Cat by pass-disconnected 02 sensor question

[Paul L]

I have a Cat by pass because I think the Sierra club in Georgia has 7 members so everyone outside of Atlanta does not need emissions testing. I suspected a faulty 02 sensor, so I disconnected it and subsequently cracked the plasic connector, so I left it disconnected. Is there any advantage to no oxygen sensor? I'm pretty sure this is why I run rich. Is this correct? Without a catalytic converter, am I causing any harm in not having my 02 sensor hooked up in my Motronic car?

[sammyg2]

Running without an O2 sensor on your car will cause it to default to limp home mode" and will run rich.
Downside to this (besides wasting money on unburned fuel) is that you are screwing up the air around you and you run the risk of increased cylinder/piston wear and valve guide wear.
The extra fuel can wash the oil off of parts and increase the wear.
Fix it right.
BTW, in personal testing I found absolutely no measurable increase when switching between a cat bypass pipe and a cat.
It made slightly more noise but had no other significant impact to the pertformance of the car.
A K&N air filter made as much difference as the cat bypass pipe.

[Jascha]

The advantage is mostly to the oil /gas suppliers (who are happy to know you are blowing off gasoline dollars)

Yes, you will continue to run (idle rich) and pollute your breathing capsule without justification or performance (driveability) advantage

At the heart of the Motronic is a closed-loop control (Lambda) that wants to keep the air/flow ratio ~ 14.72 and CO levels down. The oxygen sensor provides feedback information about the combustion efficiency (air-fuel mixture). Without it, the engine management system simply reverts to a fixed (non adaptive) mode (rich mixture)

[Wil Ferch]

Jascha means "at the heart of a *USA spec* Motronic system is a close loop", etc etc....

Euro versions did not use a cat..hence no O2 sensor..hence open loop....
( except for special-order cat versions as a Euro tax hedge).

If you get a performance chip form (say) Steve Wong, you will find that the chip will by-pass the closed loop feature ...and give you Euro+ programming..and solve any rich running and/or idle fluctuation issues to boot. Nice "drivability" improvement too.

Wil

[rteague]

On the dyno cat bypass gave me 10 more hp. The disadvantage is you could get caught. I really want everyone to get behind a dodge diesel pickup and tell me they are not polluting. Oh yea roll the window down and take a good wiff. r.t.

[sammyg2]

diesel pollution is much different than gasoline pollution.
apples to oranges.
One is mostly soot or ash, that is what you are seeing from the diesel.
Gasoline pollution contails more harfmul components.

Do you still have the dyno sheets? Where there any other changes/modifications made?

[rnln]

by pass cat gain or no gain, on P car. I read both side of the comments everwhere and very confused now. According to the basic concept, of course there should be some gain at high end. Can someone prove the gain? Thanks.

[ruf-porsche]

The only gain in cat bypass is that it lessen your wallet by about 150 clams so that should lighten the load in your car so you should be a little quicker.

LMAO to all the fools that brought into the Cat bypass scam.

[andfar]

If that's the case, then what should I spend my money on first: Wong chip? K&N filter? Clewett ignition wires? The aim's to improve low-end response without going overboard.

_________________
1986 911 Carrera 3.2 Targa

[hytem]

Unless you're tinkering with the car yourself, you're better off with the oxygen sensor hooked up--which means using the cat unless you hook the sensor up another way. The mixture gets screwed up without it. My own experience.

[rw229]

Unless your cat is clogged, I agree there is little to no performance enhancement. The value is in the weight reduction (for those who care) and a significant reduction in heat. (a very good thing)

Though testing is not required for my car, I have heard that a well tuned Carrera (with the o2 sensor) can pass a sniffer check with a bypass in place.

Originally posted by ruf-porsche
The only gain in cat bypass is that it lessen your wallet by about 150 clams so that should lighten the load in your car so you should be a little quicker.

LMAO to all the fools that brought into the Cat bypass scam.

[Jascha]

Originally posted by hytem
Unless you're tinkering with the car yourself, you're better off with the oxygen sensor hooked up--which means using the cat unless you hook the sensor up another way. The mixture gets screwed up without it. My own experience.

Actually, the O2 sensor's role is unrelated to whether you have a cat in place or not. It measures O2 level in the exhaust gas entering the cat and feeds that information to the DME which does its thing to keep A/F ratio of about 14.7 : 1 (14.7 kg of air for every 1 kg of fuel). In metric units: ~10,000 liters of air for combustion of ~1 liter of fuel (.)

Indeed, maximum theoretical power occurs at 0.9 (rich-side) of that value and maximum fuel consumption at 1.05 (lean-side) of that A/F set point...

[Jascha]

Originally posted by Wil Ferch
Jascha means "at the heart of a *USA spec* Motronic system is a close loop", etc etc....

Euro versions did not use a cat..hence no O2 sensor..hence open loop....
( except for special-order cat versions as a Euro tax hedge).

If you get a performance chip form (say) Steve Wong, you will find that the chip will by-pass the closed loop feature ...and give you Euro+ programming..and solve any rich running and/or idle fluctuation issues to boot. Nice "drivability" improvement too.

Wil

Thanks for the qualification, Wil…

Basically, the oxygen-sensor control loop (Bosch calls it Lambda) is superimposed upon the fuel quantity to be injected and thereby achieves optimal combustion (theoretic stoichiometric A/F ratio of 14.7). In principle, it can be added or subtracted depending on your desired intentions (power, fuel economy, low CO & HC levels).

Parenthetically, the NOx levels will in fact reach their highest peak at this optimal setting of A/F ratio -reason enough for the Catalytic converter (no free NOx lunch here!)

[Nine9six]

Originally posted by andfar
If that's the case, then what should I spend my money on first: Wong chip? K&N filter? Clewett ignition wires? The aim's to improve low-end response without going overboard.

You are OK with your thoughts on SW chip and wires, but forget about the K&N, as they are worthless. Its been proven many times over, and they dont filter as well as your OEM unit.

[Paul L]

My by-pass has a mounting spot for the 02 sensor. I have one installed but am not sure how old it is or if it is good. Unfortunately, as a rule out looking for a short a while back, I cracked the single wire plastic male/female connector in the engine compartment. It seems I was running just as rich before I disconnected it. The plastic connector seems to have a lot of insulation at the connecting point. Is there a reason for that? Can I just cut the wire on each side of the connector and solder it back together, thus fixing my ham hands situation I created? Does running rich indicate a bad sensor in the first place?

[ianc]

Euro versions did not use a cat..hence no O2 sensor..hence open loop....

As Jascha said, the functions of the O2 sensor and the cat are unrelated. The cat just provides the mounting point for the O2 sensor.

If you get a performance chip form (say) Steve Wong, you will find that the chip will by-pass the closed loop feature

Steve Wong's chips do not cause the car to run in open loop mode, they still evaluate signals from the O2 sensor and use them to correct the mixture.

Sorry to pick on you Wil...

ianc

[Wil Ferch]

I'll stand corrected with proof...but I think you're wrong on this.

A Steve Wong chip will take the (performance) goodness of the Euro club sport model and go just a tad further in a pre-determined A/F mix range ( against RPM or load) and also a pre-determined ignition advance curve. It does not ( AFAIK) use the O2 sensor as feedback to maintain a 14.7 A/F ratio. If it does...maybe only at idle ( or slightly above)...or such.... to comply with idle/low speed emissions testing. Talk to Steve for verification but I'm fairly certain about this.

No worries...I don't feel picked-on.....we're here to uncover "truth"....

The O2 sensor and cat ARE ( in an OEM sense)...related. Because the cat works only on a narrow, near-stociometric range. Too rich...as for improved performance...and the cat would start to glow.

The Euro cars w/o cat..then ..had no O2 sensor...

- Wil

[ianc]

Talk to Steve for verification but I'm fairly certain about this

Hmmm... I don't know what changes Steve makes to the AF ratio depending on the O2 sensor inputs that are received, but I know that the sensor still operates. My car has one of his chips, and I have observed the idle mixture change drastically on an EGA after plugging the sensor back in, so I know his chip is still listening. Even the factory cuts out the O2 signals and runs in open loop when the WOT switch is engaged.

And you're right that the cat can only do its job within a narrow band, which is controlled by the O2 sensor. Still though, there is no reason why someone with a cat bypass couldn't run one for increased efficiency if desired; it does not depend on the cat for anything,

ianc

[ianc]

Can I just cut the wire on each side of the connector and solder it back together, thus fixing my ham hands situation I created? Does running rich indicate a bad sensor in the first place?

To answer your question, yes, you certainly could solder the pieces back together and have it work. If you are going to that trouble, you may as well replace the sensor though. There is a very inexpensive (compared to the Porsche part) Bosch sensor for a Ford that will work equally well. Here are some pics showing the Bosch part # to order.

The Porsche sensor and the replacement:

[Wil Ferch]

Here's a link to a previous Steve Wong post...(there might be better ones to cite)...but he essentially says the O2 sensor functions only on idle speed and low engine load. Implying that to get the performance and drivability improvements you want *elsewhere* on the engine load/speed curve.....the O2 sensor is being ignored and ends up as open loop....

This makes sense because if the O2 sensor were to be active all the time...you'd get back to stock 14.7:1 ratio...it's the only point an O2 sensor can control to. But to get better performance, you want to richen the mixture a bit and also go a bit more aggressive on the ignition curve. A *fully* ( i.e. *always*) functioning O2 sensor won't allow you to do that.

Steve Wong chip...in today...

- Wil