EASY Carrera HP increase?!

[TopsailBeach]

I've read the treads about this....and even Wayne's admonition for Motronic engines, but I need advice on this one.

With the O2 sensor unplugged on my '86 coupe, the seat dyno tells me that it's running much better. No lag in lower rpm's, hard acceleration through the rev limiter with no flat spots. The guy who has worked on this car for the past 17 years swears that it gets better performance this way (and I agree, having tried it with and w/out the O2 sensor plugged in) because the intake manifold gaskets leak a bit due to age, and by running it full rich all the time, it really has more power. He also tells me that just like other race cars, keeping the engine rich maintains power, and also keeps the engine cooler (the antithesis of running too lean, which tends to overheat the engine).

Okay, I'm confused. What's the truth?

[twin plugged targa]

I believe you are correct, the car will run richer. If you run the car hard, this is fine for the engine, but if you run at idle, or slow, then I think you will foul the plugs up!.
Also I have heard that running the car rich will damage your Catalytic converter (if you are running with one!).
I found my 86 Carerra, ran better with the O2 sensor unlpugged to a certain extent. It stopped a fluctuating of the revs, but increased the idle.
I eventually found it easier to replace the sensor and use a cat bypass which produced a better perfomance and sound!.
hope this helps
Ben

[Jim Smolka]

A disconnected O2 sensor may be masking other problems.
An O2 system will try to maintain a Lamda signal around 1.0 (14.7 to 1 Air to Fuel Ratio), except under full throttle. A 911 motor will generate the most HP around 13 to 1 AFR. This may account for the increase in HP. Might be worth installing a wide band O2 sensor and reading the signal so that you could simply check the O2 reading as you drive by tapping into the signal.

[ischmitz]

I agree that disconnecting the O2 sensor will not give you more HP. It'll simply take the Motronic into open loop all the time. Maybe your sensor is bad and that's why you see the performance increase. The motronic has what you call a limp mode where it uses some defaults for sensors that are not present. If your sensor gives some really bad readings the limp mode does better than the sensor values.

I would try a performance chip and a working O2 sensor. You might be surprised how much more power is waiting to get unleashed from your 3.2. Let me know if you are interested in one of those chips.

Ingo

[Bill Verburg]

I had my chip burned on a dyno. It's Definitely richer everywhere for max power and throttle response. I'm sure that open loop non O₂ mode is a fair imitation.

[TopsailBeach]

So.....I can spend $115 or so for a new oxygen sensor and $230 or so for a Steve Wong chip, or I can leave the sensor unplugged. Hummm...

[ischmitz]

How about this one: you spend 115$ for a new sensor to decrease the chance of fouled plugs ($) and a messed up cat ($$) down the road and I'll send you a chip. If you like the chip you pay me what you think it's worth to you or you'll return it.

It all depends on how you look at things......

Ingo

[jazzbass]

Here is a site that contains some facts about DME:

http://frwilk.com/944dme

This site is a great resource for the Porsche DME system.

Click on the "Lambda Inside" link on the side. You'll get a detailed explanation on the O2 (Lambda) system of the DME. From this page (and looking at both the sample schematic and the real 911 DME schematic), unplugging the O2 sensor will not make the DME run the car rich. In fact, in this case it will simply run using the base fuel map, which was the case for all Euro cars. The author notes that the Lambda system is only used to fine tune the base fuel map, and makes few changes to the map at that. Most of the site deals with the RCA 1802 based DMEs, but the 8051 systems are similar.

If you want the car to run rich, you'd need to tie the input of the 02 sensor back to the +5V supply of the DME through a 1k resistor. If you want to lean it out, ground the O2 sensor.

[Steve W]

Disconnecting the O2 sensor only plays with the part throttle fuel mixture. That in itself may increase the sense of throttle response, but does not affect the mixture at all in the full throttle maps as the O2 sensor is ignored in this situation. So at full throttle you are getting no extra fuel than you are for a stock motor, so effectively at full throttle, you will get no extra hp and be no faster. The only way to get more fuel at full throttle is in the programming. This becomes more critical as other mods are performed to the motor. It also does not optimize the ignition tables, which is the other half of the power and efficiency equation.

Many guys have posted in the forums over the years how much their fuel efficiency went way down when their O2 sensor was either disconnected or failed. With gas at ~$2/gal, it will add up fast, not to mention the potential wear it can place on your cat. A performance chip utilizing the input of the O2 sensor to maintain lambda@1 through everyday light load part throttle situations with a more fuel efficient part throttle ignition table, yet programmed for the additional fuel needed under high loads and full throttle will give you the best of both worlds without any compromises.

[Sonic dB]

go to oxygensensor.com and order the Walker replacment sensor...its much much cheaper than OEM and works just the same.

[Lorenfb]

JazzBass is correct; Disconnecting the O2 sensor will NOT cause the DME to
run rich and will NOT damage the cat, if the AFM and fuel pressure is correct.
A well adjusted AFM and about 38psi pressure on a 3.2 should have a CO level
of 1% - 1.5% and less than 200 HCs. These will not damage the cat or the engine.

Early Euro 3.2s ran without the O2s and have better response than U.S. cars,
even without the higher compression and different timing maps. The fuel
economy will not necessarily be reduced significantly. Yes, the O2 is ignored
at full throttle, but 90% of driving is at mid-throttle where not having an
O2 really helps.

Grounding the O2 will cause the DME to go rich and a voltage greater than .6V
with cause the DME to go lean. Try it, you'll get black smoke when the O2 is
grounded.

Good Luck
Loren
'88 3.2