I'm curious to hear what the A/F ratios others are seeing.
Seems the 4.2L XKR's are calling for a 10:1 range (Really fat) at WOT

Per a few dyno charts I've seen the 5.0L XKR's are calling for a 12.5:1 at WOT

Are others seeing this?

Ideally the best performance for a supercharged engine is in the 12-12.5:1 range, not sure why the 4.2's are set so rich.


Second question would be:
Has anyone discovered a way to get into the stock ECM and adjust the MAF tables and timing?
I know there are tuning options out there, However I'm not sure if these are standardized XKR-S tunes being dropped on the ECM or if they are actually tuning the A/F and timing.

I'm contemplating a piggy-back style system between the MAF and the O2 sensors so that I can control this. Ideally it would be much easier if I could adjust the Called A/F in the ECM.

Regards,
D. Fricke

 

I doubt that the stock sensors are wideband, so I don't think a piggyback with the MAF will net the functionality you're looking for.

When you say, "calling for" a 10:1 AFR in the 4.2, what are you referring to? The 12-12.5 AFR at WOT on a dyno chart is from a wideband sensor measurement... usually one that's been temporarily run up the tailpipe by the dyno operator.

Apologies if you already know all this. But agreed: a wideband-measured 10:1 is pig rich.


Rich

 

With the Jaguar IDS tools you can read the values from the wide band sensors, though you get an amp reading, which you need to translate.

I guess it has more to do with safety/longevity to have it rich, though your numbers look richer then I would have expected, the 4.2 engines are normally above 11 or so iirc. This could be a faulty reading, or there is something else at play.

 

Yes Rw99 this was with a tailpipe sniffer and Innovate software. The baseline a/f is around 10:1 which is very rich for a stock tune. I've seen a few dyno sheets with this engine and seems the stock tune is set to this.
By "Calling for", I am referring to the MAF transfer function table.
The stock table values I believe are set to desire this rich ratio on the 4.2. I will need to verify with the IDS tools as Avos mentioned.

I agree on the piggyback not achieving the functionality I'm looking for. It is possible, but when in Closed-Loop tuning will be quite the headache. I'll need to do some research on the MAF and Front O2's to determine the best approach to deal with the fuel trims.
Ideally, I need to just get into the factory program and adjust the tables.

With the plans I have for the engine, I would feel more comfortable knowing I'm able to control these values and have an "engine happy" tune.


Thanks for the reply guys.

Regards,
D. Fricke

 

Stock sensors are wideband. 10 looks wrong i.e. something wrong with the measuring or car has a fault you don't know about, as others have never seen 10 - see various dynos posted over the years.

 

Thanks, I'll do a few more pulls and sample farther up stream to see if this gives me a more accurate reading. I do not have any faults currently and the engine is low mileage (which doesn't mean a sensor could not be failing)

I have not been able to locate any other 2007-2008 4.2 dyno charts with A/F. My guess is they may be running this rich to keep the CATS hot for emissions. If anyone knows of a location, please paste reference in a link or post. Thanks.

I'm investigating an ideal way to adjust this A/F with minimal negative effects. I'm thinking about developing a module between both MAF's and ecm to manipulate the resistance therefore controlling the fuel at WOT. There may be some open loop to closed loop tune-ability, so I can simply make the unit switchable. This way I can dial in the A/F for WOT where desired.

 

People have posted dynos for other 4.2 R cars such as STRs - same engine.

 

Thanks, Yes, same base engine, however minor differences in throttle inlet, VVT (depending on year) and I'm sure tune as well as base HP. Thus, I would like to compare apples to apples vs. making an assumption that the same a/f was desired in the ECM.
If someone has a 2007-2008 that can post a un-tuned dyno and A/F that would be great.

Thanks for the help.
-D. Fricke

 

Interesting project, maybe you will glean some well sought after info for tuning these motors. I did get a baseline dyno last year and the facility was supposed to have done an A/F but after they did it and the ratios were missing they told me the wideband was malfunctioning, so sadly no help there. Hopefully someone else has done it, though I am not aware of anyone here who has done a tune on the 4.2. I also suppose someone with IDS and a tune could provide before and after numbers for ratios, trims and more.

 

I'm thinking about purchasing the Jaguar IDS as well so that I can monitor the STFT AND LTFT functions in relation to MAF.
I'm hoping these engines stay in open loop during WOT as I have had experience with past Ford Projects. I know Ford recently (2011 I believe) switched to staying in Closed loop during WOT which can be a headache to tune if these ECMs do the same.
If the setup stays in open loop, I can alter the MAF voltage to reflect the leaner desired A/F but also give me full adjustment to A/F at any point. What I'm thinking I will do is have this controller switchable based upon throttle voltage. At WOT , the unit can turn on and only adjust during this scenario. By adding in a WBO2, I can monitor the WOT A/F and constantly adjust voltage to both MAF across range. With making a minor tweak from a 10:1 ratio to 11.8:1 I do not see the ECM taking any timing out and I should be able to see the desired power increase.
Certainly a learning process, but I believe the logic works.
Assuming all goes well, this also opens the door for higher lift or altered cam duration.
I would rely upon a tune if I felt confident that the tune was not a standard tune. Per what I'm gathering with lack of information provided about how these tunes are being created, I'm thinking the tunes are simply the XKR-S ecm programming read out and dropped onto the XKR ecm. I have not had a tuning company contact me back to clarify if A/F and timing are parameters they can adjust.

Regards,
D. Fricke

 

Jaguar makes the SC cars rich so you don't blow a hole in the piston from pre-ignition. Nothing to do with the cats.

With a forced induction motor you can blow it up in micro-seconds with a lean condition. The engine electronics are set very safe so the bypass valve will open to reduce boost and the timing will be pulled back.

But both of those take time. The rich mixture is there all the time protecting the engine until those other techniques can be used to reduce the intake temperature.

What hot rodders found out is if you can lean the mixture just a bit under boost you will gain power. This is because the engine should run on stoichiometric mixture (regular people call this the air-fuel ratio) for best power. For a gasoline engine this is usually considered to be about 14.7-15.1 to 1.

Jaguar had to balance power output against engine safety. So since they have to warranty the car they went safe. It worked because you don't hear about Jaguar SC engines blowing up!

We have been told that VVT does not add much to a SC motor. I don't know if that is true or not. Supposedly the reason Jaguar added VVT to the 2006 and up 4.2L was for emissions reasons and not added power.
.
.
.

 

More power... how much is wanted cos you have to spend more to get more as you know. Leaner is risky but safer is any of NOS, better intercoolers (*), better SC such as TS (twin screw), etc.

(*) monitor IAT2