The MAP reading is listed by the OBDII reader. If there is not a sensor (I haven't searched to find out) then I am not sure what information it is pulling for 'MAP psi'.

I reconnected the stock MAF and intake, did a hard reset, and will see where the trims go with that in place.

 

map sensor is on the rh intercooler if I remember.

Did you disconnect the battery when you swapped tb's?
Air leaks from the crush gasket fitted underneath, as they're one shot they need to be replaced each time the tb is changed.
I've seen serious botches with sealant and whatnot before to cure this unmetered leak.

 

Yes, the battery was disconnected when the TB was removed and replaced. No, a new crush gasket was not used. Thank you for the suggestion!

 

The sensor on the RH intercooler is intercooler air temperature. I do not believe there is a map sensor on an X-308 SC.

 

@spark my memory isn't the best as it's a long time since I've delved under the bonnet for issues!

WTF is this then? LNF1622AA?? SENSOR-MAP 100798-5230 DENSO JAPAN???????

This is connected to the throttle body usually, when I installed one of my R engines I had a hissing noise, a major unmetered air leak....this tube connects to a 'T' if I recall and it might just be the leak you're trying to find Dan. (snapped T, unhooked from the system in some way, look for small black tubing that connects to the MAP if it's not going into the bottom of the MAP there WILL be a leak....the MAP is on a bracket next to the wiper motor assy, remove the centre bulkhead cover to see it. The tube is attached usually with a small cable tie to keep it tight on.

I hope this fixes it

Sorry Spark, 1-0 lol!

 

My memory ain't so good either! In fact, the AJ26 engine, which is what is in both of my XJRs does not have a MAP sensor, but indeed the AJ27 SC engine does! (I did not think I could have missed that)
Apparently, though, according to the Jaguar training manual, it is not used in fuel mapping, but only as part of the evap system. And, unfortunately, it is between the throttle plate and the SC, so it cannot be used as a boost gauge either. But yeah, you are right Sean, if it has a leak, like any other part of the air plenum system, it will play havoc with fuel trim. Anyone wanting proof should monitor their STFT and pull out the oil dipstick- watch the STFT rise!

 

I want to make a couple of points.

I have many times before commented that the STFT pid should be utilized in diagnosis only very rarely. STFT normally bounces around wildly during engine operation. That is it's function, to counter IMMEDIATE perceived fueling errors. It's other function is to purposely drive the fuel system back and forth across the zero correction threshold. That sets up the sinus rhythm in the O2 sensor operation, so the ECM can monitor the O2 sensors and know all is well. When that sinus rhythm is upset it can also respond.
You should also forget about the idea of 'total correction'. While an instant where you have +15% ST and +15 LT does equal a total correction of +30%, that is ONLY an INSTANT. The next moment will give something else, say, -18% ST and +15 LT. That instant your total correction is -3%. Get the picture??

Now for a diagnosis tool, STFT can be of value, just like Ross indicated with the dipstick comment. I used that very thing in my Fuel Trim paper a couple years ago. By pulling the dipstick and watching the STFT response, you confirm the system is working and responding. By watching STFT and spraying a combustible like carb cleaner on a suspected vacuum leak, you can confirm the leak if the STFT goes negative when you spray.

But normally, you should basically ignore the STFT. It only becomes important if it begins to TREND one way or the other. When it TRENDS positive, you will confirm that when the LTFT shifts positive to compensate. When that happens, the STFT stops TRENDING positive and TRENDS back to zero. Attached is a screen of a diagnostic session after a purge valve repair. This confirmed the repair was good. This is a 20 min. drive monitoring LTFT in the various RPM and Load Ranges. All load ranges are with a LTFT very near zero, that's perfect, I'm happy that my repair is confirmed. Now look at the table at the lower left. You can see the upper and lower extremes [min/ave/max] in the columns. You can see the LTFT stayed quite low. Now look at the STFT. That went from -18% to +21%! And this car is operating perfectly! This is my point, the STFT has value, but only limited value to us for diagnostics. The LTFT is what really tells the story.

Now, to the OP's MPG complaint. The fact this has occurred with two different engines, and seemingly with or without the modified pulley, I question whether the trans torque converter clutch is operating. If you don't have the TCC locked, the usual hit is about 3 MPG. I would try to confirm the TCC operation, even if you have to see a trans shop for assistance.

 

As suggested by XJRGuy, I hooked up my OBDII scanner, started the car, and got out my can of carb cleaner. While watching the STFT %'s, I sprayed the cleaner in different areas that have been suggested as possible leak sources. As XJRGuy said, the STFT % will decrease or go negative when the cleaner hits a leak. And, it did. As suggested by Sean, the area around the base of the TB where we should have used a new gasket (but didn't) sent the % strongly negative. So, I will order a new TB gasket. While I am in there I will also replace some of the rubber vacuum hoses and connectors that people have suggested as possible leak sources.

I will post an update afterward. I may still look into the TCC solenoid after getting the leaks removed if my mileage does not change much.