Question. Disco 2 99-02 and 03-04 has different part number for that part. i cant find any difference in pics. Is there is one?

Thx!

 

99-02 = 4.0L V8 which had a smaller intake tube/MAF body/air box lid. The 03-04 4.6L had a slightly larger intake tube/MAF body/air box lid. However the MAF sensor itself = identical.

People will argue with me here, but you can run either of those on either engines. Reason I say this = the Throttle Body Assembly on both engines are 100% identical. Which means the difference in performance is so TINY LR didn't even bother to bore out the 4.6L TB housing to actually allow more airflow into the engine.

 

Thank you for the detailed answer!

 

No problem

 

The only issue with running an early MAF housing on a later truck and vice versa is that the ECU will register different amounts of air because the sensor itself takes up a different percentage of the cross sectional area of the housing. This means the smaller housing will cause the truck to run more rich, and the bigger housing will cause the truck to run more lean.

 

Yeah that makes sense, but I haven't noticed any difference in my 04 with the smaller tube. I had to replace it due to the original falling apart and I couldn't locate a good 4.6 unit.

 

Partially correct, if the 02 work fueling is controlled completely by 02, MAF only in play if 02s are dead.

 

Ignoring the fact that this engine management system apparently manages the mixture solely by exhaust emissions, this is not how I understand the MAF to work. Feel free to correct me if I'm wrong. The ECU is measuring the amount of voltage required to heat a wire to a specific temperature, The volume of air passing over the wire will reduce the temperature accordingly and this fluctuation is how the ECU determines air mass entering the engine, and subsequently how much fuel to add. Also, velocity will increase using a smaller diameter intake into an identical throttle body in front of a larger displacement engine. This should help even out any cross-section variance. I've added a larger throttle body to one of my cars without adjusting the diameter of the MAF housing and the ECU had no trouble keeping the mixture stoich. Finally, the engine should not run lean or rich due to a larger or smaller MAF housing, as it's the ECU's job to adjust the fuel level to match the air volume via O2 sensor output..

 

You've got it mostly correct. ECU control strategy is one of redundancy and priority. The ECU takes some basic inputs, ECT, MAF, RPM, TPS, and looks at a 3d fuel map. That gets it in the ballpark, then it uses the 02 for closing the loop. If the 02 tells it to adjust too much, you get a fuel trim max error code. The changes discussed in this thread do throw off the maf reading, but apparently not enough to throw a trim code. Sometimes injectors leak, sometimes they are plugged a little bit. The 02 closed loop adjust for that in a way the MAF cannot.