RobertISaar Posted April 2, 2009 Report Share Posted April 2, 2009 went to the store today with wifey, stopped on the gas station to put in some midgrade (its always .02 more than regular, so i figure its cheap insurance). and i start to twist the gas cap and i hear either pressure or vaccum rushing in/out. i realize i'll have to listen more closely next time i take it off. got to wal-mart decided to unscrew the cap to listen and not only did i hear it come out(pressure), i saw whatever causes that distortion from the fumes go at least a foot out. this would explain why when after driving for a while, the blms in the gp always start to go low (like 105 at idle) i'm assuming it would have to be the CCP system acting up somewhere. any ideas, tricks to find out what it is? Quote Link to comment Share on other sites More sharing options...
rockfangd Posted April 3, 2009 Report Share Posted April 3, 2009 i would say the vented gas cap is not venting properly anymore. I have my way of testing them but some are not so comfortable with it lol Quote Link to comment Share on other sites More sharing options...
RobertISaar Posted April 3, 2009 Author Report Share Posted April 3, 2009 i would say the vented gas cap is not venting properly anymore. I have my way of testing them but some are not so comfortable with it lol lets hear it... i have a feeling it involves "pressure testing" it through the use of body parts? Quote Link to comment Share on other sites More sharing options...
rockfangd Posted April 5, 2009 Report Share Posted April 5, 2009 thats right they sell a fuel cap tester but usually i clean the threaded area of the cap and suck in and then try to blow into the cap. When done properly it should suck fairly easily but you should not be able to blow out through the cap at all. Think of it as when the cap is on the car you want it to suck in but not blow out. But caps are so reasonably priced i would just replace it and be done with it Quote Link to comment Share on other sites More sharing options...
RobertISaar Posted April 5, 2009 Author Report Share Posted April 5, 2009 thats right they sell a fuel cap tester but usually i clean the threaded area of the cap and suck in and then try to blow into the cap. When done properly it should suck fairly easily but you should not be able to blow out through the cap at all. Think of it as when the cap is on the car you want it to suck in but not blow out. But caps are so reasonably priced i would just replace it and be done with it thinking likewise.... say i go to the local meijer/wal-mart/autozone, whatever. is there a specific thread or style or something i should look for so that it will work with the GP or is everything standardized? Quote Link to comment Share on other sites More sharing options...
1990lumina Posted April 5, 2009 Report Share Posted April 5, 2009 Honda ones fit. Quote Link to comment Share on other sites More sharing options...
RobertISaar Posted April 5, 2009 Author Report Share Posted April 5, 2009 i really hope that was to suggest they were standardized, not that i should actually put honda parts on a GM vehicle. Quote Link to comment Share on other sites More sharing options...
Q-Ball Posted April 5, 2009 Report Share Posted April 5, 2009 So when you open the gas cap, the pressure sound is not good? If thats the case, I better get me a new gas cap. Quote Link to comment Share on other sites More sharing options...
RobertISaar Posted April 5, 2009 Author Report Share Posted April 5, 2009 well of course its not good... when it builds pressure the car starts to run rich due to the extra pressure in the system. that and if it gets too bad it will probably cause the seam on the tank to leak/burst... Quote Link to comment Share on other sites More sharing options...
Robby1870 Posted April 5, 2009 Report Share Posted April 5, 2009 well of course its not good... when it builds pressure the car starts to run rich due to the extra pressure in the system. that and if it gets too bad it will probably cause the seam on the tank to leak/burst... LOL.....there is a thing called a fuel pressure regulator. It regulates the fuel pressure near the injectors. Secondly, the amount of pressure to actually cause the tank to fail is WAY more than the very little bit of build up that it takes to makes the sound. My carb'd truck does more of "whooshing" sound when I take the gas cap off than any fuel injected car I've owned. A carb'd system is around 2-5psi fuel pressure and a fuel injected car is around 40-50psi. i really hope that was to suggest they were standardized, not that i should actually put honda parts on a GM vehicle. This is also ridiculous. It's a gas cap. I bet there's one or two vendors that make gas caps for every car brand. Quote Link to comment Share on other sites More sharing options...
Robby1870 Posted April 5, 2009 Report Share Posted April 5, 2009 It's the same thing that happens when you set a gas can in the sun and the container expands. Then, you remove the cap and you get the whooshing sound. That is all that is happening. It is the venting of excess pressure of the gaseous gasoline only. It has nothing to do with actual fuel pressure. There is a vent in the gas cap that prevents this mostly, but if you remove the cap while the cap is venting then you will get this sound. Quote Link to comment Share on other sites More sharing options...
RobertISaar Posted April 5, 2009 Author Report Share Posted April 5, 2009 so the car running rich isn't due to tank pressure? this car doesn't use a returnless fuel injection system does it? does this car have a charcoal canister? shouldn't that allow the engine to suck in the fumes that way less gas fumes get released? say the tank does have a weak seam, the extra pressure could cause it to start leaking, yes? i'm sure the added weight of the fuel above the seam would contribute as well... Quote Link to comment Share on other sites More sharing options...
Andrew Posted April 5, 2009 Report Share Posted April 5, 2009 the pressure just isnt enough to burst a seam. Quote Link to comment Share on other sites More sharing options...
jtwmechanic Posted April 5, 2009 Report Share Posted April 5, 2009 first off the fuel pressure reg has nothing to do with gas tank pressure. the fuel pressure reg stabilizes the amount of fuel line pressure for the injectors. gas tanks a vented through the gas cap on every one i have ever seen. think of your gas cap like radiator cap it should hold back a little but when pressure gets to great then it should let the pressure through. Quote Link to comment Share on other sites More sharing options...
jtwmechanic Posted April 5, 2009 Report Share Posted April 5, 2009 fuel injected motors that run rich are usually directly connected to a emmisions problem like a bad o2 sensor. Quote Link to comment Share on other sites More sharing options...
Robby1870 Posted April 5, 2009 Report Share Posted April 5, 2009 first off the fuel pressure reg has nothing to do with gas tank pressure. the fuel pressure reg stabilizes the amount of fuel line pressure for the injectors. gas tanks a vented through the gas cap on every one i have ever seen. think of your gas cap like radiator cap it should hold back a little but when pressure gets to great then it should let the pressure through. Yeah, that's what I was saying. Even if this excess gaseous gasoline pressure was causing too much line pressure there is always the fuel pressure regulator to control it. fuel injected motors that run rich are usually directly connected to a emmisions problem like a bad o2 sensor. I agree. This is usually the case. so the car running rich isn't due to tank pressure? this car doesn't use a returnless fuel injection system does it? does this car have a charcoal canister? shouldn't that allow the engine to suck in the fumes that way less gas fumes get released? say the tank does have a weak seam, the extra pressure could cause it to start leaking, yes? i'm sure the added weight of the fuel above the seam would contribute as well... There is a charcoal canister. The fuel rails do have a return line. The gas tank is two pieces of stamped sheet metal welded together around the edges. Technically if the seams were in the right place the added weight of gasoline ontop of them would cause a slight increase in stress at the seam. However, because of where the seam is (basically parallel to the plane that represents the top of the fuel level) this doesn't happen. This is why on giant water tanks you can see the seam in the same place (around the tank, horizontally) and not vertically around the tank. I haven't heard of automobile gas tanks bursting on their own. It just doesn't happen. Quote Link to comment Share on other sites More sharing options...
RobertISaar Posted April 5, 2009 Author Report Share Posted April 5, 2009 first off the fuel pressure reg has nothing to do with gas tank pressure. the fuel pressure reg stabilizes the amount of fuel line pressure for the injectors. gas tanks a vented through the gas cap on every one i have ever seen. think of your gas cap like radiator cap it should hold back a little but when pressure gets to great then it should let the pressure through. Yeah, that's what I was saying. Even if this excess gaseous gasoline pressure was causing too much line pressure there is always the fuel pressure regulator to control it. fuel injected motors that run rich are usually directly connected to a emmisions problem like a bad o2 sensor. I agree. This is usually the case. so the car running rich isn't due to tank pressure? this car doesn't use a returnless fuel injection system does it? does this car have a charcoal canister? shouldn't that allow the engine to suck in the fumes that way less gas fumes get released? say the tank does have a weak seam, the extra pressure could cause it to start leaking, yes? i'm sure the added weight of the fuel above the seam would contribute as well... There is a charcoal canister. The fuel rails do have a return line. The gas tank is two pieces of stamped sheet metal welded together around the edges. Technically if the seams were in the right place the added weight of gasoline ontop of them would cause a slight increase in stress at the seam. However, because of where the seam is (basically parallel to the plane that represents the top of the fuel level) this doesn't happen. This is why on giant water tanks you can see the seam in the same place (around the tank, horizontally) and not vertically around the tank. I haven't heard of automobile gas tanks bursting on their own. It just doesn't happen. i guess i was making this much more complicated than it really is..... i just find it odd that the car only seems to run rich at idle after its been running and driving around for at least 10 minutes..... or at least it thinks its running rich. Quote Link to comment Share on other sites More sharing options...
jtwmechanic Posted April 5, 2009 Report Share Posted April 5, 2009 besides the vent tubing is not high pressure type line it would leak the pressure out first. high pressure lines only needed between the pump and the rail. a bad o2 can cause to run in closed loop which in return may cause rich burn after warm up. bad temp sender also can cause this problem (kinda like a stuck choke) Quote Link to comment Share on other sites More sharing options...
RobertISaar Posted April 5, 2009 Author Report Share Posted April 5, 2009 besides the vent tubing is not high pressure type line it would leak the pressure out first. high pressure lines only needed between the pump and the rail. a bad o2 can cause to run in closed loop which in return may cause rich burn after warm up. bad temp sender also can cause this problem (kinda like a stuck choke) bad temp sender doesn't seem very likely: when its running and moving the temp gets to 205 MAX and drops down to 195. then it keeps cycling 205-195-205-195. maybe thats the sign of a failing sender/sensor, i don't know. i always look at the datalogs and think its a strange pattern but whatever, it seems like both the thermostat and temp sensor are working to me if the engine can keep that close of a tolerance of the 195 the stat is(should be) rated for. Quote Link to comment Share on other sites More sharing options...
Robby1870 Posted April 5, 2009 Report Share Posted April 5, 2009 The car has two temperature senders. One for the gauge cluster, one for the ECM. If the one for the ECM has gone bad you really won't be able to tell since the gauge one is still working correctly. Quote Link to comment Share on other sites More sharing options...
RobertISaar Posted April 5, 2009 Author Report Share Posted April 5, 2009 The car has two temperature senders. One for the gauge cluster, one for the ECM. If the one for the ECM has gone bad you really won't be able to tell since the gauge one is still working correctly. i watch both.... dataloging captures the one the PCM sees and my eyes watch the guage cluster. Quote Link to comment Share on other sites More sharing options...
jtwmechanic Posted April 5, 2009 Report Share Posted April 5, 2009 right, there are 2 senders one for guage and one for ecm and if the ecm sender is faulty it can cause over fueling.also would have been helpful to know about datalogging in first place. does it translate the ohm value of the sender to degrees for you. the comp doesn't see it in degree. Quote Link to comment Share on other sites More sharing options...
RobertISaar Posted April 5, 2009 Author Report Share Posted April 5, 2009 right, there are 2 senders one for guage and one for ecm and if the ecm sender is faulty it can cause over fueling. they both seem to be spot on... rising and falling to 205-195. so either they're both out of whack the same amount and direction or its not my issue... Quote Link to comment Share on other sites More sharing options...
Robby1870 Posted April 5, 2009 Report Share Posted April 5, 2009 Temperature sender is not your problem. You say "running rich" but how rich? You are data logging, so what's your A/F? Quote Link to comment Share on other sites More sharing options...
RobertISaar Posted April 5, 2009 Author Report Share Posted April 5, 2009 Temperature sender is not your problem. You say "running rich" but how rich? You are data logging, so what's your A/F? target a/f is gonna be 14.7:1 BLM was hitting around maybe 105 at the worst, but the ECU was still able to correct at this point so its still 14.7:1. taking 128/105 its 21.9% richer than ideal. but it was in closed loop and within the range that the ECU can adjust so if it was not correcting it would have been...... around 11.75-11.5:1. unless i'm wrong about the way ECUs function under closed loop, it was still a stoich mixture. Quote Link to comment Share on other sites More sharing options...
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