Fuel tank pressurized

[Northern]

That's a great thing to check but wouldn't the car run erratically if that was the case? I would have also thought something like that would have resulted in throwing an OBDII code... I labeled everything pretty comprehensively when I did the swap, but I will certainly double-check. However, isn't the fact that I get 12v when I ground the plug to chassis an indication that 12v is intended for the plug? Still trying to make sure I understand the behavior of the switch.

It should throw a code for that, but I was just looking at the ETM and the IAT wires are Green and Green/Brown so it's not the IAT.
I can't really visualize what other connectors are there.

Hopefully my other post helps with switch behavior, I should've responded to both at once lol

[Northern]

At the risk of giving too much information and making this way more confusing, here's what I've gathered about the charcoal cannister purge logic:

The attached pic is from ba114 years ago when he found the tables to repurpose for boost control in this thread

The values in the cells are PWM Duty Cycle that the ECU is pulsing the valve,
I think the x axis is TPS % and the Y axis is either Load or MAF, but you can get a general idea of what sort of conditions the valve is opening more vs less.

Also I think these tables do not apply when:
Engine stopped
Engine starting
Engine in post start

so TL;DR is, don't bother trying to look at valve behaviour with the engine running or looking at whether you see a GND through the ECU

[RenaissanceMan]

At the risk of giving too much information and making this way more confusing, here's what I've gathered about the charcoal cannister purge logic:

The attached pic is from ba114 years ago when he found the tables to repurpose for boost control in this thread

The values in the cells are PWM Duty Cycle that the ECU is pulsing the valve,
I think the x axis is TPS % and the Y axis is either Load or MAF, but you can get a general idea of what sort of conditions the valve is opening more vs less.

Also I think these tables do not apply when:
Engine stopped
Engine starting
Engine in post start

so TL;DR is, don't bother trying to look at valve behaviour with the engine running or looking at whether you see a GND through the ECU

Really appreciate all the info!! This is certainly helpful. Based on all of this I'm still assuming I should be seeing 12v on that connector with just the key turned on, though. The Bentley reiterates this as well, but maybe I should find another source to back that up. I'm going to continuity test the ground (brown) wire today and go from there. I know I could just set this up like an earlier car and just use the canister and a one way valve, but I've gotten a little obsessed with wanting this to work as it is supposed to. :)

[RenaissanceMan]

The ECU switches pin 68 to GND to activate the valve, I don't know what the logic is for the ecu to turn the valve on/off and I wouldn't bother trying to check for ground at the pin, just check resistance between the GND pin and pin 68 of the ECU connector.

If the plug is correct, and the continuity check is good, I'd look for blockages in the lines either visually or by popping the gas cap off and trying to blow air down the lines to the tank

Quick follow-up... Continuity checked out on the ground wire, and no blockages in lines. Not sure where to go next. Hate to think I have a faulty ECU; seems unlikely to me. You think it's possible that when the ECU was flashed for my swap/mods that the ground switching at pin 68 could have been somehow deactivated???

[Northern]

Faulty ecu or somehow getting turned off in the flash is possible but I think it's very unlikely.

Like if someone was doing a swap and wasn't going to run an evap valve, the easiest way to get it to not throw a code is to turn off the Diagnostic Trouble Code for the evap valve so it doesn't trigger a CEL if it is missing, but that shouldn't affect the functionality.

I'm going to ask some people who know more than I do about this and get back to you.

Could unplug the vent at the tank end of the hard line and drive a few days to be sure it stops building pressure. I guess it goes all the way to the expansion tank and through the cover under the RR wheel arch. If bypassing the valve like this lets the tank vent properly, it rules out any sort of issue there?

[RenaissanceMan]

Faulty ecu or somehow getting turned off in the flash is possible but I think it's very unlikely.

Like if someone was doing a swap and wasn't going to run an evap valve, the easiest way to get it to not throw a code is to turn off the Diagnostic Trouble Code for the evap valve so it doesn't trigger a CEL if it is missing, but that shouldn't affect the functionality.

I'm going to ask some people who know more than I do about this and get back to you.

Could unplug the vent at the tank end of the hard line and drive a few days to be sure it stops building pressure. I guess it goes all the way to the expansion tank and through the cover under the RR wheel arch. If bypassing the valve like this lets the tank vent properly, it rules out any sort of issue there?

Thanks again for the insight! FWIW if I disconnect the vent hose from the valve in the engine compartment, the fuel tank doesn't pressurize. Not sure if I mentioned that before, but maybe worth pointing out as I continue to test. I will also try what you suggested. It is still bothering me that I'm not seeing 12v at the connector at the valve with the key turned on (engine not running), because I know that the valve does work when it gets 12v.

[Northern]

So it's been a while since I messed with EWS deletes and swap stuff, but I was reminded that the "Control Bits" in MS41 that you need to modify to remove EWS also controls Evap functionality and some other stuff.
If this is some sort of off-the-shelf swap tune, they may be deleting "emissions" stuff this way but clearly not the best way if it causes this issue.

More info here, but it's a bit of a deep dive. Also keep in mind anything after the first post is pretty dated info and maybe wrong.
https://www.romraider.com/forum/view...p?f=42&t=11140

Before shelling out for another ECU or flash, I'd still try to see if unplugging the line solves the problem, just to absolutely rule out anything in the fuel vent system.

[RenaissanceMan]

So it's been a while since I messed with EWS deletes and swap stuff, but I was reminded that the "Control Bits" in MS41 that you need to modify to remove EWS also controls Evap functionality and some other stuff.
If this is some sort of off-the-shelf swap tune, they may be deleting "emissions" stuff this way but clearly not the best way if it causes this issue.

More info here, but it's a bit of a deep dive. Also keep in mind anything after the first post is pretty dated info and maybe wrong.
https://www.romraider.com/forum/view...p?f=42&t=11140

Before shelling out for another ECU or flash, I'd still try to see if unplugging the line solves the problem, just to absolutely rule out anything in the fuel vent system.

Aha... well, this was indeed an 'off-the-shelf' tune from Markert Motor Works that was matched to my mods list at the time... I'm going to reach out to them directly and inquire now that I know it's possible this could be related. I will also unplug the line at the tank end as you suggested.

[RenaissanceMan]

WELL...... After much tracking and research I was able to get in touch the gentleman who did the flash on my ECU and apparently they deactivated the purge valve functionality, so I guess I've been chasing my tail on this. I sure appreciate all of the help, especially from Northern who contributed a ton to the conversation. I learned a lot in the process. For now I'm just planning on emulating the older cars' setup and I will run a one-way valve between the charcoal canister and the intake.

[RenaissanceMan]

Follow-up: Configured the venting like the early E30s, replacing the actuated purge valve with the BMW one way valve (part # 11631707770) and routed vent lines to the canister and valve accordingly. No more tank pressurization, yay!!!