Fairtax4me Posted July 29, 2014 Share Posted July 29, 2014 There will be some pressure buildup in the tank with a properly working evap system. If you DONT get a woosh from the tank there may be a leak somewhere. How does the fuel trim look since the reset? Does it still give the same code? Link to comment Share on other sites More sharing options...
1 Lucky Texan Posted July 29, 2014 Share Posted July 29, 2014 There will be some pressure buildup in the tank with a properly working evap system. If you DONT get a woosh from the tank there may be a leak somewhere. How does the fuel trim look since the reset? Does it still give the same code? It's my understanding, as fuel is used, external air would be brought through the carbon canister into the tank to prevent a vacuum. It seems slightly lower-than-atmo pressure would be more likely than higher? Link to comment Share on other sites More sharing options...
Pgh_Scoob Posted July 29, 2014 Author Share Posted July 29, 2014 I know there is going to be some pressure in the tank but from other vehicles the "whoosh" is about a 1/4sec long or so but at points mine is closer to 1.5sec long which is what made me start thinking into it.... The fuel trims did start to go down after reset but only to like 18% before the light came back on... And yes still the same code The light also lit back up on its own and has remained on without filling up or anything and my fuel mileage isn't as bad as I thought just a bad gauge... For now I have only filled it with 8.5 gallons and went 160 miles so just about 19 MPG which isn't terrible but in just gonna run it this time til it quits and see if anything comes from it Link to comment Share on other sites More sharing options...
Fairtax4me Posted July 29, 2014 Share Posted July 29, 2014 It's my understanding, as fuel is used, external air would be brought through the carbon canister into the tank to prevent a vacuum. It seems slightly lower-than-atmo pressure would be more likely than higher? In the middle of winter, sure. But when its hot gasoline will evaporate quickly and raise the pressure in the tank faster than the engine can use fuel and draw the pressure down. Also the excess fuel that didnt get sprayed through the injectors returns from the engine already warm, and it just gets dumped into the tank, which shakes everything up and causes the fuel to evaporate more. There's also an exhaust pipe right below the middle of the tank. Not to mention just driving the car makes the gas slosh around in the tank, which causes it to evaporate, and pressure to build. The evap system does have a way to limit how much pressure builds in the tank by venting through a valve on top of the tank. The valve sends vapors to the evap canister, and after the fuel vapor is collected by the canister air is let out through the filter by the canister. But the tank has to reach a certain pressure before the vent system opens. A 1-1/2 second woosh is pretty normal on a warm day after the car has been driven. Even if only a short distance. Link to comment Share on other sites More sharing options...
1 Lucky Texan Posted July 29, 2014 Share Posted July 29, 2014 (edited) In the middle of winter, sure. But when its hot gasoline will evaporate quickly and raise the pressure in the tank faster than the engine can use fuel and draw the pressure down. Also the excess fuel that didnt get sprayed through the injectors returns from the engine already warm, and it just gets dumped into the tank, which shakes everything up and causes the fuel to evaporate more. There's also an exhaust pipe right below the middle of the tank. Not to mention just driving the car makes the gas slosh around in the tank, which causes it to evaporate, and pressure to build. The evap system does have a way to limit how much pressure builds in the tank by venting through a valve on top of the tank. The valve sends vapors to the evap canister, and after the fuel vapor is collected by the canister air is let out through the filter by the canister. But the tank has to reach a certain pressure before the vent system opens. A 1-1/2 second woosh is pretty normal on a warm day after the car has been driven. Even if only a short distance. yeah, I know about the pressure control valve and the tank's vent valve too. Just seems 1.5 seconds shouldn't be 'normal'. I could MAYBE see a little of that happening after a day or 2 temp cycling in a warm climate followed by a short trip to the gas station before the ECU cycles any valve, but, the whole system is designed to PREVENT a whoosh of vapors escaping to the atmosphere. Those vapors are 'supposed' to be adsorbed in the carbon canister. We're in the midst of fighting an issue with my MIL's Forester not taking fuel (or only taking it at EXTREMELY slow rates) so, I've tried to educate myself a little about the tank's evap and fueling systems. Lots of ways that stuff can fail. There's failed valves, gummed-up valves, saturated canisters, spider. mud or frozen condensation clogged tubing - it's crazy! But the vent valve 'should' prevent much pressure build-up, unless the canister or its drain 'system' is clogged with spiders or something. My MIL's Forester sits outside and can go several days without driving. And, when driven, is only driven very short distances. No permanent solution to the fueling problem after 2 visits to the dealer - just returned after visit 3. We'll see how it goes. I think PGH should closely examine the evap system back there at the tank. But I admit it's a longshot. Edited July 29, 2014 by 1 Lucky Texan Link to comment Share on other sites More sharing options...
Pgh_Scoob Posted July 30, 2014 Author Share Posted July 30, 2014 Yes thats exactly where I have been leaning towards... for now. And with looking up the EVAP system it is rather straight forward for operation and I am trying to determine if there might be a sticking valve allowing either excessive pressure or vacuum to build up on the tank... BUT with any other evap system issue I have seen come through my shop there was never any running issues or random no starts... Plus I have smoked tested my entire EVAP system multiple times but unfortunately I am unable to test any individual components to ensure they are working properly. Link to comment Share on other sites More sharing options...
1 Lucky Texan Posted July 30, 2014 Share Posted July 30, 2014 the green connectors under the dash might cycle the valves. Won't tell you if they or their hoses are plugged, but you should be able to feel them vibrate. Or, as said, try running a day or 2 with the gas cap loose. If the car behaves the same, my suggestion is all wrong. Link to comment Share on other sites More sharing options...
Pgh_Scoob Posted July 30, 2014 Author Share Posted July 30, 2014 Ok I will give that a try and what are the connectors called... Or are they just EVAP testing connectors? Do I supply power to them to cycle the valves. Link to comment Share on other sites More sharing options...
heartless Posted July 30, 2014 Share Posted July 30, 2014 they are general diagnostic connectors - not just for evap - they will cause many things to cycle on/off or open/closed, including radiator fans, fuel pump, and various other solenoids. Link to comment Share on other sites More sharing options...
Pgh_Scoob Posted July 30, 2014 Author Share Posted July 30, 2014 Ok thanks and do I just connect them together or do I hook a scan tool to it... I am gonna do some research on those connectors but any info is greatly appreciated Link to comment Share on other sites More sharing options...
heartless Posted July 31, 2014 Share Posted July 31, 2014 just connect the green pair to cycle the relays and stuff - no scan tool needed. Link to comment Share on other sites More sharing options...
Pgh_Scoob Posted August 19, 2014 Author Share Posted August 19, 2014 Ok so its been a while since I have posted anything about this and unfortunately I dont have any repair news.... but after doing more searching around and reading other forums I am leaning towards my MAF sensor being the culprit. I have done some tests with watching live stream data and comparing RPM's to G/Sec on the MAF... which all checked good. But after messing around yesterday and checking live stream data I did notice that If I snap the throttle to high RPM's sometimes the sensor will show no change in readings but other times it will show the spike of G/Sec for the MAF.... I know the MAF is constantly monitored and should constantly be feeding back readings and information to the ECM... Correct... and there shouldnt be any reason as to why it would be ignored? Please correct me if Im wrong on this. Oh and checking my LTFT it is still high but its at 19% so not as bad as the 22%+ that I was seeing A few other things I have noticed are I do get a slight surge upon light acceleration / cruising but no jump in RPM and no jump in speed. Its almost like a tranny slipping but my speed stays constant and if I put my foot into it I will speed up with proper RPM rise unlike a slipping tranny that will fight to speed up while RPM's rise and it feels like its in the engine... Its hard to explain almost like a very efficient burn for a quick moment. I am also still having the intermittent no start and actually had it die on me one day while in traffic.... Starting from a stop and gave it a bit of gas and then it shut off... No buck or anything just cut out. It would crank but not start... A few minutes later it started right up.... I was chalking that up to the fuel pump but dont think a faulty fuel pump would set this code and after reading one post with a confirmed fix it was the MAF sensor... And I believe they stated intermittent no starts and stalls. So with leaning towards the MAF sensor I checked my local salvage yard and they are available for 15 bucks... but is it even worth it to go with a junkyard one or should I just try to confirm this as the problem and then replace with new.... trying to put as little amount of money as possible in this rig but still need it to be dependable... Greg Link to comment Share on other sites More sharing options...
mikec03 Posted August 19, 2014 Share Posted August 19, 2014 Yea, a faulty MAF will stall the car and prevent restarting. And then after an hour, it will restart. And it's random. And it doesn't set codes very often. If you suspect the MAF, go to the junk yard and replace it. It takes only 5 minutes. By the way, in my case, it cost $30 so you are getting a bargain. I don't think that they fail very often so a junk yard replacement will probably last the life of your car. Link to comment Share on other sites More sharing options...
Pgh_Scoob Posted August 19, 2014 Author Share Posted August 19, 2014 cool thats what I wanted to hear!!!! Thank You. The hardest part of trying to research possible fixes for this code is damn near impossible... The best I found until the other day was I replaced a bunch of parts and now it comes on intermittently or there is never any update to what happened... Hopefully this works and I will keep this updated. Thanks, Greg Link to comment Share on other sites More sharing options...
Pgh_Scoob Posted September 7, 2014 Author Share Posted September 7, 2014 FIXED!!!!! REPLACE MAF!!! I know its been a bit since I posted but I am confident in saying it is fix. I really kinda quit worrying about it for a little while because other than the light the car seemed to be driving fine.... but then it started randomly cutting out in morning traffic on my way to work... So I went ahead and grabbed one out of the junkyard and so far so good..... I checked my Fuel Trims and LTFT was down to 5.5%!!!!!!!!! Definitely much nicer than 22% Plus now I know what my car should really run like.... For what I thought we just quirks of and old car were in fact driving issues.... Poor throttle response and surges you could say while cruising or light throttle and rough idle at times... It has only been a few days but already I am seeing a great improvement in performance. It took me so long to finally just go do it was simply because with a snap on scan tool looking at live data and going through the Diag. procedure for the MAF it always checked good. But thanks for all of the help guys and anyone fighting this hope it helps Greg Link to comment Share on other sites More sharing options...
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