Cat by pass-disconnected 02 sensor question
 

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?

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.

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)

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

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.

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?

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.

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.

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

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.

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.

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...

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!)

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.

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?

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.

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

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

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

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:

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.

http://forums.pelicanparts.com/showthread.php?s=&threadid=131858&highlight=Steve+ Wong

- Wil

http://forums.pelicanparts.com/uploa...1159759516.jpg

Cut:

http://forums.pelicanparts.com/uploa...1159759566.jpg

And soldered back together:

http://forums.pelicanparts.com/uploa...1159759590.jpg

The sensors get slow when old, and cannot react quickly enough. HTH,

ianc

To add to Ianc's excellent pictoral.....here are some part numbers I posted a while back in my infamous debate with the Bosch rep ( air under the wires indeed !)...anyway..here are some parts numbers you may find interesting to avoid the "Porsche tax" on these very similar parts:
---Wil
=========================================

Summary follows:
- the various O2 sensors pretty much act the same way, in terms
of output signal vs input readings, however...
- there are various ceramic types, and for the three-wire
heated systems , various heater strengths ( 12W and 18W)
- for the mid 80's , 3.2L Carrera's, using DME control... you
may substitute:
Bosch 13913, 3 wire unit originally intended for
Ford applications. I believe this has an 8" lead, and you must splice -in
the original Porsche connectors ( more on splicing caveats later).
Bosch 13953, similar 3 wire unit for Fords, but
with ( I believe) 16" long connectors.
Bosch 15725, Bosch "universal" , with universal
connector kit that avoids certain problems compared to using generic
connectors ( again, more later).
Bosch 15726... an alternative to 15725....also OK
to use for 3.2L Carreras.
Bosch 15715, 4 wire .. NOT OK to use ( more on 4
wire later).
By the way , the "long" and "short" Bosch part numbers relate as
follows. The short number ( ex. 15725) is the last 4 digits of the long
number with a "1" in front of it ( long number .... 0258005725 ).

Wil, Ian, I guess I can clarify the Euro chip questions. Up until about 2003, chips I provided for the 84-86 Carreras were supplied with what is essentially a European/ROW version performance chip, which runs open loop and does not utilize a O2 sensor just like the Euro cars. This maximizes part throttle response as you do not have a O2 sensor modulating the mixture back to 14.7:1, and allows one to maintain a stronger torque curve at high loads. All U.S 87 to 89 Carreras have always been sent closed loop chips. In 2004, a change was made in that all 86-86 Carreras were suppled with a 4k performance version of the 24 pin '87 U.S. chip, which does run closed loop. The programming was refined and tuned to the point that there was now minimal performance difference between a closed loop U.S. and open loop Euro chip. The advantage is that it allows you to continue to meet emissions and with a improvement in fuel efficiency. If a owner of a early version 84-86 chip with the Euro program wishes to upgrade to the 4k '87 U.S. program, an exchange can be provided at no charge.

Disconnecting an O2 sensor with a stock chip essentially runs the car open loop, almost like a European version chip, but not quite. Part throttle fuel maps in a U.S chip are programmed to essentially follow a lean 14.7 AFR at low mid rpms, while they go overly rich at higher loads/rpm to provide momentary fuel enrichment to offset the O2 sensor, and to keep the cat cool under sustained high speeds over 120 mph. If one still wishes to operate open loop all the time, optimial performance is obtained by providing a part throttle fuel map designed for open loop operation.

Steve...thanks for the clarification but I think you mean 86-88 or 86-89 in your sentence that starts with "In 2004".....no ?

But that doesn't seem right either ...as the last 3.2's ( 1989) were 28 pin chips , right?

You mean that a change was made ( by you !) that allowed you to come up with a ( always) closed loop chip that gets used with the later 3.2's that were originally delivered with 4K programming....vs the earlier ones that were delivered with 2K programming, where this was not possible. I believe there never was a Steve Wong 2K chip that was *always* closed loop throughout it's range...right? Instead, you used a slightly more aggressive mapping of the Euro chip that was open loop.

- Wil

No Wil, I meant exactly as I stated. The 24 pin 87s and the 28 pin 87-89s were always closed loop. You are right in that I never had a 2k performance chip that was *always* closed loop. The performance was always subpar because closed loop in the 2k program was tighly locked. Not so with the later cars. So I originally suppled the 84-86 Carrera's with a 2k Euro perf. chip. I made the change in 2004 to go to a closed loop 4k chip for the 84-86s, however it required a DME jumper move to enable the 4k operation for those DMEs that were not already enabled (mostly the 84s and some 85s). This decision was based largely on providing a chip that would better pass emissions tests in the U.S. An open loop Euro chip would have a more difficult time passing, depending of how out of tune the motor was. Closed loop operation is much more tolerant of out of tune motors as it maintains the stoichiometric ratio for emissions testing. Since you have a pre 04 version program, you would have an open loop Euro chip, while Ian's 87 has a 24 pin 4k closed loop U.S. chip.

Thank you Steve, but if you bear with me for a moment....I'm confused by your "no" answer..as I don't see a difference between what you're saying and what I'm re-stating in different words... (for my own clarity of understanding)

I'm focusing on your statement ( for the archives record) with your sentence that starts with ..." In 2004, a change was made in that all 86-86 Carreras ...."

Can you correct the model year range?...do you mean 84-86?...and seeing that 84's and early 85's came from the *factory* with 24 pin chips...do you (further) mean a change was made *by you*... in that you can now offer this 4K version of the Wong chip for these 84-86 years (?)....but in doing so we need to make the jumper conversion ???

If this is the case, then I think we're saying the same thing....

BTW.....if I take you up on the offer to get a 4k version of the chip ( to replace the 2K version in my early 85..and doing the jumper conversion)...would that change tend to eliminate the (apparent) rich running at idle I seem to have now ( on an otherwise GREAT running car). It seems to me as I coast to a stop light with the window down....I get a strong whiff of rich exhaust smell if I have an open window.

- Wil

Will, all 84-86s were 24 pin chips. Most of the 84s and some of the 85s were 2k limited, and require a jumper mod to enable a 4k chip. Most all 86s were already 4k enabled and do not need the jumper mod. See the DME update page here for more info: http://www.911chips.com/dmeconvr.htm
Shoot me an email and we can arrange a update: steve@911chips.com

Hey Ianc, thanks for the post. This board has saved me thousands. I do not see the pictures or part numbers for the ford 02 sensor you mention in your post.

Look on the box in the first pic. 13913.

ianc

Thanks Ianc. I didn't realize the post had gone over to 2 pages.

I have a question for Steve W. (and I will re-pay you with a chip one day for my 84 assembled 1985 911) Do you agree with the those who claim I am harming my engine by having the 02 sensor disconnected? I have a cat by pass. It does run rich. And for those who think I'm wasting gas I wonder how this compares to your car. I get 22 mpg highway at 80 MPH. I've never tested it at lower speeds as we get to speed around Georgia.

Ahhh. ..Ianc shows the box with the parts numbers AS well as the post I have above with parts numbers.....what's so hard to find ???

- Wil

Paul, if you have a stock chip, I don't think you are harming your engine with the O2 sensor disconnected. Some people do it to increase the apparent throttle response from the slightly richer mixture, but it shouldn't be so rich that you should notice it. Check and adjust your base idle mixture to spec, which also influences low part throttle air fuel ratios. Running open loop with the stock chip is fine assuming the state of the rest of your car is in tune, otherwise closed loop compensates for inconsistencies in engine state of tune. Running open loop would also suffer a reduction in fuel efficiency unless your fuel maps are programmed for open loop operation. On my car and customers cars in the U.S., at a constant 80 mph, average fuel consumption can be anywhere between 24-29 mpg. Open loop UK customers get around 25mpg mixed driving. I think your 80 mph open loop 22 mpg is fine, however you'd probably see 24-25 closed loop. Better to just fix it or find a way to connect it. Simple is to just use a male and female spade connector to connect the two black wires. The white wires are just the preheater curcuit and are not necessary.

...and the white ( heater) wires are non-directional...any white can connect with any white.....

In case anyone wonders about this while splicing in "generic" or Ford O2 sensors with Porsche-plugs.....

Wil

BTW, what I described above is the making of an Air–Fuel monitor, especially if you choose not connect your O2 sensor –the output signal is dangling for the taking. I have seen these sold commercially and someone clever on this list shows us how to build one:

http://www.pelicanparts.com/techarticles/mult_air_fuel_monitor/mult_air_fuel_monitor.htm

…just a suggestion: cut the wires as far as you practically can away from the new O2–sensor body to avoid the risk of unsoldering the wire joints

Excellent advice...Jascha....

On your other point...I think you'll need a "wide-band" O2 sensor..not a "narrow band" ( as used stock for emissions, etc)...to make a useful AFM, however....

- Wil

The 1.0 volt full excursion of the standard sensors should suffice to cover the 14-15 A/F ratio range of interest. Since the A/F ratio - voltage response relation is a sigmoidal curve they all come short in being accurate, in the tail ends of interest (12-16). Wil, you are correct that the "wide-band" type might do a better job in the nonlinear range…

Jascha

sub'd