"It is not the man who has too little, but the man who craves more, that is poor." - Lucius Annaeus Seneca
Last week I was able to dispose of *most* of the storage stuff in the shop that's been causing a "disturbance in the force". What's left is either brand new and therefore of some value - and so needs to be sold, or can be donated to the appropriate venue. Anyway, it's a huge relief to have a big chunk of work space returned.
I rolled the plow/trash truck out and rolled the Subaru in. I'd mentioned previously that there was a "check engine" light and a generic trouble code P0440 (EVAP system fault). Several websites recommended replacing the gas cap, as that's inexpensive and is often the cause of these issues. I did that and reset the code - which returned a couple of days later.
I'm not an expert on this emissions and diagnostic crap, but I (usually) enjoy figuring out stuff, so here we are. When your car is shut off, a vent valve opens and allows your fuel tank to vent the fuel vapors off into a charcoal canister (the EVAP canister). The canister scrubs the flammable fuel vapors, while letting your fuel tank release pressure as the fuel warms or cools.
Once the car is started, the vent valve shuts. A different valve called the Purge Control Valve opens, and this valve opens a line to the intake manifold on your engine - which is at a slight vacuum. This second valve puts the EVAP canister and your fuel tank at a slight negative pressure, burning off the vapors that accumulated in the canister.
The engine management system is looking for this slight negative pressure whenever the car is in operation, and will throw a P0440 (EVAP fault) code and turn on the check engine light if it doesn't see the slight negative pressure.
My job today was to figure out why the sensor wasn't seeing the slight negative pressure. It took two days to return after I first replaced the gas cap on the car, so it may be an intermittent issue.
Armed with a couple of schematics and a new toy, I set about trying to find the source of the P0440 issue. I hand wrote a few notes about where issues are frequently located. Not much of this mattered in the end.
I bought this Chinesium smoke machine, which calls in the instruction manual for "mineral oil" to turn into smoke. I found this a bit humorous, as mineral oil is also used as a laxative.
Below after unboxing this piece of garbage. It has a pre-set pressure regulator, set at 1/2 psig, so that you don't blow hoses off or split open your fuel tank. It comes with a hook to dangle it from the hood, 12 volt power cables, a short fill hose, long smoke hose, a tool for something or other, and an air fitting - which did not fit my system. The needle valve on the top right adjusts air flow into the device, and therefore smoke flow. Smoke exits at the bottom rear of the box, which is where the long hose attaches.
Fortunately I keep spare air barbs that allow all air tools to connect up.
So I got this thing all set up, and after a bit of adjusting the needle valve on the right side of the machine, it started gurgling and making smoke!
Below: Air supplied, power supplied, more or less upright, filled with mineral oil. Ready to turn on.
Does it make smoke? Yes. Yes it does!
It took a fair bit of adjusting with the needle valve to get that stream of smoke. With smoke available, I began to troubleshoot where there might be a problem.
Below is the pressure sensor on the left, and the "Pressure Source Switching valve", which I think places the pressure sensor online or takes it offline. I tested the valve with 12 volts. It opened and closed properly, shutting off the smoke when I energized it.
Next I pushed the smoke backwards towards the fuel tank - to check hoses back to the Purge Control valve. That's when the problems began with the smoke machine. There were no smoke leaks, so the smoke backed up, and began condensing - turning back into mineral oil inside the smoke line. It filled the smoke line completely with oil and stopped making smoke.
When I removed the smoke tube, oil drained out - everywhere. It kept dripping - all over the engine, all over the floor, all over the smoke tube itself. Very messy, indeed. After I completed feeding smoke in from under the hood, I spent several minutes clearing the smoke tube of oil and getting the machine to make smoke once again.
Next, I removed the gas cap to smoke test the fuel tank, filler neck, and EVAP canister. This tested the system on the other side of the Purge Control valve. It took forever for the machine to start making smoke again - the tube still kept spitting out blobs of air and mineral oil instead of smoke.
After I was finished with the leak testing, I hung the the smoke line up to draining of oil in the shop overnight, and then reset the "check engine" code.
I never did find any source of leakage for the fuel tank or hoses while it was filled with smoke. Perhaps the purge valve is not opening correctly 100% of the time, perhaps the vent valve is not closing 100% of the time, or maybe the little filter is partially clogged. All of these are cheap, and all will get replaced if the check engine code re-appears.
UPDATE September 3:
Drove to work on a cool morning, no issues. Drove home on a very hot evening (93 degrees F), and the check engine light turned on. Placed an order for a new Purge Control Valve. It should be fun to replace :\
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