running a little lean, understanding O2 sensors

[flee27]

I have a relatively new to me 1984 3.2 Targa. The car runs good, I think. I have fixed all the oil leaks, checked/adjusted valves, changed fluids, done a leak down and compression test.

The car has a bypass pipe installed and everything else is stock as far as I know. When I got the car the plug for the O2 had deteriorated and the O2 signal wire was not connected. I have spliced the O2 signal wire back together.

With that info being stated, visually looking at all 6 plugs they consistently look like the motor is running lean. I have read a lot of threads on the O2 sensors, if they are needed, etc. I will test the O2 sensor this weekend. But from what I have read a bad O2 sensor/not having one will create a rich condition and not a lean condition.

I am looking into a AFR meter so I can see what the AFR actually is. If anyone has input on what they have used and liked let me know.

I am attaching my leakdown/compression numbers. Something going on with cylinder #1 for sure. Sounds like an exhaust valve issue from the leak down noise. Both tests were done with a cold engine.

Looking for any experiences and opinions. Thanks to all the awesome members on this forum.

Foster

[r lane]

If you are consistently getting that number on #1, then probably a worn out exhaust valve. Pull the lower valve cover, roll the engine over until that valve is off the seat, and then with a small pry bar, see what type of back and forth movement you have in the valve stem. Mileage? I have had mixed results with having the original 02 sensor installed. With a straight pipe you are probably better off with it deleted. LSU 4.9 wide band 02 sensor for testing. Other than a chip, there is little you can do with the mixture. Some adjustment at the airflow meter. Bob

[Schulisco]

Technical background information about O2 sensors:
https://www.hella.com/techworld/ae/Technical/Sensors-and-actuators/Test-lambda-sensor-4379/

The (US)Carreras got heated voltage jump probes in general. If they go bad the signal amplitude gets more narrow and in lower frequency than before.

When the signal is missing for the Motronic / L-Jetronic ECU it will fall back in some kind of a limb home mode. Yes, for engine protection it will run a bit richer.
But: As the Carreras run in general way more lean than the earlier Bosch CIS cars the spark plugs are more lighter / greyish compared to the CIS spark plugs which were more dark / brownish. I camnot say if a missing O2 signal will also cause a more brownish colouring of them or not.

I would check the exhaust manifold temperatures with a IR temp gun to see if a cylinder runs hotter or colder than others. Hotter means it's running (too) lean(er). Then I would measure the O2 probe signal if it's oscillating between 0,1 & 0,9volts with a 1-2Hz frequency.

Cold engine is not optimal to get reliable leak down results.

Before going nuts I personally would fill an injection cleaner additive in the gas tank and go for a longer relaxed spin of at least 1-2hours to get the residues burned. If a valve doesn't close properly on a cold engine due to carbon residues this often may disappear when heating up and driving some time with medium load to get the car back to life, even when it sat for a long time (6months+). This cleaner may help clogged injectors to get them free and improve the spray pattern. This is one of the common reasons for running issues on Carreras.
If the issue then persists then you know that it might be more serious...

And not to forget the mixture switch at the ECU: Make sure that it is set correct for your engine. More details: https://www.swchips.com/fuelsys.html

Thomas

[ErrorMargin]

Originally Posted by Schulisco

…Then I would measure the O2 probe signal if it's oscillating between 0,1 & 0,9volts with a 1-2Hz frequency…

How do you tap into the O2 sensor signal?

[Schulisco]

Originally Posted by ErrorMargin

How do you tap into the O2 sensor signal?

The 930/16 has lambda ECU under the passenger seat. From the big black connector I tapped into the signal line to attach a multimeter.

[proporsche]

i`d say forget the oxy sensor -most likely you do not do smog check where you are,right?No need to have at all...concentrate on the cyl no.1...recheck the valve adjustment on that cylinder.

Ivan

[wazzz]

Originally Posted by Schulisco

The 930/16 has lambda ECU under the passenger seat. From the big black connector I tapped into the signal line to attach a multimeter.

Its a 3.2 not a SC. Different setup.

[Schulisco]

Originally Posted by wazzz

Its a 3.2 not a SC. Different setup.

Partially correct. The ECU on a Carrera sits under the drivers seat...

[911obgyn]

Very good info above, my experience with a 3.2 85 had been sitting for a couple years, did a cold compression test and the # were all over the place. Used that as a bargining point and got a good price.
Brought it home and did the maintainance you mentioned, drove the snot out of it and a month later the compression numbers were within 10% of each other, i think it was rusty valve seats.

[911obgyn]

Working O2 sensor will improve mileage, did have to replace intake gaskets and all the rubber vacuum bits to get it running right. I got an innovate wide band kit and set it up as a test rig to dial in idle CO for Cal smog.

[Bill Verburg]

Originally Posted by flee27

I have a relatively new to me 1984 3.2 Targa. The car runs good, I think. I have fixed all the oil leaks, checked/adjusted valves, changed fluids, done a leak down and compression test.

The car has a bypass pipe installed and everything else is stock as far as I know. When I got the car the plug for the O2 had deteriorated and the O2 signal wire was not connected. I have spliced the O2 signal wire back together.

With that info being stated, visually looking at all 6 plugs they consistently look like the motor is running lean. I have read a lot of threads on the O2 sensors, if they are needed, etc. I will test the O2 sensor this weekend. But from what I have read a bad O2 sensor/not having one will create a rich condition and not a lean condition.

I am looking into a AFR meter so I can see what the AFR actually is. If anyone has input on what they have used and liked let me know.

I am attaching my leakdown/compression numbers. Something going on with cylinder #1 for sure. Sounds like an exhaust valve issue from the leak down noise. Both tests were done with a cold engine.

Looking for any experiences and opinions. Thanks to all the awesome members on this forum.

Foster

The O sensor needs outside(i.e. reference air) air to compare to the exhaust flow, the reference air is delivered to the O sensor through the lead containing the signal and heating wires. Your repair to the connector is likely blocking the reference air flow path.

when the O sensor is disconnected the Motronic goes into open loop mode and the car runs fine, but usually a little richer

[mikedsilva]

Originally Posted by Bill Verburg

The O sensor needs outside(i.e. reference air) air to compare to the exhaust flow, the reference air is delivered to the O sensor through the lead containing the signal and heating wires. Your repair to the connector is likely blocking the reference air flow path.

when the O sensor is disconnected the Motronic goes into open loop mode and the car runs fine, but usually a little richer

ya just gotta love this guy!

[flee27]

This weekend I removed my O2 sensor from the cat bypass pipe and installed a wide band sensor (AEM) and gauge. The gauge will read to 18. Idling the gauge doesn’t read because it is over 18. Steady throttle at 3k and 4k RPM reads in the 17s. Only time it goes into the 14s is under hard acceleration. A couple of times under hard acceleration and load (up a steep hill) it dropped into the 13s.

As stated in my original posts the plugs looked lean. Would the above numbers confirm this? Is so I read in another thread about reindexing the gear in the AFM?

Looking forward to the continued education. Thanks

Foster

[Dr J]

Over 18 at idle is way too lean. The car will not be happy at all. If it seems to idle ok, I would not believe the gage. Something is fishy here.

[mysocal911]

Originally Posted by flee27

This weekend I removed my O2 sensor from the cat bypass pipe and installed a wide band sensor (AEM) and gauge. The gauge will read to 18. Idling the gauge doesn’t read because it is over 18. Steady throttle at 3k and 4k RPM reads in the 17s. Only time it goes into the 14s is under hard acceleration. A couple of times under hard acceleration and load (up a steep hill) it dropped into the 13s.

As stated in my original posts the plugs looked lean. Would the above numbers confirm this? Is so I read in another thread about reindexing the gear in the AFM?

Looking forward to the continued education. Thanks

Foster

Yes, but you need to check:

1. fuel pressure ~ 32 - 34 psi
2. for air leaks
3. check for binding of the AFM flap as it rotates
4. stock DME ECM chip

Then you can loosen the spring in the AFM, 1 tooth @ a time.

[mikedsilva]

Originally Posted by flee27

This weekend I removed my O2 sensor from the cat bypass pipe and installed a wide band sensor (AEM) and gauge. The gauge will read to 18. Idling the gauge doesn’t read because it is over 18. Steady throttle at 3k and 4k RPM reads in the 17s. Only time it goes into the 14s is under hard acceleration. A couple of times under hard acceleration and load (up a steep hill) it dropped into the 13s.

As stated in my original posts the plugs looked lean. Would the above numbers confirm this? Is so I read in another thread about reindexing the gear in the AFM?

Looking forward to the continued education. Thanks

Foster

Im relatively inexperienced compared to some others, but from personal experience with wideband gauges etc, I found my engines didnt like to idle when it got leaner than 16afr. I can't imagine an engine would idle if it was truly above 18 but again, I'm speculating.

Can you post a link to the exact setup you are using? gauge, sensor etc, especially if it is a kit?

Does the sensor need to be calibrated before use?

Maybe you have an exhaust leak after the engine but before the sensor and it is sucking drawing in outside air...

[flee27]

This is the link the the gauge kit

The plug color is the only thing that makes me think the car is running lean. They are not ashy but are definitely white without and tan color to them. All the plugs looked pretty consistent in color. I will pull one and take a picture to post.

I don't have a lot of experience driving other 911s so my point of reference is small. The car seems to run and drive fine. Pulls through the RPM range evenly, definitely becomes more lively above about 3500 RPM and idles fine. Occasionally when coming to a stop the idle stays high around 1500 RPM. Most of the time it returns to its normal around 800 RPM. The only driving issue I have noticed is if you are on relatively flat ground and driving slow, like a parking lot, and giving just enough throttle input to maintain speed the car will start a small lurching motion. Either have to coast or give it a little more throttle input. Can't just drive around at 5ish MPH.

I will look for vacuum leaks, check fuel pressure, and the AFM to see if I find anything that looks amiss. The WBO2 kit is new. Is there anyway to verify it is working other than installing it into another known properly running car?

I am also skeptical of the readings because the car basically seems to run good.

Appreciate the help.
Foster

[proporsche]

as i mentioned ..forget the O2 sensor you have no CAT and the car drives fine ..just add 1/3 of a turn on the fuel mix...
Ivan

[proporsche]

here

[Schulisco]

Originally Posted by flee27

This is the link the the gauge kit

The plug color is the only thing that makes me think the car is running lean. They are not ashy but are definitely white without and tan color to them. All the plugs looked pretty consistent in color. I will pull one and take a picture to post.

I don't have a lot of experience driving other 911s so my point of reference is small. The car seems to run and drive fine. Pulls through the RPM range evenly, definitely becomes more lively above about 3500 RPM and idles fine. Occasionally when coming to a stop the idle stays high around 1500 RPM. Most of the time it returns to its normal around 800 RPM. The only driving issue I have noticed is if you are on relatively flat ground and driving slow, like a parking lot, and giving just enough throttle input to maintain speed the car will start a small lurching motion. Either have to coast or give it a little more throttle input. Can't just drive around at 5ish MPH.

I will look for vacuum leaks, check fuel pressure, and the AFM to see if I find anything that looks amiss. The WBO2 kit is new. Is there anyway to verify it is working other than installing it into another known properly running car?

I am also skeptical of the readings because the car basically seems to run good.

Appreciate the help.
Foster

1. Did you checked if the spark plugs are correct to the engine?
2. As stated before - Carreras run leaner than previous cars, so the face of the spark plugs may still ok tough
3. AFR 17-18 is way too lean, AEM gauges are no scrap in general, I would cross check the gauge and the sensor on another car which is known running good
4. There's a mixture switch on the Carrrera ECU - check out on what it's adjusted, more info here: https://www.swchips.com/fuelsys.html
5. Get a smoke generator and chase for vacuum leaks
6. Another known issue on Carreras may be the mass air flow meter, it's sensor is driven by a resistance which may fail over time, if this measures to less air, the mixtue may get more lean than desired:
https://forums.pelicanparts.com/porsche-911-technical-forum/406792-3-2-air-meter-way-will-lean-rich.html
https://forums.pelicanparts.com/porsche-911-technical-forum/1032105-air-flow-meter-adjustment.html
https://forums.pelicanparts.com/porsche-911-technical-forum/805201-3-2-motronic-air-flow-meter-wiper-arm-re-tracked-wow.html
https://www.youtube.com/watch?v=4pFxhJO4jXc

Replacing the catalyst with a bypass pipe may let the exhausts flow faster which also can cause a leaner mixture. But not that much IMO. The O2 sensor will be damaged when you solder the connection. As Bll said - they use some free air molecules within the sensor cable for reference. Soldering may clog this. That's why these cables always have plugs instead.

As long as we don't know exactly what the issue(s) on your car is don't change anything else unless it's proven wrong/defective! So go ahead step by step and urgently rule out vacumm leaks! When you cure the issue by doing something else without ruling out the issue you will run into other issues sooner or later.

Thomas