a/c vent backfire (1 Viewer)

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My 1987 FJ60 will have an occasional "backfire" puff come through the a/c vents during startup. Happens only once and is minor. Will happen again is left to sit a bit and restarted. I know of another FJ60 that does this also. It smells exhaust like in nature which is odd since the a/c vents are isolated from any exhaust. The heat/AC controls are mechanically operated so to the best of my knowledge there is no vacuum operated items under the dash that would contribute to this. Anyone out there run into this and know what the cause, and more importantly, the cure is?

Thanks...Don
 
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Any thought as to why or how that backfire ends up comping through the a/c vents? The dizzy backfire seems like a possibility, just not sure how that mini explosion is transmitted into the vent system and into the cab.

Thanks..Don
 

Godwin

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It's not coming through the AC vents. In the firewall under the passenger side dash is a filter which is vented to the dizzy. Pop the hood and you can follow the tube from the cap of the dizzy back to the firewall. Unburnt exhaust gasses are sometimes present in the cap and when you crank the engine the initial spark under the cap sets off a small explosion which you then hear and smell in the cab. It just seems to be coming from the AC vent. The filter is buried under the carpet and kinda up behind the duct work. A small pain to reach. I have had these explosions be forceful enough to actually blow holes in the side of the caps. Even with a big chunk missing from the distributor cap the 2F kept right on plugging along.
 
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Godwin,

Thanks. i was able to get a hit on a search based on clues from Hullendersauce (dizzy explosion) and saw your post. That sounds exactly like what the problem is. It never occured to me that the fresh air source would come from the cab.

Don
 

65swb45

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Mountain Goat said:
I've been dealing with this one too. I took me about a year to figure it out. Any idea what can be done about it? I'm tired of replacing emissions components and distributor caps.
Thinking about it logically, since the other line goes to the air cleaner, which is negatively pressurized with vacuum coming from the carb, it would stand to reason that the hose running to the cab was designed to be a dry, filtered air source to replace the vacuum being created inside the cap. Sooooooo, barring a total restriction in the filter, you should be able to just move it from its current location in the cab to one in the engine compartment that you trust to stay dry.

Or is that too simple?
 
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Mine just did that this morning and I scared the s*** out of me. Glad its something relatively easy to deal with.

Hodag
 
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I am glad that I am not the only one that is experiencing this issue. It seems on mine that it is coming from the rear heater under the front passengers seat, but I guess that it is dizzy related....weird.
Everyone once in a while it does it, and always scares the s*** out of me.

Adds to the chatacter
 

Godwin

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65swb45 said:
Thinking about it logically, since the other line goes to the air cleaner, which is negatively pressurized with vacuum coming from the carb, it would stand to reason that the hose running to the cab was designed to be a dry, filtered air source to replace the vacuum being created inside the cap. Sooooooo, barring a total restriction in the filter, you should be able to just move it from its current location in the cab to one in the engine compartment that you trust to stay dry.

Or is that too simple?
I've done something like this twice.

Once when I installed an FJ60 distributor into my FJ40, ran the tube up to the firewall and capped it with a cheap fuel filter.

The setup for the 3FE'd FJ60 is similar, the intake line is capped with a cheap fuel filter. In this instance I had had the engine out and the in-cab filter was exposed for a few weeks. About 4 months post reinstallation the distributor died. The electronics under the cap were corroded. I replaced the distributor with a new one, which lasted about 6 months. Replaced the distributor a second time, but with this one I disconnected the intake from the in-cab filter. This setup has been in place several years now and no more dying distributors. I still have no idea what may have contaminated the filter sufficiently to, over time, ruin two distributors.
 
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There should be a vac control valve between diizzy & air filter housing.
purpose of valve: not allow gassy vapor to 'drift' back into dizzy when engine shut down...
the valve should be hanging by a clip' under passenger side of air filter housing...
 
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soggy60 said:
There should be a vac control valve between diizzy & air filter housing.
purpose of valve: not allow gassy vapor to 'drift' back into dizzy when engine shut down...
the valve should be hanging by a clip' under passenger side of air filter housing...

On mine, my farting distributor had actually blow through this vacuum control valve. I could blow through from the control side to the switched side. Replacing the vavle didn't seem to help. What did *appear* to help was replacing all of my vacuum lines to fix a different problem. Now I rarely hear it.
 
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Old post I know, but a very funny thing.

Several of the previous post metnion it scaring the s*** out of them. Well I had heard it a couple of times when I had started the 60 up. And yes it scared me terribly, dust rolls out from under the dash and everything else. But by the third time or so, I knew what it was. It does it very seldom, maybe once a year.

This fall my wife and jump in the 60 and I fire it up, and it let off a good one, really loud, dust flew and everything. My wife nearly jumped out of the car as we backed out of the driveway. She kept asking waht was that, what was that. We were five blocks down the road before I could stop laughing and explaint to her that the distributor sometimes does that and tell her about the funny vent under the dash.

God my side hurt after that, the expression on her face was hilarious.

I never really knew why it did that till now. Too funny when it happens like that, always unexpected.
 
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wow that i always wondered what that was, i tought it was some sorta fuse
in the radio.
 

Cruiserdrew

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I thought it meant one of the vsv's in the evap system was going bad. I had the pop once, called Cruiserdan about getting a vsv, and the shaman worked his magic, and I didn't need it. It's never popped since.
 

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