jbradshaw77

Hello,

I did use the Search function but was unclear as to what exactly I need. If someone could please advise I would be grateful.

I have an 1986 Firebird SE, V6 Automatic. I get very poor MPG (~12mpg). There is a very strong odor of gas coming from the driver's side door area. This has been the case before and after I removed the charcoal canister, which unfortunately had no effect on the MPG.

I want to attempt replacing the gas cap, but I would like to know if I need one that is vented or not. I am seeing very mixed results on these threads. Does anyone have a definitive answer?

Thanks so much,
J

Drew

iTrader: (58)

Next time you fill up, look under the car at the gas tank, and check for signs of wetness around the joint from the filler neck to the fuel tank. There's no support for the filler neck. Between manufacturing defects and age, the joint can crack or otherwise leak.

jbradshaw77

Thanks so much for your reply. I did as you recommended and checked however I detected no cracks or leakage. Would you happen to know simply if my car would require a vented cap, or a non-vented cap?

J

vinny R

I believe all these cars use a 3 click cap and are not vented. The system needs to hold pressure so a vented cap would not be able to achieve this, There is a vent system that runs to the charcoal canister so you don.t smell the fumes. It sounds like you have a problem with this. I would recommend putting the canister back and tracing that vacum line all the way back to the tank to see if you have a leak in that line.There is a small check valve in that line back near the fuel tank. I have seen a ton of folks have issues with that check valve, Not sure what it is called and not sure if you can get a new one either. There are multiple threads that show how to rebuild it IF that is the issue.

Not real sure that any of this is related to bad MPG,

OrangeBird

iTrader: (1)

Lets get one thing straight here before we even start ; NO third gen , not a one , from it's introduction in 1982 through it's replacement by the fourth gen in 1993 , was built with a "vented" gas cap ! And , a properly functioning factory third gen fuel system emits no detectable fumes whatsoever , and , gets pretty good gas mileage as well ...

Now , this "playing engineer" and removing the factory designed emission controls has put you all that much further from solving your original problems . ARE you a fuel systems engineer , with the full knowledge of how to design and/or redesign a car's emissions control systems ? I thought not , otherwise you wouldn't be here asking such questions !

Does the above sound prickish ? Good ! I hope so , removing parts of your car without a clue as to how the system is designed is a perfect recipe for things like never being able to find out why your smelling fuel and getting poor mileage . Can the emissions control system cause such troubles ? Of course it can , and the RIGHT course of action here is to repair the fault within the system , rather than following the knuckle dragging mantra of "I'm just gonna rip out all this emissions crap and then it'll run like a racecar" . Now , If you EVER want your car to operate correctly , here's what you gotta do ;

Start by putting back each and every piece you hacked out of it , starting with the charcoal canister and finishing with all the other vacuum hoses and such that may have gotten removed along the way . Only with the fuel system in it's 100% factory configuration can you begin to diagnose why you smell gas and get bad mileage . You do realize your cars computer is specifically designed to work with ALL of the factory designed systems in place and removing any of them without a comprehensive plan to eliminate them , ECM wise , will make the car run worse and not better , yes ?

Does the above sound like too much "tough love" ? .... I hope so , I'm a mean old bastard sometimes , but what I've told you here is the 100% truth , no matter how ugly the facts may seem ....

jbradshaw77

Thank you both for giving me a straightforward answer on the gas cap.


I appreciate your extra input and will take it all into consideration, however, the only thing I removed from the car was a 32-year-old charcoal canister -- nothing else. I did this based on the numerous threads I found on this site suggesting that the canisters can become clogged, and that some folks had success removing them and achieving results. I would hardly consider this "playing engineer," and I certainly had no plans to remove any vacuum hoses or other parts of the car. My initial inclination was to replace the canister -- however, under the advice of my mechanic, and gleaning from the threads I have read on here, it was not necessary. If you are of a different opinion I appreciate that, however I think you may have jumped the gun a little in assuming I have taken to haphazardly ripping out pieces of my car.

Drew

iTrader: (58)

Lots of stupidity around these parts, specifically surrounding things like emissions equipment, and removing this or that for perceived advantages. When someone says something is unnecessary, and to 'delete' or 'gut' or whatever phrase, you can usually take it with a huge grain of salt.

The only vent from the tank is passed thru the charcoal can to filter pollutants. If someone removes the can and leaves the line open, it'll vent to atmosphere and stink. If a person caps the vent line, the tank won't vent.

The proper way to correct a problem is to isolate the issue, and replace the faulty part(s). Simply removing a part seldom fixes an issue.

jbradshaw77

Thank you for clarifying this. My poor understanding was that there might have been some sort of "blockage" due to clutter in the charcoal canister, but I now understand why it is necessary. Do you recommend purchasing a brand new canister, or do you think the old one may be fine? Is there a way I can test the old one?

Drew

iTrader: (58)

There are diagnostics and flowcharts in the service manual for troubleshooting problems with the evap system. The first thing I'd be checking is all the rubber. At this point, most of the rubber is questionable. Beyond that you might want to look for older threads. Google works best, just type your search terms and thirdgen.org and it'll find older threads with those terms.

Here are a few threads that may be worth a look.

https://www.thirdgen.org/forums/tech...-pressure.html
https://www.thirdgen.org/forums/tech...e-my-fuel.html
https://www.thirdgen.org/forums/tpi/...ter-noise.html
https://www.thirdgen.org/forums/tpi/...-pressure.html
https://www.thirdgen.org/forums/hist...ent-valve.html


By the book, the service method for the canister is to replace. I seem to remember a recent thread about cutting the can open and replacing the charcoal. Normally I wouldn't think it'd be necessary to do that, but I guess it could be an option.

https://www.thirdgen.org/forums/tech...ebuilt-my.html

TheFryer

yup. most of my emissions was removed before i even got the car. only thing left was the charcoal canister and egr. all the lines that came from the motor to it was dry rotted and cracked open or just plain fell apart. i have a locking vented gas cap on mine and it dont help with the smell at all. your stuck with it till you do something about it. in my case i am getting more rubber line payday, and i have some wire loom to help shield it from some of the heat of the intake. going to replace it all to the canister, then replace the lines going to the fuel tank just so i know they are new. if that dont help i will replace the canister. my egr is getting a blocking plate, and my ecm will get a new prom to remove it from the ecm.