3.6 Transplant issue with the o2 sensors.
 

Been a while since I last posted on here, have had my head down for the last 3+ years trying to get the 3.6 transplant completed on my Boxster racing car (with some family and work related interruptions)...

I am 99% done and race ready, but have a strange issue I can not fix and wonder if this is due to incorrect conversion from 7.2 to 7.8 DME and the changes in pin allocations, or something else - Might even not be a problem at all?!?

So I have a 2000 Boxster S racing car, and have installed a 2002 996 3.6 engine along with the 7.8 DME, everything looks to be running and working and I do not have any errors registered with the Durametric (apart from stuff I have removed as it is a racing car). But when I look at the live values for the o2's I am getting no adaptation values - they are stationary as follows:
.- Adaption range 2 (FRA) bank 1 = 1
.- Adaption range 1 (RKAT) bank 1 = 0
.- Adaption range 2 lower (FRAU) bank 1 = 1
.- Adaption range 3 uppper (FRAO) bank 1 = 1
.- Adaption range 2 (FRA) bank 2 = 1
.- Adaption range 1 (RKAT) bank 2 = 0
.- Adaption range 2 lower (FRAU) bank 2 = 1
.- Adaption range 3 upper (FRAO) bank 2 = 1

I can not figure this out, and either:
.- I have removed a component from the system which is preventing the dme from running adaptation (I removed all emissions stuff - racing car)
.- There is an issue in the Durametric?
.- The pinout for the o2 connectors are not the same between the 7.2. and 7.8 dme as indicated in the factory manual I have been working from? (I did disconnect the o2's and start the car and instantly got error codes on the Durametric)
.- Everything is working as it should, and I do not understand how to read the live values in the Durametric?

Pulling my hair out here, any pointers or advice?

I have been trying to find definite descriptions of these terms for a while and have had limited luck. From what I have cobbled together from the interwebs is this;


These are all long term fuel trim adaptations.

rkat is idle adaptation and should be at 0.

Fra is running adaptation and should be at 1.

Frau/frao are different load range for the running adaptation. Cannot find defined rpm or load ranges, but they should also be at 1.

Here's the best single website I have found about this.

https://www.callasrennsport.com/blog/porsche-986-996-987-997-fuel-trim-information

In other words, your fuel trims are perfect!

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Thank you for your input and good link.

You are correct, in theory based on the numbers my engine is running perfectly, but I did a run with the Durametric attached and the numbers NEVER change, so no adaptation at all, and this can ot be correct.

I did some searching and found this discussion from some years back where someone in Germany has the same problem with a racing car that has been modified in very much the same way - but the discussion was never concluded and he never posted the results or fix :(

https://www.renntech.org/topic/53016-afr-values-not-adapting-rich-injection-time-too-long/

If this is a race car why are you worried about O2 sensor signals or fuel adaptation related to O2 sensors?????

Because the signal from the pre-cat o2 sensors is used by the dme to adjust the air / fuel mixture. At the moment my car is running in open loop, which is not giving the best ratios at best, and will make the car run lean at worst.

Yes the DME uses the signal from the O2 sensor to adjust air/fuel mixture.
But it does that to regulate the temperature of the catalytic converters.
O2 sensors and fuel trims are about catalytic converter performance.
Not engine performance or power.
If this is a race car I assume you removed the Catalytic converters.
If you did remove the catalytic converters then your O2 sensors are serving no purpose.
Open loop fuel maps will work just as well or possibly better for power.

14.7-1 is the best ratio for lower emissions.
Not the best ratio for power.

Narrow band O2 sensors as used in these car are not very accurate at anything but 14.7-1
Also they don't even measure outside of about 1% away from 14.7-1

Interesting, and good to know.

i do still have racing cat converters, as they are stipulated in the regulations. But I am focused on performance of the engine and not the converters. So you are saying that I do not need to worry about the adaptation of the fuel mixture by the dme?

I thought the pre-cat o2 sensors were to manage fuel mixture and the post-cat o2 sensors were for emissions?

If you have to have Cat converters then you do need adaptation of fuel mixture so that the Cat converters function correctly.
The air /fuel ratio that allows Cat converters to work is not the same air/fuel ratio that makes power.
You can't have both at the same time.

Pre-cat O2 sensors are to manage fuel mixture "for Cat Converter function" Post cat O2 sensors monitor Cat converter function to make sure pre cat O2 sensor are doing there job.
They are both for emissions.

Google: Catalytic Converters find the Wikipedia article on Cat Converters.
Read the whole article. Pay particular attention to the segment on "Three way Cat. Converters".

You are correct, the precat sensors adjust the fuel mixture. As blue said, it is related to emissions. Performance is a big factor too though. If you lean out beyond 14.7, you get a more complete burn of the fuel (14.7:1 is stoichiometric but in the real world, especially with our style injectors, it does not result in a complete burn) which will result in more power but also MUCH more heat. This will damage cats, but it can also damage the motor. On the other hand, while you start to lose caloric efficiency as the mixture becomes more rich, you gain the cooling effect from unburned fuel and this helps the motor perform better at sustained high loads. That is why open loop should run a bit on the rich side. The excess fuel will damage cats though, so there's another tradeoff.

You said youre stuck in open loop? I don't see how that's possible if you're not getting a CEL. That's just not how the dme is configured to operate. Additionally, even if you have a ROW tune, the dme is still looking for the precat sensors. If they're not there, the dme will throw a CEL.

If you're really concerned about this, get an aftermarket AFR guage wide wide band sensor. Bosch makes an excellent sensor and the kits are not expensive or difficult to install. They mount into standard sensor bung (m18x1.5) and easy to install. I ran mine up the back side of the engine bay, under the intake plenum, and through the center console tunnel up to the dash, less than an hour start to finish. It will give you a much more meaningful number to use.

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Installing an aftermarket AFR guage is a good idea. Can I install this in the bung I have for the post-cat o2 sensors, as I do not need these. Or do I need to install the AFR before the cat?

The best position for a wideband sensor is in the header collector. Post cat exhaust is leaner than the gases in the header/collector. How much leaner depends on a lot of things. I know some guys will temporarily clip an afr sensor in the end of the tailpipe for reads while tuning. I don't have any direct experience with this technique by you may want to just try it and see how your reads look. If they look off, then I would install it precat if possible.

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