Cadillac Owners Forum banner

1 - 13 of 13 Posts

·
Registered
Joined
·
19 Posts
Discussion Starter #1
Swung by O'Reilly's today to have them scan my 2008 RWD STS 4.6. They gave me code P0455: evaporative emission control system leak detected ( gross leak).
Is that something that can cause something that feels like hesitation or a misfire? The suggested fix is a new gas cap, so I ordered an OEM cap from Rock Auto.
 

·
Registered
Joined
·
655 Posts
Sometimes it's the gas cap, but also often it's not. I have that code and the gas cap did not fix it. My mechanic thinks it's the evap canister vent valve. Had the system smoked and no leak detected, but the valve only operates under certain parameters. Usually a faulty vent valve makes gassing up difficult as it causes the pump to keep shutting off when not full, and starting after filling up can be difficult. Not sure about the hesitation/misfire, but I don't think it would cause that.
 

·
Registered
Joined
·
19 Posts
Discussion Starter #3
Sometimes it's the gas cap, but also often it's not. I have that code and the gas cap did not fix it. My mechanic thinks it's the evap canister vent valve. Had the system smoked and no leak detected, but the valve only operates under certain parameters. Usually a faulty vent valve makes gassing up difficult as it causes the pump to keep shutting off when not full, and starting after filling up can be difficult. Not sure about the hesitation/misfire, but I don't think it would cause that.
Interesting, the gas pump shuts off on me all the time at Safeway...I figured I was holding the handle at the wrong angle.
Yeah, I was expecting to see which cylinder was misfiring, I suspected a coil.
 

·
Registered
Joined
·
655 Posts
Sometimes people top off the tanks by squeezing every bit of gas out of the nozzle. I saw a guy do this for 5 min, shaking the car between them :rolleyes:. This can cause the pump itself to malfunction for the next guy to gas up. For the misfire, I would suspect a coil/connection as well...any codes?
 

·
Registered
Joined
·
19 Posts
Discussion Starter #5
My car has never had an MIL turn on. The only code was the P0455. Speaking of which, I don't find a Evaporative Emissions Control vent on RockAuto, does it have another name?

It has had the TPMS light kick on, one of them is dying...unrelated.
 

·
Registered
Joined
·
237 Posts
Sometimes it's the gas cap, but also often it's not. I have that code and the gas cap did not fix it. My mechanic thinks it's the evap canister vent valve. Had the system smoked and no leak detected, but the valve only operates under certain parameters. Usually a faulty vent valve makes gassing up difficult as it causes the pump to keep shutting off when not full, and starting after filling up can be difficult. Not sure about the hesitation/misfire, but I don't think it would cause that.
Is there a purge valve AND a vent valve? I see them both mentioned in various threads.
 

·
Registered
Joined
·
19 Posts
Discussion Starter #7
Back to the misfire...I replaced my plugs about 2 years ago, but I noticed a bit of oil wetness in a couple plug valleys. Can a leaky valve cover gasket foul plugs and cause intermittent misfires? It occurs regularly at low RPM, we're talking less than 1800, in 6th gear under load. Doesn't occur while cruising on a flat, but uphill or accelerating.
 

·
Registered
Joined
·
655 Posts
Is there a purge valve AND a vent valve? I see them both mentioned in various threads.
In short...yes. The purge solenoid is on the engine (at least in the N*), and the vent valve (solenoid) is part of the charcoal canister near the gas tank. The vent valve takes in fresh air, and the purge solenoid takes gas fumes stored in the canister and exhausts them into the combustion chamber to be burned.
 

·
Registered
Joined
·
655 Posts
Back to the misfire...I replaced my plugs about 2 years ago, but I noticed a bit of oil wetness in a couple plug valleys. Can a leaky valve cover gasket foul plugs and cause intermittent misfires? It occurs regularly at low RPM, we're talking less than 1800, in 6th gear under load. Doesn't occur while cruising on a flat, but uphill or accelerating.
Usually a leaky valve cover gasket. Have you pulled the coils and plugs to see if they are contaminated and in what shape they are? If not, you could start there. That type of misfire, from a member in another post on fuel and pinging, can be due to low octane fuel and/or contaminated fuel.
 

·
Registered
Joined
·
19 Posts
Discussion Starter #10
Usually a leaky valve cover gasket. Have you pulled the coils and plugs to see if they are contaminated and in what shape they are? If not, you could start there. That type of misfire, from a member in another post on fuel and pinging, can be due to low octane fuel and/or contaminated fuel.
I have not pulled the plugs recently, it's been about 2 years. The was oil down there, but not what I thought was an alarming amount. I'll check again this weekend. Interesting note about low octane/contaminated gas, I've been buying 89 for a while now, down from 92.
 

·
Registered
Joined
·
237 Posts
In short...yes. The purge solenoid is on the engine (at least in the N*), and the vent valve (solenoid) is part of the charcoal canister near the gas tank. The vent valve takes in fresh air, and the purge solenoid takes gas fumes stored in the canister and exhausts them into the combustion chamber to be burned.
Thanks!
 

·
Registered
Joined
·
78 Posts
Usually a leaky valve cover gasket. Have you pulled the coils and plugs to see if they are contaminated and in what shape they are? If not, you could start there. That type of misfire, from a member in another post on fuel and pinging, can be due to low octane fuel and/or contaminated fuel.
Low octane fuel will not by itself cause a misfire, unless the octane one is talking about is like 75 or lower. Contaminated fuel? Definitely.

I have replaced all kinds of valve covers and spark plugs, when they were down in the well and they have been covered in oil. Amazingly, they are almost never misfiring. So is the oil in the spark plug hole a concern? Yes, get that leak fixed. But for a misfire, on these cars it is usually a bad coil or spark plug, sometimes a fuel injector. Misfiring under a load is usually a spark misfire, not a fuel injector misfire.You could track it down by seeing which code it is (take notes) and moving the suspect coil and spark plug to a different cylinder (take more notes) and see if the misfire code moves to that cylinder. Yes if may take a little time to develop the code, depending on how bad the misfire is. For example, if you have only a P0305 code indicating cylinder 5 has the misfire, move the coil to cylinder 3 and the plug to cylinder 1, putting the known good coil and plug in cyl 5.
 

·
Registered
Joined
·
655 Posts
Low octane fuel will not by itself cause a misfire, unless the octane one is talking about is like 75 or lower. Contaminated fuel? Definitely.

I have replaced all kinds of valve covers and spark plugs, when they were down in the well and they have been covered in oil. Amazingly, they are almost never misfiring. So is the oil in the spark plug hole a concern? Yes, get that leak fixed. But for a misfire, on these cars it is usually a bad coil or spark plug, sometimes a fuel injector. Misfiring under a load is usually a spark misfire, not a fuel injector misfire.You could track it down by seeing which code it is (take notes) and moving the suspect coil and spark plug to a different cylinder (take more notes) and see if the misfire code moves to that cylinder. Yes if may take a little time to develop the code, depending on how bad the misfire is. For example, if you have only a P0305 code indicating cylinder 5 has the misfire, move the coil to cylinder 3 and the plug to cylinder 1, putting the known good coil and plug in cyl 5.
The wording was a little confusing, yes. What I meant was the low octane fuel was for pinging, contaminated fuel for misfire (and a variety of other issues), valve cover gasket as a possible cause for the oil he encountered.
 
1 - 13 of 13 Posts
Top