Is There Too Much Pressure In Your Fuel Tank, Do You Smell Gas Fumes? How GM Evap System Works

[@nobodyever6515]

Thank you for this wisdom. I replaced the canister on my 91 s10 but an now going to look into things a little deeper! Well spoken and great explanation✌️

[@bitsofwisdom460]

Thanks, glad to be of help.

[@kmas8229]

I swear man, you're a psychic. I think I have too much pressure in my tank. If I park the car after a long drive in hot weather and remove gas-cap there's hissing. Almost sounds like fuel is boiling (Blurp blurp). Ordered a new vent-valve (the one in left rear wheelwell) and the valve just by the charcoal canister a few weeks ago. I already have a oem non-vented fuel cap so I hope it'll fix it. I don't smell any fuel though.

[@kmas8229]

It's hard to refuel now and then, with the pressure triggering the filler-gun to stop the filling.

[@bitsofwisdom460]

@@kmas8229 I only smelled fuel on occasion, like after a hot weather run in traffic. The tank would build enough pressure to push open the vent valve in the rear. I have issues fueling, but I think that is unrelated. I have an aftermarket tank, but it ought to be like factory. If I'm 10 or 12 gallons down, I can fill the first 4 or 5 gallons at full rate, but after that I need to go slow.

[@demenACE]

That valve you point out that failed was very common in the year model.

[@mikebruegger8654]

Great information! I'm going to check the valve on mine as I do tend to smell fuel. I know my rear vent is good as I cleaned and rebuilt it. Thanx, looks like an easy check

[@bitsofwisdom460]

It's worth a check. I know there are times where that rear vent may still pop off, but this purge valve operating properly can certainly minimize it.

[@AV131082]

@@bitsofwisdom460 Very helpful video, by the way, did you ever film a video regarding the chassis lubrication points?, thanks and have a nice day!

[@MegaWatching]

I sold my 1987 Iroc Z for this reason. I regret selling it so I bought an 88 Iroc Z but this one is driving me crazy with code 36 MAF Burn-Off. I went through the tree of trouble shooting to the last step. "Disconnect Burn-Off relay, Ignition On, Probe CKT 900 with a test light to ground. Light Off, but Volt meter reads 0.44 dc. Will keep trouble shooting till I find the problem. Well I subscribed to your channel you have great info. Thanks

[@vildebill2000]

I had same on my 1987 corvette . No need to trouble shoot. Just change the 2 relays. Don't cost much and solved my codes

[@DenisVassiliu]

Hi teacher Dan, I am your new subscriber. I want to tell you that this is the first time that I subscribe to a KZbin channel. I do it as a way of thanking you for all your time and dedication to helping others by passing on your knowledge and experiences that are very useful. For me all your teachings on your channel have been very useful, since I have a 1986 Firebird Trans Am 305 tpi automatic with BW 3.27 rear axle with t-top and 4 disc brakes. With that said, here is my first question: why did you choose a third generation Camaro for your project? Did you consider it superior to other generation car alternatives or was it just a closer opportunity?

[@bitsofwisdom460]

Thank you for subscribing and for your comments. It was an opportunity, yet it had some special significance. I wasn't searching for one, but rather found this car and was intrigued. First, I saw this car sitting in the garage, appearing to be complete yet clearly parked for a long time. I did some quick checks and research with the RPO label and the car's condition. It appeared to completely original. There was evidence that the original owner had taken great care of it and yet had never come back to return it to the road. It was the proverbial car that someone had just parked and put a cover over - waiting to be found and restored. Then, it was a special model. As a GM employee with a long career, I had been working in an engine / transmission dynamometer test lab when these tuned port engines first appeared and when the IROC was introduced. The port injected engines were quite an advancement in a day when a standard 5 liter V8 made 140 or so HP. In addition, I had worked on the transmission / axle and related parts of the 4th Gen cars, so I had some background on the Camaro line. As a car guy, it looked like a great challenge and opportunity to put an essentially historic car back on the road. As I worked, I came to better appreciate how good this car was.

[@truthtime4924]

Hey Dan, i own a 1983 z28 h.o is been changed to carburetor. Yesterday I tried removing the entire canister but it made it worst. Today I picked up a new purge valve hooked it all up took it for a drive and issue still remains. The car runs great when I first get in it and drive , once it’s been driving for about half hour and it gets warmed up it mainly happens on the highways once I’m going 50+ it starts to hesitate and if I don’t let off the gas it will only get worst until I’m there hitting the gas and the engine revs in a weird way doesn’t sound like how it would normally is almost like if you stuck the engine inside a bucket the sound it makes sounds deadened until it can’t go anymore. I notice my gas filter in the engine you can see the gas boiling inside it even after the new check valve. Fuel pump also gets x10 louder. Hoping you might know something about this

[@bitsofwisdom460]

Well, not sure about your conversion. So, that was a crossfire engine with two throttle bodies and electric pump? If so, there would have a fuel pressure regulator and return to the tank. In your conversion, is there regulation and fuel return? The TBI units would normally have higher fuel pressure than the carb, probably 10 psi vs 3 to 5 psi with an in tank pump. The purge valve on injected engines keeps a psi or two pressure held on the tank. Bubbles in the tank can be fuel boiling due to low pressure combined with hot fuel. A fuel return will help take hot fuel back to the tank. That can help and hurt. Keeps the line cool, but send hot fuel back to the tank and heats the tank. Generally a net positive.

[@jesseortiz8829]

Interesting that you put this video up cause mine is a 91 z28 and I dissembled the fuel vapor canister lines . So I thought the purge solenoid came off the top of canister. It look like it did but does not so I broke tube under solenoid. Now that I’m wrapping up the rebuild the car smells like gas really bad up by the canister. Since then I hv read in forums that you can buy the new solenoid and canister from a 93-02 camaro which is still available. I still need to buy also vent valve from rear of car

[@bitsofwisdom460]

I had a question from someone who watched my earlier video asking for more detail, so it seemed to be a good time for it. The suggestion that the newer canister could work is worth investigating. As long as the solenoid is still the same normally open type, the ECM ought to command it. Just would need to compare the coil resistance so that the ECM driver will still work ok. I expect that it should be compatible.The controller teams try to keep commonality as much as possible so that different controllers can be used in different models, but always worth a check..

[@jesseortiz8829]

@@bitsofwisdom460 I was mistaken it’s the canister and purge solenoid from a 93-95 camaro . The threads I have read are saying it’s plug and play . Works perfect

[@philcoomer6449]

Thank you sir! My canister is not hooked up. Recently I started hearing bumping from the tank and it does sound like my pump is cavitation.

[@bitsofwisdom460]

@@philcoomer6449 When I removed the fuel tank control valve for testing and attached the vent line straight to the canister, I did not expect to see a problem. I expected that a pump submerged in the fuel ought to work fine. It was quite a surprise. But when I installed the new valve it really cured the issues.

[@alexcat321]

In ur previous video, u said u had an idling issue where when u drove the car for an hour, after restarting it it wouldn't want to idle. Did the idle air control valve finally fix your issue? I had this issue pop up today... And I also smell gas. I replaced my vent valve. in the rear, but not the purge valve near the canister.

[@bitsofwisdom460]

Yes, I did change out the IAC. I actually reinstalled the factory original part that I replaced just because it was old, while I waited for a warranty replacement part. The car was running well so the new replacement part is still on the shelf. Perhaps one of these days I'll swap it. In my car, the rear was venting because the front purge valve was bad.The rear doesn't vent any longer.

[@JohnSolito]

Hi Dan, My 1987 5.0 IROC is experiencing the same things… after driving it for awhile it gets jerky at low speeds, can smell fuel, I can also release a lot of pressure when removing the gas cap. I’m not hearing any boiling sounds from fuel tank. Both purge valves test good as well the valves are receiving good vacuum when cracking the throttle. Electric control valve on canister is also working properly. Any other ideas what to check?

[@bitsofwisdom460]

I'm not sure, but here are some thoughts. I have observed that having a functioning purge system is necessary, but not sufficient to stop all smell issues. For reference, my experience is that in warm / hot weather and low speed stop and go traffic (like the Dream Cruise...), I think the hot fuel vapor exceeds what the purge system can handle as hot fuel is circulated back to the tank from underhood. At low speed / idle, the underhood temp is higher and fuel flow is low, so the regulator sends a lot of hot fuel back to the tank. The purge valve will by design hold some pressure on the tank, so you will get some pressure release at the cap (but not nearly the amount with a bad purge valve). My read is that the jerky feel at low speed is the purge system working as designed. If the canister is full of vapor and you tip in lightly, the ported vacuum will open up the valves and you get a sudden rich flow of fuel vapor for the engine to handle while throttle opening is low. If I tip in harder and dilute it somewhat, it clears and runs fine. If this continues and the purge system can't vent enough through its orifices, the overpressure valve in the back will open and vent the excess vapor. Perhaps there is an issue with canister capacity or internal flow that it cannot handle the volume of vapor, but I don't have a way to measure that. I would think the canister would just push it through the carbon granules and out the filter at the bottom. My sense is sometimes the driving conditions just overrun the system and I don't have a solution. As a side note, If I run on the highway, I can run at much higher ambient temps and not have an issue when I come to a stop - until I get a long slow stretch.

[@JohnSolito]

Yes, what you described is the same for me… everything runs fine for awhile after coming off the highway. It’s the slow traffic or cruising through the neighborhood at 25-30 mph is when it acts up some. Appreciate your feedback @@bitsofwisdom460