Was out for a ride Sunday and stopped for gas after about 20 miles. Upon loosening the gas cap, the tank vented pressure for about thirty seconds after which the car would not accept gas past a dribble from the nozzle. Put ten gallons in and resumed the ride. After another thirty miles parked in my driveway and decided to check for pressure again. This time the pressure was even more than when at the gas station, so much that fuel blew out of the filler. I'd never had this problem before and did notice once or twice that the car was slightly sluggish off the line, otherwise fine. The car did not throw any codes or light the check engine light, nor did it get hot. It runs cool anyway and never got over 188*. I tried searching the forum but found very little relating to this issue. Any help or advise would be appreciated.

The car is a '99 with H&C, A&A V2Si, full exhaust.

 

Pull your codes and see what you have. Not at home but something is wrong. Not that familiar with the evap system but this could my chance to learn.

 

Your fuel cap is a NON VENTED CAP. That being said the pressure has to go SOMEWHERE.

Here is where the CHARCOAL CANISTER comes into play. When the car is shutdown, the tank is allowed to vent pressure (fuel vapors) into the charcoal canister and it STORES the vapors. When the engine is at NORMAL operating temp, closed loop ect.. the PCM tells the evaporative emissions system to SUCK the vapors into the intake manifold and burn them in the normal combustion process.

Your evaporative emissions system isn't working properly and SHOULD be throwing a DTCs for the following reasons:

Excessive pressure in the tank sensed by the fuel tank pressure sensor.

Are you the orig owner of the car and if not,, that part of your PCM could be tuned out thus not throwing a DTC. You should have a Check Engine Light CEL if the pressure is that great.

Bill

 

Just curious where is the charcoal canister located?

 

In the rear of the car. Its mounted on the inside of the passengers side frame rail

You can ALMOST see it in this picture on the right just below those hard lines for the passengers side tank... The white tag is on the wiring harness for it.

 

[QUOTE=Bill Curlee;1589525499]In the rear of the car. Its mounted on the inside of the passengers side frame rail

You can ALMOST see it in this picture on the right just below those hard lines for the passengers side tank... The white tag is on the wiring harness for it.


Nice pic Bill... I like the mods you've done to your car!
Actually thanks for the post great info...

 

I have to keep the title in the car... COPS keep pulling me over because they think it a big go cart!

Actually,, its the GM Bowling Green Museum Frame C5 Show Piece. They have several of them.

Early pre production 97:







Balsa wood/ fiber glass laminated floor panel!







They have a very early pre production 97 frame in the museum and this one, which I believe is a 98 late model or 99

They also have a C6 ZO6 frame just like this one!

C6 ZO6 Aluminum Frame:

 

Mr Curlee

I knew it wasn't your car, I was just kidding you...
But, after 25k post and 14 years on the forum I'm sure you have seen some pretty interesting post...

Thanks again for the cool pics.... I hope to make the pilgrimage to the Corvette Meca and visit the shrine and do homage to the corvette gods
...

I think it would be cool if you and some others would do a thread on the most ridiculous/dumbest/silliest things you have come across in all the years you have been helping the corvette community... just don't use any of mine...

 

MAN,, ,, You were FIRST on the list of post to make a thread on!


LOL!


8VETTE7

I have been known to disassemble the ZO6 to figure out a problem for someone or take a picture. Just not to that extent!

It would be cool to ride around in a naked C5!

Bill

 

Bill...was that a Freudian slip... Did you mean to say...
It would be cool to ride around naked in a C5...

 

I you saw me naked in a C5,, you or me would have been on a serious case of CRACK!

 

Thanks for the replies. As stated, no CEL. There are actually a few codes but none related to the EVAC system.
P0103HC - MAF - Tuned out to not throw CEL.
U1016H
U1064H
U1096H
U1160H

 

Pretty sure they will vent after x amount of pressure.

If I remember correctly, there's holes & a spring in the cap

 

Here is a link to the system description. It would seem that the vent solenoid or pressure sensor may be the issue.

http://www.teamzr1.com/ubbthreads/ub...at&Number=1918

 

Once again, thanks for the replies. I *may* have found the problem. I removed the purge solenoid and tested the resistance. I found the first test at about 950 ohms just holding the leads on the solenoid pins. Got gator clips attached to eliminate the possibility of a poor connection and read 850 ohms. I then tapped on the body of the solenoid and watched the meter read 1200 ohms. More tapping and the resistance was all over the place until finally settling on 26 ohms. I figured I was home free...until I put power on it...and it worked. Through experience I know the intermittent problem is the worst to deal with. So for less than thirty bucks I just ordered one as well as a canister solenoid.

 

Thanks for the update... be sure and let us know after install how all is going... hope it ends your quest to find the problem...

 

obd2 uses a fairly similar system across most cars. the tank vents to charcoal but usually has an EVAP purge solenoid that triggers whenever the manf tells it to. typically when the car is warm. vapor is released and enters the intake system

a faulty evap solenoid should trigger a code but might not. i had this issue on a honda a few years back and the solenoid still tested okay but would not open correctly

if the c5 actually has a tank pressure sensor i would imagine that code would be in the DLC as bill mentions

 

When you pull the OLD one out,, take a few pictures and if you can dissect it and figure out the cause of the failure,, THAT would be a BONUS PLAN!

We have a small moth here in the Northeast that will lay eggs in a specific size hole. One car manufacture found out the hard way that they were having fuel tank vent valve failures because that moth layed eggs in the vent hole and covered them with a MUD PLUG!

They had to do a recall on that vent valve and put a filter on the vent hole..

 

Update:
I received the purge solenoid and canister solenoid earlier in the week and brought the car to work to install. We do our own vehicle maintenance and I'm lucky enough to have access to a lift. Anyway, it is a 23 mile trip to the shop and upon arrival I pulled the codes before shutting down. No codes other than what I previously posted. Shut it off and pulled the gas cap...no pressure. So, I believe the purge solenoid was the culprit based upon the inconsistent resistance test readings. Popped on the new purge solenoid, replaced the canister solenoid which was also very easy once I cracked the code on how to get the old one off, gave her a new fuel filter (armpit full of 93 octane burns ) and fresh Royal Purple and a Royal Purple oil filter. I did a 30 trip back home and pulled the gas cap and again, no pressure. I did also buy the fuel tank pressure sensor but did not tackle that job today. If she builds pressure again that will be my next step. I'll post if she acts up again, but I think she's fixed.

 

good job

research royal purple with this car though. it's a PAO based group 4 base stock with no real seal modifier or at least not one that works. PAO base stocks shrink seals and can harden them. amsoil has a nice seal additive pack in their PAO oils if you like PAO, i just have personally seen more c5s develop leaks with royal purple than any other oil ever. on a new car it takes a long time for this to happen. on one the age of the c5 it may happen in just a couple years of use.

redline is a group 5 ester oil and actually by nature swells seals. mobil 1 high mileage also has a seal conditioner added to what's more or less a very refined group 3 base stock. these are my two favorite oils for older high performance or air cooled applications....they just seem to leak the least. redline also has an extremely high ZDDP level. great for high cylinder pressure, air cooled or full blown race engines

rather than debate pros/cons of various base stocks the seal angle on a c5 is one that's worth paying attention to simply because of the age