Would a vent valve cel cause my mpg's to drop? - Camaro5 Chevy Camaro Forum / Camaro ZL1, SS and V6 Forums

6bangerBOOM · 11-27-2013, 10:33 PM

Took my car to the shop yesterday after it died out while I was parked on the phone. Well, I cut it off before it died, but it suddenly sounded and felt like a cam lope. The mechanics told me I had a cylinder misfire and code p0499 showing. They said the vent valve wasn't a huge issue and I could fix it after thanksgiving.

On my drive home today, however, things didn't sound right. Idle wasn't rough but it did seem kind of labored. And the exhaust drone was much deeper than normal. Lastly, my mpg was right at 24 for the trip which consists of about 8 hours of highway. Normally I'm in the upper 20's/low 30's.

Would the vent evap valve malfunction cause all this or do I have another issue that hasn't thrown a cel?

TooCool5 · 11-28-2013, 11:32 AM

You could search other thresd on vent valve and ask the members it happened to about MPG's.
Its a large repair on the 10's Maybe they made an access door in your yr.

6bangerBOOM · 12-03-2013, 03:04 PM

Update: I finally got a chance to look under the hood after all the thanksgiving madness settled down and found that the mechanics had left the evap line disconnected from the purge valve on the back of the engine. Reconnecting it seems to have made my idle smoother (though I'm not sure that this is the real issue). There still seems to be some exhaust rattle sometimes when I'm stopped at a light, but overall idle feels healthy again.

Rock-It Man · 12-03-2013, 03:27 PM

Do you still have a misfire?

I had a misfire on another car (not Camaro) caused by rodent damage, and it made the mpg calculation fluctuate.

6bangerBOOM · 12-03-2013, 03:54 PM

No, I can tell that my problem isn't completely solved but my idle is better. No misfire though. What was weird was that all my usual engine sounds seemed to have shifted 1000rpm's sooner than normal. My 2000rpm deep drone was at 1000rpm. The throaty engine note I get at 3500rpm's from my CAI was audible at 2500. Not sure what the deal is but I'm taking her back in tomorrow.

6bangerBOOM · 12-15-2013, 04:34 AM

Issue resolved. The mechanics left my evap line disconnected, so I drove about 1000 miles from TX to GA fuel-rich. I changed all my sparkplugs out (including the brand new one the mechanics had put in for the misfire...which was gapped at 0.054... the bastards), and did a round of seafoam. There was a tremendous amount of carbon build-up so she was smoking like hell after the seafoam. I finished the night up with both MAF and throttle body cleaner. She's back to normal. I feel like I should ask the mechanics what the hell they were thinking (if one spark plug was fouled you'd think the others might be as well), but I think I'm just going to buy a code reader and handle small stuff like this on my own. Lesson learned. Will be googling a new shop though.

TooCool5 · 12-15-2013, 01:30 PM

You got it, do it yourself and get it done right.
Got my own reader also.
I could tell you story after story on this subject.

11-27-2013, 10:33 PM	#1
6bangerBOOM Drives: 2016 1SS SW Join Date: Jun 2013 Location: N/A Posts: 1,443	Would a vent valve cel cause my mpg's to drop? Took my car to the shop yesterday after it died out while I was parked on the phone. Well, I cut it off before it died, but it suddenly sounded and felt like a cam lope. The mechanics told me I had a cylinder misfire and code p0499 showing. They said the vent valve wasn't a huge issue and I could fix it after thanksgiving. On my drive home today, however, things didn't sound right. Idle wasn't rough but it did seem kind of labored. And the exhaust drone was much deeper than normal. Lastly, my mpg was right at 24 for the trip which consists of about 8 hours of highway. Normally I'm in the upper 20's/low 30's. Would the vent evap valve malfunction cause all this or do I have another issue that hasn't thrown a cel?

11-28-2013, 11:32 AM	#2
TooCool5 Drives: 2010 Camaro 1LS 3.6 LLT V6 325 HP Join Date: May 2009 Location: LS Posts: 4,245 View My Garage	You could search other thresd on vent valve and ask the members it happened to about MPG's. Its a large repair on the 10's Maybe they made an access door in your yr. __________________ 2010 Camaro Auto, Inferno Orange, Titanium Interior, Gearhead Wheels AIRAID CAI

12-15-2013, 04:34 AM	#6
6bangerBOOM Drives: 2016 1SS SW Join Date: Jun 2013 Location: N/A Posts: 1,443	Issue resolved. The mechanics left my evap line disconnected, so I drove about 1000 miles from TX to GA fuel-rich. I changed all my sparkplugs out (including the brand new one the mechanics had put in for the misfire...which was gapped at 0.054... the bastards), and did a round of seafoam. There was a tremendous amount of carbon build-up so she was smoking like hell after the seafoam. I finished the night up with both MAF and throttle body cleaner. She's back to normal. I feel like I should ask the mechanics what the hell they were thinking (if one spark plug was fouled you'd think the others might be as well), but I think I'm just going to buy a code reader and handle small stuff like this on my own. Lesson learned. Will be googling a new shop though. Last edited by 6bangerBOOM; 12-15-2013 at 04:45 AM.

12-15-2013, 01:30 PM	#7
TooCool5 Drives: 2010 Camaro 1LS 3.6 LLT V6 325 HP Join Date: May 2009 Location: LS Posts: 4,245 View My Garage	You got it, do it yourself and get it done right. Got my own reader also. I could tell you story after story on this subject. __________________ 2010 Camaro Auto, Inferno Orange, Titanium Interior, Gearhead Wheels AIRAID CAI

12-03-2013, 03:04 PM	#3
6bangerBOOM Drives: 2016 1SS SW Join Date: Jun 2013 Location: N/A Posts: 1,443	Update: I finally got a chance to look under the hood after all the thanksgiving madness settled down and found that the mechanics had left the evap line disconnected from the purge valve on the back of the engine. Reconnecting it seems to have made my idle smoother (though I'm not sure that this is the real issue). There still seems to be some exhaust rattle sometimes when I'm stopped at a light, but overall idle feels healthy again.

12-03-2013, 03:27 PM	#4
Rock-It Man 376 cubic inches of fun Drives: 2023 Camaro ZL1 A10 Join Date: Jul 2010 Location: MA Posts: 4,043 View My Garage	Do you still have a misfire? I had a misfire on another car (not Camaro) caused by rodent damage, and it made the mpg calculation fluctuate.

12-03-2013, 03:54 PM	#5
6bangerBOOM Drives: 2016 1SS SW Join Date: Jun 2013 Location: N/A Posts: 1,443	No, I can tell that my problem isn't completely solved but my idle is better. No misfire though. What was weird was that all my usual engine sounds seemed to have shifted 1000rpm's sooner than normal. My 2000rpm deep drone was at 1000rpm. The throaty engine note I get at 3500rpm's from my CAI was audible at 2500. Not sure what the deal is but I'm taking her back in tomorrow.