Charcoal Canister, VSV and Fuel vapor seperator question for 73 (1 Viewer)

[Cgn1976]

Hey everyone,

I've been trying to figure out what to do on my set up for the charcoal cannister, VSV, evaperator seperator setup. Read a lot of threads on this, but I'm still not sure what to do. I've been a getting a little pressure in the tank when I run it. I know my VSV is dead, so I did what I saw in a thread about this in the 40 section a while back, where I ran out of the canister into the bottom of the air cleaner, figuring there'd be a little pull all the time. I tested the canister and it flows good. I realized yesterday that the check valve at the seperater has to be bad as I tried to suck and blow air through it and lets a tiny bit of air through both directions, but certainly isn't working like a one way check valve and has so much resistance there's no way the pressure from the air intake is gonna overcome it, which I suppose makes sense that the pressure is building up. I'm going to try to track down the right check valve, although so far all I see is one for 75 and later. I'm thinking it's probably the same, but will pull it later to make sure. (see below for what I'm seeing online)

So my thinking at this point was that since my VSV is dead, I'd just connect the output of the cannister straight into bottom of the carb where the output on the VSV sent it (red hose) back when it worked. I know this is supposed to only operate when the truck is running 15 mph or more, so my question is, is this a terribble idea to run it straight in all the time? If it is, what else should I do? I saw a supposed rebuilt VSV on ebay, but I have no clue if my speed sensor set up works either. I'm not having any gas fume issues, but I do need to deal with pressure issue and I'd ideally like to send it back into the system to burn, although I have no smog to pass in New Mexico because the truck is 30+ yrs old, so I can literally do whatever. I just want it to not smell and not stress the tank/system. I saw guys doing vented gas caps, bypassing the system. Any thoughts are helpful. Thanks!

 

[RUSH55]

A small draw on the tank via engine vacuum should be okay. Not sure what range would be considered adequate or acceptable. Might check each port with a gauge just to see.

 

[Cgn1976]

A small draw on the tank via engine vacuum should be okay. Not sure what range would be considered adequate or acceptable. Might check each port with a gauge just to see.

A small draw on the tank via engine vacuum should be okay. Not sure what range would be considered adequate or acceptable. Might check each port with a gauge just to see.

Thanks for that. I was thinking pretty much that, but I don't really know if too much engine vac would create too much negative pressure build up.

I found a long thread about gutting a check valve in the cannister that also talked about an autozone substitute with fewer ports. I noticed mine has no working check valves because I could blow/suck air though all ports evenly.

I also pulled the check valve at the evap separator and saw it's cracked and not working right. It resists flow both ways. Can't find the part online but it looks just like the one for 75+. I'm guessing it's about the resistance level in the unit and isn't that when they went to the 2f? Hate to waste $50 but I think I'm gonna buy one and try it.

I ran the cannister to the port on the carb where it came off of the VSV/VCV last night and it drove great and had no pressure in the tank when I got home, but like I said is that too much pull? I'll grab a vac guage and see. This is the thread I think I saw about using pull off the air cleaner because there was mention of that. Thats the way I had it but there didn't feel like any vac being pulled. I'd guess broken check valve at the back was preventing it from doing anything. I'm gonna run it like this for a while and get the new check valve and see how much vac there is.

On another note I solved a slight fumes in the cab issue. There were no or failing gaskets at the tail gate, especially on the bottom and one side so there was essentially a 1/2" wide crack for most of the gate letting exhaust in. It got real bad when windows were down. Used some temp foam home window gasket tape as a test. Smell gone. New stuff ordered. Another step closer to not being snuffed out by this beast!

 

[Cgn1976]

Thanks for that. I was thinking pretty much that, but I don't really know if too much engine vac would create too much negative pressure build up.

I found a long thread about gutting a check valve in the cannister that also talked about an autozone substitute with fewer ports. I noticed mine has no working check valves because I could blow/suck air though all ports evenly.

I also pulled the check valve at the evap separator and saw it's cracked and not working right. It resists flow both ways. Can't find the part online but it looks just like the one for 75+. I'm guessing it's about the resistance level in the unit and isn't that when they went to the 2f? Hate to waste $50 but I think I'm gonna buy one and try it.

I ran the cannister to the port on the carb where it came off of the VSV/VCV last night and it drove great and had no pressure in the tank when I got home, but like I said is that too much pull? I'll grab a vac guage and see. This is the thread I think I saw about using pull off the air cleaner because there was mention of that. Thats the way I had it but there didn't feel like any vac being pulled. I'd guess broken check valve at the back was preventing it from doing anything. I'm gonna run it like this for a while and get the new check valve and see how much vac there is.

On another note I solved a slight fumes in the cab issue. There were no or failing gaskets at the tail gate, especially on the bottom and one side so there was essentially a 1/2" wide crack for most of the gate letting exhaust in. It got real bad when windows were down. Used some temp foam home window gasket tape as a test. Smell gone. New stuff ordered. Another step closer to not being snuffed out by this beast!

 

[Cgn1976]

Reading a little more about these, I guess they are supposed to flow both ways but have more resistance one direction, presumably letting air into the tank direction? This thing actually works that way, although it's letting a little air out of the leak. I actually would hear it squealing out of the leak in the truck sometimes, but I didn't realize what it was. I'm gonna JB Weld it up and flush it out and see what happens when I put it back in. Read that leaving no check valve means essentially the tank is open to the atmosphere so moisture can get in based on hot/cold temp cycles. It's pretty damn dry where I live so I'm not really concerned about that, but if this thing can live a little longer then great. If not $50 dollars in the new one I suppose.

 

[J Mack]

Not sure what range would be considered adequate or acceptable

I agree with you, a metered vacuum leak can be compensated for in the tune if the value is known and consistent, I wouldn’t randomly start removing metered orifices and or check valves with metered orifices and start replacing them with an unknown value component or worse yet just eliminate them all together.

It will take someone smarter than me to tell @Cgn1976 exactly what’s going on inside that valve but it looks and sounds like a metered check valve to me and should be replaced with a like unit.

 

[RUSH55]

If the tank is sealed with the exception of the vent hooked to manifold vacuum, would that still be considered a leak? Probably would until that desired vacuum is reached, which would then depend on the volume. I’m sure there’s an equation out there. Replacement of the valve would be the best fix, what’s the next best?

 

[Cgn1976]

I agree with you, a metered vacuum leak can be compensated for in the tune if the value is known and consistent, I wouldn’t randomly start removing metered orifices and or check valves with metered orifices and start replacing them with an unknown value component or worse yet just eliminate them all together.

It will take someone smarter than me to tell @Cgn1976 exactly what’s going on inside that valve but it looks and sounds like a metered check valve to me and should be replaced with a like unit.

If the tank is sealed with the exception of the vent hooked to manifold vacuum, would that still be considered a leak? Probably would until that desired vacuum is reached, which would then depend on the volume. I’m sure there’s an equation out there. Replacement of the valve would be the best fix, what’s the next best?

When I've searched for the 90917 10012 above I get pretty much everywhere selling the 90917 10020 for the 75-77. I have no idea if it's the same or not or if the minor difference is enough to work or be a problem. Not seeing anywhere that I can get the right one. I did just see a 90917-10067 on ebay that looks the same, but I have to assume the differences have to do with amount of restriction in either direction.

I just remembered I bought the Emissions manual for 73 and that says the check valve openeing pressure when tank has positive pressure is:
160-300 mmAQ (6.30 - 11.81 in AQ) or 11.7-22.1mmHg (0.46-87in.Hg.

When it has negative pressure it's:
300-600mmAQ (11.81 - 23.62 in AQ) or 22.1-44.1mmHg (.87-1.74in Hg)

So what the hell does that mean lol! Seems its saying there's more resistance on the valve for tank negative pressure than positive pressure, so easier to let pressure out than in. Just to get an idea for my feable brain to grab onto, 300mmQA is .4628 psi so thats clearly not a lot of pressure.

I used the old interwebs and found plenty of converters to get it to psi, pacals, etc...so I guess I know more now, however what I'm not seeing anywhere are the specs on any of the check valves that are for sale!

 

[J Mack]

Replacement of the valve would be the best fix, what’s the next best?

They took my Toyota nerd decoder ring away a long time ago but keeping it stock would be the best option on an otherwise stock Pig.

With that said I would plug the vacuum line running back to the tank and build my own charcoal canister and vent the tank through that, charcoal canisters are easy to make and do a good job of letting the tank vent without the smell of fuel all the time. Good chance this is what you’ll be doing when you get to that part on your build.

 

[Cgn1976]

They took my Toyota nerd decoder ring away a long time ago but keeping it stock would be the best option on an otherwise stock Pig.

With that said I would plug the vacuum line running back to the tank and build my own charcoal canister and vent the tank through that, charcoal canisters are easy to make and do a good job of letting the tank vent without the smell of fuel all the time. Good chance this is what you’ll be doing when you get to that part on your build.

If I could go straight stock I would. VSV doesnt work and can't find right year correct check valve! To be clear JMack, you're saying don't send any fumes into the manifold to burn and just let if vent through a cannister? Pretty sure I saw people doing that would at least connect the outlet that goes to VSV to the air cleaner so there's a little pull, but I'm open to whatever's gonna work.

 

[J Mack]

To be clear

I don't do Toyota and there are more qualified people than I to give you a good direction.

Pretty sure I saw people doing that would at least connect the outlet that goes to VSV to the air cleaner so there's a little pull

It is better for the environment to burn all vapor rather than let it escape to the atmosphere and most of the newer cars are a "closed system" for this reason, I drive old cars and all my fuel tanks are direct vented to atmosphere through a charcoal canister. "Open System"

 

[Cgn1976]

I don't do Toyota and there are more qualified people than I to give you a good direction.

It is better for the environment to burn all vapor rather than let it escape to the atmosphere and most of the newer cars are a "closed system" for this reason, I drive old cars and all my fuel tanks are direct vented to atmosphere through a charcoal canister. "Open System"

Got ya. yeah I figuered burning them would be better, but the part that I don't fully grasp and am trying to figure considering I don't have a functional VSV relates the speed sensor part of the stock system. Stock it only sends fumes to burn at 15 mph or more. So my question is it better to send them in all the time to burn even at low rpm/temp or not all and just let them vent?

To me I'm really more concerned with the tank pressure situation. I'm at 5500 ft and routinely go up and down 1000ft going around town and more if I hit the mountains close by. Add that to 100+ degrees in the summer and the tank pressure has me most cocnerned. I haven't really had and gas smell issues. I park it outside so no worries there.

Open system sounding simpler.

 

[J Mack]

Open system sounding simpler.

Yes and I’m a simple guy that likes to keep things simple.



The concern for you right now is creating too much of a vacuum “leak” in your system and running your engine too lean. An engine running too lean for extended period of time is a bad thing.

 

[Cgn1976]

Yes and I’m a simple guy that likes to keep things simple.



The concern for you right now is creating too much of a vacuum “leak” in your system and running your engine too lean. An engine running too lean for extended period of time is a bad thing.

Understood

 

[WarDamnEagle]

When I've searched for the 90917 10012 above I get pretty much everywhere selling the 90917 10020 for the 75-77. I have no idea if it's the same or not or if the minor difference is enough to work or be a problem. Not seeing anywhere that I can get the right one. I did just see a 90917-10067 on ebay that looks the same, but I have to assume the differences have to do with amount of restriction in either direction.

I would buy the 75-77 and run with it. There might not be any difference operationally. It could just be a material change for example that resulted in a different part number.