The MAF has 2 ground wires to / from at the ECU and a splice and is one wire at the MAF

The splice can be messed up to not providing the MAF a ground on the Black / White wire

And who knows what may be crossed wired from the previous owner

 

Pin 1 will be the only wire with 12 volts on it so the pin 2 will be the MAF ground

Note that you have 2 " ground " pins one for each IAT and MAF sensor

So that pin 5 will be opposite side of pin 1 ( 12 V so meter precaution when reading )

You have the AJ27 engine and the sensor may have come from a AJ26 engine of different wire colors ,

See thread

https://www.jaguarforums.com/forum/x...-please-76312/

This pic is for your AJ27



The term IAT feedback and ground may not be the correct term to use in the wiring guide breakout sheet in how the thermistor works

negative temperature coefficient (NTC) thermistor , the common resistor R would be inside the ECU , point A would be your reading after reference voltage applied by the ECU

So your ground on pin 5 would not be zero but the internal resistor and this would throw you off in troubleshooting

Pin 1 will be 12 volt power to the MAF

Pin 2 will be a true zero ground for the MAF

Pin 3 will be the return signal from the MAF to ECU of 1.2 volts DC at the proper idle speed

Pin 4 will be the reference voltage of 5.0 volts DC from the ECU to the IAT

Pin 5 will be the internal ground through the ECU with the " blocking " resistor inside in order to get a IAT reading other then zero volts out of the thermistor , Vout

 

This will be the key to tracing the wires first, and I would wager that once the correct wires are where they need to be, things will clear up. My weekend has been totally immersed in finding my tools and not blowing my cool. So, two complete days of sorting, tossing and arranging my shop and tools. Now, I can tackle that beast!

 

Working with the correct MAF sensor part # ?

Genuine Air Flow Meter And Hoses-4.0 Litre-v8 For Jaguar Xj 1998 - 2003 (from 812317 To F59525) Classic | Jaguar Land Rover Classic Parts

 

This is the new MAF previous owner put on.

 

It’s a complete gamble if the new aftermarket part is any good. I’d personally look for a used oem one and clean it out good. I’ve tossed many slightly used aftermarket MAF in the trash after the car comes in for running issues. I don’t just shotgun a guess at the MAF, I verify they’re no good by using a known good used oem MAF from one of our parts cars first then I look at the STFT & LTFT. I’m just saying that don’t dismiss the MAF because it looks new.