Evap leak after walnut blast
 

Did a walnut blast on my 100k mile 2008 MCS and drove it for the first time (just around the block) yesterday, then today on my way home from work, which would have been the 4th start/stop cycle, I got a CEL and a message on the BC to check gas cap. It seemed to clear itself shortly after and stayed gone during the 40 mile drive but came back after a grocery stop and didn't clear. Gas cap was tight, and code was 27AC which I can't find in the Bentley manual but my Autophix scanner describes as DMTL - Major Leak.

I usually avoid accepting coincidences so I'm thinking it's likely related to my interaction with the fuel tank vent valve when I removed the manifold. Are there any known common or likely failure modes with this process? All I did was disconnect one hose (which was particularly difficult) and one electrical connector, and I'm certain I reconnected them, though it's possible something failed to fully engage. Is cracking one of the hoses a likely culprit? Or is there a tiny o ring in the hose connection that might have fallen out, or a clip that loses its muster being disengaged and reengaged after 11 years worth of heat cycles? Or by chance a rogue walnut particle found its way into the connection preventing a seal?

The only other variable that could be unrelated to my work in the engine compartment is that when it happened, it was 79F outside which is the warmest condition I've driven it in since purchase, by about 10-15 degrees. So, it's kinda back to the coincidence thing but if there's something in that system that would be more sensitive to heat, that would be good to know as well.

Certainly could have created a leak somewhere but if the gas cap is original it is time for a new one. They can seem tight but still leak due to old seal.

I'm not sure how to tell if it's original - the rubber seal is a pale green and there isn't any BMW part number on it, nor does it have the same printing on it as the genuine BMW caps I'm seeing online, so I think it's not, but I have no idea how to tell how old it is.

I reset the code and put the cap on extra tight; it made it the 40 miles to work without giving me the CEL, which it did yesterday, so I'll see if it happens again this afternoon. Either way I'll probably order a new cap and if it comes back I'll just live with it until I replace the vacuum pump in a couple weeks and have the intake tubing out again.

New gas cap, reset code, and got the "close gas cap" message again, so I guess I'll be diving into it when I change the vacuum pump next week. Crossing my fingers it's something obvious cause I'm only about 0.1% more interested in buying a smoke test setup than I am paying someone else to work on my car.

Any update on this. I just got the "close gas cap" message for the first time yesterday. Came back this morning with a check engine light. Car drives fine so I'm not too concerned.

If it just happened at random, start with tightening your gas cap and if that doesn't fix it, buy a new gas cap. I don't know how many start/stop cycles it takes to reset itself 'cause I was just clearing the code every time I tried something new.

Mine started immediately after I had the intake manifold off for cleaning the intake valves, which includes disconnecting the tank ventilation valve, so I suspect there's a connection. I've been busy and out of town so I haven't had a chance to dig into it yet, but I suspect I either didn't get that connection fully seated or a stray piece of walnut shell found it's way into the connection or the purge valve and is preventing a seal. I'll be replacing the vacuum pump this weekend and plan to investigate while I have some things disassembled for that.

Thanks for the reply. I checked the gas cap and it was tight. Already have one in my shopping cart. BUT... When doing the thermostat, I removed the intake manifold. Is the tank ventilation valve also referred to as the purge solenoid vacuum line? That connector was a PITA to remove. Thought I got it back on correctly but maybe not.

Edit: #5 is the part I'm referring to. Is that the connection you mentioned?

https://cimg0.ibsrv.net/gimg/www.nor...84db103285.png

Yes, that is the valve I'm referring to and yes, the connection between the hose (5) and the valve (1) is the connection I removed. I also remember that connection being particularly troublesome to remove and have wondered if I damaged it in the process.

Sounds like we may very well be facing the same, or at least a very similar, issue.

After getting the 'close gas cap' message yesterday, I popped the hood when I got home. I heard a hissing sound that I hadn't noticed before. Didn't think much of it as hot engines make a lot of noises and after repairs I'm alway hypersensitive (paranoid?) and hear/see things I hadn't before. Now I wonder if it could be a vacuum leak at that connector. I tried to identify where in the engine bay the sound was coming from but couldn't. Will listen again when I get home tonight.

this is my first dealings with a malfunctioning EVAP system, so I'm not 100% positive, but I think it's under pressure, not vacuum. Then when the solenoid opens it's exposed to the vacuum of the manifold to purge the pressure.

If I knew how to force the leak detection pump on I would try listening for a leak, but I don't know when it runs on it's own or if I can force it with the scan tool I have.

Checked codes when I got home. Only one: 321C: Fuel tank ventilation system and purge air system, minor leak. I cleared it but haven't driven the car since. Unlike yesterday, I didn't hear the whistling sound from the engine bay after shutting the car off so who knows if that was related.

The vent pipe that connects to the breather valve is about $50. Nice to know that it isn't too expensive if it needs to be replaced.

Took a short drive this evening. Got the gas cap message again but no CEL. Ordered the gas cap. I'm not convinced that it will take care of the problem but it's the logical place to start.

If you drove it again today I'd guess the CEL came on again. For whatever reason, the CEL isn't activated for these codes until the second run cycle with the gas cap message.

Yeah, it was back this morning. I'm not going to do anything with the purge vacuum line until I try the new gas cap when it arrives next week. Will be interested to hear if you find that connector is loose or damaged.

Replaced vacuum pump, which as it turns out was from 2015 so probably just wasted $120 and I expect to still have intermittent boost and brake pedal stiffness that I'll have to figure out. But while I had it all open I pulled the tank vent tube and inspected. There were a couple of walnut particles in there, but otherwise the connection looked undamaged but worn, and it was fully seated. I blew it out with compressed air to make sure it was cleared and put it back on. We'll see what happens when I take it to work on Monday.

I've also stumbled onto some threads that refer to this valve causing a hard start /long crank after filling the fuel tank, which I've experienced on one tank after the light came on. So now I'm beginning to entertain the idea that the purge valve went bad and my messing with it really was coincidental. If my light doesn't go away I'll probably do the valve and hose next.

"close gas cap" came again today, so my R&R and cleaning didn't do the trick. Guessing the rubber O-rings have hardened and won't reseal now that they've been disturbed.

It also was hard to start this morning after buying gas. That's the second time it's happened and both followed having the system open, so maybe that's somewhat to be expected? If it does it when I haven't had the system open I might condemn the purge valve, but right now I'm resisting the urge to go with the belt-and-suspenders approach and I'm just going to try the hose first. I also am in need of a new valve cover since it appears mine is clogged up and holding pressure in the crankcase.

Sorry to hear it's still a problem. I hope the hose does the trick and you don't have to replace the valve. Given that it happened just after taking the system apart that seems to be the most likely explantation.

(Saw your other thread -- glad you don't need a new valve cover.)

I didn't get the gas cap message or the CEL on the way home, so I thought maybe it was another one of those things where the fact that I opened the evap system triggered it once and that's all I would see. But I did get the message again, still with no CEL, this morning. I think to trigger the CEL it has to detect a leak on two consecutive start/stop cycles, so maybe I did make some improvement but there's a time or temperature component that is causing it to still remain, just less frequently. I won't be able to do anything with it until after this weekend so I'm not in a rush; I think I'll wait a few days and see what happens before I buy a new hose.

Have you made any progress with diagnosing or repairing yours?

I get the gas cap warning most of the time. I cleared the CEL the first time it occurred but not since. The new gas cap is scheduled to arrive on Thursday. If that doesn't fix it, I'll probably remove the air box and try reseating the hose before ordering a new one.

I've considered that there might be something that could bring some resilience back to the O-rings and restore their ability to seal, I just don't know what that substance might be and don't know where to start since I don't know specifically what the O-rings are made of.

The new gas cap arrived a day early. Put it on this evening and cleared the code. Will see what happens when I drive it tomorrow.

hope it works for you.

Mine has been giving the gas cap message but only off and on all week, and even went a whole day without getting it at all, so I was wondering if a few heat cycles was helping the O-rings regain their seal. But it came on twice in a row and finally triggered the CEL this AM so I went ahead and ordered the hose.

No gas cap messages today. After driving a little, I filled up with gas to see if that would affect it. Drove to work and back successfully. It will take several days before I get optimistic.

I hope the hose fixes yours. The valve isn't too expensive but it seems like you've been through quite a lot with your car in a short time -- would hate to see you have to put even more into it.

The gas cap message came back today. I was almost certain it would return before long.

Before I order the vent pipe, is there a way to check if the breather valve has power, without removing the airbox and manifold? I wonder if maybe I didn't make a good electrical connection when reinstalling the intake manifold.

Today I tried to replace the vent pipe that connects to the breather valve. "Tried" because about 6 inches from the breather valve, the pipe runs through some sort of "clip" that was designed by the Marquis de Sade. Both the vent pipe and the fuel line that runs to the HPFP go through it. Could not figure out how to get the vent pipe out of it. Anyone care to share the trick? Thanks.