High dwell on 911 SC ‘81 lambda (US)

[mysocal911]

Originally Posted by Funracer

Pin 2 to O2 sensor. .2 ohms
5 GRND. .2
7 to 15C switch. .3 ohms
8 to OXS relay. .4
12 ECU to AEC and 15C switch .1
14 ECU to AEC. .1
15 ECU to FV to OXS relay. 2.8 ohms

Pins 12 & 14 each need to be checked for being grounded, i.e. one lead of the ohmmeter on one pin
and the other lead touched to the chassis. Those pins go to the enrichment relay (AEC) & MUST not be
grounded! You should also disconnect the AEC with the engine running and check the the duty cycle.

[Funracer]

I had a long alligator clip wire so used the negative battery post.

All pins on the ECU said O.L.

All pins on the connector said O.L. Except 5 And 16 (grounds) Showed .3 and pin 15 (ECU to FV to OXS relay) showed 4.2 ohms

Is the line between ECU plug and FV shorted? Or maybe the line from FV to OXS relay?

[Bob Kontak]

Originally Posted by Funracer

pin 15 (ECU to FV to OXS relay) showed 4.2 ohms

That's definitely not infinite resistance (OL = Open Loop) but I'll let the smarter guys speak.

[AndrewCologne]

@ Funracer
The resistane of the FV should read 2 - 3 ohms.
The ECU iself does not provide 12v power to the FV. The FV gets its power from the OSx relay. The other (ground) connection on the FV is connected to the ECU where the ECU applies an interrupting/pwm ground signal on that FV connection. Its pulse width length results in the FV's dutycycle.

Btw. your ECU unit comes with the correct Bosch part no. for a '83 vehicle.

So when all ECU "pin lead to ground" checks result ok, then its also worth checking the inner part of the ECU for water marks or similair.

[Funracer]

Originally Posted by AndrewCologne

@ Funracer
The resistane of the FV should read 2 - 3 ohms.

Mine reads 4.2 ohms. What does that indicate?

To refresh everyone’s memory, if it is over 15C (switch open) which for me in Florida is most of the time, if I unplug my O2 sensor FV should go to 50% duty cycle. Mine does not change at all. I have been trying to get my DC to read 45% for a couple of months now.

I purchased a new O2 sensor on eBay from Walker Products part 250-2103. It was listed as the right part for 1983 911. It has the full harness including the rubber grommet and a continuous wire to the plug. Car ran fine with it for a month but if anyone knows this to be a sensor that will not work for me I can reinstall the old one.

Thanks for all your time and responses

[Funracer]

Originally Posted by AndrewCologne

Do the tests MySocial911 recommendet, especially check the reference voltage at pin 2 of the ecu with o2 sensor unplugged, should be 0.5v.

Can someone please explain in detail how to check this. I am checking both the O2 plug and pin 2 for .5 VDC? Both with O2 unplugged? I have the fuel pump jumpered should I leave it like that or put the relay back in. Start the engine and check inside the O2 plug for .5VDC? Or can I just go to run?

Sorry for all the questions. I’d love to take a class in automotive electronics.

[AndrewCologne]

Originally Posted by Funracer

I believe the 15C switch is working properly. It goes to 65% when grounded. It is almost never below 20C here. If it were the switch would ground and take the FV to 65% if O2 disconnected. It’s either the O2 circuit or the OXS ECU that is not doing what it should. I will be investigating further today I hope.

Originally Posted by Funracer

Mine reads 4.2 ohms. What does that indicate?

Well in a few posts before I read from you ...

15 ECU to FV to OXS relay. 2.8 ohms

Which would fully comply to the specs.

So when do you read 2.8 and when 4.2?

[AndrewCologne]

Originally Posted by Funracer

Can someone please explain in detail how to check this. I am checking both the O2 plug and pin 2 for .5 VDC? Both with O2 unplugged? I have the fuel pump jumpered should I leave it like that or put the relay back in. Start the engine and check inside the O2 plug for .5VDC? Or can I just go to run?

Sorry for all the questions. I’d love to take a class in automotive electronics.

No, ... with everything at factory default plugged to the ECU, OX Relay etc, you just pull the o2 Sensor cable/socket from the plug in the rear left engine compartment.

Then you connect the DMM red connection to the contact of that (orange) plug, the other DMM connection to ground.

Start the engine or bridge the fuel pump relay in the fuse box at the front.
Both do provide current to the ECU. With the ECU powered, you read the DMM if it shows 0.5v.

[Funracer]

Originally Posted by AndrewCologne

No, ... with everything at factory default plugged to the ECU, OX Relay etc, you just pull the o2 Sensor cable/socket from the plug in the rear left engine compartment.

Then you connect the DMM red connection to the contact of that (orange) plug, the other DMM connection to ground.

Start the engine or bridge the fuel pump relay in the fuse box at the front.
Both do provide current to the ECU. With the ECU powered, you read the DMM if it shows 0.5v.

Done. It show .5 VDC

[Bob Kontak]

Originally Posted by AndrewCologne

Then you connect the DMM red connection to the contact of that (orange) plug, the other DMM connection to ground.

This is why you listen to the guys that have experience.

I was thinking you had to back pin out of the Lambda box connector at #2 and I would have no clue how to do that easily.

Now that it has sunk in what to do, I feel the fool and see you have already performed this test. Ha!

Just for discussion. Another simple test is to check the unplugged O2 sensor side of that connection while the car is running. Let it warm up and it should read between 0.1V to 0.9V. 0.1v indicating lean exhaust. 0.9V indicating rich. You literally can get your idle AF mixture roughly close to 14.7:1 by adjusting the 3mm adjusting screw until it reads 0.5V.

[Funracer]

Originally Posted by AndrewCologne

Well in a few posts before I read from you ...

Which would fully comply to the specs.

So when do you read 2.8 and when 4.2?

2.8 ohms was from the wire continuity resistance from ECU plug 15 to OXS relay pin 87A as in the Bentley diagram.

The 4.2 ohms was ECU plug 15 to battery negative post for ground. All the other pins to ground showed OL except 5 and 16 which are BRN ground wires.

[mysocal911]

Originally Posted by mysocal911

You should also disconnect the AEC with the engine running and check the the duty cycle.

Was this done? With that done and with the O2 sensor disconnected, the duty cycle should be close to 50%, if not the Lambda ECU is bad.
Again, the Lambda system is extremely simple to diagnose!

[Funracer]

Originally Posted by mysocal911

Was this done? With that done and with the O2 sensor disconnected, the duty cycle should be close to 50%, if not the Lambda ECU is bad.
Again, the Lambda system is extremely simple to diagnose!

I’m done for the day. I will do that test tomorrow afternoon.

[Funracer]

Interesting occurrence, at least to me.
Reconnected the O2 and fuel lines etc. Hit the starter engine started fine ran a bit rough but not to bad. Then shut it off intent on doing more tomorrow.

Then looked under the seat and realized I had not plugged in the OXS ECU connector!
Funny I would have thought it would not start or run with that not plugged in but it did.

Plugged it in and restarted. Ran super smooth but I have not heard it run for a few weeks so maybe that is why it sounded so good.

Tomorrow I will do the AEC test as suggested by mysocal911

Thanks again for all the troubleshooting help. All of you be well and stay 6 feet apart!

Later

[Funracer]

Originally Posted by AndrewCologne

@ Funracer
So when all ECU "pin lead to ground" checks result ok, then its also worth checking the inner part of the ECU for water marks or similair.

Looks pretty clean. Nothing burned or separated that I notice.

[AndrewCologne]

Originally Posted by Bob Kontak

Just for discussion. Another simple test is to check the unplugged O2 sensor side of that connection while the car is running. Let it warm up and it should read between 0.1V to 0.9V. 0.1v indicating lean exhaust. 0.9V indicating rich. You literally can get your idle AF mixture roughly close to 14.7:1 by adjusting the 3mm adjusting screw until it reads 0.5V.

Bob,
yes with o2 sensor unplugged ... this is a very useful approach to set up the base/initial CO setting and check the sensor. Well almost, cause with this you try to reach the lambda 1 ballpark (swinging between 0.1 and 0.9v) and before cat Lambda 1 on this engine will result between approx. 1.0 and 1.8 CO % vol. (forget about those charts in the www saying lambda 1 or even AFR 14.7:1 equals a 0.0 CO % Vol., even not measured after the cat). Then after re plugging the o2 sensor the duty cycle of the FV should swing around 50%. Just turn the CO adjustemnt screw a bit more CW till you get a swinging about 45% which gives you a noticable plus of enrichment when accelerating.

Nevertheless I dropped that antique design ECU and developed a new ECU device from scratch where only the original Case and its connector/socket exist for a proper plug'n play install. You can set up almost everything and its totally CPU controlled. Even compensating wrong WUR cold pressures are possible. An optimized WOT enrichment is possible via adjustment where wideband sensors are also supported and can even spot and keep a perfect achieved lambda 0.85 when accelerating.
Im using, testing and optimizing it since almost 1 1/2 Years and works nice.
The dutycylce now does not fluctuate with +- 15% anymore but only with small +- 5% and so also a nice smooth non oszillating idle is the result and no more of that "pull" feeling when crusing.



And every state of duty cycle, lambda, engine temp, sensor volt, etc can be checked via a LCD display. To that ECU you can even connect a 5bar pressure sensor signal wire (installed between the WUR and the FD) to for permanent control pressure monitoring.

[Funracer]

Way over my head but really cool. Maybe you will market them someday?

[AndrewCologne]

Yes, I will sell them on request.

[Sub8]

Originally Posted by AndrewCologne

Yes, I will sell them on request.

Nice idea. Rough cost, if that's allowed here?

I run the classicRetrofit CDI unit, couple that with the above and you've got a pseudo mapped SC.....fuel and spark.

[AndrewCologne]

Hi Sub8,

well, till now no production in series is planned. This is a private handmade prototype and it's tested since about 18 month. It's developed concept and coding routines are done by myself with assistance of an engineer of electrical engineering regarding the electrical assembly.

Further questions regarding costs or purchasing in this state via PM.

The classic Retrofit is a superb solution and Im thinking of purchasing one as well.
But regarding this ECU concept the thought of a "pseudo mapped" injection with still a K-Jet is not possible.

The solution above till now is totally lambda based, means till now no further hall sensors, no further mapping sensors or whatever need to be installed.
For optimal plug'n play compatibility without any further electronical modifications I kept the original wiring and sensor signals. Means the existing throttle switches i.E.
The only further swap which is needed is the little 15c switch on the right chain housing which will be changed to a 120°c sensor, enclosed with the ECU unit.

So the old ECU unit will simply changed with this one where the LCD-display – if connected – can be put into the ash tray for realtime reports while driving. Adjustments via software will be done via USB.



The optimal mixture will still be achieved by the frequency valve which is driven by this ECU as before. But as here a CPU is handling the whole job, its possible to optimize many engine running states like a smooth idle, direct and optimal lambda 0.85 enrichment at acceleration or WOT and ... the support of Bosch LSU based wideband sensor controllers on the market like Innovate, PLX, AEM is given. With that it could also be possible to achieve specific mixtures for idling, cruising and accelerating/WOT. I think thats your point.

It will work with the original unheated o2 sensor, the heated o2 sensor from the 3.2 Carrara and as mentioned above with wideband sensors/controllers.


While developing and testing I and two other testing people with the same 930/16 engine figured out many interesting behaviors of the K-Jet of these US SCs.