sanchez

I have recently purchased an 1981 911SC coupe. The engine was supposedly rebuilt by first owner, but I have no records to indicate this. I do know he upgraded to hydraulic tensioners, added a pop-off valve, and added just about every Carrera update (H-4's, short shift kit, etc.) The engine runs strong, doesn't smoke, burn any oil, or leak.
The odometer indicates 151,000 miles, but is a 160MPH unit installed before my purchase, so actual mileage is unknown.
1) The valves seem to get very noisy after the oil gets hot. Do my valves need to be adjusted?
2) Will disconnecting my O2 sensor (just the wire, not the actual sensor) and running in open loop give me more top-end? The car pulls very well from low RPM, but seems to fade after 5000 RPM.
3) I drained and refilled the transmission case. I was only able to get 2 1/2 quarts in before the fluid poured out of the fill hole. Is this normal. All manuals indicate 3+ quarts to fill.

john walkers workshop

you will have a smoother idle and no surge when cruising if you disconnect the oxy sensor and set the CO to 3.5% don't expect any HP increase though.
if the valves are noticeably ticky, get them adjusted.
6 pints roughly on a drain and refill.

Trak Ratt

John, I agree w/what you said about disconnecting the O sensor, but thought by not having it constantly leaning out your mixture it would produce more HP on a CIS? Not much but measurable.

gr8fl4porsche

"The engine... doesn't smoke, burn any oil, or leak."


Are you sure you bought a 911??

sanchez

Thank you for the info. This is my first Porsche. I looked for about 18 months before deciding on this one. Every time I go outside, I look under the car, expecting to see some oil -- but so far nothing has appeared. The previous owner was a Porsche mechanic -- took excellent care of it.

Chuck Harmon

I also agree with the no O2.I feel the engine runs better without one.I hope you used Swepco Transmission fluid ! I also run a cat by-pass on my 83SC, you do not need that nasty old catalitic converter.Get a valve adjustment and you'll be set.

Ed Bighi

I disconnected my o2 sensor years ago because the control box got flooded and fried when I forgot the windows down in a classic South Florida monsoon. I felt the car ran better and later went ahead and picked up an 83 euro fuel distributor that is designed to be used without an o2. Even better. I disconnected the o2 in a cis Audi I used to have and these weird things it used to do stopped completeley. It probably had a bad o2 though. Nonetheless, they do run better without them. I still passed emissions easily with both cars since cis cars tend to run very clean. Cleaner than most Motronic cars I own and have owned.

ZCAT3

I am getting the proverbial rough idle at a few spots in the RPM range but the car (87 911) runs quite well otherwise. I suspect like others the O2 sensor is crapping out. How do you disconnect this? I know there is a wire somewhere on the driver's side of the engine bay that controls the O2 sensor - but which wire is it?

Rick Lee

I just replaced my O2 sensor on Sunday in my '87 Carrera. It looks like a 1/4" black speaker cable and comes in just to the front left side of the driver's side upper valve cover. Unplug it and then use a flat tip screwdriver below to pull the grommet out. Use a 22mm open end wrench to get the sensor out of the pipe or cat.

Ed Hughes

If your car's power fades at 5K, then I'd think something was wrong. If I'm not mistaken, the HP curve keeps climbing 'til well in the 6k's. Mine is strong ALL the way to redline. In fact, you mention pulling well at low RPM's, my low R's pale by comparison to the higher R's.

sanchez

Ed, My power peak is 5500 RPM. I believe the 3.2 had a higher HP and TQ peak. (5900 RPM and 4800 RPM, respectively). My 3.0 is known for having a relatively flat torque peak, although it does come "on cam" above 4000 RPM. I guess my question to 3.0 SC owners is this: Should the power keep building past 5500 RPM, or does it level off until redline? Would the CAT being clogged-up cause this? I use the car for pleasure and don't need to hit redline before every shift, but I'd like to think it is making all the power it can in stock form. Any ideas?

Wil Ferch

Wait, wait , wait....
This thread started out disconnecting the O2 sensor on 3.0 cars...somewhere along the line we made a big leap of faith (starting with ZCAT3's post)...and now we're talking doing this for DME 3.2's

-- Wrong ---

DME's run on a different principle with regard to O2 sensors. These should be kept functional !!

---Wil Ferch

ZCAT3

Hi Wil - I spoke to my mechanic about the roughness in the idle at 2500-3000 PRM or so (someone referred to this as a hunting feeling - which I think is a good description as the car feels to be looking for a smooth idle but can't seem to find it). He said to go ahead and unplug the O2 sensor to see if it made a difference. So I did and the idle smoothed right out. The car definitely feels better. One caveat is that my car has an aftermarket custom chip from PowerHaus in it (installed prior to my ownership) so perhaps the new DME is programmed to work with the O2 sensor disconnected (a fairly common practice I understand).

Wil R. Ferch

Bill:
All you managed to do is troubleshoot your system. The 3.2 will go overly rich when you unplug. 3.o's are different in that you can unplug and reset richness one time.

You should go further into your troubleshooting for the 3.2. Maybe a bad O2 sensor. Check related threads.

--Wil Ferch

ZCAT3

Wil - I would be willing to bet the O2 sensor is not performing correctly, but as this is merely an emmissions related aprt disconnecting it should not be a problem (should it)? I know on my 930, we like the car to run a bit rich as it performs better.