Help Troubleshooting the EVAP system

[geronimo]

For the past few months I've had a P0452 computer code which is a low voltage signal from the fuel pressure sensor.

I've noticed that along with this, my mpg has gone down. I believe my evap system isn't purging which is what has caused the mpg downgrade.

In an effort to fix the problem, I detached the battery for a couple minutes to reset the pcm, But after 5 minutes of driving my check engine came right back on.

Any ideas to troubleshoot this? Could it be the fuel system or just an electronic problem? I've thought of a few ideas that are less costly than sending it in to the mechanic. Let me know if they're worth pursuing:

1) Replace the fuel cap
2) Replace the o2 sensor (I got an o2 sensor fault a few months back and never had it replaced, could that cause my evap system to not purge?)
3) Replace the PCM computer

Any ideas on my next step would be greatly appreciated

[CREWZIN]

I tried doing my usual searches and didn't come up with anything pacific. What I did find was a general answer....

P0452
that means there's a leak in the evaporate control system,that can be anything from a loose gas cap to a bad hose ,anything that goes from the gas tank to the canister tank can have a leak in it,you ll need to check all the hoses and the gas cap look at the seal real good on the cap make sure its in good condition,any hose loose or bad will set that code,good luck with it.

[geronimo]

Thanks, that helps.

In regards to finding the leak. I've heard that some shops will use a low pressure nitrogen smoke machine to find leaks. Anyone know what this usually costs?

[geronimo]

Update: Found this at Automotive Evaporative Emissions Systems

'manufacturers are now beginning to install fuel tank pressure sensors. These sensors will allow the PCM to apply a vacuum to the fuel tank to see if it is capable of maintaining a system vacuum. If the system is unable to maintain a vacuum, it has the potential to emit HC into the atmosphere, and it will illuminate an indicator lamp in the driver’s information center. This light is most commonly marked as a gas cap light or gas door light.'

I have a feeling this is closely aligned to the fueld tank pressure sensor.

Here's to hope... cheers!

[CREWZIN]

The "loose cap gas" syndrome happens a lot on newer cars. On my wife's new KIA if you don't click shut the cap at least 3 times, the engine light will pop up a few miles down the road and sometimes takes a day or two to go away after you stop and tighten it the right amount of turns. We've told a few people about it on this forum also.

[MX-5]

Originally Posted by geronimo

shops will use a low pressure nitrogen smoke machine to find leaks. Anyone know what this usually costs?

My EVAP machine costs about $2500, plus fluids.
$89 covers the EVAP testing with the machine, $5000 factory scan tool, and a tech with 2 degrees & 25 years experience.
That's a good deal for all that!

[bobdole369]

How about measuring the voltage on the fuel pressure sensor in question - then measuring the rail pressure - this will tell you if you actually have a problem.

My P0441 ended up being that the washer fluid nozzle leaked fluid on the wiring harness and shorted a wire. Just that one though, frickin weird.