5.0 canister purge valve
 

1993 5.0 HO motor. It was built back in 1996, so up until a year ago the canister purge valve was wired up backwards to the ECU. The symptoms I was getting was a gas smell after the car has been ran extensively and sitting at a stop. Short trips were ok. The car has to be driven long enough to completely saturate the charcoal evap canister before you can start to smell the gas fumes.

After I figured out the purge valve was wired up backwards I thought I was fixed but I just did a ton of city driving today (something I normally don't do) running errands and low and behold the gas smell is back and coming from the canister.

From my understanding of how the thing is supposed to be wired up, the valve receives a constant 12v power and then opening and closing the valve is controlled by the ECU connecting to and disconnecting to ground. This is a foreign concept to me and I am no electrical engineer but I believe my understanding is correct.

I haven't traced the wire to see that the ground wire is connected to the proper ECU pin. Assuming it is wired up correctly, and knowing it was hooked up backwards all those years and not working, could the ECU be damaged?

The car passes CA smog just fine with the purge valve not working, that is rather funny.

Mine smells like gas, too. I am going to inspect the in-line check valve on the vapor line between the tank and purge valve next. I thought I had it fixed when I cleaned the gunk out of the gas cap vent. The good news is that after letting the car sit undriven for 11 months, all of the gas smell has disappeared.

Ahh, mine is very much the evap canister and the purge valve not working.

The valve itself works fine if I directly apply 12v and ground to it. Just when wired up to the ECU it never appears to cycle...or maybe it does but doesn't cycle enough so maybe it is Ford By Design(tm).

I am thinking of wiring in a little l.e.d. to the circuit so I can see it while I am driving and see if the circuit ever turns on.

Right now, I have the canister caps off and plugged up so the fumes have no place to go. I used to run a small exhaust line to the exterior of the engine bay so things can still vent and not be a fire hazard. Not sure what will happen with things capped off and the fumes have no place to go and pressure may build up in the canister and back feed somewhere.

HI All,
I suffered with this issue for 2 years until I was able to find a good solution. I use the Ford EECV ECU and it has a built in purge valve strategy routine (that cannot be modified with the SCT tuning software) which I relied on to drive the Miata purge solenoid. However as the V8 miata configuration heats up the tank and gets it pressurized ever so efficiently, the ECU's standard purge routine could never fully evacuate the charcoal canister. So the car ended up with fuel smells in the cabin and from beneath the hood during long idle periods in traffic or when parking the car in the garage after a long drive. The reason for this is that if the solenoid does not activate to suck the fumes back into the engine, and the charcoal canister can not sink the fumes within the charcoal, they just vent to the atmosphere.

To fix the issue I bypassed the ECU's purge canister triggers and ran a 12V programmable timer to open and close the Miatas purge valve. I used a routine of 2 secs of purging every 6 minutes. This would start and stops the solenoid as the car is running. You can hardly tell its working unless you are idling and it cuts in, the engine revs drop by 25-50 rpm for a second and then returns to normal. It works a treat and the car never ever smells of fuel anymore.

This was a big deal for me as I drive the car daily, and on some long drives where I was stuck in traffic the fuel vapor smells would give me a headache.

So I would advise that all the standard Miata Evap systems and pipes be left in place 100%. If your ECU can handle it let it drive the Miata purge solenoid and see if that evacuates the tank vapors properly. If not running a separate timer to trigger the solenoid is a great way to fix this.

Timer was purchased from Buy Off Delay Timer Relay Online | Timers.shop

Cheers