BMW M50 gas smell on occasion after WOT

EDIT: Issue solved, but I'll leave here so as to "own" my personal stupidity......BLUF: I can swap an engine, rebuild brakes, assemble suspensions, etc....., but I apparently cannot attach hoses to the correct places.

So it's the rally e30 with an M50TUV from a 5-series swapped in. Anyhow, in normal driving and most of the time racing no smells. But every once in a while if I'm at WOT for a longer burst I sometimes whiff a gasoline smell in the cabin (both at rally and rallycross). I never smell it if not at WOT.

At a rallycross, after the run when the car is back in grid there is usually a faint gasoline smell from under the hood (other people can smell it as well).

- Charcoal canister and vent system is all relocated to the back of the car, so none of that is up front, so it's not causing the smell.

- I have extensively and repeatedly checked the fuel lines (all new rubber, all clamps tight, no sign of leaking). On a rally car, leaks are usually obvious because they can be seen in the dust. Lines from the pump (in the back of the car) to the filter (in engine bay) no signs of leak. No signs of leaks in either the pressure or return lines (again, all the hose is new and correct with high-quality clamps).

- No indication whatsoever of fuel injector leaks. Injectors are 6 months old with brand-new o-rings. The layer of dirt around all six of them is undisturbed and identical. No indication of any leaks at the FPR either. 

In short, I can't find anything in the fuel system at all that even remotely indicates any fuel leaking.

- Crankcase ventilation hose is also new - one end to a (new) elbow into the (new) intake elbow, and is tight. The CCV fitting into the valve cover does seem less snug than it seems it should be (I put a new o-ring on it), but maybe they're like that on this engine.

- If I open the oil filler cap after the car has been on, there does seem to be a slightly gasoline-like smell from in there (that was today, and oil was changed yesterday). Car had only been run about 10 minutes since oil change. No evidence of any oil leakage at the VC or oil filler cap. 

- Only thing I can think of (which I haven't yet checked) is maybe a spark plug is loose and allowing fumes to travel up? Seems like an odd thing (plus the coil boots would presumably seal that out anyhow), but I did see a mention of that on some BMW forum at some point.

-There is an extremely small exhaust leak down under the passenger floor (where the header meets the exhaust), but I wouldn't think that would make it into the car while moving on course/on stage - airflow would carry any smells from that behind the car (and it's not an exhaust smell, definitely gasoline). 

Any other ideas?

Check the plugs, cause why not? 
Let the car sit overnight, and smell the oil in the morning. If it smells like gas, you need to start looking for problems. Gas in the oil= mixture is too rich, injector pattern is not atomizing, bad rings...  nothing good if the oil smells like gas...

Does it use oil? How much/month? Stumbles at idle or other issues? 

Recon1342 said:

Check the plugs, cause why not? 
Let the car sit overnight, and smell the oil in the morning. If it smells like gas, you need to start looking for problems. Gas in the oil= mixture is too rich, injector pattern is not atomizing, bad rings...  nothing good if the oil smells like gas...

Does it use oil? How much/month? Stumbles at idle or other issues? 

Runs absolutely perfectly, no stumbles, no hesitations, Even with solid motor mounts it's smooth as butter.

The gas smell is literally only after a long day of racing. i don't smell it at all early on in rallies or rallycrosses, usually more torward the end of the day when the car has been running hard for a long time. Yesterday when I let it idle for 10+ minutes there was no trace of any gas smell other than faintly when I opened the oil filler cap. When I drained the old oil last weekend I didn't notice any gassy smell from the oil itself. It doesn't burn any significant amount of oil. Maybe half a quart (if that) during an entire stage rally being run hard the whole time. Certainly no more than any other older car I've ever owned, never any blue smoke. I didn't rebuild it, so I'm sure it has the original rings and I'd expect a small amount of blowby on a 25-year-old engine with 150k miles on it, used for racing. But again, no evidence of anything out of the ordinary. 

It just struck me to switch back to my stock DME (the one in the car jas a Dinan chip) just to see if maybe the Dinan tune is too rich compared to stock. 

In reply to irish44j :

It could be the tune, but that'd need to be a lot of extra fuel.
 How do your spark plugs look? Have you read them?

I think you are experiencing a condition called "stand off" or "spray back". The actual source of the fume is the inlet opening of the air filter. You may find some small accumulation of fuel within the filter housing. This is unusual in a log manifold, but a common condition with individual throttle bodies. On some Weber carb set ups you can see it if you run the engine without air filters. Also frequently visible with Hilborn/ Lucas injected BBCs.  It always has a specific RPM component, and with pulsed injection requires a large throttle opening.

TurnerX19 said:

I think you are experiencing a condition called "stand off" or "spray back". The actual source of the fume is the inlet opening of the air filter. You may find some small accumulation of fuel within the filter housing. This is unusual in a log manifold, but a common condition with individual throttle bodies. On some Weber carb set ups you can see it if you run the engine without air filters. Also frequently visible with Hilborn/ Lucas injected BBCs.  It always has a specific RPM component, and with pulsed injection requires a large throttle opening.

This has generally been my theory on the issue over the past number of events where I've noticed it. Possibly related to me having a short-ram cone filter and not a stock multi-chamber airbox that might mitigate it. Especially since the intake elbow runs downhill from the TB (and from the PCV port). 

In reply to irish44j :

Yeah, look in the filter. The downhill elbow traps a little raw fuel in a place where the air velocity is too low to pick it back up into the engine.

Pulled the plugs, they were not as tight as I would like them to be but were not loose either. Plugs look perfect and no sign of any buildup from running rich. Compression looked great across all six. So yeah I'm going to go with fuel getting caught in intake elbow. I did order a new PCV valve just to be safe since I think this one is really old.

You should certainly be able to shut the car down immediately and get under the hood and smell the leak somewhere. I have deleted the charcoal canister and capped the evap valve and have an open line from the fuel tank vent and still do not have any fuel smell issues. I would take this pretty seriously until you get it sorted though. Possibly the seal on the fuel tank under the back seats? Fuel line connection at rail or fuel injector orings are most likely but again I would think you could chase that with your nose?

Olemiss540 said:

You should certainly be able to shut the car down immediately and get under the hood and smell the leak somewhere. I have deleted the charcoal canister and capped the evap valve and have an open line from the fuel tank vent and still do not have any fuel smell issues. I would take this pretty seriously until you get it sorted though. Possibly the seal on the fuel tank under the back seats? Fuel line connection at rail or fuel injector orings are most likely but again I would think you could chase that with your nose?

The smell is definitely from the driver's d engine dide of the engine bay because it can be smelled while going at high rates of speed if the windows are all closed with no outside ventilation and only ventilation via the fresh air ducts. All of my charcoal canister and fuel tank vent stuff is at the back of the car, and nothing back there spells remotely gassy. All of the fuel lines and injectors can be easily viewed and there is no evidence of any leaks. but again the fact that this really only happens after you have had the pedal mashed to the floor and lift hard would indicate that is just some fuel vapor below back into the intake. The fuel system runs on the same pressure regardless of throttle (except at the rail itself) if it were a leak in the fuel system it would be constant regardless of what kind of driving the car is doing. There is absolutely no fuel smell during normal driving or idling. 

And once again this is more like an occasional whiff under very specific conditions immediately after going wide open throttle to full lift, than a constant strong smell. 

just to wrap this up - problem solved.

Apparently last time I was messing with the fuel/evap system (probably when I put the new tank in over the winter), I somehow switched the two (nearly identical) lines coming off the vapor/overflow canister in the rear wheel well.

So instead of fuel in there draining back into the tank, it was running into the hose going to the front of the car where the charcoal canister originally was (that hose was still there, but it wasn't supposed to be attached to anything at either end!). Which explains why it only happened with a mostly-full fuel tank and after hard driving where the tank was sloshing fuel up into the overfill reservoir, because that's the only time liquid gas actually gets up there.

And at the same time, my gas tank drainback line was basically just venting to atmosphere, so probably had some gas smell at the back of the car as well. 

So, that was dumb. The moral of this story is: When you have near-identical hoses right next to each other and take them off for some reason, best to actually mark which one is which so you reattach them to the right places and things won't smell like gasoline.