Hey all, I noticed this on one day of tuning last week but it seemed to go away after that day. The car was normal at first, but then started running about 0.6-0.8 AFR leaner than normal at WOT, and I couldn't figure out why. My car started smelling like raw fuel, and I tried to look for a fuel leak in the engine bay, but couldn't find one. I just saw a post by jooyoung saying that he had an issue on the track where having less than half tank of fuel caused the car to misfire and smell like a fuel leak.

However, I had about 3/4 tank of gas, and was driving straight, not turning. I "think" I had the same issue though since the car was running noticeably leaner and smelled like raw fuel. However, it wasn't bad enough to be a noticeable misfire in terms of power delivery. What could cause this? It was on a 90 degree day. Could it be timing or boost? I wasn't getting more knock than usual. Since that day, I've logged in 80 degree weather and the car is back to normal (without making any significant tuning changes). Any ideas? Thanks!

 

lean shouldn't smell like fuel (rich = fuel).

Have you checked all the lines under the hood (including the line under then plastic cover that should have been clamped on from the factory)?

 

I thought that misfire can cause the car to run leaner, but smell like fuel (due to all the unburnt fuel from the misfire). From what I've read, that theory seems to make sense. My guess is the wideband doesn't pick up the unburnt fuel from the misfire? Or am I completely wrong? It seems like other people have had similar issues on other cars (AFR leans out, smells like fuel, due to misfire).

The car doesn't just smell like it's running rich, it literally smells like I'm standing in a gas station with a puddle of fuel near me I don't think this is due to a leak, as the car is back to normal now. I think this is a tuning issue. However, I haven't closely checked all the lines (I just couldn't pinpoint a direct source of the fuel smell from the engine bay). I "think" it was coming from the exhaust. Where should I specifically check for leaks within the engine bay? Thanks!

To add a little more data: Fuel trims were all < 5%. I noticed this with the windows down and also with the A/C on, even with recirculating air. Not sure if it got into the car too much, or if it could hint that there is a physical leak near the fuel pump? I didn't really notice the smell unless I was stopped, and then it became overwhelming quickly.

 

Bump Update with more info on above post.

 

I just checked the spark plugs and they are all ok. A lot of black carbon on the threads, but the insulator and iridium tip look fine on all of them. I'm confused why this only happened once and the car seems fine now. No more fuel smell....very odd?? I also looked everywhere under the plastic engine cover (fuel rail etc) for leaks and couldn't find any. I'm pretty sure all the clamps that should be there are there.

 

If your engine misfires its normal to have leaner AFR because you have unburnt fuel & air.The lambda sensor picks up more oxygene concentration & reads leaner mixture.Have you noticed any excessive vacuum from your fuel tank when you take the fuel cap out?

 

Thanks, that makes sense to me. I haven't really noticed excessive vacuum from the fuel tank, but I honestly have never paid that much attention to that. What would excessive vacuum indicate?

 

If for some reason the fuel tank breathing system not works properly you end up with excessive vacuum which causes the fuel pump to struggle to pick up fuel.So there is a chance to have misfires.