O2 sensor delete - how to do it?
12-24-2005, 03:34 PM
#1
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O2 sensor delete - how to do it?
I am in the unusual situation of having a U.S. spec car with O2 sensor and cat converter in a country (the UK) where for this model year I don't need them. 
The UK cars don't have a cat or O2 sensor but must have something else plugged into the wiring loom in it's place and perhaps a different coding plug as well?
Does anyone know what should be fitted and preferably have pictures of them in place?
If I deep six the cat and O2 sensor are there any downsides to be concerned about?
Has anyone in the US with a test pipe deleted their O2 sensor as well? Hell, perhaps there is a market for ex UK O2 sensor delete parts?
Cheers and have a good Christmas.
Chris
The UK cars don't have a cat or O2 sensor but must have something else plugged into the wiring loom in it's place and perhaps a different coding plug as well?
Does anyone know what should be fitted and preferably have pictures of them in place?
If I deep six the cat and O2 sensor are there any downsides to be concerned about?
Has anyone in the US with a test pipe deleted their O2 sensor as well? Hell, perhaps there is a market for ex UK O2 sensor delete parts?
Cheers and have a good Christmas.
Chris
12-24-2005, 04:02 PM
#2
Burning Brakes
There's a plug at the very back of the engine compartment by the firewall just in front of where the heater blower is. The attached pic is off an early car, so it may look a little different.
Just unplug this cable, and the car will run fine. The effect of the O2 sensor is to "back off" of performance and change the timing/mixture etc. to reduce the emissions and therefore performance. See this page - http://frwilk.com/944dme/ it's probably the definitive set of information on the 944 DME.
you can then either cut the wire to the 02 sensor and leave it in place to plug the exhaust, or find a cap to thread on. As to removing the cat - you will probably pick up 5-10 HP at this point in the cars life as a 20 yr old cat will be mostly clogged.
Just unplug this cable, and the car will run fine. The effect of the O2 sensor is to "back off" of performance and change the timing/mixture etc. to reduce the emissions and therefore performance. See this page - http://frwilk.com/944dme/ it's probably the definitive set of information on the 944 DME.
you can then either cut the wire to the 02 sensor and leave it in place to plug the exhaust, or find a cap to thread on. As to removing the cat - you will probably pick up 5-10 HP at this point in the cars life as a 20 yr old cat will be mostly clogged.
12-24-2005, 06:34 PM
#3
Drifting
you will net better fuel economy with the O2 sensor in place. One way or another, at full throttle the car ignores the sensor so practical performance is not reduced with it.
12-24-2005, 08:13 PM
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Change the jumper to the DME to ROW (Rest Of the World).
Remove the O2 sensor and put in a bung plug.
Cut out the CAT and put in a straight pipe.
Now, if you want to go back to closed loop, you can.
Remove the O2 sensor and put in a bung plug.
Cut out the CAT and put in a straight pipe.
Now, if you want to go back to closed loop, you can.
12-24-2005, 10:09 PM
#5
You will lose performance before the DME switches to open loop if you remove that sensor.
That is usually what people do who are not experienced with EFI because of other mechanical problems.
Usually it is to cure a lean stumble caused by an intake leak because of the resultant rich mixture when removing the sensor.
A 944 will start and run at around 11.8:1 AFR at 60 F before the Lambda comes online.
If you have no Lambda, you will run this AFR ALWAYS (before look-up tables are used).....NOT GOOD.
That is usually what people do who are not experienced with EFI because of other mechanical problems.
Usually it is to cure a lean stumble caused by an intake leak because of the resultant rich mixture when removing the sensor.
A 944 will start and run at around 11.8:1 AFR at 60 F before the Lambda comes online.
If you have no Lambda, you will run this AFR ALWAYS (before look-up tables are used).....NOT GOOD.
12-24-2005, 10:36 PM
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Does that O2 sensor connection unplug or unscrew? I pulled the plug out and as I was pulling the plastic inside broke into a million pieces. I noticed some threads on the other end, like it was meant to be unscrewed.
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12-24-2005, 11:39 PM
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Originally Posted by special tool
You will lose performance before the DME switches to open loop if you remove that sensor.
That is usually what people do who are not experienced with EFI because of other mechanical problems.
Usually it is to cure a lean stumble caused by an intake leak because of the resultant rich mixture when removing the sensor.
A 944 will start and run at around 11.8:1 AFR at 60 F before the Lambda comes online.
If you have no Lambda, you will run this AFR ALWAYS (before look-up tables are used).....NOT GOOD.
That is usually what people do who are not experienced with EFI because of other mechanical problems.
Usually it is to cure a lean stumble caused by an intake leak because of the resultant rich mixture when removing the sensor.
A 944 will start and run at around 11.8:1 AFR at 60 F before the Lambda comes online.
If you have no Lambda, you will run this AFR ALWAYS (before look-up tables are used).....NOT GOOD.
12-25-2005, 03:15 AM
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Originally Posted by special tool
You will lose performance before the DME switches to open loop if you remove that sensor.
That is usually what people do who are not experienced with EFI because of other mechanical problems.
Usually it is to cure a lean stumble caused by an intake leak because of the resultant rich mixture when removing the sensor.
A 944 will start and run at around 11.8:1 AFR at 60 F before the Lambda comes online.
If you have no Lambda, you will run this AFR ALWAYS (before look-up tables are used).....NOT GOOD.
That is usually what people do who are not experienced with EFI because of other mechanical problems.
Usually it is to cure a lean stumble caused by an intake leak because of the resultant rich mixture when removing the sensor.
A 944 will start and run at around 11.8:1 AFR at 60 F before the Lambda comes online.
If you have no Lambda, you will run this AFR ALWAYS (before look-up tables are used).....NOT GOOD.
12-25-2005, 02:50 PM
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Cheers all.
One I noticed the following on the FR Wilk site mentioned above:
"When the DME is set for ROW (ROW & EURO), that does not use the lambda sensor or catalytic converter, the fuel map below is used. The fuel increases with load for good power. The US version of the Part Throttle Fuel Map is designed to be flat to support the Lambda sensor and not for power. The general impression that the EURO 944 is a better performer is not just another myth."
My car is running fine at the moment but I am sorely tempted to test this out. A slightly louder exhaust note replacing the cat with a test pipe would be a plus too; OK call me shallow.
Hope you're having a good holiday.
Chris
One I noticed the following on the FR Wilk site mentioned above:
"When the DME is set for ROW (ROW & EURO), that does not use the lambda sensor or catalytic converter, the fuel map below is used. The fuel increases with load for good power. The US version of the Part Throttle Fuel Map is designed to be flat to support the Lambda sensor and not for power. The general impression that the EURO 944 is a better performer is not just another myth."
My car is running fine at the moment but I am sorely tempted to test this out. A slightly louder exhaust note replacing the cat with a test pipe would be a plus too; OK call me shallow.
Hope you're having a good holiday.
Chris
12-25-2005, 03:42 PM
#11
Three Wheelin'
I recommend keeping it US specification stock for the following reasons:
1. Mechanically, a US spec engine is manufactured with a lower compression ratio to take advantage of an average fuel to air ratio or 14.7:1.
2. A US spec DME is wired to use the input from the O2 sensor to maintain an average fuel to air ratio of 14.7 to 1.
3. A US spec engine is manufactured to provide "normal" low end torque based on the amount of exhaust back pressure due to the exhaust restriction from the CAT.
4. With the O2 sensor disconnected a US spec DME is wired to set the injector duty cycle to provide an overly rich fuel to air ratio. This is done to prevent detonation (knock or ping). This mixture will waste fuel.
To sum up, if you do remove the CAT, remove the O2 sensor and switch to a ROW DME, you will have a "sick" engine that wastes fuel and is down on low end torque.
1. Mechanically, a US spec engine is manufactured with a lower compression ratio to take advantage of an average fuel to air ratio or 14.7:1.
2. A US spec DME is wired to use the input from the O2 sensor to maintain an average fuel to air ratio of 14.7 to 1.
3. A US spec engine is manufactured to provide "normal" low end torque based on the amount of exhaust back pressure due to the exhaust restriction from the CAT.
4. With the O2 sensor disconnected a US spec DME is wired to set the injector duty cycle to provide an overly rich fuel to air ratio. This is done to prevent detonation (knock or ping). This mixture will waste fuel.
To sum up, if you do remove the CAT, remove the O2 sensor and switch to a ROW DME, you will have a "sick" engine that wastes fuel and is down on low end torque.
12-25-2005, 04:02 PM
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Hmmmm...if there's a more aggressive fuel map by switching the DME to run in RoW mode, then I'm also tempted to do this!
In my '88, I've raised the CR and I'm running a 2.5" hi-flow cat with 2.5" exhaust. I may have a cam soon also. At that point, the car should be running leaner than stock, so I might actually gain some power by switching to the RoW mode (beefier fuel curve)...right???
In my '88, I've raised the CR and I'm running a 2.5" hi-flow cat with 2.5" exhaust. I may have a cam soon also. At that point, the car should be running leaner than stock, so I might actually gain some power by switching to the RoW mode (beefier fuel curve)...right???
12-25-2005, 05:46 PM
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Chris, keep us informed on how this works out. Here is a link that talks about switching the DME to ROW.
https://rennlist.com/forums/showthre...hlight=ROW+DME
With a 944, people are picking up 10 or so HP by deleting the CAT and running ROW. Look at the chart wizkid918 has in this post.
https://rennlist.com/forums/showthre...hlight=ROW+DME
https://rennlist.com/forums/showthre...hlight=ROW+DME
With a 944, people are picking up 10 or so HP by deleting the CAT and running ROW. Look at the chart wizkid918 has in this post.
https://rennlist.com/forums/showthre...hlight=ROW+DME
12-25-2005, 05:59 PM
#14
Badass - why did you qoute me?
Did you think that there was something I was unaware of with how the 951 dme operates? LOL.
I can tell you the afr's of a bunch of different 951 motronic configurations from having wideband on them at idle.
Note - bosch wideband comes on before the narrowband - so I can see the dme go into closed loop.
Did you think that there was something I was unaware of with how the 951 dme operates? LOL.
I can tell you the afr's of a bunch of different 951 motronic configurations from having wideband on them at idle.
Note - bosch wideband comes on before the narrowband - so I can see the dme go into closed loop.
12-25-2005, 06:36 PM
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Hmm, this is getting interesting.
Specifically for my car the '87 'S' I have found out that there was only one DME and the map was changed to compensate for local fuel or presence/absence of cat by using the jumper/coding plug.
Also the workshop manual, the 'Technical Specifications' book (bought here in the UK) and "Original Porsche 924/944/968" all agree there is only one compression ratio of 10.9:1 with no regional variations.
There may be spec differences in earlier engines but as alluded in the links given by beab951 (thanks) my engine is single spec for the whole world. Therefore it seems if I used a UK front box and coding plug with no O2 sensor it would be exactly the same as an original UK '87 'S'. No sick car.
As to wasting a little fuel, at the low mileage I do a year, personally I don't care even at UK prices. None of the changes would be irreversable anyway.
I will investigate in the new year but I have one last question. One of the links mentions an "altitude compensator switch", anyone know if this is relevant to my car model and if it was USA only or ROW as well?
Cheers,
Chris
Specifically for my car the '87 'S' I have found out that there was only one DME and the map was changed to compensate for local fuel or presence/absence of cat by using the jumper/coding plug.
Also the workshop manual, the 'Technical Specifications' book (bought here in the UK) and "Original Porsche 924/944/968" all agree there is only one compression ratio of 10.9:1 with no regional variations.
There may be spec differences in earlier engines but as alluded in the links given by beab951 (thanks) my engine is single spec for the whole world. Therefore it seems if I used a UK front box and coding plug with no O2 sensor it would be exactly the same as an original UK '87 'S'. No sick car.
As to wasting a little fuel, at the low mileage I do a year, personally I don't care even at UK prices. None of the changes would be irreversable anyway.
I will investigate in the new year but I have one last question. One of the links mentions an "altitude compensator switch", anyone know if this is relevant to my car model and if it was USA only or ROW as well?
Cheers,
Chris