350 TBI o2 sensor

[iamtherealJayy]

So same truck as my 700r4 thread.
1990 Chevrolet Blazer, original 350 tbi 127k miles. I got it and it cranked forever and idled super high. Rebuilt the tb and it idles fine now(has gasket was shot) if it’s cold it still cranks forever but you also have to give it just a little throttle or it stumbles and just stalls as soon as it starts. I believe I reset the IAC per procedure, jump ab on aldl, ign on 30 seconds unplug iac and remove jumper? I noticed when I bought it that it had headers, later found out that’s all it had, really didn’t seem all that loud for open headers lol. Anyways, it’s headman headers, clearly not super old because they aren’t completely rusty. There’s an o2 sensor **hole** in the drivers side collector. Would just a factory replacement work here? Is the o2 sensor super required? They’re cheap enough I’ll replace it and hopefully it’ll resolve my issue a little and make me get the best fuel mileage I suppose?
They’re long tube headers, I forgot to mention that. I’m working on getting the exhaust done but I need an o2 sensor or plug the hole

 

[gmbellew]

without 02 sensor installed, the computer should be throwing an error code and it will also not leave open loop. that means it uses MAP, CTS, VSS, and RPM to control fueling without feedback from the O2 sensor. normally, when O2 sensor gets warmer up, the ECM uses the O2 sensor to fine tune fueling which should result in better fuel economy.

 

[iamtherealJayy]

I don’t believe it’s throwing any codes? When I had the Aldl jumped it was blinking code 12 but the ses light isn’t on. It smells rich it burns your eyes to be around it while running for extended time. I blamed part of that on just being open headers.
Edit: let me ask this, say there is an o2 sensor just floating around under the truck, where could I find it? There’s no way I’m going to find it from above, I’ve read about it being a purple wire? Is it a single or multiple wire plug?

 

[gmbellew]

for stock - O2 sensor goes in the driver side manifold near the exit to the exhaust. wiring is a single wire coming down from over the transmission from the engine bay

 

[iamtherealJayy]

Aright single purple wire, smaller gauge I suppose? If I buy a factory replacement will it get enough heat from the long tube headers or would I have to make a heated o2 work? I used to have some tbi manifolds but I think I traded them off for a holley 1850 I dunno

 

[bucket]

Aright single purple wire, smaller gauge I suppose? If I buy a factory replacement will it get enough heat from the long tube headers or would I have to make a heated o2 work? I used to have some tbi manifolds but I think I traded them off for a holley 1850 I dunno

You don't need the heated O2 sensor, it may just take slightly longer before it goes into closed loop. I tested that years ago on my daily driven TBI Suburban, there was little to no difference between the two, except for really cold mornings. But I don't think the headers changed that anyway, I think the results would have been similar with a heated O2 in stock manifolds.

 

[iamtherealJayy]

If I can just throw an o2 sensor in and it’ll be good I’ll go ahead and get reducers and keep the headers, if I can’t then I reckon I’m on the search for tbi manifolds

 

[iamtherealJayy]

Should a replacement o2 sensor screw into the hedman hedders? I don’t know what thread the o2 sensors are I’ve never had to replace one.

 

[bucket]

Domestic O2 sensors are all the same thread and pitch. 18mm from what I remember. The bung that is on your header has probably been welded in, if they are longtubes.

 

[iamtherealJayy]

Yes they’re hedman long tube headers, still have probably 60% of the paint on them and the bung(read a different forum that had bung censored) is right before the collector, I think they’re the ball seat style collector? Lumpy looking. I’ll throw an o2 sensor in and get a set of reducers and do the exhaust.
Edit: I don’t know on the 18mm part, I tried to pull an o2 from a 305 manifold and a 7/8” wrench fit

 

[bucket]

I had those same headers long ago, I had to weld a bung into the driver's header. 7/8" and 22mm are pretty much the same size.

 

[iamtherealJayy]

This ones already got the thing welded in, assuming it’s the correct nut, new o2 should just go right in? Could no o2 sensor cause the issue cranking? Once it’s warm it seems to start right up but cold it cranks longer than my 87 by a mile and it won’t stay running unless it’s got a little throttle for a few seconds.

 

[bucket]

It's possible that it's the cause of the long crank. It's weird though because if there's a major O2 sensor problem, it "should" cause more of a problem on a hot start than cold.

 

[iamtherealJayy]

I’ll look into it more later, I haven’t ran the truck a lot but I have got it up to temp twice. It started up without throttle prior to tbi rebuild but it idled so high it didn’t matter, I’m hoping it’s just an iac issue, something simple.

 

[Redfish]

Edit: let me ask this, say there is an o2 sensor just floating around under the truck, where could I find it? There’s no way I’m going to find it from above, I’ve read about it being a purple wire? Is it a single or multiple wire plug?

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