I just bought a 2015 f-250 with the 6.2 L gas engine and 201,000 miles. It had been a fleet truck with 3 previous owners. When I was looking at it the owner said occasionally it was hard to put gas in it and he didn't know what that was about. Driving it home it showed a prompt to tighten the gas cap. I did but that didn't change anything. The first time I checked the gas milage. It was getting under 9mpg after going 65 or slower with no load or towing. The previous owner said they were getting around 14 when I asked.

Soon after the check engine light came on. I had it checked and the DTC code was P0442 (EVAP) system leak (small leak .04-inch). Suggested parts are Canister Purge Valve/Solenoid. I replaced the gas cap in case it was cracked or bad gasket, but it wasn't that. I asked a mechanic friend about it and he recommended getting it smoke tested to determine where the leak is. He said, you could spend a lot of time and money replacing things before finding the leak. Finding a place that can do that would be over an hour away at a ford dealership at a rate of 200 dollars an hour for diagnostics. Does anyone have trouble shooting advice besides giving the system the smoke test? Or, is a smoke test the best option? Also is it bad for the engine to be running it with a EVAP leak and would a EVAP leak affect my gas milage? I'd hate to replace the canister purge valve and solenoid and find out it wasn't that. The truck is running smooth and starting easily.

Regarding the poor gas milage, I don't know the condition of the plugs or the last time it had a tune up. I cleaned the air filter and the tires pressures are good. Any suggestions on troubleshooting that? It seems 9 or below mpg is awfully low for no load or towing or city driving . I live at 7800 ft, could high altitude be dooming me to low gas milage. The previous owner was driving at altitude as well and reported 14mpg.

Any thoughts on either of these issues is appreciated. Thanks

 

If you didn't reset the code after replacing the cap it will take awhile for it to clear if that was the problem. The evap system doesn't check the system continuously just ever so often, can't tell you how often. The slow filling check the rubber hose where it goes between the frame and bed to see if it's collapsed. Check all the hoses and connections for the evap system including the tank vent line. If you don't have a reader that can clear codes just disconnect the battery for a couple of minutes to clear it.

Denny

 

Plugged evap cannister can cause slow filling gas tank

 

Thank you, I haven't had a problem filling the tank although I've only put gas in a few times so far. The previous owner mentioned that he couldn't fill the tank so he had to drive it up on a block to do it. That made no sense to me, especially since it was a sporadic or occasional issue. Somehow something seems wrong with pressure in the gas tank or system,which I think could be consistent with an EVAP leak?

I'm trying to find out the best way to track down the EVAP leak and if the smoke test recommended by a mechanic is the best way to go. Also doesn't under 9 miles mpg seem abnormally low? I'd love to hear how anyone has found or addressed an EVAP leak?

Thanks

 

Unless there is a common failure point, they are generally pretty difficult to find. I'd start checking the soft lines running to EVAP cannister. Not sure where EVAP is on this truck, but hopefully it is towards the rear near the tank. I've had a cannister clog on a different vehicle which caused abnormally high gas tank pressure. That pressure increase would then potentially amplify the leak.

I made my own smoke machine with PVC plumbing parts, a resistive wire, tiki torch wick and baby oil. You can google/youtube how to make one! Only takes a few mins to make and less than $50 in parts. You then can connect it to regulated air pressure from a compressor and pressurize the system. It works for finding intake leaks as well. For the tank, you may need to sacrifice a gas cap or find a suitable EVAP line you can connect to.

My opinion is that the EVAP leak wouldn't affect gas mileage, but who knows. I would probably replace air filter, fuel filter, spark plugs (pull one and just check condition first) and clean your MAF. You can also try just disconnecting the battery for a few mins and see if that resets the computer fuel mapping.

 

You have a high mileage truck that has a lot of electrical components (modules). You will eventually need a good scan to to do any work on this vehicle. Now is a good time to get Forscan and learn how to use it. The software is free and a very good adapter is about $100.

Next you should read up on how the EVAP system works. It's complicated. Here is a good resource but there are many more across the Internet.
https://www.motor.com/magazine-summa...ation-testing/

Using your new understanding of the the EVAP system and Forscan you can troubleshoot by looking at data like the fuel tank pressure, purge valve status etc.. This takes some effort and homework but in short time you will have the tools and knowledge to tackle any future problem. As a bonus you can use Forscan to look at fuel trims and other items that affect gas mileage.

https://www.ford-trucks.com/forums/1...ces-index.html

 

I average about 10 mpg per my Fuelly app but 90% of my driving is pulling a 4K trailer in city for work or 3k camper in bed for fishing. Should average 12 to 14 empty driving

 

I average about 10 mpg per my Fuelly app but 90% of my driving is pulling a 4K trailer in city for work or 3k camper in bed for fishing. Should average 12 to 14 empty driving Evap canister is above spare tire

 

Thanks, good information and advice.