

[slcfj62]

Well that adds some excitement to the "What can go wrong with my Cruiser" list. Isn't the elaborate vacuum line to the distributor cap that sucks air from inside the cab through the little filter supposed to prevent the build up of fumes in the distributor cap? That is the only think I can think of that could cause this.

Of course, maybe it is just your Rig telling you it is time for a tune up!

 

[fliphkd778]

Yeah that's what has me wondering; why didn't the vent relieve pressure? Maybe it saw full vacuum and collapsed?

 

[sk8salomon]

in the past month i've put plugs, air filter, oil change & filter and just yesterday dizzy cap and rotor button. it did fail emissions check last month by only a few hydrocarbons. i usually just dump some additive in the gas tank and it lets me pass.

 

[SARCruiser]

If you had teeny tiny bit of fumes backed up in there from when you shut off the engine the last time, I would imagine that the brief moment of cranking before if would have ignited from the spark wouldn't have been able to fully evacuate the cap.

It wouldn't take much gas fumes at all in that tiny space to cause detonation.

 

[soggy60]

The plumbing associated with the dizzy cap breathing involves a 'valve' that should close when engine is off....
Changes in cabin air pressue ( open / close door) can cause air flow to or from dizzzy cap; valve 'clamped' just under air filter preclude suction from cabin to draw gas vapors from carb (via air cleaner housing) into dizzy cap.
Vle is either missing (and you've been lucky in the past) or stopped working (clogged or little vac hoses to it fell off)

 

[sk8salomon]

The plumbing associated with the dizzy cap breathing involves a 'valve' that should close when engine is off....
Changes in cabin air pressue ( open / close door) can cause air flow to or from dizzzy cap; valve 'clamped' just under air filter preclude suction from cabin to draw gas vapors from carb (via air cleaner housing) into dizzy cap.
Vle is either missing (and you've been lucky in the past) or stopped working (clogged or little vac hoses to it fell off)

ok, this makes sense because in the past, sometimes i've heard a very light pressure sound from under the passenger dash, kinda like a pfffttt at startup. Then i will smell something like what gunpowder smells like when exploded. Remember those little "Snap Pops" we had as kids that would pop when you throw them down? It smells like those things did. Maybe this VLE you talk about is bad? I'll get my manual out when i get home and see where it is located. Thanks.

 

[Elbert]

had that happen on my vortec one time....replaced the rotor button and the cap and all was good. Truck backfired...and then I was stranded...never knew why...has not done it since.

 

[Willman]

Wow...no joke about the tune-up thing...

 

[FJ40Jim]

ok, this makes sense because in the past, sometimes i've heard a very light pressure sound from under the passenger dash, kinda like a pfffttt at startup. Then i will smell something like what gunpowder smells like when exploded. Remember those little "Snap Pops" we had as kids that would pop when you throw them down? It smells like those things did. Maybe this VLE you talk about is bad? I'll get my manual out when i get home and see where it is located. Thanks.

This symptom indicates that the dissy cap vent system has not been working properly for some time.

The Vacuum Control Valve is clipped to the leg under the aircleaner, just above the dissy. It is not real clearly shown or described in manuals, because it is not part of emission control systems (not in emissions FSM), but is not a world standard 2F part (not in 2F manual).

 

[sk8salomon]

This symptom indicates that the dissy cap vent system has not been working properly for some time.

The Vacuum Control Valve is clipped to the leg under the aircleaner, just above the dissy. It is not real clearly shown or described in manuals, because it is not part of emission control systems (not in emissions FSM), but is not a world standard 2F part (not in 2F manual).

Thanks Jim, I was hoping you would chime in with some wisdom. This pic isn't of my truck but I was hoping to identify the VCV you talked about. You rebuilt my carb in 2006 but that was probably many rebuilds ago for you to remember.

 

[haryv]

check the oil for fuel dilution. possible that fumes migrated up the distributor shaft and built up in the distributor housing. In all my years, never heard of this happening. This kind of reminds me when I was a teen, could not start my moms car on a cold day and brought over a family friend to look under the hood while I tried to start it. The egr valve exploded and coated the face of the friend in black soot. I almost laughed But he was okay.

Easy way to check for hydro carbons in the oil is bring it to a garage with a 4 way gas emissions analyzer and have the mechanic sniff the oil cap opening for excess fuel. Its possible there is fuel in it possible from a leaking fuel pump diaphragm if, that style is mounted to the engine and runs off the mechanical eccentric.

 

[FJ40Jim]

Thanks Jim, I was hoping you would chime in with some wisdom. This pic isn't of my truck but I was hoping to identify the VCV you talked about. You rebuilt my carb in 2006 but that was probably many rebuilds ago for you to remember.

Yes, that is the VCV hiding under the air cleaner.

 

[shauntobin]

Distributor cap exploded 78 FJ40

As the title says. One turn of the key early in morning, a loud bang and mine was shattered to a much greater degree than in the OPs pic.

Not sure how to procede and any help or insights that might have come by since this original post would be greatly appreciated. I'm in Hawaii.

Mahalo

 

[Mark W]

No further insights needed. Jim explained it correctly. This is not a common event, but it is not unknown either.

I can not remember right off the top of my head if thr '78 used a VCV in the venting system. It was the first year for the vented cap and IIRC it did not.

Chances are well in your favor that if you simply replaced the cap and did nothing, you would never have this happen again. Make sure that the intake line for the venting system (routed through the firewall to a small air filter) is not clogged. If it is, as the distributor cools it will tend to try to suck air from the air cleaner assembly and this is how the fumes are drawn in. Even without the valve, of the intake side is open to air flow, you should not have this problem.

If you have a VCV that is not functioning properly, it an b replaced. If you do not have one, one could be retrofitted. But even without on the odds of this happening again to you if the rest of the vent system is working are extremely remote.

Mark...


Mark...

 

[Dynosoar]

Wrap the cap in duct tape so when it explodes again (which it won't) it will be still in one piece and drivable. We do this on desert racers so a rock or other debris won't shatter the cap.


Dynosoar

 

[FJ40Jim]

Pre-emptive duct tape repair: Brilliant!

The factory dissy cap boot (that is missing off most trucks) might have a similar effect, both protecting against rock damage, and keeping the exploded cap pieces in close proximity.

 

[shauntobin]

Distributor cap exploded AGAIN 78 FJ40

The new dissy cap lasted almost three weeks before exploding again. This time is was not after sitting over night but it had been sitting for seven hours.

There is no VCV valve as far as I can tell. The hose from the cap to the air cleaner does not appear to be clogged. Not sure duct tape would have saved it as it is literally blown to bits.

My question is whether I should look into retro fitting a VCV valve and in the meantime after a put a new cap on what measures should I try to prolong its life past three weeks.

Should I disconnect tube from cap before i let it sit any length of time at all?

Any help would be greatly appreciated.

Thx, Shaun

 

[Miloslavich]

My question is whether I should look into retro fitting a VCV valve

Shaun- this is what you should do for sure.

a properly working VCV valve will vent the dizzy cap while the engine is running, and prevent gas vapor from a hot carb bowl from traveling down into the dizzy cap when engine is off and the truck is sitting.


i'd seriously look into retrofitting the VCV back in there, and ensuring all of the vac lines are properly hooked up


hope that helps

 

[Trapper50cal]

Time to read the Desmog thread/novel......