Vacuum pressure when removing fuel cap - solenoid?

[iamdub]

That one doesn't appear to have the audible continuity function. But, yes, you can still check it. Just put it on the lowest Ohm range. If there's no continuity, you should get something on the screen besides a number. Some meters say "Inf" or similar meaning "infinite" (open circuit). The beep is much more convenient because you can keep your eyes on your work and just listen for the beep. Also, some displays are slower to respond than the beep. This is really helpful when diagnosing an intermittent issue due to movement. You hook up the meter and slowly move the wire around while listening for a beep. It may only be for a split second, but at least you'll find it much more easily than slightly moving the wire while having to watch a display that may not react quickly enough.

 

[retiredsparky]

You are smart to be concerned about vacuum in the fuel tank. Vacuum can make the fuel pump work harder, shortening it's life. If the vacuum is strong enough the engine can run poorly and have low power due to a lean condition caused by low fuel pressure. Mysterious codes could then appear when the PCM cannot solve the lean condition. A lean condition over a long time can damage the engine also.

 

[DonnieBrasco]

That one doesn't appear to have the audible continuity function. But, yes, you can still check it. Just put it on the lowest Ohm range. If there's no continuity, you should get something on the screen besides a number. Some meters say "Inf" or similar meaning "infinite" (open circuit). The beep is much more convenient because you can keep your eyes on your work and just listen for the beep. Also, some displays are slower to respond than the beep. This is really helpful when diagnosing an intermittent issue due to movement. You hook up the meter and slowly move the wire around while listening for a beep. It may only be for a split second, but at least you'll find it much more easily than slightly moving the wire while having to watch a display that may not react quickly enough.

Finally getting back to this. I'm under the hood as we speak. Sadly I don't have my meter to test continuity right now. But I did get the valve/solenoid (still not sure what's what) off and attempt to blow through it. No bueno. Can't blow through either end. Possible that it's stuck closed? I'm REALLY hoping this is all it is and I can just replace this part. It's only like a 30 buck part, yeah? Thanks again for all your gracious advice and guidance.

 

[iamdub]

The tank being under vacuum would be from the valve being stuck open. Next step is to check the circuit. With the key on, one wire should have 12V (I don't know which one, but you have a 50/50 chance) and the other should have nothing unless the PCM is commanding a purge. Until you find a meter, try putting 12V to that solenoid. I don't know which one is positive and which is negative, but just put 12V to one and the negative to the other and listen for a "click" and see if you can then blow through it. Remove voltage and it should be closed off again. This would rule out a failed solenoid.

 

[DonnieBrasco]

With the key on, one wire should have 12V (I don't know which one, but you have a 50/50 chance) and the other should have nothing unless the PCM is commanding a purge.

You're talking about the wiring harness that connects to the solenoid/valve, yes?

Until you find a meter, try putting 12V to that solenoid. I don't know which one is positive and which is negative, but just put 12V to one and the negative to the other and listen for a "click" and see if you can then blow through it. Remove voltage and it should be closed off again. This would rule out a failed solenoid.

I think I'm confused on this suggestion. When you say put 12V to that solenoid, do you mean one of the two prongs on the solenoid where the wiring harness connects to the solenoid? 12V from what? I think it's just too early for me and I'm having brain farts.

ETA: FWIW, my check engine light is gone and it's not creating a vacuum anymore, at least not yet. I'm sure this is just because I took the solenoid off and put back on last night.

 

[iamdub]

You're talking about the wiring harness that connects to the solenoid/valve, yes?

Correct. It's a simple circuit of two wires- one positive and the other negative. It's just that the negative "shouldn't be negative" unless the PCM has it connected to ground (the negative side of the battery- not directly to the battery, but to vehicle ground).

I think I'm confused on this suggestion. When you say put 12V to that solenoid, do you mean one of the two prongs on the solenoid where the wiring harness connects to the solenoid? 12V from what? I think it's just too early for me and I'm having brain farts.

Yes, kinda. You get 12V from your battery. If I don't have jumper wires with alligator clips handy, I like to use a piece of speaker wire because it's already two wires and one is marked, usually by a stripe on the jacket or the wire itself is bare copper and not silver. Put one wire on the positive terminal of the battery and the other wire on the negative terminal. Touch the loose ends to the solenoid, one to each terminal. It should click and allow you to blow through it. If the click is faint or it is still blocked, swap the wires around on the solenoid's terminals and test again.

ETA: FWIW, my check engine light is gone and it's not creating a vacuum anymore, at least not yet. I'm sure this is just because I took the solenoid off and put back on last night.

The solenoid/valve could have just been stuck. You messing with it may have shook it enough to unstick it. Fuel vapors are what go through it so it's possible that it gummed up a bit and stuck. Or it's just getting weak and intermittently failing before it fails for good. Maybe spray some carb cleaner into it from both ends, shake it, activate it a few times with battery power, spray again, etc. and reinstall it. It may never act up again after that. I know a replacement is only $30, but if you're already in the garage and you have a few minutes to kill...

 

[DonnieBrasco]

Correct. It's a simple circuit of two wires- one positive and the other negative. It's just that the negative "shouldn't be negative" unless the PCM has it connected to ground (the negative side of the battery- not directly to the battery, but to vehicle ground).



Yes, kinda. You get 12V from your battery. If I don't have jumper wires with alligator clips handy, I like to use a piece of speaker wire because it's already two wires and one is marked, usually by a stripe on the jacket or the wire itself is bare copper and not silver. Put one wire on the positive terminal of the battery and the other wire on the negative terminal. Touch the loose ends to the solenoid, one to each terminal. It should click and allow you to blow through it. If the click is faint or it is still blocked, swap the wires around on the solenoid's terminals and test again.



The solenoid/valve could have just been stuck. You messing with it may have shook it enough to unstick it. Fuel vapors are what go through it so it's possible that it gummed up a bit and stuck. Or it's just getting weak and intermittently failing before it fails for good. Maybe spray some carb cleaner into it from both ends, shake it, activate it a few times with battery power, spray again, etc. and reinstall it. It may never act up again after that. I know a replacement is only $30, but if you're already in the garage and you have a few minutes to kill...

Ahhh ok that all makes total sense now. I'm going to keep my fingers crossed for a few days and see how it does.

Now I seem to have a very minor oil leakage right at the drain pan screw that I need to figure out what's going on. Might need to replace the washer on the bolt. I'm curious why rubber washers aren't used instead of steel? Would the oil break them down or something? I realize I'm highjacking the thread some but hell, it's my thread.

 

[iamdub]

In that use, they'd probably use Neoprene since rubber would break down when exposed to petrochemicals. But still, it's a soft gasket being twisted on by who-knows-who with who-knows-what. Does ANYONE use a torque wrench to tighten an oil plug?! If a soft gasket were used, a specific torque value would need to be used and that just ain't gonna happen. Besides, what if the gasket tore and wasn't noticed? Not everyone parks on concrete and someone might begin a cross-country trip right after having their oil changed. Oil could be constantly dripping and that's too much of a liability. I don't know if they still do it, but when my ex-wife had her Honda, they required the use of a new aluminum washer every time the oil plug was reinstalled. I liked that idea and bought a handful of the washers since I changed my own oil. I would engrave the mileage into the old washer and keep it on her keychain so we'd know when the next change was due. Anyway, some manufacturers use a gasketed washer, which is nice, but will still wear out after so many compressions and twists. For the cost and peace of mind, I'd just get a new drain plug (with washer if available) and install it at my next oil change. I'd stick to OEM for something so cheap and I'd even check Amazon first.

 

[DonnieBrasco]

In that use, they'd probably use Neoprene since rubber would break down when exposed to petrochemicals. But still, it's a soft gasket being twisted on by who-knows-who with who-knows-what. Does ANYONE use a torque wrench to tighten an oil plug?! If a soft gasket were used, a specific torque value would need to be used and that just ain't gonna happen. Besides, what if the gasket tore and wasn't noticed? Not everyone parks on concrete and someone might begin a cross-country trip right after having their oil changed. Oil could be constantly dripping and that's too much of a liability. I don't know if they still do it, but when my ex-wife had her Honda, they required the use of a new aluminum washer every time the oil plug was reinstalled. I liked that idea and bought a handful of the washers since I changed my own oil. I would engrave the mileage into the old washer and keep it on her keychain so we'd know when the next change was due. Anyway, some manufacturers use a gasketed washer, which is nice, but will still wear out after so many compressions and twists. For the cost and peace of mind, I'd just get a new drain plug (with washer if available) and install it at my next oil change. I'd stick to OEM for something so cheap and I'd even check Amazon first.

That makes total sense. I'm gonna go ahead and order a replacement plug for the next oil change. Excellent advice. Can we be neighbors? You might get tired of me hollering across the fence for advice.

 

[retiredsparky]

Another likely cause of vacuum in the fuel tank is a lack of venting when the vehicle is driven. As fuel is used, volume of fuel is reduced, volume of air is increased. If the vent system is not functional, vacuum can result, especially over longer trips, between tank fill-ups.