Just noticed something interesting. I capped off the EVAP input line when coming into the house to type up my results. Maybe in here around 30mins. Went back out to put the system back together and when upcapping the EVAP system, around 3-5 seconds of flow came out of the gas cap. I capped the system back off with a pressure regulator on it and will see how high the gauge reads in the next 30-60 mins. Could be that my air input line was venting the pressure rather than the vent valve.

 

Gauge moved so little in 30mins might as well been nothing. Normal pressure from a warm day when opening gas cap.

Ordered some 1/4 npt schrader valves, low pressure gauge, and various 1/4 npt attachments and a manifold. Will update next weekend as the parts will take a few days to get here.

 

I'm not quite done yet for today, but wanted to update while taking a break.

I got a nice 0-5 psi gauge which I promptly destroyed when I mistakenly hit it with 120psi from my compressor. I thought I had turned it down to 40psi, but even with 40psi I may have destroyed it as well. I was quickly pulsing the 40psi to the tank....but the setup below is much more controlled. I should have been smarter than the above...but live and learn.

Now to plan B. I was able to use the flow valves to my advantage as they don't completely stop flow. There is a slow leak to them when fully closed. that allowed me to slowly build pressure while watching my mityvac gauge.

At first, I could not get the tank to hold any pressure. I racked my brain on this until I wondered if the air pressure was somehow going out on the injector end via the return line or feed line. So I started the car, then put pressure to the gas tank. It then started to build pressure as I put air from my compressor into the system. I think this shows that the check valve on the pump has a slow leak. I've known this for a while as it takes a couple pump primes to avoid extended cranking times if the car sits for a while. It also may show that fuel injector valves designed to hold pressure with liquid behind them may not hold low pressure air.

Using a mechanic's stethoscope with only the hose, I could hear airflow from the fuel tank pressure relief valve under 3psi. I don't know an exact number as I destroyed my low pressure gauge, but I will order another one and test next weekend. I want to put a number to when that thing actually opens and closes.

My theory on the air flow going out the injector end revolves around that I think the injectors need liquid pressure behind them to seal. I don't think I have any old one's to test this theory, but the fact that it started to build pressure when I fired it up tells me it had to be going out that end.

I'll update with more a little later or next weekend when I get a new low pressure gauge.....I hate I destroyed it. It was a nice gauge.

Around 2psi of pressure in the tank is a good 5 seconds of venting when cracking the gas cap. This is still nothing like vapor release I experienced at the start of this ordeal. I'm hoping that cleaning the fuel tank pressure relief valve fixed it....but got some more testing to do.

 

I started searching on winter gas vs summer gas......the gas in my Z is from early March. I'm wondering if this is contributing to my pressure issue. I'll do more testing on the EVAP system tomorrow.

8-14-22 edit:Feeling a bit under the weather today and it's raining off and on, so going to postpone rechecking this until next weekend. As of right now, I think the system is working okay after cleaning the fuel tank pressure relief valve. Just need to put some numbers to the fuel tank pressure relief valve operation.

https://aaaliving.acg.aaa.com/auto/w...ratures%20rise

Reid Vapor Pressure
The difference involves the fuel’s Reid Vapor Pressure (RVP), which is a measure of how easily the fuel evaporates at a given temperature. Winter-blend gas has a higher RVP because the fuel must be able to evaporate at low temperatures for the engine to operate properly. Summer-blend gas has a lower RVP to prevent excessive evaporation when outside temperatures rise. That evaporation can cause vapor lock in an engine on hot days and contributes to unhealthy ground-level ozone and smog levels.

It’s All About Butane, More or Less
Summer-blend gas contains 2 percent butane, but that percentage is higher in the winter blend. Butane is used as lighter fluid and is a secondary ingredient in fuel canisters used for gas grills and camping. As a fuel, butane is less expensive than other gasoline components, but its high volatility limits how much can be included in summer-grade fuel.

 

Did my testing of the fuel tank pressure relief valve. It's opening at 1.8psi. That's almost double what the factory manual spec states. That's good to allow around 5 seconds of venting at the gas cap with 2psi in the tank. I have two evap control valves. The oem one that came on the car and one around 5 years old. The oem one is opening at around 0.4psi and the newer one around 0.6-0.8psi. So the newer one is operating closer to spec.

At this point, I think I'm going to run out the winter gas and get summer in it. I do know for sure that at least the tank is venting at a reasonable pressure....even if it is double the factory spec. I'd like to get a new fuel tank pressure relief valve, but they are discontinued from what I can find. I'm not sure if a third gen one would work okay as they are making them again.

Next hot day I'll take it out driving for an hour or so and see if the same problem happens. If so, that may mean that the fuel pump is running very hot despite the reasonable external gas tank temp. Other than the winter blend fuel, that's the only other thing I can think of that would produce such an amount of fuel vapor to overpower the vent system given what I've tested.

I did a couple videos of my testing I may post up on my youtube channel. Not sure if they are good enough for posting....kept screwing up the takes. However, I may post them incase someone finds what I did useful.

 

Forgot that I didn't put a period on this one.....the fuel tank vent valve was the problem. I have not had a massive pressure build up since disassembling and cleaning it. My AC is low on refrigerant as one of the schrader valves has a slow leak. As such, I've not taken it for an extended trip on a hot day, but so far, so good.

 

Thanks for the follow up !

Was it the white plastic pressure vacuum relief valve, or the vent valve on top of the tank for the line going to the EVAP canister? Guy who bought my Formula had problems with both. High pressure caused by the 20+ year old Bosch in-tank aftermarket fuel pump going bad and overheating.

pressure/vacuum relief:

http://shbox.com/1/fuel_pump_wiring.jpg

EVAP pressure control valve:

http://shbox.com/1/evap_system.jpg

 

Sorry Injuneer, just noticed your question.

It was the fuel tank vent valve in your first picture.

The EVAP pressure valve tested fine. My readings on it below.
I have two evap control valves. The oem one that came on the car and one around 5 years old. The oem one is opening at around 0.4psi and the newer one around 0.6-0.8psi. So the newer one is operating closer to spec.

One clue that escaped me was that I was having intermittent problems with the gas pump handle kicking off with me when filling up at the gas station before the tank pressure issue happened. I think that backs up the vacuum/pressure gas tank vent valve being seized up with around 26 years of dirt until I pulled it apart and cleaned it.