Cat by pass-disconnected 02 sensor question

[ianc]

Cut:



And soldered back together:



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

ianc

[Wil Ferch]

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 ).

[Steve W]

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.

[Wil Ferch]

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

[Steve W]

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.

[Wil Ferch]

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

[Steve W]

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

[Paul L]

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.

[ianc]

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

[Paul L]

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

[Paul L]

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.

[Wil Ferch]

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

[Steve W]

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.

[Wil Ferch]

...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

[Jascha]

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

[Jascha]

Originally posted by Wil Ferch
...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

…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

[Wil Ferch]

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

[Jascha]

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

[SCWDP911]

sub'd