Lambda System functioning ?

[mysocal911]

"In your opinion, am I wrong in assuming that the single wire narrow band 02 sensors' black wire (from the sensor to the connector pin) is unshielded ?"

The O2 signal wire was shielded from the factory. Hopefully no one replaced it
with an unshielded wire.

"And, if there is a shielding problem, it is between the pin connection and its path to the ECU ?"

You have to do resistance measurements to determine that.

"I am trying to understand why with a low warm CP (around 2.95 bar) and a .85 V 02 sensor signal (both indicating a rich mixture), the measured duty cycle of the FV is over 80% which as I understand it indicates the ECU trying to react to a LEAN mixture ?"

The duty cycle is not being calculated correctly if the above is true, or the Lambda
ECU is bad, very unlikely though. Check the previous posts.

"One thought I had was that the high 02 voltage was somehow being attenuated on its path from the connector to the ECU, and telling it to further richen the mixture ?"

Unlikely.

"If I checked the connection at the ECU at the appropriate pin (number ?), should I be getting that same .85 V ? If not, and it is lower than .5 V, this would explain the inconsistency right ? I could then focus on that critical path."

As mentioned before, the O2 sensor input to the ECU is pin 2. You should measure
the same voltage there as at the sensor.

[simsalabim]

Thanks again all.

Dave, I did quite a bit of online research on the single wire narrow band sensor that I have (as well as an examination of the recently removed one) and the conclusion seems to be that there is NO shielding on the wire leading from the sensor to the connector. The lead from the connector to the ECU is another story. Thanks for the verification of the voltage check at the ECU pin-out.

Paul, I am happy to hear that the slightly oscillating idle at warm is an indication of a functioning closed loop. I kept thinking that it was a symptom of "hunting" and therefore an indication of a poor mixture or other problem. Also, the analog dwell meter seems like a cheap investment and I will look around. Thanks .

In the meantime, after repairing the 02 connector (as shown), and leaning out the mixture screw by around 1/4 turn, I brought it to full warm and retested the FV duty cycle % and now it does in fact "dither" steadily between 65% - 75% at idle.

The car actually starts, warms up, runs on the road and warm starts very well at this point. It runs better than it ever has since the rebuild and installation, and while I am tempted to leave well enough alone, I want to get my warm control pressure up to spec (another .6 bar) and see what happens .... Also, I want to determine whether adding an additional enrichment function (vacuum enrichment is part of the digital wur and was not included in the stock wur) to the stock throttle enrichment switch, is at all beneficial or in fact detrimental to engine performance. At that time, I will decide whether it makes more sense to disconnect the switch or the vacuum advance and just run with one of them. Any thoughts here ?

A million thanks,
Bill

[psalt]

The best way to make that decision is to measure your AFR's under load with a wide band O2 sensor (before the cat). My experience is that most lambda SC's run a little lean under WOT which is one reason they can't tolerate much ignition advance. Optimum advance for a wide VIA hemi like the 911 is in the mid to high 30's BTDC, but the factory chose to limit the advance to 25 BTDC. If you have the octane, you can usually run more advance with AFR's in the low 13's. When you set the dwell to 25-35 you are really only effecting the WOT and cold mixture, because the system pulls the average mixture back to stoich when in closed loop.

[mysocal911]

"Dave, I did quite a bit of online research on the single wire narrow band sensor that I have (as well as an examination of the recently removed one) and the conclusion seems to be that there is NO shielding on the wire leading from the sensor to the connector. The lead from the connector to the ECU is another story."

The O2 wire is shielded from the sensor itself as should be obvious if one checks
the outer shielding near the O2 sensor and the other end at the ECU. Also obvious
is the fact that the O2 sensor has only one connection point, but that doesn't imply
that no shielding exists. Based on this, one should not have had an issue with how
the O2 sensor is wired. It hardly takes an online research to determine this.

[blpetry]

Originally Posted by psalt

The best way to make that decision is to measure your AFR's under load with a wide band O2 sensor (before the cat). My experience is that most lambda SC's run a little lean under WOT which is one reason they can't tolerate much ignition advance. Optimum advance for a wide VIA hemi like the 911 is in the mid to high 30's BTDC, but the factory chose to limit the advance to 25 BTDC. If you have the octane, you can usually run more advance with AFR's in the low 13's. When you set the dwell to 25-35 you are really only effecting the WOT and cold mixture, because the system pulls the average mixture back to stoich when in closed loop.

Good stuff in this post... So what you're saying is that while trying to tune to 50% may be what the factory recommends for optimum emissions for cold starting, some benefit may be gained by tuning to 25/35% to ensure you don't go lean at WOT? And you might be able to get more advance out of it too? I'd never heard that before but it makes sense.

[scarceller]

These motors should run no leaner that 13.0AFR at WOT some may say 13.2AFR is OK but I'd run them at 12.8 to 13.0AFR and no leaner than this. You really need a WideBandO2 controller to accurately see the AFRs. Don't ever let these engines run lean under load they detonate and melt down! I have a permanent installed WBO2 AFR gauge on the dash and it's the very best money spent to get one if you don't have one. These AFR gauges give you a clear indicator of how fuel and air are burning in the cylinder and you have an instant visual aid via the gauge.

[simsalabim]

So if I understand things correctly, some extra WOT enrichment (provided by the digital wurs' additional vacuum enrichment) is - if nothing else - a good added protection against the possibility of running too lean (detonation) during high load running ?

Any downsides besides fuel economy ?

Bill

[mysocal911]

Originally Posted by scarceller

These motors should run no leaner that 13.0AFR at WOT some may say 13.2AFR is OK but I'd run them at 12.8 to 13.0AFR and no leaner than this. You really need a WideBandO2 controller to accurately see the AFRs. Don't ever let these engines run lean under load they detonate and melt down! I have a permanent installed WBO2 AFR gauge on the dash and it's the very best money spent to get one if you don't have one. These AFR gauges give you a clear indicator of how fuel and air are burning in the cylinder and you have an instant visual aid via the gauge.

You need to tell the 911SC guys how you tune the 911 3.2 engines for more torque
by tweaking the timing and AFRs. The 911 3.2 engine is basically a 911SC with a longer
stroke (4mm longer) and basically the same CR. Little to no performance tuning has
been discussed for the 911SC as has been for 911 3.2. Sal, help these guys!

Note: Sal has his own performance chip for 911 3.2s.

[scarceller]

The SC is a bit more tricky to properly tune and fuel because of 2 reasons:

- No air flow compensation for IAT or Altitude. That air plate and funnel measures Air Flow not Air Mass and the system has no compensations built in. Keep in mind that air becomes lighter (less dense) as IAT goes up and also as Altitude increases. This means that as it becomes lighter your mixtures will get richer. So as you climb in altitude you will get richer, and on a hot day you also will be richer compared to a cold day. Simply cold air at sea level is the best for these motors or any motor. Because of this lack of compensation you can't afford to go lean in cold temps so you MUST set mixture for a target no more than 13.0AFR at sea level and 0C temp this gives you the safety margin you need for cold temps and low altitudes. But it's a compromise that as IATs go up and Altitude increases your AFR goes down. Simply go back to physics 101 with law of gasses and you can run the numbers, you'd be surprised how much the density of 1 Liter of air changes by simply increasing IAT from 0C to 40C and/or going from 0ft to 6000ft elevation.

- Next reason the SC is tricky is it has no computer controlled timing to correct ignition across all engine conditions. If recall I think the SC engine runs about 25deg adv ignition at WOT above 4000RPMs and that's the factory spec. But you can easily run 30deg adv safely with 93 octane fuel so long as the AFRs stay in the 12.5 to 13.0 range. You really need a load dyno to find peak torque for a given RPM. I'd lock the dyno in at 4000RPMs pull a quick WOT pull for 5 seconds and record torque at the stock 25deg ign. Then increase adv to 27deg and repeat, then 29 and so on. But you need a good knock sensor to be sure you don't have detonation, although the torque number will also drop significantly with knock. My bet is you'll find optimum ignition possibly as high as 35 deg!

Here's some other thought exercises: All the early cars 1968-1973 ran ignition of 30-35deg advance and these motors had much smaller bores. Engine dynamics follow a rule of thumb that as bore increases so does ignition advance if nothing else changes. It simply takes longer for the flame front to reach the edges of the cyl. This means that these motors lost efficiency as they increased bore! It makes no sense for a 2.2L engine to be at 35deg ign while the sister 3.0L engine is at 25deg. For some reason the factory detuned the 3.0 and 3.2 engines.

Taking a well running 3.0L and installing a decent WBO2 meter and then a few dyno pulls at 4000, 5000 and 6000RPMs will show what ignition the motor wants, once you know this a good distributor shop can build the curve for the distributor.

I've also had the idea for a very cool project, take a 3.0L and install the 84-89 motronic system into it and tune it. That would result in a very interesting engine with proper timing for all conditions.

One last thought: my personal 3.2L Euro engine runs 30 deg advance without issue and I hold my AFRs at 12.8 across the RPM range at WOT. The 3.0L engine should easily tolerate the same ignition as the 3.2L in theory. And my engine is a Euro with higher compression running at 30 deg on 93 octane fuel.

[scarceller]

Dave,

Thanks for the kind words. I've spent a lot of time understanding the 3.2L engine and how to really extract peak torque from these motors but the principles are the same for tuning most engines. Bottom line is set fuel in the 12.5 to 13.0AFR and then the magic is all in the timing. For those interested in really learning how this is done I suggest you buy both books by Greg Banish, search Amazon for him and you'll find the books. Those 2 books have the secrets easily explained and why ignition is so important to get correct. Best money spent getting those books, I also have him as a contact reference now and we chat engine dynamics from time to time. The other thing that's very important is knowing exactly how much air the engine is ingesting and you can NOT beat a modern day MAF meter for this as it measures Air Mass spot on! I run a lab grade hot film MAF in my car these days and it's amazing how well it works.

Originally Posted by mysocal911

You need to tell the 911SC guys how you tune the 911 3.2 engines for more torque
by tweaking the timing and AFRs. The 911 3.2 engine is basically a 911SC with a longer
stroke (4mm longer) and basically the same CR. Little to no performance tuning has
been discussed for the 911SC as has been for 911 3.2. Sal, help these guys!

Note: Sal has his own performance chip for 911 3.2s.

[psalt]

It makes no sense for a 2.2L engine to be at 35deg ign while the sister 3.0L engine is at 25deg. For some reason the factory detuned the 3.0 and 3.2 engines.

Sal,

The reason is history. After the oil embargo, Porsche decided that advertising lower fuel consumption numbers for each new model would be very important to maintaining image and sales. They decided that increasing compression was the way to go in 1980 and 1984, but with the unleaded fuel mandate, this required detuning the ignition advance. The later SC fuel spec is 87 CLC octane.

The later 3.0 and 3.2 are very different engines in terms of knock sensitivity. The SC has much smaller ports and runners that boost the low rpm torque peak. Unfortunately with a distributor it is very hard to reduce the advance around this point. An SC that runs hot will ping like crazy at 4000 rpm with 30 BTDC timing. One of the the best things you can do with a stock SC is get the hot breather oil out of the intake. The higher temps and oil dilution raises the engine's octane requirement.

[simsalabim]

Well, after finally programming the digital wur for the correct warm cp, the engine runs quite well now when fully warm. Better than it ever has in fact, smooth, even torque, quieter and more powerful. So far, so good ...

Now the problem is that during warm starting, the wur shoots the cp up to around 3.8 and varies it around that number for close to 8 minutes before bringing it back down to the 3.4 bar that it is set to. The digital wur representative insists that this is the fault of my car, and that it is because the system pressure is leaking down incorrectly. He states that my 81 sc should hold at least a 1.5 bar system pressure for weeks, months and even years and though my leakdowns are well over the 1.3 bar and 1.1 bar minimums after 10 and 20 minutes, those numbers do not apply to my situation.

I cannot find any literature regarding the final leak-down to zero pressure time for this car and I am wondering if anyone out there knows what I should be getting ?

Thanks

Bill