Why does it smell so rich? (FAST)

[carbuff]

Hi guys,

Every since I've had my car running, I've thought the car ran and smelled rich. I've played with all the settings in my FAST setup, but I'm still convinced it's rich for some reason!

If I'm standing in the garage and have the car running for 5 minutes, I walk into the house and I smell horrible from the exhaust (gas smell). ACK!

At idle, I have the FAST requesting an AFR of about 14.4:1. I have the VE tables adjusted to be approximately at that point, so there is very little correction.

Obviously, I'm running the wideband option on my FAST system. I have a 377ci SBC, I'm running 36# injectors with a fairly large solid roller. Now, I realize that some rich smell will be present due to the size of my cam. But this seems excessive to me!

I guess my question is, can the O2 sensor be reading incorrectly if there are no parameters out of range on the dashboard? And, is it possible for the exhaust to smell THAT rich if the O2 is truly reading 14.4:1?

Thanx for any thoughts!!! I'm tired of stinking up the place!

Bryan

 

[Craig Smith]

With a big roller the O2 sensor may not be getting much of a signal at low engine speeds, which can make it read artificially lean. This being the case, just try leaning it out some more at an idle and see what happens. My guess is that you will actually be able to lean it out enough to raise the idle speed some and get rid of the smell.

 

[TurboJim]

Carbon Monoxide (Rich) is odorless. Hydrocarbons are not. My bet is if you put the car on a 5 gas, you would see a combo of high hydrocarbons and NOx, both of which stink. Hydrocarbons are a product of overlap (among other things) NOx is a product of chamber temps. I forget the number but I think it was ~9ppm NOx will KILL you. High timing can cause BOTH gases to rise. Overlap can casue high HC. Heres a thought...fatten the car up and see if it changes. Or play with timing and see if it changes. Its hard to say "My car is fat and it stinks" when you dont really know. Especially when the FAST is telling you its NOT fat. If anything, its lean at 14.4:1.

If you can get 5 gas readings on your car, I can try to help you reduce whatever is out of whack.

 

[fast4d]

I still get the "hydrocarbon" smell due to my cam. but it's no longer running rich since I idle in open loop. The 2 smells are different.

It does run a bit rich during warmup but that's necessary to keep the engine running smoothly.

 

[TurboJim]

I used to idle/off idle mine in open loop, but the transitional sag was too disgusting to bear. I run it in closed loop now....hell...its got it, why not use it right? At Bob C's suggestion, next time I'm scrwewing with it I think I'm gonna try a 400rpm table next, maybe give me a little more resolution to squeak out that crappy spot.

 

[ijames]

A mechanic friend who is a whiz at tweaking carbs once told me that "if it makes your eyes water it's rich, and if it stinks it's lean" . I'd add that if the exhaust smells like gasoline it's also rich, while lean is a kind of "rotten" smell.

 

[TurboJim]

Right. Lean = HC and possibly NOx (until you get to ~16.5:1 where NOx formation drops off)

 

[carbuff]

Thanx for the responses! I will experiment and let you know what I find. Unfortunately, the car isn't drivable at the moment to get it to an exhaust analyzer, but I will try that once I can drive it again (suspension apart).

If I understand correctly, some are suggesting that I reduce the timing and see what effect it has. I believe I am running 26 degrees of advance at idle, with the timing trim set to a maximum of 1 degree. So, it would be between 25 and 27 degrees at idle. Does that seem excessive for a SBC? I am rather ignorant when it comes to ignition timing...

I will try that first and see what happens. Then I will try to fatten it up some and see what I get. If I go any more lean, the engine seems to hunt more for its idle. So I think I'm about as lean as I want to go for idle...

Again, thanx for the help! I will post back results when I have them. Any more thoughts, as always, appreciated!

Bryan