thebruce

Not exactly sure which of the C4 forums this should go in, but I've got an EFI question and figured there were enough gurus around here to set me straight.

I'm converting my '74 SB to EFI. Going to start with TPI and a prominator, then get into the sexier stuff once I get the hang of EFI tuning and get over rod/jet withdrawal.

I was planning on sending my headers in to get O2 sensor bungs installed in the collectors, with the thought that I'd switch the sensor from dide to side periodically to confirm that both cylinder banks are operating about the same. However, I'm now thinking that I'd rather just install an H-pipe as close to the header flange as physically possible, and put the sensor there (the car has duals w/o cats). I'd save some money and not have to worry about giving rust a place to start eating away at my jet-hot coated headers.

Will a 3-wire (heated) O2 sensor work in a H-pipe, or is it too far downstream? I am assuming that I would need a heated sensor to make this work.

Any input would be appreciated.

Bob B.

dock351

bump

ZylaRace

It will work in the H pipe. As long as it is a heated unit.
You didn't say which ECM/PCM combo you are going with, but I'll guess it is a 165 ECM.
W/ this approach, you won't be able to see differences from L->R bank. The 165 is batch fired. Isolating a bad inj will be a bit more difficult. (Not that that is a huge deal.)
Make sure you use a good GND when you wire the O2. The exh pipe may or may not be a good gnd,.... that far back,.... over time.

CFI-EFI

It will absolutely need to be heated. Since it will be located out of the mainstream, mixture adjustments may be delayed, and inappropriate when the occur. This doesn't sound like a good idea, to me.

RACE ON!!!

thebruce

Thanks to all for your input. Hadn't really thought about the delay in getting the exhaust to the sensor. I'm going to pull the headers anyway, so I guess I'll go ahead and have the O2 bungs added to both.

ittlfly

The futher upstream for the bungs, the better. At that point, you may just need 2- one wire O2's if you can get the bungs mounted far enough forward.

thebruce

If I put them in the header collector (long tube headers) will I be able to get away with a 1-wire?

CFI-EFI

Probably not, But give it a shot and see. In a previous post you mentioned an O2 in each header. Is your ECM set up to monitor two O2s?

RACE ON!!!

PS. I goofed. You said "collector". For some reason I was thinking "reducer". The closer to the engine, the less the chances are you'll need a heated O2. You have a better chance with the collector.

thebruce

Should have been more clear-- one sensor, with the other location plugged when not in use (W/B o2 or just switching sensor to confirm banks are basically the same).

What is the stock sensor on TPI vehicles? Does it matter what year? My system is off an '88 Vette (MAF for the time being, SD very soon).

ittlfly

I think the 88's have only 1 - O2 sensor. If you are using the ECM from the 88, then it is probably set up to monitor only 1..O2. However, there are enough programers here on the forum that could tweak the prom for reading 2-O's, one on each bank. If you can get those bungs welded in just below where the 4 tubes join into the collector, you MIGHT get away with a 1 wire. They need to get up to 600F to cause the ECM to go closed loop.

ZylaRace

The 165 ECM used one O2 sensor.
If you plan on only driving around SD, you can probably get away w/ a single wire O2. As it is probably easier to add the heated O2 now, I'd do it now.
Typically you need a heated O2 for long tube header, collector locations.

VR'92

I sure did.

JCAIRE2