VSV for EVAP issues

Guys I’m having problems with this solenoid valve opening and closing rapidly when it is supposed to be open. I ran everything through the FSM checks and everything checked out good. I did not check the vapor pressure sensor to make sure the correct voltage is fed back at various pressure (vacuum and positive); however I did not think this is the issues as I have no check engine lights.

so I tested voltage on the positive side to the negative side of the valve pig tail and got only 6 volts and I got 14 volts from the negative battery to the positive pigtail; so I thought I would see 8 volts in the negative side of the pigtail but I measured 0 volts. No continuity on beg battery to negative side of pig tail; I checked ohms and got 3.3 mohms; I got the exact same reading in the adjacent switch that switches between the vapor canister and the fuel tank for sale of checking system operation. The vsv for evap wire goes to the fuse box but the other one goes back behind the engine and probably to the engine wiring harness.

I disconnected the vsv for EVAP and jumped from the battery to the valve and it worked fine.

ive been told that it is probably a bad ground. I recently took out the efi relay for testing compression, took the valve cover offf and cams out, redid plugs to coil packs....

This bugs me and messes with the engine idle... videos to come shortly.

 

I bought a used sensor and it did not make a difference; I had the same issue on a 2001 Jetta and replacing the sensor fixed the issue. Seems like there is an issue with the signal coming from the ecu...

I wish there was a wiring diagram for all the sensors

 

Yes you need the FSM and the factory wiring diagram/schematic. Somebody here is bound to have it. So you're a 1997 Tacoma regular cab 4wd, are you the 3.4 V6? And manual transmission? I'm asking so the right diagrams get shared when someone can help us out with that.
I think whoever suggested checking your grounds, did so on the basis of only seeing the 6V instead of the full 12VDC. And its a good suggestion but I imagine you've already double checked all the grounds and fuses and that stuff.
So should that voltage either be 0V or the full ~12VDC+(whatever that gets to)? Meaning, is seeing 6V indicative of something amiss?

 

It’s 2.7 liter auto

 

The evap valves are ground switched. You won't have continuity to ground unless the ecm is commanded the valve open. You should have battery voltage on the positive side of the connector, which it sounds like you do (14v). Checking pins between the pigtail shouldn't show anything if the valve isn't commanded open. If it is, then you would get your ground. What makes you think the valve is causing your problem? What is the actual problem, low idle? Typically the evap valves will throw a code if the act up.

 

No codes. The valve switches on and off rapidly after the engine warms up making a thumping sound.

 

I didn't see you had the 3rz. I think those are controlled by duty cycle. That might be normal.

 

I’ll get a video tomorrow and maybe other 3rz owners can chime in if they have the same thumping sound from opening and closing quickly.

 

I know the exact sound you are talking about! It drove me crazy. I had the same problem on my 3.4 v6 with no code. I tried replacing the vsv and all the rubber hoses but still no change. The only thing that worked for me was installing a new "square" style charcoal canister with the resonator on the breather vent. I got that canister from a 2002 4runner and its been quiet ever since! I'll try and get some pictures for you

 

Video of the thumping/whooshing sound.
https://youtu.be/s6rDQyYxKVw

 

This looks the same style I have

 

Does yours have that little resonator?

 

Yes.

 

I tested out the charcoal canister per the fsm and everything passed.

 

Damn that’s weird. That is the exact same sound I was getting too, but mine would only happen in short cycles never longer than 5 secs or so. It would only happen at low rpm and at idle. I was also getting air built up in my gas tank. When I was having this problem some guys recommended I change out my vapor pressure sensor. But my 1995.5 is odd and doesn’t have one. Have you tried running it with the VPS unplugged?

 

Just FYI, I have a 99 3RZ with the same charcoal canister as pictured above. Keep in mind there are variations in those canisters (mine actually has a check port on the hose form the VSV for EVAP to the canister.

My VSV for EVAP switches on and off rapidly once warmed up. I had asked on here previously and everyone said it was normal. 01-04 will have a different experience since the charcoal canister is below the bed. I believe this style canister is only on ~97-00 3RZs. I did swap my VSV for EVAP with another used one with the same results. I don't have any issues, codes, or problems, so I assume that it is functioning correctly. The only other thing that you could really test is to swap the whole canister, but that would be expensive.

EDIT: What makes you think it's messing with the engine idle? I highly doubt that is the problem. I suggest properly cleaning the IAC valve in the throttle body (look this up, there is at least one thread on here about it).

 

If you are having a engine idle problem associated with this it might just be a vacuum leak in the purge line to the intake manifold.

 

Checked all of those and replaced most. Idle is okay.

 

Sounds like it is normal;