MAF issues, reduced performance

mm3846

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The fuel trims are not terrible - just a tad rich at idle and cruising (but really pretty good), but it goes too rich at high idle 2500 rpm. Not enough to set off a light, but I’d say its outside of normal range at that one point.

Rich means not enough air (dirty filters), too much fuel (leaking injectors, rich EVAP canister), or a bad sensor someplace. Not sure about the stall with the special programs light.

Air noise near the PCV sure sounds like a torn diaphragm. I’d replace those and check fuel trims again. But a torn diaphragm will make trims go way positive, not negative.
Thanks for the info. Air filters are new (a couple months ago), DMTL pump is a little over a year old but I was really fighting with EVAP stuff and filling the fuel tank last summer. Possible that the canister got soaked in fuel and now isn't bad enough to be bad all the time?
 

mm3846

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Threw a P0442 small evap leak and the "check fuel tank cap" warning on my way home from work yesterday, so we're back around to the beginning of the issue again. If this is all that comes up, I'll wait til after the recall work to dig deeper into it since all that stuff gets disconnected.
 

16FujiDisco

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I’ve recently noticed that the “clutch” on my gas cap is weaker than before. This resulted in my getting a check gas cap message after a fill up and I knew I had put it on. When I checked, the cap was barely on but it would click like it was tight. I had to actively push and turn simultaneously to get it on before premature clicks.
 

Rover Range

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I’ve recently noticed that the “clutch” on my gas cap is weaker than before. This resulted in my getting a check gas cap message after a fill up and I knew I had put it on. When I checked, the cap was barely on but it would click like it was tight. I had to actively push and turn simultaneously to get it on before premature clicks.
Sometimes, when you fill up the fuel pump nozzle can push the fuel filler pipe in. The fuel cap sealing surface of the filler pipe will be below the surrounding rubber housing. When you install the fuel cap, it won't seal against the filler pipe.
When that happens, you have to grab the filler pipe with a pair of pliers and pull it back up/out.
 

mm3846

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Ok, fueled up again this morning, truck stalled out about 1/8 mile later at a red light. Idle was rough, a normal person probably wouldn't notice but I could tell. No codes other than the P0442 small evap leak.

more live values:

idle
hATgVrq.png


3/4-ish throttle, pulling 3k rpm ~50-55
M4leurd.png


1700rpm or so, cruising after the pull
M4leurd.png


any ideas from the resident pros? I haven't had the time to replace those PCVs yet, I'm doing that tomorrow evening and have some time to do more troubleshooting if there are some other values I should post up.
 

jlglr4

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That’s super rich. Since it’s tied to refueling, I’m guessing you are getting fuel into the evap canister on fill ups, and when that purge valve opens, the mixture is getting too rich. If you get enough fuel in the canister, it can actually pull liquid fuel right up through the purge.

Topping off the tank can create this problem, but I also seem to remember some problem with the filler neck (but I never heard what exactly the problem was) that was causing fuel to get into the evap line.
 

mm3846

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That’s super rich. Since it’s tied to refueling, I’m guessing you are getting fuel into the evap canister on fill ups, and when that purge valve opens, the mixture is getting too rich. If you get enough fuel in the canister, it can actually pull liquid fuel right up through the purge.

Topping off the tank can create this problem, but I also seem to remember some problem with the filler neck (but I never heard what exactly the problem was) that was causing fuel to get into the evap line.

I don’t top off, first click and I’m done. I had to do the TSB on my Silverado regarding the vent valve so I’m privy to that stuff. I’m thinking I may have saturated the canister last year when I was having issues filling the truck? I was hoping this would all go away after the fuel flange recall is done since most of this stuff has to get disconnected do that… lol..
 

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