Hey everyone,

Recently I have been having an issue where my 05 evo 8 has been running really rich after getting gas. No matter how much gas I put in ($10, $20, full tank), after starting it, the car will drop below 10 afr and try to stall. The only way to keep it running is to rev it a bit and try to drive. When driving the car will still run kinda rough, however will begin to smooth out the more I drive it. And if I let the car sit for a couple hours after getting gas and start it up, everything is fine. On a side note, I've also been having an issue where my car has been running rich when the temperature outside is 70°F+ outside. Not sure if these issues are related or not.

Was wondering if this could be a bad fuel pressure regulator or something else with the fueling system? Ive already replaced spark plugs, checked for boost leaks, and nothing has changed. I'm completely stumped, any help is appreciated.

 

It could be the FPR sticking closed when the cold fuel hits it after filling up, or a clog in the fuel return line. The only way to diagnose it is with a pressure gauge on the fuel feed line into the rail. Should be 33psi at idle and 43psi with the vac hose disconnected and your thumb sealing the end of the hose.

 

I had a similar problem with a different car. The aftermarket EMS I was using had the output for the evap purge solenoid inverted....meaning it was on when it needed to be off, and vice versa. Changed that parameter, flashed it, and it was fixed.

I’m not sure that is going to help at all, but who knows. Troubleshooting weird stuff can definitely get frustrating.

 

Great thanks! Just bought the ultimate racing adaptor, will update with numbers once I get it.

 

So today, the car decided to act up again. However, unlike before (when it would stall after getting gas), this time it stalled after a warm start, which was a first. I went on an errand, and the car drove fine to my destination. Then, when I came back to the car, about 20 minutes later, and tried to start it, it kept stalling. After about 30 seconds of revving it to keep it alive, it began to idle smoothly, however, the AFRs were 11.5-13.5 and were like that the whole drive home.

Was able to capture some of it on video:

 

You need to see if your purge valve is sticking open pulling in fuel vapors when it shouldn't. There are some awesome videos by scanner-danner on how to diagnose this. Do some learning on youtube.

 

Is the car tuned on speed density? Using the fuel temp sensor?

 

Yes, the car is tuned on speed density and using the fuel temp sensor.

 

Thank you! Will look into this.

 

There was an excellent video series about a hyundai with a purge valve issue.

The same logic will work with your car. In order to repair something, you must first understand in detail how it works (words from my old dad)

 

Could be your fuel pump relay going bad and the pump getting stuck in high speed mode.

 

Thank you!

Update: Took the Purge Valve off today, tested it, and it is working fine.

 

Update #2: Replaced the FPR and front o2 sensor (saw it was acting up a little in evoscan) and nothing changed. Car runs great for about 20 minutes, then will drop down in AFRs. I also parked the car for about 5 min and tried starting it back up, and the same issue happened again with a warm start; it kept trying to stall. I'm stumped

 

Checked the fuel pump relays, they're all good.

 

Disconnect your vacuum line going to the fuel pressure regulator and see if the diaphram is ripped. If it is, gas will come out where the vacuum line was.