thomjpster

Hi, Long time Lurker, 1st time poster here.

I'm finishing up building a custom set of headers, and I'm curious if if I should put an O2 bung in both headers.

FWIW here's a quick snapshot of my junk:
'68 Jeepster, 340" Buick V8, TH400 blah blah

I'm currently gathering parts to move to FI using a 1227747 ecm, TBI, I think I have the ESC distributor (or lack of) figured out.

I believe a 7747 can only uses 1 O2 sensor, but are there any advantages during tuning to having another O2 sensor available?

I can only think of one Con, I'll need 2 sensors

Thank you for being gentle
Thom

Dave_Jones

I'd suggest adding the bung now, especially if you're going to have the headers coated once they're finished. But if you want, you can hold off on installing the second sensor and just plug it closed for now. You'll appreciate the extra bung later for toubleshooting problems such as a leaky header flange, or misfire on a single cylinder that would throw the sensor off on one side. Or if you later buy a WB O2 sensor.

thomjpster

Thank you sir

That's an excelent reason to try and make room

One side is easy, the other is gona be tough because of the transfer case.

Thom

Dave_Jones

If it makes things easier, you could put the bung a little further downstream in the exhaust pipe instead of the collector, and use a heated sensor. The single wire O2 sensors need to be well forward to get hot enough to work, but it's a very easy swap to a 3-or 4-wire heated type. (a search here for "Delco AFS-74" should net you plenty of info).

Also, all WBs are heated, and they seem to do better a bit further downstream as well.

thomjpster

Thanks again Mr. Jones
I'll add a bit of info to try and help.

searching the diyefi archives, it looks like the WB O2 will still work all the way at the end of the tailpipe.

I can squeeze it in just before the balance "H" pipe, that should work.

I verified the Delco AFS-74 sensor is 18mm threads, so I picked up a 2 pack of 18mm spark plug anti fouler. $5.99.

I couldn't source a cheap bolt localy to plug the hole. All I found was $5 SST bolts

To plug up the hole I found Autolite 386 spark plugs $1.20 each

Thom

RBob

iTrader: (1)

I use the same. The lawn tractor uses them so I end up with a used one per year

As for putting the O2 way down the line, this will increase the transport delay. I don't recommend going too far. And never past the CAT.

RBob.

87blueracr

with all that down about the O2 bung and all that, what about wiring in another 02 sensor, how do i do it to keep the voltage output the same on my car. i have the 1 wire sensors from the factory and i would like to run dual sensors. how do i wire them up.

thomjpster

If you ECM only looks at 1 O2 sensor, I think that's all you can use unless you make some fancy averaging combiner thing.

I'm adding an extra bung so I can move the one sensor to the other side, or add an extra sensor for a AF guage, or WBO2 sensor. I'll make the wiring harness so I can move it to the other header if I want.

Everything I've seen says that measuring one side will be good enough. The TBI will feed both banks equally, so in theory, they should be the same.

Hope this helps.

Thom

AM91Camaro_RS

yeah, i had wondered about an averaging device to run two sensors also. is there any way (fairly simple) to do that??

87blueracr

in theory when you run something parallel, you don't change the voltages going to each component, you change the amperages, so if you were to wire them together you would have the double the voltage, just double the amperage. i don't see why you couldn't put a small varriable resistor in the circut to cut the voltage and amperage in half. you should put a fuse in there too just to make sure that there isn't too much amperage going to the ecm and frying something, but i will do more research and let you guys know. just incase anyone is wondering about my credentials, i have 45 credits from the navy for working on electronics on aircraft. i will talk to a couple of buddies and see what we can come up with. shouldn't be too hard to do for all of us sparkies!
i know that i would rather run 2 o2 sensors than one, and i know that am91 would too, so let me see what i can come up with. can someone please email me the normal operating range voltages and amperages as am about 3,000 miles from my car at present

TheGreatJ

Running 2 O2s in parallel is not going to be very feasible. It's not just a simple voltage signal, it's actually more of a waveform than anything else. The difference in transport delay between the two banks could cause issues with the readings, not to mention what would happen if one sensor went bad and the other did not. You're better off just putting a bung in each side, plugging one hole, and running on a single sensor. If you want to wire in a second sensor just for the purpose of datalogging, that could be beneficial, but don't try to use them both for fuel control.

Unless, of course, you go to a split fuel trim setup like ODBII cars, and use one O2 to control the fuel trim for each bank. That's a whole different can of worms.

gnatshop

I have the same situation - I have 2 oxygen sensors mounted and would like to be able to check each bank of cylinders.
I have the wiring from each sensor running in through the firewall and can manually connect either one to the ecm.
This should help troubleshoot any mechanical problems from bank to bank.

To make life easier, I'm thinking about using a single pole double throw switch to select which cylinder bank the ecm was receiving data from. Does anyone see any problems with that?

David

87blueracr

thanks thegreatJ, after thinking about it some more, i think that i am gonna let it alone like you suggest,

Gnatshop, yes i do. this is why. the more parts you have, the bigger chance that something will go wrong! enter the phrase anything that can happen, will happen! the less you allow the possibility for something to happen, when it hits the fan, it will be a easy fix! Know what i mean