Perhaps the O2 sensor was disconnected by an owner that thought he'd make a bunch more power without it. There are people that think that way. Who knows?

CIS troubleshooting works best with a methodical approach. Most people go at it with the mindset of "this symptom"="that cause" and they try to shortcut the process. They usually run around in circles. There are threads on this forum that go on for months, while they throw darts at the problem.

My suggestion would be to start with eliminating some variables. For one, yank the wide-band crap and put in a stock Porsche O2 sensor. Stock, as in the right type and with its original connector. Don't introduce anecessary variables by using an unheated sensor, one from a Mustang, one that's had the connector hacked, etc. Then, find a known reliable way to test the duty cycle.

Personally, after verfying there wasn't an ignition problem, I'd look at the fuel pressures. Then I'd check for air leaks. I'd make sure all of the ancillary crap was working, like the auxiliary air valve, etc. I'd check easy things like temp sensors and microswitches. Then I'd concentrate on one thing at a time, like operation when fully warm. That would include measuring and setting the CO with a gas tester. Then, I'd probably tackle the cold running and warm running issues, if there were any.

JR

Edit - posted this before I saw javadog's last post.

Bite your tongue.

Open up the Lambda box connector and enrichment connector. Go to town testing continuity. O2 sensor. All the throttle switches - should be able to push the gas pedal in increments to find when they go on and off.

Check resistance on the temp sensors. The specs should not be that hard to find.

Check all of your wiring again assuming you made a bone head connection.

Check connections between the Lambda box and enrichment box.

I can send you my box for a test if all else fails, assuming it will work in the 83 with the slight difference javadog mentioned. Tony has boxes as well.

JR -

Appreciate the feedback. I've already done most things on your list with the help of guys like yourself, ossiblue, Bob Kontak, Jim Williams and boyt911sc (I'm sure I've missed somebody but thanks to everyone!).

Here's a quick summary:
- new plugs, plug wires, rotor and cap around 2k miles ago
- WUR was re-calibrated by Tony
- smoke test performed by local shop showed no vac leaks

Short of getting my hands on an oscilloscope as Jim suggests, the Innova unit I have seems to be more reliable on dwell. I was looking at the OTC 3980 and the Innova 3340 multimeters.

If I can't trust the wideband AFR is reading the exhaust correctly then all bets are off. I just checked the documentation and it claims "no calibration required." No idea how many miles on the old O2 sensor. I might throw it back on there over the holidays to see if it makes a difference as you suggest. I'm not really inclined to buy a new one. I'm seriously thinking about going the SSI route and ditching the O2 altogether.

The matrix info javadog posted is eye opening. I had not a clue.

I always thought if you ditched the O2 sensor you lost WOT functioning. Not the case.

So you lose a little mpg on a long cruise. At least you don't have to worry about plugging up the cat.

Step away for a while. :-)

Happy holidays.

SSI's are great, but I'd keep the O2 sensor. Better mileage and driveability.

JR

Sage advice. Over the holidays is probably the best chance I have at get some time to sneak off to the garage though so I'll probably be trying to knock out some other stuff on the P-car to do list.

Y'all have a Merry Christmas and a Happy New Year! Or a Happy/Merry Chrishanakwanzimus if you're a PC person. Y'all are the best!

Oh yea... I will look at the info JR posted later. It's too small to read on my phone.

Hi JR, thanks for posting this...

But my larger question is: What documents are the pages you posted taken from? What publication? Porsche document? Does it have a name? (etc., etc.)

I know that the first year of Lambda was '80. This system had no enrichment relay. Then the next year was a change in the ECU and addition of the enrichment relay, the idle microswitch, the 35˚C switch, and in '83 another ECU number. I am doing my best to document the details of all this, including the transient timed enrichments, and when they occur. The Porsche Workshop Manuals I own have none of the detail I am after. I have set up a bench test to try and gather this information, which I intend to publish on my CIS Primer site, including oscilloscope waveforms to show what the Frequency Valve is doing, and at the same time, what the test pin is showing. I have already done an '80 Lambda and an '82.

If there is available documentation out there covering the detail I am trying to gather such as you have shown in your post, I would like know to where I can obtain copies. It seems a shame for there to be such documentation available, and not be able to include it for the benefit of the Porsche community, both for my own use for the Primer, and to include on my References page.

If you like you can drop me an email with any information you can furnish.

tirwin -

Here's another tidbit of information from my bench testing observations -

Although I don't have a functional block diagram of the ECU, and don't how exactly how it does what it does, the O2 input to the ECU from the sensor "knows" what range of values it's looking for from the sensor. It does a good job of knowing if it's looking at an open circuit, or a working sensor. For example, Zero volts is different from an open circuit.

But it needs to be looking at something it recognizes as being valid. If you confuse it by attaching something it's not familiar with, it can do funny things to the output to the FV. For instance, touching the disconnected O2 input to the ECU with a fingertip carrying all sorts of stray voltage, even in the millivolt range, causes it to make the duty cycle extremely erratic. It's looking for a more or less DC voltage. Millivolt AC voltages (60 Hz stuff on your body from around the shop), to my observation, make it nuts.

As javadog suggested earlier, if you are going to hook up an O2 monitor to the ECU, best to use one the ECU has been trained to recognize.

IMHO.

Jim,

Just throwing this out for discussion, but is it possible that the wideband unit is putting out a changing signal too rapidly and thereby causing the ECU to try to react too quickly? I guess this is where an oscilloscope would be handy.

Not arguing with you and JR but I am confused by the fact that others have reported using a wideband O2 with success and even the same model as mine. I think it would be generally useful for everyone to understand what the difference is.

Kinda makes me wonder about the future of these ECUs. I wonder if Porsche would ever share the details? You'd think that if we could go from a desktop computer having 32k of RAM in 1983 to an iPhone in 2013, we could build a modern replacement for the ECU.

Tirwin,

I think you are making a lot of false assumptions based on bad data. Focus on getting an accurate reading of the duty cycle cold open loop, then in closed loop. This can usually be done with a $5 Sears dwell meter from a garage sale. It sounds like you never got valid default readings. Some people get confused with the fact that a high open loop duty cycle means rich, but a high closed loop duty cycle means it is actually too lean and what you are looking at is the compensation factor. The first step in dialing in a Lambda SC is to fit Bosch normal plugs, disconnect and plug the vacuum retard and set the high speed timing to 25 BTDC. Reset the idle to 950 rpm. If then you have bad idle performance when reconnecting the O2 sensor, you likely have vacuum leaks at the injector sleeves, boots, throttle shaft, etc. The throttle switches need to be working and adjusted properly for the ECU to use the correct count between corrections. Minor vacuum leaks should have no effect at WOT. It is quite normal for a Lambda SC engine in perfect condition to have a oscillating idle when hot in closed loop. They did this when new. Some people are so anal about idle performance they disconnect the sensor in stupidity to get a steady idle and shorten the life of the engine. Personally, a Porsche is for driving.

Psalt,

Yep, I'm trying to get good data. I bought the Actron a while back after not having much luck turning up an old-school dwell meter. Figured it was worth a shot at $19. Hard part seems to be finding a piece of equipment you can trust.

I have a lead on an oscilloscope I can borrow for a while. Been watching Fleabay too...

No arguments with me... I don't even have a real Lambda car in my garage to further experiment with. The ECU and Acceleration Relay which I used for bench checks have been returned to the person that was kind enough to loan them to me. I can only report what I found using my home-built test setup; again, no real car with real throttle switch 1 and throttle switch 2, coupled by the shaft on a throttle body. I wired a 2P3T switch to open the microswitch contacts at the same time the Throttle Switch idle contacts open, not exactly as it's supposed to work when using two physically different switches. The microswitch is supposed to open with the slightest movement of the throttle shaft, and the Throttle Switch with 2 to 3 degrees of movement, according to the factory shop manual version I have.

From researching part numbers I know that the ECU changed from the '80 YM to a different one for '81 and changed again for '82 - '83. The throttle switch number changed in '81. I don't have any information as to what the internal changes might have been in the ECU or the switch contacts.

Somewhere out there is someone who could improve on the ECU. The issue with a redesign of the ECU is - why would anyone want to do this? The CIS system is basically old technology. I have a soft spot in my heart for folks who own 911s with CIS and would like to keep them running for what ever reason. On a personal basis I own such a car, an outlaw '73 911 with a rare 3.1 CIS engine - circa 1979, pre-Lambda. But to try and re-design any component of CIS would simply be a one-of-a-kind labor of love or an experiment, with no hope of any monetary gain.

The Porsche engineers behind the basic and Lambda CIS are long gone. Trying to get technical information from a live Porsche person on CIS is an exercise in futility. Every now and then a publication on CIS will rise to the surface for the Porsche community to see, such as that which javadog was kind enough to share on this forum.

There are folks who repair these ECUs who understand how they work, at least well enough to check and repair them. At $350 per repair, they are already making a decent return.

Lambda CIS works pretty well, even after 30 years. The idea that you would modify the system without ever knowing if it is functioning correctly is silly. I have worked on several cars with a second FV on the control pressure line, which makes the post 35% throttle mixture (WOT) programmable with a stand alone ECU. The stock system works quite well and can be set up to provide very good performance with a few tricks that come from experience, not in any of the literature. Most of this is already in the archives of this site.

psalt,

I'm not talking about modifying, just wondering what happens in the future when original ECUs become scarce. I guess that's why some people go back to carbs and others go to aftermarket EFI.

Back to the topic... I think I'll have an old oscilloscope by tomorrow that so can play with for a while.

I checked around the local FLAPS today and I got blank stares when I asked about a dwell meter. One guy said "yea we carry those" and then promptly showed me a $5 multimeter. :)

I even called a couple of local mechanics. One guy said he has one but it's in storage and he's not sure where it is. I'll keep looking...

I will have an oscilloscope later today. I'm told it's military surplus. LOL Can't wait to see this thing.

I want to see what the wideband O2 puts out. Jim, do you happen to have results from the stock sensor. If not I can put the old one back in and compare.

So you know what to be looking for with your new scope, here is a scope photo on my scope of a 65% duty cycle. One full cycle of the 70 Hz wave form has been displayed by adjusting the horizontal sweep to 10 cm an triggering the sweep on a negative slope. The top trace is the input from directly at the Frequency Valve (a real frequency valve was used on the bench), and the bottom trace is the ECU monitor point at the test connector. For in-car testing, most people will never see the top wave form. The FV ON time is the bottom portion of the bottom trace. This equates to what a dwell meter would be reading, and what my duty cycle meter was reading.

http://forums.pelicanparts.com/uploa...1387741526.jpg

I know approximately what the voltages are from the O2 sensor. I have an adjustable voltage source I used on the bench so I can know where the switch-overs occur from 50% duty cycle to richer or leaner. The thing that the bench test can't simulate is the engine's exhaust feedback to the O2 sensor, so in effect, closed loop operation is not possible on the bench. The feedback loop is broken at the constant voltage of the O2 "simulator" (A variable resistance potentiometer.)

Lambda for the stock one wire sensor is 0.45 volts. This sensor is more of a switch than a sensor, and it cannot be used to determine AFR. The ECU knows 0.8 volts is rich and 0.2 volts is lean, but 0.36 is not 20% leaner than stoich. It is like throwing darts, you miss to the right, compensate, miss to the left, then walk the dart into the bullseye. Amount and frequency of the compensations is determined by the ECU and the mode it is in. The system can compensate for a 20% error, so when you are adjusting the mixture using the dwell meter in closed loop, you are really only adjusting the WOT open loop AFR, because the system brings the average AFR back to stoich in closed loop. Once the throttle is opened 35%, the sensor is irrelevant and if there is a problem under load, it is something else. Have you tested the 15C switch ?

Jim,

Thanks for the info! It might be Thursday or Friday before I get some garage time. I've bid on a couple of old dwell meters. Maybe I'll get one soon.

psalt,

Thanks for that explanation. Haven't had more time to test. I've got several things to check for - the switches are definitely on the list. On the lambda of the stock sensor, yes that is my understanding. The charts I have seen show exactly what you describe.

Duty Cycle test results - '82 Lambda ECU
 

I have posted the results of my bench checks of the '82 Lambda ECU/enrichment relay on the CIS Primer. The link shows in a chart format the first of the three temperature modes and their duty cycles along with links to the other 2 modes.

These 3 charts confirm the information shown on the photos of the service manual posted earlier by javadog. As soon as I can get flat-bed scans of the actual pages of the service manual I will post them on the Primer. Note the duty cycle numbers in the charts are in actual % measured by a Duty Cycle meter, and are not dwell meter numbers.

I haven't yet located an '83 ECU to test. Supposedly, the only difference is the 25 second enrichment mentioned earlier.