Stall while removing gas cap

[ns158sl]

So I have been fighting an issue after say a drive, if you pull the gas cap loose while the engine is still idling, itll pretty much flood itself and die. I can get a log of that shortly. I do have a log of a warm start which seems to be the same issue. It will flood itself and die. I am thinking it has to do with EVAP but not quite sure. The HPT PID doesnt read tank pressure correctly but I double checked with a Snapon Scanner and the voltage matches. It already has a new purge valve, vent valve, and a charcoal canister (all ACDelco also).

Im open to any more tests or ideas. I know Greg H advised to put an orfice into the purge solenoid. I might have to, but but figured Id start a new thread on this.

I find it odd if there was an issue with the EVAP system, no faults are active.

[ns158sl]

Ok I have something related to EVAP going on. I have steady state tuning this thing and it isnt going as well as it should, lol. I am reviewing the log and just randoming you can see tank pressure changes violently and get a huge rich spike. Seems right around 50ish KPA at any of the RPMs. Seems the purge solenoid is 100 and the vent is open the whole time.

[edcmat-l1]

Why not just TEE in a vacuum gauge after the evap solenoid? I've seen them stick open several times.

[ns158sl]

Well it is commanding 100 percent almost all the time. I dug around in alldata for more of an explanation on when it purges vs tank pressure. I've replaced that purge valve yesterday and then cycled it Koeo with a scanner to make sure it was changing with the PWM.

Eric

[ns158sl]

Well I honestly think it was the gas cap not vacuum breaking. It didnt do the stall during warm up after start. It still dies when I pull the cap after the car is running. Rightfully so being it goes pig rich. It is hard to believe the canister is already failed being it is less than 5k miles and was a Acdelco. Being I can't find any info on this I'm thinking I still have a mechanical issue. I would be curious to compare to another cammed car and see what happens.

This is a stripped down log, you can see the tank pressure equal out before it dies, thats when I pulled the cap.

Second log is it will become rich for a split second around 50ish KPA. Now PE enable is 50 KPA. It is not entering open loop or anything as it seems, but you can see uptick in injPW and tank pressure voltage raises. This thing is starting to make no sense.

Thanks again.

[gtstorey]

Do you keep pumping gas after the pump first kicks off.

[ns158sl]

Nope, honestly ive been staring at the logs vs tune and stumbled across the purge PWM, table 25012, ive reduced it to match stock idle airflow vs PWM to current engine. Ill try that tomorrow. Ive yet to figure out the rich spike at 50-52 kpa. It does it at almost all RPMs. Again, Ill hit the dyno tomorrow and report back.

[ns158sl]

So reducing the duty cycle under that low flow table made all the difference for my startup and idle issues.

Still havn't figured out the around 50 KPA where it gets a huge rich spike and throws off the trims from 50 kpa to 80ish. It is weird because it is like a light switch around that KPA the Tank pressure voltage spikes. Im debating on reducing all the duty cycle tables but i figured there would be a better method than just reducing it by 50 percent or something. Im surprised this is like the only thread on EVAP, other than just filtering out the decel cells.

[GHuggins]

Reducing the PW is the same as cutting the flow down. Basically the same thing as the orifice. Just wish gen V's had these tables or maybe they do and just haven't been found yet? Your tune itself needs to be set up to handle changing loads better. It should be able to take a 10% change in fueling and not start surging. I know cams make that hard to do, but I would go that route on top of reducing the PW. Take care of the PW now along with any swings from the O2 settings then dial in your fueling. FWIW, I've never adjusted the mid or high flow tables on gen 4's, not to say in your instance that may not be required?

[ns158sl]

So thats the part I don't follow. I mean this is steady state loading with good RPM and I can hear the engine lug down. Go back and look at the logs and yep, InjPW comes up, EVAP goes to a hundred, tank pressure goes into a vacuum, Fuel trims go hay wire lol. This shouldnt be anything related to catalyst? I cant find a general denominator other than it seems like around 50ish KPA no matter the RPM.

[ns158sl]

So I have adjusted the EVAP tables quite a bit now and it seems to be getting way better data. I guess at this point Id like to see a log of a stock vehicle and compare purge DC vs tank pressure voltage. I say that being it seems when the tank voltage goes up (vacuum), thats when the trims go nuts and screw with the fuel trims. Where I ended up at is already probably fine. But, if a guy can see a log of a stock vehicle and say the ECM keeps the tank pressure/vacuum/voltage at a certain point, then a guy could adjust the EVAP table without the blinders on. I know EVAP is a moving target. Right now, for me, it is not. Its a returnless fuel system and climate controlled within around 65 degrees F. Just kicking it around being me VE table has been completely off and im 90 % sure that was the culprit. I guess the only other thing I would like to know is the threshold between low, mid, and high flow tables.