930 CIS Characterization

[Hokie6]

It seems that I've dived head first into the 930 CIS rabbit hole in an attempt to troubleshoot my '86 930 rough running issues. After starting out with the assumption that the 930 O2 ECU system was similar to the 911SC, I've come to realize that it's a good bit different in operation. I had actually concluded that my ECU was defective, but decided to reverse engineer the electronics and system before replacing it, and what I discovered was interesting. It turns out that the ECU was not defective, and the response is not what was expected. So, I'm hoping to document the system and present what I've found in the hopes that it may help others. There seems to be a good bit of info on the 911 system (911 CIS primer and others), but not much that I've been able to find for the 930 (please correct me if I'm wrong).

In a nutshell, the 930 CIS does not provide any fuel enrichment below 35° C - only above. Below 15°C, duty cycle is maintained at 50% in both open and closed loop mode. (This does not take into account the WUR which does provides enrichment at boost pressure)

Between 15°C and 35°C, the DC is again maintained at 50% while in open loop. In closed loop mode, the system will adjust DC from 10 - 90% striving to maintain a 14.7 AFR. The exception to this is WOT, where DC is held to 50%.

Above 35°C, the open loop response seems to mirror the 911 system, though enrichment is bumped to 75% (vs. 65% for the 911) and a few other differences.

Also, about 3k rpms, the O2 heater gets disabled. There seems to be a mistake in the wiring diagram, and my assumption is that the speed relay is cutting the heater out about 3k which shouldn't affect the operation (?). Still working on that one -

I need to spend more time on characterizing the closed loop response mode, and will update that in the future. Ideally, I would like to pull some sort of logical chart together (perhaps similar to the 911 primer). Perhaps if this is useful, someone could help out and pull together a 930 CIS primer site?

For starters, this is an overall schematic of the O2 ECU and Fuel Enrichment system that I've constructed -



This is still a work in progress, and may change in the future after I've had some more time to play with it.

Any thoughts or feedback would be appreciated -

Dale

[mark houghton]

I haven't delved that deeply into this subject but my thoughts are that what your discussing is the Lambda control system, run by a magic ECU under the drivers seat, coupled with an oxygen sensor and frequency valve (and a throttle position sensor?). The intent is mostly to lean out the mixture below a certain rpm (I don't recall what the cutoff rpm is, maybe 2000?).
You also mentioned the WUR creating enrichment on boost. True, but it also enriches things when cold and plays a critical roll in managing fuel control pressure to the injectors (excuse me, you already know that). So really, the Lambda and WUR are separate independent systems.
Personally I run and tune without the Lambda system by leaving the 02 sensor unplugged which keeps the frequency valve in constant 50% open loop. Keeps it from being forced to run lean at lower rpms (I think the original intent was for emission purposes to keep the catalytic converter hot). I don't run with a cat or functioning Lambda.
A good to have is the Bosch Fuel Injection and Engine Managment book. Great reference tool for our K Lambda.
Just my 2 pennies worth.

[RarlyL8]

The Lambda system is a piggy back on the CIS with the sole function being emissions reduction during idle and cruise. Another piggy back system that further complicates operation is air injection. I can guarantee that after 40 years neither of these systems is working optimally.
A lean condition is the typical Lambda system failure mode. Describe the rough running condition you are experiencing, when does it occur? What are the characteristics?
The CIS Primer is located on my website home page.

https://www.rarlyl8.com/

The plan was to add the 930 info but time has not permitted much movement on that. I'd be glad to include data on the Lambda system from anyone that wishes to submit their findings.

[mark houghton]

That's a nice primer Brian. I didn't know it existed.

[Hokie6]

Rarlyl8 -

You're welcome to add this to the CIS primer if it helps. Maybe it's best to send it directly to you so you can pull it together with the 911 CIS primer info?

I had a thread going about the rough running condition (Thoughts on poor running/ mixture?), but have put it on the back burner until warm weather returns. I currently have my '83SC engine torn down to fix an issue with smoking on start up. I look forward to the day where everything works the way it should!

[flightlead404]

I no longer run it in my car, but pretty sure that the O2 sensor/frequ valve system is only closed loop when at "idle".

what RPM defines idle I can't really remember. Mark mentions 2k above, I though it was 2,500 but I could be completely wrong. Above that speed and subject to the other constraints mentioned the system is at 50% dc.

[Hokie6]

It appears that the system will run in closed loop mode up to about 3000 rpm when the speed relay switches in, disconnecting the O2 heater and pulling the 15°C line low (ECU P7). This effectively sets the DC to 50%. I believe the WUR then controls enrichment under boost above 3k.

[PelicFrank]

This is awesome work! It’s great to see someone diving deep into the 930 CIS system and documenting the findings. I agree there’s not as much detailed info out there for the 930 compared to the 911, so your research will definitely be valuable. I’d be happy to provide feedback once you’ve had more time to finalize the schematic and closed-loop data. Keep it up, looking forward to seeing more!

[RarlyL8]

I have quite a bit of info amassed over the last few decades on the 930 (and 934) CIS including many conversations with German Bosch Engineers and those now consulting for Porsche classic. Jim Williams (creator of the CIS Primer) started to add my info then passed the Primer to me before it was completed. I will continue to keep it available to the public but don't know when I can get back to adding more 930 content. Jim was an Electrical Engineer who really understood the Lambda system. He repaired and modified many units. I on the other hand loathed the system and ripped it out at every opportunity. The Lambda function limits the 930 fuel distributors capacity, and you can't have that getting in the way of a good time.

[Hokie6]

Finally pulling everything together for characterizing the 930 CIS Lambda ECU system. It's relatively straightforward, though a bit disappointing as there isn't much in the way of enrichment as I was expecting like the SC system until temps > 35°C.

Hopefully this will help someone out in understanding the 930 CIS Lambda system better, and aid in troubleshooting -

Here is the characterization chart:




The main take-aways are:

1) On power-up, duty cycle is held to 50% for about 1.5 minutes, or until starter is
activated. Operation then continues as follows:

2) Below 15°C (or RPM > 3k), no enrichment or Lambda operation occurs. Duty
Cycle (DC) is held to 50%.

3) Between 15°C and 35°C (RPM < 3k), no enrichment occurs, but Lambda operation
is active in closed loop mode. The O2 sensors and ECU adjust the DC of the timing
valve to help maintain a mixture of ~14.7 AFR. DC is held to 50% at Wide-Open-
Throttle (WOT).

4) Above 35°C (RPM < 3k), enrichment only occurs from Idle -> Tip-in (TI), and TI
-> Cruise for about 3 seconds. Lambda operation is active in closed loop mode. The O2 sensors and
ECU adjust the DC of the timing valve to help maintain a mixture of ~14.7 AFR.
DC is held to 50% at Wide-Open-Throttle (WOT).

5) For RPMs > 3k, DC is held to 50%. Lambda operation is blocked and no
enrichment occurs. O2 sensor heater is disconnected from power.

6) Boost pressure of ~0.5 bar to WUR, enriches mixture (taken from
manual) (above 3k)


It's interesting to note that the 911SC provides some enrichment (>50%) across the board , yet the 930 only provides enrichment above 35°C. So, what were the Bosch/Porsche engineers thinking? Was this a change for emissions? Or turbo related? The ECU and fuel enrichment modules are not that different, and it would be interesting to see how the 930 responds to changes to make it similar to the 911SC by modifying the electronics.

[RarlyL8]

Lambda in the 930 application is strictly an emissions control item. Enrichment is a function of the WUR with boost reference. The SC functionality is different, there is no boost so no need for extra enrichment. There is no vacuum reference as the Lambda system can perform enrichment to the degree needed for the non boosted engine. The non-Lambda SC WUR uses a vacuum port to lean out the mixture at idle and cruise, when the engine is not under load. I believe the only thing the engineers had in mind was satisfying smog certification regs, no finicky manual tuning required to get the %CO to such a low level.

[Hokie6]

The 930 is well known for being a slug below boost, so it's surprising to me that there is nothing supplied for tip-in below 35°C as with the SC. Comparing the WUR cold CP, there is really not much difference between the 930 and SC units (non-boost), yet the SC runs 60% DC; the 930 50%. Between 15°C and 35°C, the SC provides a short 75% DC on throttle transition, and 65% WOT. Nothing for the 930. Above 35°C, the 930 provides some enrichment on transition, but WOT stays at 50%. This is all below boost. Obviously the WUR enriches the mixture on boost, so no need for the electronics to provide anything there. Maybe the thought was that the car didn't spend much time below 35C, and there were issues with emissions during this time. Dunno -

In troubleshooting the running issues with my car, I really thought the ECU was bad because it did nothing (except for the Lambda operation) below 35C. This what started me on the journey of characterizing the ECU system, and it's been an interesting learning experience. I did find that my 35°C switch was inoperative, so hopefully that will make a difference in performance. It'd be interesting to modify the system to provide enrichment below 35C, as providing some enrichment on throttle transition should help waking it up a little before boost? Maybe as a future project -

[flightlead404]

Originally Posted by Hokie6

Finally pulling everything together for characterizing the 930 CIS Lambda ECU system. It's relatively straightforward, though a bit disappointing as there isn't much in the way of enrichment as I was expecting like the SC system until temps > 35°C.

Hopefully this will help someone out in understanding the 930 CIS Lambda system better, and aid in troubleshooting -

Here is the characterization chart:




The main take-aways are:

1) On power-up, duty cycle is held to 50% for about 1.5 minutes, or until starter is
activated. Operation then continues as follows:

2) Below 15°C (or RPM > 3k), no enrichment or Lambda operation occurs. Duty
Cycle (DC) is held to 50%.

3) Between 15°C and 35°C (RPM < 3k), no enrichment occurs, but Lambda operation
is active in closed loop mode. The O2 sensors and ECU adjust the DC of the timing
valve to help maintain a mixture of ~14.7 AFR. DC is held to 50% at Wide-Open-
Throttle (WOT).

4) Above 35°C (RPM < 3k), enrichment only occurs from Idle -> Tip-in (TI), and TI
-> Cruise for about 3 seconds. Lambda operation is active in closed loop mode. The O2 sensors and
ECU adjust the DC of the timing valve to help maintain a mixture of ~14.7 AFR.
DC is held to 50% at Wide-Open-Throttle (WOT).

5) For RPMs > 3k, DC is held to 50%. Lambda operation is blocked and no
enrichment occurs. O2 sensor heater is disconnected from power.

6) Boost pressure of ~0.5 bar to WUR, enriches mixture (taken from
manual) (above 3k)


It's interesting to note that the 911SC provides some enrichment (>50%) across the board , yet the 930 only provides enrichment above 35°C. So, what were the Bosch/Porsche engineers thinking? Was this a change for emissions? Or turbo related? The ECU and fuel enrichment modules are not that different, and it would be interesting to see how the 930 responds to changes to make it similar to the 911SC by modifying the electronics.

Possible to get larger/original size chart? I'd like to keep that handy

[Hokie6]

Possible to get larger/original size chart? I'd like to keep that handy

Send me a PM with your email, and I will get those to you -

[barton121]

okay great.