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Emission Mystery

My car is a 2007 Hyundai Santa Fe GLS and does not want to start only after fueling. It will also die when the fuel cap is removed. There is an excessive amount of vacuum pressure released when cap is removed. The computer showed a code: P0441 Evaporative Emission Control System Incorrect Purge Flow. Is this simply a fuel cap issue or something else?

Could be either. Cheap test is to buy a new cap at a parts store, see if that fixes it. If not, off to the mechanic or dealer (it might be covered under warranty).

The problem could be any of the following

A bad purge valve in the evap system
A kinked hose in the evap system
A contaminated carbon canister in the evap system

The latter is a definite (and expensive) possibility if you are one of those folks who insists on forcing more gas into the tank after the station’s pump clicks off for the first time.

Another possibility–and this is not a joke–is a spider nest in one of the evap hoses.
For some reason that I can’t fathom, Hyundais seem to be more prone to this problem than other makes.
The cure for this one–a blast of compressed air–is the cheapest possible solution.

I believe it is the Mazda6 that is prone to the spiders. There was a recent recall.

Your purge valve is a valve opened by a solenoid when you start your car to allow the hydrocarbon molecules entrapped in your charcoal canister to be drawn into the engine and burned. The valve could be malfunctioning, the solenoid could be malfunctiong, or the charcoal bed could be saturated.

The gas tank breaths in through the charcoal bed as well as breathing out through it (the charcoal captures evaporated gas molecules). If the bed were saturated, not only would the flow through the purge valve be insufficient due to low flow through the charcoal bed, but the gas tank would also build up excess vacuum. It cannot breath in as the gas is pumped out of the charcoal is saturated.

Here’s my theory on the nonstarting and the dying. My theory is that the fuel pump is weak from struggling against a vacuum (see above) and unable to deal with the added vacuum because every time you fill it you saturate the charcoal bed again. It probably dies when you remove the fuel cap because it’d unable to deal with the sudden “head pressure”. I know, that last one is a wild one. But it’s all I can come up with.

Bottom line: I think it’s all related to a saturated canister and a resulting weak fuel pump.

By the way, do you “top off” your gas tank when you fill?

Recall or no recall, many Hyundai models are prone to spider nests in the evap system.