O2 Sensor

[cfj610]

I upgraded a GREAT running 87 R10 (2WD) 305 to a 350 and have had rich fuel issues ever since. Only other additions is the mild RV Cam and Headers

We "think" it's running rich due to the single wire O2 Sensor being installed just behind the headers on the drivers side causing the sensor to not see enough heat and operate properly since it's not near the motor where it belongs.

My question is: is it possible to install an incorrect resistor on the end of the O2 wire faking a correct reading resulting in allowing the computer to lean the fuel ratio and run better?
(and plug the bung). And if this DID work, would it likely run poorly until warmed up?

I'm totally spitballing at this point and running out of ideas. Also looking at installing this Stage 1 Computer Chip Module https://www.summitracing.com/parts/JET-28703
Any advice is appreciated and Thank You!

 

[Ricko1966]

No using a resistor and no O2 will not work. I could tell you how to input your own signal,but it would constantly change,you would constantly have to monitor it and compensate. Are you running a factory heat range thermostat? If you are running a cold thermostat the cts is going to be addingbfuel thinking the engine is still cold.If the O2 sensor never gets hot enough you will never get into closed loop.Go back to your first thread and follow the advice there,until you are getting a hot o2 sensor and into closed loop there is nothing else to do.

 

[Edelbrock]

Maybe install an O2 sensor that comes from the factory with a heating circuit? So the sensor heats itself up on its own. You would have to get one that has the same performance values though.

 

[edgephoto]

You can use a heated O2 sensor. You will have to wire up the heater circuit but that would not be hard to do.

 

[Ricko1966]

I'm an amature gynecologist,and this is an old post,I'm sure his problem is fixed. O2 sensor was not his problem. O2 is not in play in open loop. Most likely the problem is trying to run a 350 with a cam on stock 305 engine management. Also possibly bad CTS or excess fuel pressure. But not O2 sensor. Where's the guy that prefaces everything with I'm a field engineer for a major automotive company when we need him?

 

[bucket]

I'm an amature gynecologist,and this is an old post,I'm sure his problem is fixed. O2 sensor was not his problem. O2 is not in play in open loop. Most likely the problem is trying to run a 350 with a cam on stock 305 engine management. Also possibly bad CTS or excess fuel pressure. But not O2 sensor. Where's the guy that prefaces everything with I'm a field engineer for a major automotive company when we need him?

I just came across this thread and was reading along, thinking the same thing. The O2 sensor wasn't the problem, it was the cam swap on stock tuning.

 

[daveca]

My question is: is it possible to install an incorrect resistor on the end of the O2 wire faking a correct reading resulting in allowing the computer to lean the fuel ratio and run better?
(and plug the bung). And if this DID work, would it likely run poorly until warmed up?

Yes, been there, done that while engineering a propane system for a TBI.

The O2 sensor resistance is on the order of a meg- ohm, very high R. Its a small voltage source, tenths of a volt. I used a potentiometer to adjust the voltage BUT it only REDUCES the voltage, not increasing it. To adjust the voltage plus and minus requires disconnecting the sensor and using a 1,5 volt source ( AA or AAA cell) and about a 1 meg ohm pot. Be very sure to not exceed about a volt and dont connect the voltage backwards, its " feeding" a computer input.

As to why it's rich, it can be oil in the exhaust, or rich fuel. Remove and look at the O2S shell, oil or fuel?

It doesnt take much heat to operate the O2S, they all should have internal heaters. Is the heater working? A single wire sensor has no heater AND is grounded via the exhaust system, be sure the header is grounded to the engine head or run a separate O2S ground wire.

It only takes a short time of rich or oil fouling to load up the O2S surface ( ' foul' it like a spark plug) so one leaking valve guide seal can cause sensor fouling which looks rich.

This is for a test, or to ' bias' the sensor voltage up or down, it can not eliminate the sensor unless you want to just operate it in " open loop" but then, a sensor input is useless. This has no effect until the engine is warm.

Its CRITICAL to have a correct AF mixture while the engine is cold, else the computer cannot tune the mixtures, and the O2S can be fouled or destroyed before the system gets into closed loop.

 

[gmbellew]

Yes, been there, done that while engineering a propane system for a TBI.

The O2 sensor resistance is on the order of a meg- ohm, very high R. Its a small voltage source, tenths of a volt. I used a potentiometer to adjust the voltage BUT it only REDUCES the voltage, not increasing it. To adjust the voltage plus and minus requires disconnecting the sensor and using a 1,5 volt source ( AA or AAA cell) and about a 1 meg ohm pot. Be very sure to not exceed about a volt and dont connect the voltage backwards, its " feeding" a computer input.

As to why it's rich, it can be oil in the exhaust, or rich fuel. Remove and look at the O2S shell, oil or fuel?

It doesnt take much heat to operate the O2S, they all should have internal heaters. Is the heater working?

It only takes a short time of rich or oil fouling to load up the O2S surface ( ' foul' it like a spark plug) so one leaking valve guide seal can cause sensor fouling which looks rich.

This is for a test, or to ' bias' the sensor voltage up or down, it can not eliminate the sensor unless you want to just operate it in " open loop" but then, a sensor input is useless. This has no effect until the engine is warm.

Its CRITICAL to have a correct AF mixture while the engine is cold, else the computer cannot tune the mixtures, and the O2S can be fouled or destroyed before the system gets into closed loop.

Single wire O2 has no heater and relies on exhaust to heat it up.

 

[daveca]

isnt that what I said? Yes it is!

Youre trying to " educate" an automotive engineer thats done EFI system engineering.

I can get drunk and design your vehicles EFI system.

Read my comment more carefully before trying to correct me.

 

[idahovette]

^^^^^^^^^^BFD^^^^^^^^^............. tread a little more lightly, you are NOT the only one that knows these old trucks.

 

[gmbellew]

isnt that what I said? Yes it is!

Youre trying to " educate" an automotive engineer thats done EFI system engineering.

I can get drunk and design your vehicles EFI system.

Read my comment more carefully before trying to correct me.

uh- I did read it. this is what you wrote -

"It doesnt take much heat to operate the O2S, they all should have internal heaters. Is the heater working?"

i don't consider the exhaust heat to be an "internal heater" but I am also not a drunk mechanic. maybe that's where I am missing something....

I see you've edited to correct the missing information, thanks!

 

[Ricko1966]

This thread is old and dead. Rather than trying to use pots or other resistors,the correct plan would be run the correct injectors,for the engine he's running and burn a prom for the cam he installed. When you put a cam in a TBI vehicle typically lowers the vacuum. The map uses vacuum to sense load. With the lower vacuum from the bigger cam,the stock ECM and Prom thinks he's under load and adds fuel. The problem is MAP,not O2,Running the stock 305 injectors,and PROM on a mild build 350 is the root cause of the whole problem. IMHO, and I haven't been drinking,sorry,maybe I'll try that next time. Dammit I forgot to start with I am an amateur gynecologist,I think we should all preface our posts with our job titles.

 

[Ricko1966]

^^^^^^^^^^BFD^^^^^^^^^............. tread a little more lightly, you are NOT the only one that knows these old trucks.

We don't like his type around here. Anyone besides me notice he joined today at 6:30 P M. and by 8:30 P.M. he's already told us no less than 3 times he's an engineer of some kind( it varies by thread)