)2 Sensor Location?

[mattpatt]

I'm considering installing EFI on my SPF Cobra. It looks like some of the kits I've looked at (TBI style FE) say to install the O2 sensor tilted at least 10 degress UP to avoid moisture contamination. Doesn't look like there's room to do this. I've already installed sensor bungs (for carb tuning) in the collectors about 2" from where the primaries feed in - but they are tilted DOWN about 10 - 15 degrees to clear the body. Where do other people mount them and, if down, are there any problems. I wouldn't mind it it I had to change out the sensor every 1000 miles. ?????

Thx

Matt

[DonC]

Matt:
Locating the O2 sensor can be a problem for an EFI system in the Cobra.
You need to know if the sensor is a "wide band" or "narrow band" type. The most common type is narrow band although some of the newer systems use the wide band. The primary difference between the two is that a narrow band sensor needs to be located as close as possible to the exhaust ports to keep it hot enough to read accurately. They have internal heaters but they aren't strong enough to heat the sensor if it's too far away from the exhaust port.
Wide band sensors have better heaters and can be mounted farther away from the exhaust ports.
Keep in mind that the O2 sensor is just about the only way for the system to know what's going on with the fuel/air mix and it needs that information to run.
Mounting any O2 sensor below the horizontal will allow the tip to get contaminated by the exhaust stream and isn't recommended. Your idea about replacing the sensor every thousand miles is not a bad one but a bit impractical since there isn't any way to tell if the sensor has become contaminated other than the system won't run properly. It could become problematic within a few hundred miles or could go a thousand.
You may end up with a compromise as to how and where to mount the O2. If it were me I'd get a hold of the manufacturer of whatever system looks good to you and get their recommendation on where and how to mount the O2.
DonC

[mattpatt]

Thanks, DonC. The systems I've looked at have wide-band sensors. I know a lot of folks run FE on these cars but never saw/heard anyone talk about the O2 sensor. Seems like the wrong thing to do to put one in a primary pipe in close to the engine.

[DonC]

I'm runing a big block FE in my ERA with a Mass-Flo system and my O2's are mounted in the #1 and #5 primary pipes because they're narrow band and my collector is about 36" from the exhaust ports. Too far for a narrow band sensor to work. While a compromise the system works well.
DonC

[mattpatt]

Maybe I'l have to go that route.

Thanks.

[DonC]

Matt:
With a wide band O2 you have more flexibility on where you mount it. I'm just saying that mounting it in a single tube, while a compromise, is feasible.
I'll reiterate what I said before, contact the manufacturer, explain your setup/application and get their recommendations.
If I recall correctly Brent Mills put a TBI unit in his GT40 and is happy with the way it came out so it can be done.
DonC

[twobjshelbys]

I had the Roush 427IR setup (8-stack with an Accel DFI controller). Mine originally was mounted on the passenger size, fairly horizontally - that is the way it has to be. We kept getting bad feedback at idle when air would come back into the pipe and confuse the sensor. We moved it to one cylinder closer to the engine and it ran great after that. You depend on that one cylinder being "representative", but honestly, if you're only on one side, you're depending on the other side not failing either, so nothing is perfect unless you go to a dual sensor and can get it close enough to keep the sensor hot. Note that these DFI systems have a very wide capturing range and will attempt to compensate A/F when something is wrong. You'll notice it when it does.