98 v70 NA evap canister shut off valve

[abscate]

I think normally open for the stop,valve makes sense. Gas fumes can't just vent to air, they get caught in the carbon canister and never make it to the stop valve. The only time you want to close the stop valve is to for your loyal friend to test system integrity. You want the stop valve open whenever the purge valve is open..to supply purge air.

[98v70dad]

Just saw this video, seems legit, please comment on the video...

Very good video. Thanks.

He described it the same as what I understand the V70 EVAP system does. Maybe the shut off valve valve is also a tank over pressure relief and blowing on it opens it to the atmosphere until the next vacuum test. Tank vapor pressures are usually measured in inches of water. That is a very low pressure. 27.7 inches of water is 1 psi. So it would be easy to blow enough pressure to open a relief valve designed for inches of water. That might also explain the shut off valve being referred to as the vent in some diagrams.

[98v70dad]

OK. I did an operations test of the solenoid with 6v and it actuates or clicks...possibly functional. But I could blow air through it when the car was doing its diagnostic EVAP vacuum test so I determined it to be a bad part, maybe it was only jammed open. In the interest of science I did a tear down. I removed the big rubber mount bushing and revealed what looks like a date code and manufacturer. Pierburg 97T210. So this is apparently an original part...thought I'd replaced it but apparently not. This is a good example of dumbassery on my part. I should have checked this months ago.

I also removed the pancake air filter and disassembled it. Inside I found a spiders former home and a thin (1/8") foam air filter. The filter is disintegrating and has many holes in it and many missing pieces. These broken off pieces of foam could easily be sucked into the valve and keep it from sealing. One little piece is all it would take and mine had the biggest hole directly below the air intake on the valve. At this point I decided to cut up the solenoid/valve. I cut it with a hack saw around the perimeter and found that its design is quite simple. Inside is a plunger with a rubber gasket that is pushed against a sealing surface. There is also a spring to reset the position of the plunger when the solenoid is no longer energized. This is well designed and simple part. However, it will jam easily if it ingests some crud and this is fairly easy to do if there is a hole in the filter. There is no internal check valve in the solenoid valve or air filter. Its either open or closed and its only closed when energized. I could find nothing wrong with it other than being dusty inside (holes in the filter) and the possibility of ingested filter parts jamming the valve. No ingested parts fell out of it though when I cut it open.

I'm now not convinced that this was the source of my problem, but since it was an original part and it passed air (blow test) when it should have been closed (evap diagnostic test) I don't regret replacing it. We'll see ....

[sleddriver]

OK. I did an operations test of the solenoid with 6v and it actuates or clicks...possibly functional. But I could blow air through it when the car was doing its diagnostic EVAP vacuum test so I determined it to be a bad part, maybe it was only jammed open. In the interest of science I did a tear down. I removed the big rubber mount bushing and revealed what looks like a date code and manufacturer. Pierburg 97T210. So this is apparently an original part...thought I'd replaced it but apparently not. This is a good example of dumbassery on my part. I should have checked this months ago.

Using some clip leads, I energized the SOV, then pulled a vac on it using a Mitey-vac and watched the gauge for leaks. Just remember that the MV scale will read in inches of Hg and we're dealing with much smaller units.

Interesting you worked on airplanes. I had an old-school uncle who was an A&P. I watched him record everything he did on a plane in the log book. So I bought one for my car(s) and have continued the practice ever since. I still do it by hand and keep it in the car. Your just making this worse for yourself if you don't know what you've replaced and when. As if dealing with P0455 isn't bad enough on its own....

I also removed the pancake air filter and disassembled it. Inside I found a spiders former home and a thin (1/8") foam air filter. The filter is disintegrating and has many holes in it and many missing pieces. These broken off pieces of foam could easily be sucked into the valve and keep it from sealing. One little piece is all it would take and mine had the biggest hole directly below the air intake on the valve. At this point I decided to cut up the solenoid/valve. I cut it with a hack saw around the perimeter and found that its design is quite simple. Inside is a plunger with a rubber gasket that is pushed against a sealing surface. There is also a spring to reset the position of the plunger when the solenoid is no longer energized. This is well designed and simple part. However, it will jam easily if it ingests some crud and this is fairly easy to do if there is a hole in the filter. There is no internal check valve in the solenoid valve or air filter. Its either open or closed and its only closed when energized. I could find nothing wrong with it other than being dusty inside (holes in the filter) and the possibility of ingested filter parts jamming the valve. No ingested parts fell out of it though when I cut it open.

I'm now not convinced that this was the source of my problem, but since it was an original part and it passed air (blow test) when it should have been closed (evap diagnostic test) I don't regret replacing it. We'll see ....

Good you did this. Experimental Science. Now we know. There's no check-valve in the SOV assembly. You're indeed correct that if any of that foam made it into the valve, it would prevent its closing. If a leak of only 400 Pascals is enough to cause a LARGE EVAP leak, imagine what a small one is? Crikey....dam fussy.

PS: If this is true (one can blow backward on the shut-off valve), then I find it intriguing, why would any engineers design the shut-off valve this way, i.e., allowing gasoline fume to vent out to open air? Maybe the air filter blocks the air flow outward and the normal fuel tank pressure is rarely above ? 1psi. In other words, fuel evaporation alone does not create too much pressure.
Anyway, I love to learn exactly how the hut-off valve works.

You're forgetting that the CharCan is between the gas tank and the SOV's vent. Activated charcoal will absorb the expanding gas vapors. This slight pressure on the CharCan will also force air out the other end, through the SOV and into the atmosphere. My previous system description indicates the CharCan can absorb about 2 liters of vapor. Look carefully at the diagram of the tank. All the vapor is forced to the top on the left. I see now my previous post was wrong because that diagram shows a one way check valve where the fuel filler tube enters the tank. It'll be "under gasoline" when the tanks about half-full maybe, thus no vapor will be able to escape through the safety valve on the gas cap when the tank is full. So my mistake on that assumption. Which means ALL the vapor will exit through the CharCan and onto the SOV. When it becomes saturated with gas vapor, given my above scenario, even gas vapor will be forced out of the SOV, through the VENT and into the garage.

Again, when the vehicle is off, the SOV is not energized. Since it's NO (normally open), air can both enter and exit the tank through the open SOV, CharCan and VENT. Remember, the system also needs to account for changes in barometric pressure. One atmosphere = 14.7psi = 29.92" of Hg = 33.8 FEET OF WATER COLUMN! Not INCHES of water column...FEET! Further, one atmosphere = 101,325 Pascals or 101.3 kP. I noted in my earlier post just how small the vacuum pulled on the system for the EVAP test. About 1300 Pascals or 1.3kP. That's pretty tiny!

So whenever a hurricane moves into the Gulf, gas vapor will be exiting millions of tanks for hundreds of miles away! Up North, where it's COLD as long as it's HOT down here, there are no HOT garages and the air temp quickly drops, this is not even a problem compared to down here in the Southern states, where we only have two seasons: Summer and February! And where I live, we're not even having the later: It's 70°F outside and I'm in shorts! Go figure......

[98v70dad]

Well, its back. I gambled, hoped and lost. I guess I'll focus on perfecting the smoke tester now. Honestly I can't imagine having a leak because all the rubber is new except for the seal on the fuel pump and sending unit AND everything I've replaced has been OK .... no cracks, etc. Its possible that I have a leak at the throttle body or vacuum tree and the car isn't able to create the vacuum it needs to pass the EVAP diagnostic....

I've got a new part, though, and you really can't lose there, especially when the old one was 18 years old. I've replaced almost everything and still have spent far less than one trip to the Volvo mechanic. Regarding working on aircraft, the A&P mechanics worked with me but I told them what to do and they kept the records. Unfortunately, as a shade tree mechanic I am responsible for all of it and keeping records isn't something I excel at.

[cn90]

My further reading on the design of the Shut-Off Valve leads to a document published by the EPA.

My understanding is:

1. During normal engine operation, engine vacuum sucks fuel vapor from the Charcoal Canister, at the same time air is sucked into the SOV to replace the vacuum created by volume loss from fuel being pumped into the engine. So basically no fuel is vented into the atmosphere during this phase.

2. The problem is when the vehicle is parked on the driveway can have extreme temp swing (as much as 50-60 deg C in one day!).
The temp swing is less inside an enclosed garage.
But anyway, during the temp swing (diurnal temp change), fuel vapor can build up pressure that exceeds the Charcoal Canister capacity, in that case it is vented to the atmosphere: it is not much but the hydrocarbons are vented under certain situation! So I learn something new...yes, fuel is vented into the atmosphere under special situation! Wow, never though this (fuel vented to the atmosphere) could happen, but it does...


PLEASE read the pdf by the EPA in the link below!!!

http://www3.epa.gov/otaq/models/moves/d ... r14014.pdf

[98v70dad]

Good info CN90 thanks. I'm beaten down and thoroughly sick of the EVAP problem so I'm taking a break from it (mostly) today. I'll probably try smoking it again, but I tried that already and didn't have much success. The cigars I was using to produce smoke only lasted about a minute and a half the flow rate on the compressor was very low at 1 psi so in 1.5 minutes I wasn't moving much smoke in into the system. My smoke test was essentially a failure because it didn't even find the open shut off valve which I knew was there.

[98v70dad]

Cleared P0455 today and drove around quite a bit. It stayed off. Normally it will ALWAYS come on at the same stop light The only difference from the last few weeks is it is 63 F in Atlanta today and its raining. Yesterday I did an under car inspection from the top of the evap canister, across the front rail and down the side frame rail. I didn't find anything but I did a lot of wiggling of the lines. Weird. The temperature is probably the reason the light stayed off, but I did the same drive yesterday and the temp was the same and P0455 came back predictably at the usual place.

[98v70dad]

So my friend P0455 is still with me. Two days ago, I removed the vacuum tree manifold and replaced the O-ring and all of the caps. For good measure I also put a bead of permatex on before I installed the tree. No suprise...two days later the code is back. I'm beginning to wonder if I put the purge valve in backwards. Something to check next weekend.

Here's a question for the group. My daughter was famous for running over things when she drove the car. I've inspected the tube that goes from the evap canister to the rollover valve and there is on spot that looks pretty rough but it doesn't seem to be perforated. Last time I was at the dealer I asked about buying the plastic line that goes from the evap canister to the roll over valve and they weren't sure its still available. Other than the sending unit and fuel pump seals its the only thing left for me to replace....So the question.

Has anyone replaced this part with something else like PEX tubing or does anyone know a source of the original tubing?

[abscate]

A smoke test would show a hole in that tubing, or you could just cut out the damaged part and replace with generic hose.

Jeeesh.,...that's a pesky one. Mine is pesky too but comes 2000-2500 miles apart.