Cam upgrades and fault codes

Hey everyone, It has been a long time since I've posted on here, haven't had the time. But now I've got a pretty serious problem that I'm having a hard time figuring out. This same question is posted in the engineering/technical section for a little better exposure, and I figure it fits both of these categories well. This forum has been immensely helpful in the past even with the most difficult of questions, so here goes...

Land Rover Discovery 2's will typically throw a P0734 4th gear ratio incorrect fault when the MAF goes bad. Do any of you know why? I've got a few suspicions but am fairly certain that they are all wrong.

That leads me to the real problem. I've currently got 2 of these vehicles in the shop, one is an '04 that had a 4.6L V8 stock, the other is an '00 that had a 4.0L V8 stock. Both had fried their engines and were replaced with re-built 4.6L V8's with big aftermarket cams, same cam in each. Both have new MAF's. Both are throwing P0734. The '04 was throwing P0300 codes as well until I installed an older ECU from a 4.0L truck. These are both Bosch controlled engines. This same cam is running perfectly in my own truck and another customer's truck, but both of those are '96 MY's with Lucas engine management, mine a 4.0L, the other a 4.6L. Two other customers have big cams in their Bosch 4.6's, though not quite as big as these two, they're not having any issues.

So do any of you have any idea as to why this would be or how I can remedy it without replacing the cams? :confused:

Thanks for any input or speculation! :smile: