I have a slight dilemma with mounting my O2 sensor. I posted this over on the Holley Forum but the admin there just linked me three times to four different posts that covered Holley`s recommended position but not answering my actual question as I cant follow their guidelines fully.

First off the following is what Holley states for the O2 sensor mounting location.

1) Mount O2 sensor as vertical as possible to allow moisture to drain out.
2) 6" to 8" after the header tubes merge.
3) 12" to 18" after O2 sensor to prevent reversion and false lean readings.
4) Mount O2 sensor in one bank to read only one bank

First off the headers I have are shorty street headers for the '85 - '95 F150 trucks that has the O2 sensor bung in the driver side header collector but this O2 sensor location is not 6" to 8" after the four primary tubes that merge into the collector. From what I have read this will not result in a good balanced reading of bank one cylinders.


Second off is the Y-pipe I have to run, it is a Flowmaster Y pipe in stainless steel for the '84-'95 F-series trucks, there are three possible locations as marked in the following photo that I can use for the O2 sensor. Location A) is the balance tube between Bank 1 and Bank 2, this will read both banks as reversion will allow for exhaust gasses to be pulled back and forth through that tube. Location B) would be about 6" from the merger of the primary tubes in the header collector, but would be hard to achieve proper angle without putting it close to the firewall. This location would also read Bank 1 and Bank 2 as it is after the balance tube, it also is less than 12" to 18" from the Y pipe merger which means reversion would pull exhaust from Bank 2 into Bank 1 pipe from this area as well. Last option would be Location C) which would put the O2 sensor under the truck allow for a more vertical mount but it is after the Y and is reading both banks. Either way I go with the O2 sensor mount would not be ideal, either being way too close to the primary tube merger in the header collector or being in such a position where it is reading both banks.




So my dilemma is which mounting location would provide the least issues with my Holley EFI system. If I want to ensure reading just one cylinder in the header would be the most ideal but even then I don't know if it would be far enough away to exceed the 12" minimum pipe length before it hits the balance tube or the Y itself.

So what does everyone think? Go with it and throw the O2 sensor in the header and hope for the best? Or do I throw it in the balance tube and just let it read both bank 1 and 2. I wont put it on the long tube for bank 2 as there is no place to mount it with the O2 sensor being vertical enough and still be able to access the O2 sensor to remove and install a replacement when the time comes.

~Update~

I have to put this out there, I was reading over and over again the big PDF file for the Sniper installation and I keep catching on this one part that runs contrary to what is talked about on the Holley Forums. On the Holley Forums everyone says you read one bank but in the big installation document it says the following.

It clearly says true reading of all cylinders, not one bank but all cylinders. I need to figure out where did all this bank talk come from because to me reading the big instructions multiple times it sounds like to me I should plug the balance tube in the Y pipe with a O2 sensor plug and then the straight pipe after the Y-pipe measure back 6 to 10 inches and mark it drill it and weld a bung in under the truck. Realistically it would be easier to put the O2 sensor in the balance tube vs plugging yet another O2 sensor bung but Holley wants a clear reading and I am now questioning this all cylinders terminology holley used vs what everyone on the forum keeps saying that no one has corrected.

 

I would put it in the bank 2 pipe. It doesn't have to be vertical. Most O2 sensors are not mounted vertical from the factory.