So I do alot of side jobs on rovers, I have rebuilt so many D2s I can't even count and have never had this problem. 2004 discovery se with the 4.6, customer asked for more power, I guess it could bearly get up hills, he dropped it off as a non runner and to my surprise he somehow melted the wiring harness coming from the fuse box, it found its way on to the manifold and caused so many problems. I replaced the harness and during so found that he blew a headgasket and the engine was toast. I pulled it took it all apart and sent it to the machine shop had the heads shaved and block pressure tested ect. For power I thought maybe a high lift cam will help so when I rebuilt it I put a half inch lift cam accompanied with a cool air intake and high pressure fuel pump. After putting the engine back in it ran perfect with no codes except a permanent voltage supply code. It had some leaks I spent the last couple of days fixing and today when I took it out on the road it had absolutely the worst acceleration I have ever seen it's so bad it would take all day at open throttle to get a 0-60 time. I have never had this issue with one of these usually I rebuilt it, it runs great and it's on to the next but at this point I'm at a loss. Any ideas would be greatly appreciated almost everything is practically new, the only codes present are permanent voltage supply, then for abs it says rear left and right sensors are open circuits.

 

Try running it with the exhaust unbolted from the exhaust manifolds and see if it runs better. If he ran it a long time with the blown head gasket it is very possible the catalytic converters are clogged up.

A compression test on all 8 cylinders also wouldn't be a bad idea to make sure the motor is happy since reassembly.

 

compression is good thats one of the first things i checked but may be on to somthing with the catalytic I'll check and post results

 

Not in a Rover, but I had a similar situation in a Volvo 240 where the car had no power, couldn't get out of its own way, like it was gasping for air, and it ended up being a bad converter.

 

I had a 4.7 Dakota that I was always disappointed with for power. When I removed the cats I picked up 15kmh on a nearby steep grade highway.

 

After repairing a fried harness have you checked the charging voltage?

if she isn't getting a good 13+v the Trans will kick into limp mode and will only run in 3rd gear. It will take 5 min to hit 60.

the voltage cel is big red flag for me in my experience keeping a 99 with 233k as a daily driver.

 

That was my line of thinking as well. The "permanent voltage supply" code sounds like a clue to me.