'85 911 RoW Oxygen Sensor/DME Question

hcubed · 09-25-2005, 12:12 PM

About a year ago I picked up an '85 911 RoW. It's been great. Today I was doing a little work and I noticed an extra white box with four leads (brown, yellow, orange and red) running into the DME and one white one that went under the carpet somewhere else. It says "Fuel Control Unit for Porsche Carrera" and has an address for "DC Johnson and Associates" in Laguna Hills, CA. It was poorly ziptied in place and was clearly an aftermarket addition. I have also noticed that the O2 Sensor has a white wire so I'm assuming this little box was part of the federalizing of the gray market car. I'm wondering what it does and if I can remove it? I'd like to "de-federalize" the car as much as possible (obviously without removing things like the door braces). I was planning on getting a pre-muffler as well to replace the cat. Thanks in advance.

Tripp

Here's a pic of the box underneath the seat.

hcubed · 09-26-2005, 05:33 AM

bump

laddsc · 09-26-2005, 06:58 AM

I have an 85 RoW as well. There are a bunch of threads out there on hesitation issues, surging, etc. In those threads, you will see a photo of that same unit. Speculation at that point, if I remember correctly, was that it served no purpose.

I ended up unplugging my o2 sensor due to some surging issues I had. I did a bunch of troubleshooting, etc and was unable to resolve the issue. Unplugged it to see what would happen and my problem was gone. The sensor was making the car run too lean in the mid rpm range.

Also, take a look immediately in front of the front oil cooler in front of the passenger front tire. See if there is a canister there. I pulled mine and it seemed to have no purpose. It was some type of purolator canister/filter that had hoses running to the motor. The hoses had broken and it was serving so purpose so I pulled it. Still don't know what it's function was but I do know it was blocking airflow to the oil cooler.

What is this???

Good luck and enjoy the car. They are a blast.

Joeaksa · 09-26-2005, 07:02 AM

How about taking the seat off and taking a picture of the DME and how this puppy is hooked into it. I have a US 85 model and have never seen anything like that on it or the others I have seen.

JoeA

hcubed · 09-26-2005, 07:09 AM

Thanks for the info.

I can say that the wires from the unit run into the fat cable that plugs into the DME so I'll need to try and figure out which pins on the DME plug interface are connected to its wires. I'm doing the valves this weekend so maybe I'll pull the whole DME and see what's going on in there and what those wires connet to. I've heard that sometimes the federalizing agencies would add electrical components to alter the function of the circuitry (shudder...). I'll let ya know.

Lorenfb · 09-26-2005, 07:55 AM

"Today I was doing a little work and I noticed an extra white box with four leads (brown, yellow, orange and red) running into the DME and one white one that went under the carpet somewhere else."

It's a Mickey Mouse box used when the Euro cars were imported into the US
to allow for a O2 sensor hookup which the Euro cars lacked in the DMEs.
It modifies the AFM input based on the O2 voltage.

hcubed · 09-26-2005, 08:00 AM

That's what I figured it was. Can I just unplug it and throw it directly in the garbage or does the DME need some "fixing" as well?

Rot 911 · 09-26-2005, 08:12 AM

I recall a year or so ago, someone else posted pics of an aftermarket box similar to yours. As I recall it was used to work with an 02 sensor which the ROW Carrera did not have.

Joeaksa · 09-26-2005, 08:15 AM

Quote:

Originally posted by Lorenfb
"Today I was doing a little work and I noticed an extra white box with four leads (brown, yellow, orange and red) running into the DME and one white one that went under the carpet somewhere else."

It's a Mickey Mouse box used when the Euro cars were imported into the US
to allow for a O2 sensor hookup which the Euro cars lacked in the DMEs.
It modifies the AFM input based on the O2 voltage.

Loren, What happens here? Do they have to run a wiring harness from the DME to the O2 sensor when this mod is made or does the plug-in exist on all the 911 harness's and is not used on the ROW cars?

JoeA

Lorenfb · 09-26-2005, 08:39 AM

If the box is removed:

1. The AFM must be connectd properly to the DME unit.
2. The O2 sensor function will not work if a Euro box is used but the DME unit
lacks O2.
3. The pin 24 on the Euro harness for the O2 is non-existent.

hcubed · 09-26-2005, 09:27 AM

Thanks for all the info. I'll try unplugging it and hooking up the AFM correctly. I'll let you know what happens. I occassionally get mid-RPM surges in 2nd/3rd gear when not accelerating so maybe it's just the old O2 sensor.

rex140@hotmail. · 10-08-2005, 10:34 PM

Loren,

Would a US DME wiring harness attached to a Row DME 0261200051 function with the o2 sensor. And are there any other mods required.

Thanks

Ron

Lorenfb · 10-09-2005, 09:47 AM

"Would a US DME wiring harness attached to a Row DME 0261200051 function with the o2 sensor. And are there any other mods required?"

No, the 051 DME unit doesn't have the O2 circuitry and EPROM.

rex140@hotmail. · 10-09-2005, 03:59 PM

Thanks my friend

Ron

hcubed · 01:35 PM

So, several months later now, I have needed to get emissions done on the Porsche and it failed. It failed on the HC level by a couple hundred points and last year it just barely passed by 50 points. So it was time to figure out what the hell was going on and we know this magic box is too blame (well, probably). Please bare with me.

The magic box is sewn into the wiring harness by six wires. The six wires it has are orange, yellow, white with shield (so that's two pins), brown, and red. Brown is ground to the box, red is power to the box, the white wire goes to the O2 sensor on the cat and is shielded so is effectively two wires. Then the orange and yellow wires are spliced into a single black/red wire in the harness. The black/red wire goes to pin ?? (I don't remember I fill in the number later) on the DME (I have a Euro DME - 051). This black/red wire is for the NTS II (negative temperature sender - it's basically a variable resistor, the warmer it gets, the lower the resistance), the main temperature sensor for the engine located on cylinder head 3. Basically what is happening (and what is really, really bogus) is that the magic box is taking the reading from the temp sender and changing it depending on the O2 voltage. This differs from what loren said. My setup does not modify the AFM circuit with the magic box, just the NTS II reading. The idea of the NTS II in the DME is to basically increase the pulse width of the injectors as the engine heats up which makes sense - more gas when the engine is warmer. The DME adds "more gas" by increasing the duration of the pulse width to the injector. What the federalizers did is lean out the engine with the adjusters on the AFM and then use the magic box to modify the NTS signal (i.e. increase the injector's pulse width) therefore providing more gas when the reading on the O2 sensor was too their liking. It's fooling the DME into thinking it's running cooler than it really is and it's running lean! The lean running is precisely the reason for the high HC content in my emissions test.

It turns out the my O2 sensor was bad so that means the bogus magic box was never richening the mixture so it was always running lean! Anyway we've replaced that with a used O2 sensor for a VW golf that was lying around and slightly adjusted the AFM to make the car run less lean. It will be back at emissions this week and I'll let you know the results.

In the immediate future I'll be removing the cat and replacing it with a bypass and removing the magic box and just jumping the NTS-II wire back together (that's all you have to do to remove the box, we tested it). I also have to mess with the AFM, as both the lean screw has been adjusted and the knob or whatever it is inside the AFM (I haven't opened it up yet, but the large cover was glued on so that means it's been messed with before). Hopefully I can then go back to the old setup whenever I need to do emissions which will only be for three more years anyway in CT.

Wil Ferch · 10-24-2006, 07:22 AM

you mean "bear with me"....right.....

no way I'm gonna "bare" with ya buddy........

Wil

tomphot · 02-19-2009, 06:48 PM

Found this old thread about an issue I'm dealing with - here is what I have under the seat on my '85 RoW
I have one wire going into my "Mickey Mouse" box - the white wire that comes from my O2 sensor.
There are 4 wires coming out. Then, at the harness, 2 of those wires have been cut.
How do I go about taking this whole setup out of the system?

Joe Bob · Joe Bob's Garage

Disconnect it and see what happens. I would suggest putting it on an analyzer to check the fuel mix, before driving it much....

hcubed · 02-20-2009, 07:00 AM

Ah, someone else has the same piece of sh**!

Red is power to the unit, brown is ground, white is the O2 sensor. You can cut those those three and ignore them (but cap off the red wire so it doesn't short out anywhere). Orange and yellow should be connected to each other to get the wiring back to the way it's supposed to be.

If you cut away the electric tape on the harness you will see that a red/black wire has been cut and on one end is attached the yellow and the other end is attached the orange. This is so the unit can modify the signal on red/black wire (NTS II - head temperature sender). Does your car seem to be running lean? I would imagine this is the case seeing at your NTS II wire is not hooked up at all in the current configuration!

Anyway, connecting those wires will get things mostly back to normal, but you're not done yet. If you have ever taken apart your AFM you will notice it has been tampered with (by the federalizers). You will need to take the car somewhere with a quality gas analyzer and have the AFM re-tuned.

I haven't done this yet because it's expensive and I still get occasional "bucking" at around 2800rpm at a constant speed in 2nd gear. Good luck.

tomphot · 02-20-2009, 09:22 AM

Thanks - I was trying to get through emissions in GA - I had a friend take off the bypass and mput on a cat that was with the car. That's when my problems started.
My first emissions test without the cat was by far the best that I had, even after adding a cat.
I have finally figured out that the O2 sensor must be bad as I have been having warm start issues and a couple times have stalled when at idle - it would then take about 30 minutes for the car to col down before it will start again.
I'm now convinced that all this mickey mouse stuff must be the problem.
I'm going to take it all off and see see what happens.
When you say it's going to take a lot of money to get the AFM back in shape, what type of quotes have you had?