chevy 350 tbi exhaust help

[89k5350]

So I just bought hooker competition headers and dual exhaust with flowmaster mufflers all for $140!!! But I have 2 problems the exhaust is off a 85 so there are no holes for o2 sensors and my truck requires them as it is 87 350 tbi. So how and where do I put the o2 sensors in and do I need different ones for long tube headers? Also how should I try taking the stock rusty exhaust manifold bolts out

 

[swettysblazer]

You want the O2 sensors as close the the engine as possible.... Usually with the headers, guys like to run a heated O2 sensor because it is farther downstream than in the stock manifolds. I personally don't, but I run Hedman headers that are in between a stock manifold and a long tube, and I've never thrown a code with it on there. Go to an exhaust shop and have them weld a bung in and you will be good to go.


As for the bolts, be careful. They may snap off in the head, and then you're in for a headache. PB Blaster will be your friend. Just go easy with them at first.

 

[mwood1985]

best place is at the collector or just after it. you want the heat from all 4 cylinders to get to it. any worthwhile exhaust shop can weld up a o2 bung for you into a system

 

[89k5350]

any idea how to wire it. I know tbi chips makes a heated 3 wire with a pig tail

 

[swettysblazer]

IIRC, one goes to hot, the other ground, and the last is the sensor wire itself.

 

[89k5350]

so when you say hot bacically means it just needs power to it and the wire that is the sensor just sits there in the open?

 

[swettysblazer]

Hot would be connected to an ignition wire or something of the like, so that when you turn the key on the element in the sensor starts heating up. And the sensor wire should have a pigtail on it that you can connect it to.

 

[bigred88]

I did mine years ago. I got the three wire O2 sensor TBI chips sells, it's down near the collector. I don't remember how it was wired up, but I do remember that it was easy and all I needed to know came in the box. I'm sure there's a write up on it somewhere on here, too.

And x2 on the PB Blaster, Kroil, or quality penetrating oil of your choice. Soak them for days if you can.

 

[rebelgregory]

Ditto to everything. I run long tubes with an O2 at the collector. You have to run a heated sensor (3 or 4 wire) for this.

If you have a welder, you can weld in your own bung. Go to the 'Help' section at autozone and buy a set of spark plug 'antifoulers'. They are little spacers that offset the spark plug away from the combustion chamber in cars that burn a lot of oil. However, they also have the same threads as an O2 sensor. just trim it so that the probe is exposed when threaded in and weld her in.

http://www.w4wwj.com/images/FALCON/02.BMP

.

 

[454Sub]

Use a 93 S-10 O2. Then buy the matching pigtail from Autozone or equivalents shelves and then if it ever goes bad, you can just unplug it.

Down in the collector will not work unless you use a heated O2. It takes around 7min a 2000rpm for a non heated one to warm up enough in the collector with long tubes. And if you do alot of slow speed wheeling, it will stay in open loop and not run at 100%.

One wire goes to where your factory O2 hooks up, its the signal wire. One goes to ground, when you wire the ground in, make sure you do it at the separate pig tail, so you dont have to unscrew the ground to remove the O2 for whatever reason. You would be surprised how many people dont think that through. Then one goes to IGNITION hot. If its hooked up to constant it will burn up. Fusebox has a few open ignition hot sources you can use a spade connector, or buy the fancy plastic connector for. Use a 25amp fuse in that circuit. Use a test light to determine which is which, and make sure it stays hot as long as the key is on. Im fairly certain it even says Ignition above the hole for the source.

 

[dyeager535]

*IF* you want a heated O2 sensor (may or may not be necessary) buy the AC Delco AFS-74. It's the right piece. Stay away from aftermarket O2's, particularly Bosch. Delco O2's work, just pay a bit more.

As to being heated. You already have a 1 wire sensor, run it and see if it works. It will only "fall out" of closed loop at idle, if it does at all. If the vehicle is stock and everything works ok, open loop idle is ok. I ran a one wire with long tube headers for a LONG time, and never had a problem associated with the O2 sensor cooling off.

 

[89k5350]

one thing I don't understand is how am I supposed to ground it and tun a wire to ignition if the o2 sensor has a connector on the end?

 

[dyeager535]

Heated O2 is three wires, they use a weatherpack connector, you'd need the matching one (or cut it off and hardwire the whole thing) and run the three wires to the appropriate places.

Unheated O2 is just the single wire straight to the ECM.

 

[4X4HIGH]

*IF* you want a heated O2 sensor (may or may not be necessary) buy the AC Delco AFS-74. It's the right piece. Stay away from aftermarket O2's, particularly Bosch. Delco O2's work, just pay a bit more.

As to being heated. You already have a 1 wire sensor, run it and see if it works. It will only "fall out" of closed loop at idle, if it does at all. If the vehicle is stock and everything works ok, open loop idle is ok. I ran a one wire with long tube headers for a LONG time, and never had a problem associated with the O2 sensor cooling off.

If the 02 sensor does not reach 600* it will NEVER go into closed loop operation.

 

[dyeager535]

What I am saying is that people seem to jump to heated O2 sensors when in reality, SOMETIMES they aren't needed. Open loop idle was common (and even programmed by GM with some applications) so just because the O2 sensor cools off under certain conditions, it doesn't mean there is a problem. With everything working as it should, open loop idle should be no worse or better than closed loop.

I ran mine for ~10 years with a single wire O2 so I know very well how it acted in my application. With the sensor at the end of the long tube headers, it ALWAYS idled open loop. But the slightest increase in throttle (talking 50-100RPM increase over idle RPM) and it dropped back into closed loop.

No reason to re-wire/add components if it's not needed. A heated O2 did nothing for idle quality, particularly when compared to the engine being tuned right.

 

[89k5350]

ok so I think I'll just try it out with the one wire and if it don't run right or throws a code then I'll get the heated

 

[eagle mark]

I've been hearing this on the Internet for years and there's a lot of misunderstanding and one BIG point missing that no one talks about.

First the big point! If you move your O2 sensor down stream three feet from stock location you also need to change the INT VS Airflow Delay in chip. This is the time delay from fueling changes until the O2 sensor see's changes. If you don't then you get an oscillating effect in Fuel Trim corrections. Which is usually what everyone blames on needing a heated O2 sensor. Heated O2 will not fix this. If your tune is way off? You will get horrible INT/BLM fuel trim readings, then be way off in Open Loop when O2 sensor cools off!

If you run a set of coated headers, even long tube like Headman Elite? They keep in enough heat that the O2 sensor stays hot enough to keep Closed Loop Idle except for dead of winter.

If you need to weld in an O2 sensor bung? Weld it in exhaust collector and not in header. I header it will pick up one cylinder, in exhaust collector it will pick up the blend of all four... And you don't mess up a good header.

Many old TBI ECMs run Open Loop Idle anyway?

If your tune is in order and it goes Open Loop Idle? Well you won't notice and neither would emissions.

If you do run a heated O2 it won't hurt a thing. But needs to be wired in with a relay. If your fuel pump relay has a pin 87a then you can use it to turn it on.

Always mount an O2 sensor from 9 to 3 oclock pointing up! NOT LIKE PICTURE BELOW found on many EFI Conversion websites! This is the wrong way! Needs to be uphill not downhill!

HTH!

Stay Tuned!