Serious CIS improvement

BlueSkyJaunte · 09-15-2003, 01:18 PM

OK, I do not have the details on this, because when it comes to this stuff I am a "checkbook mechanic."

My '81 had been having serious cold-bloodedness, poor hot-starting, and poor warm starting. The general symptoms were backfiring (pop-off to the rescue), stumbling, and major throttle hesitation for the first 30-90 seconds the car was running. It also seemed like the revs would sag to nearly stalling when I let off the gas in neutral (i.e., coming to a stop at a light).

Well, that's all fixed now.

My mechanic's explanation: "We'd been seeing a number of cars with problems similar to this in the '80-83 model years. We had a car in with this problem that was nearly undrivable as a result. After a number of hours we traced it to resistance in the wire harness from the 'computer' to the frequency valve. We bypassed this wire at the 'computer'. Ever since we've been checking every '80-83 with these problems and it's been the same cause."

If this makes sense to anyone else, please fill me in. For my part, I'm happy, since it ends the constant fiddling I'd been paying for to get this d@mn thing to start right.

RickM · RickM's Garage

Blue,

The Wire is "Bypassed" and replaced?

BlueSkyJaunte · 09-15-2003, 01:25 PM

I'm guessing that's the case. A few issues I have with my mech's explanation:

Does my car even have a frequency valve?
Does my car have anything remotely resembling a "computer"?

He also mentioned the difference in measuring the resistance in the wire was a matter of a few "microvolts", but last I checked resistance is measured in ohms! He attributed the resistance to corrosion.

1fastredsc · 09-15-2003, 01:29 PM

The computer that translates the o2 signal to a frequency for your frequency valve is under the passenger seat. And yes your car should have it since all the 81-83's had a closed loop o2 system.

MotoSook · 09-15-2003, 01:29 PM

Could the wrench be talking about the O2 sensor wire?

BlueSkyJaunte · 09-15-2003, 01:43 PM

1fastredsc seems to have it--my wrench mentioned something about doing something with a signal from the OXS.

Superman · 09-15-2003, 01:44 PM

Like Arte Johnson used to say, "Very interesting."

MotoSook · 09-15-2003, 01:52 PM

Well..the O2 sensor signal is 0.0 VDC to 1.0 VDC, and perfect burn is at 0.5 VDC .... so how critical is the signal wire...hmmm..

A bad O2 sensor can hurt too!

jester911 · jester911's Garage

Superman, I believe he pronounced it velly intellesting.

Yeah it sounds like he was saying oxygen sensor blue. It makes sense. If the 02 sensor isn't working properly it will cause idle problems.

BlueSkyJaunte · 09-15-2003, 02:05 PM

OK, just to clarify, I just asked specifically and this was the wire from the comp to the OXYGEN SENSOR. The solution? Unplug the sensor. The sensor itself was OK, supposedly, but the resistance in the wire was screwing things up.

Sorry for any confusion.

Now we get to see if I pass emissions, since I no longer have a closed-loop system.

AZ1977911 · 09-15-2003, 02:12 PM

Hi BlueSkyJaunte,

I think I know your wrench. I trust him. He's been correct on all calls made on my ride. Go for emissions with your ride as hot as you can get it. Makes a big difference...

john walker's workshop · 09-15-2003, 02:24 PM

i always leave the oxy sensor unplugged on SCs, unless it's getting smogged. runs rougher, and surges with it attached, like the factory designed it to do. the "wire" issue would likely be the connection at the end(s) of the wire, being that the wire itself rarely fails. then it's just a matter of improving that connection.

tbitz · 09-15-2003, 05:07 PM

Typically on a cold start the computer ignors the voltage from the O2 sensor and runs "open loop" until a certain coolant temperature is reached (or in the air cooled world CHT).

Also unless the O2 sensor is heated (minimum of three wire sensor) the data coming from the sensor at low rpms (ie: idle) is worthless because the sensor has not reached the operating temperature.

Disconnecting the o2 sensor means the computer receives zero volts. If the computer is smart it detects this and lights the "check engine light" however the early 80's computer in the 911 probably thinks this is a lean condition and compensates by richening the mixture, which is probably why these cars run better with the sensor disconnected? MPG and CAT my suffer, though....

emcon5 · emcon5's Garage

There is no problem with a non-heated O2 sensor on a CIS/Lamda 911, it gets hot enough at idle.

If you unplug the O2 sensor on a 80-83 911, it will change to open loop, which runs the frequency valve at a fixed duty cycle. It should run at 85% duty cycle for 1980, 65% for 81-83.

If you unplug and ground the connection, it should go to "rich stop", at ~95% duty cycle.

Tom

geof33 · 09-15-2003, 08:59 PM

Can the O2 sensor be "deleted" in the Motronic system as well? Given it's problematic nature I'd like to rid myself of the thing if poss...

SC-targa · 09-16-2003, 04:27 AM

[QUOTE]Originally posted by BlueSkyJaunte
[B]
"My '81 had been having serious cold-bloodedness, poor hot-starting, and poor warm starting. The general symptoms were backfiring (pop-off to the rescue), stumbling, and major throttle hesitation for the first 30-90 seconds the car was running. It also seemed like the revs would sag to nearly stalling when I let off the gas in neutral (i.e., coming to a stop at a light)."

Sounds like a warm up regulator issue to me. First 90 seconds is when the mixture is controlled by the warm up regulator, isn't it. Isn't the O2 sensor out of the loop during warm up?

Regards,

Jerry

BlueSkyJaunte · 09-16-2003, 08:46 AM

Quote:

Originally posted by SC-targa
Sounds like a warm up regulator issue to me. First 90 seconds is when the mixture is controlled by the warm up regulator, isn't it. Isn't the O2 sensor out of the loop during warm up?

Jerry,

I know what you mean, we'd been screwing with the WUR periodically. And the mixture. And the timing. And the idle setting. And everything else we could think of.

All they did this time was unplug the OXS, after testing the resistance of the OXS wire.

Ya got me...

BlueSkyJaunte · 09-16-2003, 08:51 AM

Quote:

Originally posted by SC-targa
Sounds like a warm up regulator issue to me. First 90 seconds is when the mixture is controlled by the warm up regulator, isn't it. Isn't the O2 sensor out of the loop during warm up?

Jerry,

I know what you mean, we'd been screwing with the WUR periodically. And the mixture. And the timing. And the idle setting. And everything else we could think of.

All they did this time was unplug the OXS, after testing the resistance of the OXS wire.

Ya got me...