CIS - Pressures in spec, but lean reading with Innovate controller

[sigchuck]

Hi guys, I have somewhat of an oddball question for an oddball engine. I have an 83 SC 3.0 motor with early 930 CIS (and accompanying turbocharger). The system pressures and control pressures are all in spec, but I'm getting lean readings with my Innovate LC-2 controller. I've confirmed I have a real (or compelling counterfeit) Bosch 4.9 sensor, re-calibrated the sensor, moved the o2 bung to after the turbo, but still lean readings.

I guess I ultimately have a couple questions, and maybe there are some others I haven't thought of:

1. If my pressures are good, should the engine otherwise be running lean (both under boost and not)? I would think no, probably especially since I have the 930 CIS on a smaller motor, but any thoughts?

2. If the sensor is bad, would it still kind of be working? It's not pegged at full lean, just about 1-1.5 points above where I'd like it. It also seems to fluctuate with engine load, so I don't think it's "dead".

3. I've tried two different WURs - one freshly rebuilt and another a known good part, both with roughly the same result.

Thanks for the help and please don't hesitate to let me know what additional information might be helpful.

[sigchuck]

One additional question - I have headers with a slip joint that are still fairly new (probably 500 miles or less). I'm not hearing an exhaust leak, but has anyone ever experienced one with a slip joint that hasn't fully "set"?

The lean reading doesn't really improve as the exhaust heats up, so maybe this is a non-issue.

[Schulisco]

Hi.
Didn't understand your setup. Do you have the 911 SC engine equipped now with a turbocharger? And is the CIS still stock from the SC?

My personal experience with the Bosch O2 sensors together delivered within the Innovate lamba gauge is not the same quality as the original Bosch purchased seperately. Don't know why. I would replace the Bosch that came with the gauge.

Thomas

[sigchuck]

Hi Thomas, it’s an SC short block with the induction, fuel and exhaust systems from a 930. So there should be plenty of fuel.

Since posting last, I have confirmed the gauge is accurate and set up a dedicated relay to power the controller - same results, unfortunately.

Is the sensor failure typically binary - i.e., it works or it doesn’t, or does it slowly fail - i.e., it starts sending bad values.

[Chris_chch]

I'm picking that the "in spec pressures" are not in spec for the combination you have.
If you are using the SC spec, then it will be wrong, as the 930 system measures and delivers at a different rate. And vice-versa, if you are using the 930 CIS pressures, its calibrated for a low compression 3 liter engine with possibly different port sizes?

You really need to tune this to suit.. Ignore the spec pressures.. I've got a modified 930 and the pressures that actually work, are quite different to the stock pressures.

Just lower your WCP until you get a better AFR. Will need a bit of messing about with.. Its a real juggle to get them just right

[icarp]

You are in deep.. There is alot to know to make this work
You must have a Turbo WUR , there are adjustments to make for your boost , comp ratio
Size of compressor wheel, lots more . Not for the novice
You can burn through a piston in less than .5 second,,,, actually 10 times faster than that.
I advise you work with someone in person to achieve your goals .
Just my thoughts ....

Ian

[Schulisco]

Originally Posted by sigchuck

Hi Thomas, it’s an SC short block with the induction, fuel and exhaust systems from a 930. So there should be plenty of fuel.

Since posting last, I have confirmed the gauge is accurate and set up a dedicated relay to power the controller - same results, unfortunately.

Is the sensor failure typically binary - i.e., it works or it doesn’t, or does it slowly fail - i.e., it starts sending bad values.

So you're running a higher compression ratio than the stock 930? I'm not in the 930, no experiences and poor knowledge. But afaik the CR on a 930 is roughly about 6,5-7 compared to a low CR us SC engine with at least 8,5 up to 9,3...these are massive differences! I guess with that CR the engine urgently needs twin spark ignition and massive other changes beside the standard CIS equipment of the 930. You know - the leaner the mixture, the quicker the engine will knock heavily and suffering damage, as Ian already wrote.

The SCs normally have the cold start valve (CSV) in the lower airbox housing on the backside, it is normally operated by the thermo time switch (TTS) while cranking the engine only. At first "workaround" I would install a push button near the drivers seat to operate the CSV while driving and pushing the throttle to enrich the mixture and to see what the engine does. Mandatory is a lambda gauge to control the mixture. Ignition should be way more conservative than stock SC and as well 930. Max. 12-15° BTDC for the very first beginning under load. Exact ignition values must be determined on a dyno together with a knocking tool and with the lambda tool in parallel. Anything else will risk the engine...
Although I like the CIS system - in your case I would prefer to apply a modern free programmable ECU - with knocking input, ignition control etc. I'm curouis about the numbers this setup will produce...good luck!

Failing OXS sensors: Afaik the narrowband sensors will normally die slowly, they will reduce the voltage signal, it's getting more and more narrow over time or if they have been poisoned (running with way too rich mixture or oil in the exhaust fumes for too long or flames or other problems from the engine). The other reason for a sudden death are mechnical shocks (let them fall on the ground or putting them too hard on surfaces). On wideband OXS sensors I guess there will be more and more confusing signals or they stop signalling. There are some manuals available on the net how to diagnose a faulty OXS sensor.
E.g.
https://www.ngkntk.com/products/oxygen-lambda-sensors/
https://www.boschaftermarket.com/xrm/media/images/country_specific/sg/services_and_support_6/downloads_18/lambda_sensors.pdf


Thomas

[sigchuck]

Thanks, Thomas! I will take a look at those manuals, but did get a new Bosch sensor today. While the controller shows that the sensor is warmed after about 30 seconds, it's not sending much of a signal for another 30 seconds, so I'm hoping it may be a failure.

Yes, very much agree it's an oddball set up. I do have ignition timed very conservatively with the ability to retard on boost. Since the AFRs started floating up, I have kept it off boost. My initial AFR readings a few months ago (with a brand new sensor) were great under boost and in the 12s. While I'm hopeful it will be the sensor, there is some logic behind it as opposed to blind wishful thinking.

Just to reiterate, all CIS parts are 930 and the referenced spec corresponds to the parts (e.g., 930 system pressure, CCP, WCP). If the new sensor doesn't give lower readings, I'll definitely attempt the WCP adjustment on one of the WUR I have. With that being said, EFI is starting to look very tempting.

[spuggy]

Originally Posted by sigchuck

Is the sensor failure typically binary - i.e., it works or it doesn’t, or does it slowly fail - i.e., it starts sending bad values.

My understanding is that, as they age, they respond slower to AFR changes. If they get contaminated they will eventually stop providing a useful signal at all - eg an ECU will disregard the signal/mark ERROR because it's out-of-range.

Sensor lifetime will be drastically reduced by running any lead at all in the fuel - eg 100LL at the track - and there are other chemicals, such as sealants etc - that will also poison the sensor,

Free air re-calibration can help by adjusting the sensor's bias/offset to match what it is currently reading and get a bogus signal back into range. But can't/won't affect the "slow-to-respond" symptom.

[spuggy]

Originally Posted by Schulisco

My personal experience with the Bosch O2 sensors together delivered within the Innovate lamba gauge is not the same quality as the original Bosch purchased seperately. Don't know why. I would replace the Bosch that came with the gauge.

I have no personal experience with the Innovate lambda gauge. But anecdotally, I seem to recall back in the day/when they were popular, lots of people with the Innovate used to complain bitterly about how often they'd have to do a free air calibration of the sensor. Which folks with other AFR meter setups using the same sensor didn't do...

I bought a Bosch 4.9 sensor from Amazon to replace a contaminated one, and it behaves entirely as expected. I'm very happy with it.