Simple evap system control with megasquirt
 

I have an NB2 with ms3 pro Evo. The car has an engine swap, but that's irrelevant to this topic, and it's boosted. I want to do something with my evap system. It's a street and track car.

Removing the entire system means building pressure in the gas tank, and drilling a hole in the gas cap means sloshing gas onto the track.

Moving to a simple breather under the car means being a bad person and killing penguins.

I'd like to do some kind of simple evap system that could keep the tank as a closed system and then vent into the intake under the right circumstances, like stock.

Has anyone done this? I presume I could just run a simple valve that opens when the car is at mid-throttle and mid vacuum, and stays open when the car is off.

Pos-cat for the question; this is highly interesting to me as well (for the stock system, and I admit I have not searched yet). I assume it would be rather simple, since you already have the inputs (MAP & TPS), so you could wire an output to trigger the OEM "actuator"/valve?

I personally eliminated the solenoid valve and simply installed a check valve. The flow at idle is low enough that I have no issues idling as low as 600 RPM. You could use a spare digital output if you wanted to control a solenoid with RPM/map qualifiers.

IMO evap is required for applications similar to mine. Return-style system running e85. The fuel temp increase coupled with the sealed tank can cause a significant amount of pressure. I relocated the evap canister to the rear driver fender-well (where the fuel filter is located on passenger side NA). I have been through inspection and passed.

Edit: and parked in a garage, that I prefer doesn't smell like a refinery.

That's an interesting idea. I was thinking I'd want to avoid drawing a heavy vacuum on the tank at WOT, but the boost would take care of that.

What size injectors are you running? Any extra fuel could make it harder to idle big injectors.

I have a 400hp e85 capable fuel system with ID850 injectors and a DW200 pump. I can maintain a stable static idle with this setup at 550 RPM. I bet I could go under 500 if I close the idle adjust screw.

Good to know, thanks!

Ted, I'm running it with just a check valve, and so far so good. Thanks for the suggestion.

Glad I could help

Sorry if this is a dumb question but - would replacing the solenoid valve with a simple check valve also work on an NA with standalone / ms3?
I don't want to remove the canister and would like to have it actually work. :)

If I were doing a fresh install today, I would hook up the purge valve and drive it with the ECU. A little homework is probably required, but a good side project for a beginner where the risk is low, but one can experience satisfaction and provide something new in the community.

But yes, a check valve works on a NA chassis.

Anyone have an idea how much vapors a typical canister holds (days at temp) before they are released into the atmosphere anyway? Another way to ask... Ted, how many days in the garage before you begin to smell alcohol?

EDIT:
Also sparked by this thread... I'm idling at 800, but have been wondering if I could go lower. I might play with lower, now that I'm looking into improved fuel economy. When A/C is on, I like to run about 1200RPM, though, to make the system effective.

If I don't have evap in the summer the garage will smell after 1 night.

Well just replacing the solenoid with a valve is much less :effort: than either routing another wire into the engine bay or hacking into the Mazda loom but yeah I guess I could use one of the programmable outputs via conditions in tunerstudio.

But what conditions ? :hsugh:

And how long WITH evap? Not that I plan to re-install, but a question I’ve had for some time.

DNM

Well I am drawing from memory, but I believe the solenoid is already wired to terminal "X" on an early NA, so one would simply need to route that to a spare open drain output (I would probably pick an unused injector channel and wire inside the ECU case).

Conditions are pretty simple, websearch should confirm, but I would think RPM greater than say 1500 and load between 40 and 60kpa would do the trick.

No smell with check valve EVAP, ever. Gas cap doesn't let a bunch of air out when filling either.

I did discover that with hot fuel and a low tank, the purged vapors at idle would cause a rich condition (especially with gasoline IIRC). A solenoid would presumably fix this.

Yeah that's what i meant - solenoid is wired to pin 4T / Yellow+Red on my 95 EU 1.8 loom. I got unused low side outputs on my ms3 basic DB37 connector.

Ok thanks I'll look into that!

To follow up on this:

According to miata diagnostics wiki evap control on the 1.6 works like this.


And the '92 workshop manual states:
[quote]
Operation FUEL VAPOR VALVE
The solenoid valve (purge control) is controlled by duty signals from the engine control unit to perform purging
of the charcoal canister. Purging is done when these conditions are met:
(1) After warm-up.
(2) Driving in gear.
(3) Accelerator pedal depressed (idle switch OFF).
(4) Oxygen sensor functioning normally.
[quote]


Now, regarding the 1.8 system I couldn't find any specifics on the web. Closest thing to working conditions I could dig out of the german 93 1.8 workshop manuals was this diagram:
Attachment 228195

So tl;dr during partial load with warmed up engine, acceleration and full load conditions the purge solenoid is venting. In all other conditions it is disabled.


So rpm > 1000 + map(40-60kpa) would also cover partial load on a cold engine where the solenoid should stay disabled. How can I also cover coolant temp with only 2 possible conditions for my programmable output ? :dunno:

MS3 with loops can stack in the CLT along with the other two parameters.

DNM

Activating the EVAP without calculating the consumed fuel volume and just letting it apply a strong vacuum inside the fuel tank is a bad idea and will likely cause the fuel tank to crack in the long run.