o2 sensor disconnect it?

[usafa]

Kinda parallel with the recent thread on CO adjustment.

I have an 88 930 w/BB exhaust/heat exchangers. The O2 sensor is intalled in the new system.

I understand you need to disconnect the sensor before adjustment of A/F. Where should it be disconnected? Remove the sensor from the exhaust? Or unplug the elec connection?

If the elec connection, what does that look like? I've followed the elec line up to the engine compartment, but cannot find it's terminous. Anyone with pics or a good description?

Thanks

[Argo]

On my 88 non-turbo, it's in the engine compartment, driver side, about the same general area as the coil/fuel filter, on top of the frame rail between the coil/fuel filter and the upper valve cover (nearer to the coil/filter). There's a circlip mounted to the top of the frame rail that secures it; it's a simple male/female black plastic connector amongst some other electrical wire bundles. It should be fairly easy to find; turbo's may be different, tho.

Argo
88 Targa'm

[usafa]

Hey Argo,

Thanks for the info. I'm still unsure of which plug it is. There are two similar plugs in my car at that location. See the photo.

Does yours look like the plug I am pointing to?

[Wayne 962]

Why would you want to disconnect this? As soon as you unplug it, the car will try to start compensating for an incorrect mixture?

-Wayne

[usafa]

It was my understanding that in order to set A/F mixture at idle, the O2 sensor must be disabled. It would then be reconnected before driving. Correct me if I'm wrong.

[usafa]

Hey, I'm no expert. I'll check this out more tomorrow (I mean later today), when I'm awake.

[Wayne 962]

I don't think that's correct, but I may be mistake on these Turbo cars...

-Wayne

[ewave]

Wayne and usafa,

On my 89 (930) Turbo to adjust the A/F mixture, I had to first disconnect the O2 sensor, so that the system was running open loop. The DME has an internal bias, so it read a disconnected O2 sensor as perfect A/F ratio and sets the frequency valve at 50% duty cycle.

With the O2 sensor disconnected you then adjust the A/F mixture screw. I used the technique where you adjust the screw so that when you slightly push on the air metering device, the RPM drops very very slightly. This is because you adjust the A/F ratio to be slightly rich. When you push on the airflow meter, the fuel injection system thinks even more air is entering, and it adds even more fuel. If the RPM picks up when pushing on the airflow meter (causing extra fuel to be added) the mixture was too lean.

After you get this done, you hook the O2 sensor back up. It then runs closed loop, and undoes the slightly rich bias when you are idling OR at only part throttle. When you go to WOT it goes back to open loop, and the slightly rich bias prevents (hopefully!) detonation.

BTW, after adjusting this way my car passed smog test in Dallas with out a catalytic converter. This was in 2001 before they started doing the rolling dyno test.

Forgot to answer your question about which connector is to the O2 sensor. On my car, it is black, about 1.5 inches long, and 1/2 inch diameter. If you follow the lead it goes to a grommet in the sheet metal engine shield next to the valve covers. The connector has a kind of rubber feel to it, and required pulling hard with both hands to get apart.

[Joe Bob]

Isn't there TWO sensors on the 3.2 motors?

[ewave]

mikez,

??? This is a 89 3.3L turbo engine, and it only has one O2 sensor. Same on my 87 3.2 Carrera, (only one O2 sensor).

[usafa]

ewave, thanks for the info. That's "kinder" how I understood the process, but wasn't sure. I also was led to believe that the 88 930 didn't use a DME, but it does. A quick look in my little 911 Red Book told me that the DME was introduced to US 930's in 86 with the intro of the 930/68 engine.

Ok, so the O2 sensor plug is near the grommet in the engine sheet metal? I'll have to go out and take a look. Raining like crazy right now though.

I don't plan on disconnecting the O2 sensor permanently, just want to be educated when I take the car to the shop for A/F mixture adjustment. The last shop I had it in for major service set my CO% to factory spec (he told me about 1%) when he knew I had HP mods that warrent a richer idle CO%! Just hope I haven't broken any rings or damaged a piston!

I may have to invest in a CO meter and do it myself.

[ewave]

usafa,

A couple of other comments:

The "DME", if that's really the right name for the control box, is not very sophisticated in the 930. All it can do is mildly adjust the A/F ratio by changing to duty cycle to the frequency valve . This changes the working pressure in the fuel injection system. The DME that is in the 3.2 Carreras manages spark advance and fuel quantity. The 930 really have a version of the CIS. The brain has no control over timing. If you look at the distributor, it has TWO air/vacuum lines and also has a centrifugal advance. Some people might call this a kluge, some might see it as mechanical beauty. Being a micro controller guy, I just look at all this costly mechanical stuff and think that today it is easily replaced with a $1.0 micro.

Second comment has to do with the airpump/air injection. My 89 930 had one of these, and it added air to the six exhaust manifold outlets. This was done to conform to US emissions. My guess is that the combustion chamber is running really rich and producing all sorts of nasty unburned hydrocarbons. They injected the air into the exhaust manifold to help burn all this stuff. I removed the airpump AND the catalytic converter. As you can imagine burning all that extra fuel in the exhaust manifold creates lots of heat, and we've already got enough of that here in Texas! If the airpump is installed and running, and you measure the CO level at the exhaust, you are going to get a really screwed up reading because of the extra air that is being added by the air pump. I never really studied the plumbing the air injection system, so I don't know if you can disable the air injection on these cars when you are tuning them by monitoring the exhaust CO level. If your car has any mods, it's probably very likely that this air pump has already been removed. If you are looking for it, it's at the front of the engine on the drivers side.

Paul

[usafa]

Paul,

Yes I still have the air pump and the belt is in place. However, I don't think the system is operational. At least one air hose running up into engine compartment to what looks like an air valve is disconnected from the system below and there is an open connection on that air valve. Will have to monitor operation when I get it back together. I'm guessing the system is totally inoperative because the exhaust system has been replaced with a BB turbo header/heat exchanger system.

Have to r/r the intake manifold for repairs, thus the disassembled state in my pic.

Thanks for the info.

[usafa]

If you look at the pic above, the "air valve" I referred to is the silver job directly below the elec plug I have pointed out. You can see the open connection at the bottom left of this part. It is open when running. I cannot find where that line should run normally as it is completely gone. Maybe to the stock air intake box which is now gone?

I should be receiving my workshop manuels next week and hopefully will sort this out with the additional info therein.