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I have a 1986 Dodge B250 van with the 5.2L Chrysler V8, one of the last years before they switched to fuel injection. It's a camper conversion van, has low mileage and runs/drives great.

Since I got the van I noticed pressure builds up in the gas tank, such that when I go to fill, especially on a hot day or after a long stretch of driving, a serious amount of fumes gush out when I remove the gas cap. This can last a good 10 to 15 seconds.

Last spring I investigated to try and fix the pressure issue and figured out that the EVAP canister is entirely missing, the line that should run to the carburetor is gone entirely, and the lines coming from the top of the gas tank have been cut.

Since I discovered that, I have been loosening the gas cap before I drive to allow the tank to vent and avoid the crazy pressure build up, which seems dangerous.

Is driving with the gas cap loose a workable long term solution? Is there any concern with having that open hole on the carb. where the line from the charcoal cannister used to go? Should I try to find a cannister and try to re-install it?.

My real question is what I should do about this, if anything.

Any theories on why somebody would rip out the EVAP are also welcome.

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The tank should be vented, and done properly it should vent into a canister. The purge line to the carb is less important, but a hole in the carb under the butterflys is likely creating a vacuum leak.

I can't speculate why people remove things like that. Probably an imagined performance gain unlocking hidden horsepower by removing all those evil "emissions" devices. Or maybe it just rotted and broke.

In any case, the gas tank needs to breathe - in both directions, to keep the pressure balance in the tank. The lines must have been cut and plugged, otherwise it would vent the raw fumes just fine - although that's not a proper or safe solution.

Junkyards will have tons of these from that era, and the cost should be very low.

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  • Thanks Steve, I'm just cutting my teeth on mechanical work so I really appreciate the insight. I have noticed it tends to lope at idle, some googling tells me that's a common side effect of the vacuum leak. Sounds like my long term plan is to reinstall the canister and run new lines, which I think means dropping the tank. Short term I'm going to cap that leak on the carb somehow and keep running with the gas cap loose to allow venting.
    – Cameron Roberts
    Jan 25, 2018 at 12:51

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