Engine can not rev

[GigerStrife]

Hi Guys,

I have a 2005 Mazda 6 TS2 143hp diesel that has developed an issue.

The engine will not rev above 2000-3000rpm in any gear. When it reaches said revs, it drops to idle again. If you sit in neutral with your foot on the accelerator the engine just cycles (Revving to 2000rpm and then back to idle and so on)

I can easily take the car to 70 providing I change gear before 2000rpm.

I have attached my scanner to the car which has revealed no fault codes. I have no lights on the dash either.

I have tried cleaning the MAF with carb cleaner to no avail.

Just to mention this car has had the Cat and DPF removed by previous owners.

Thanks,
Pete

EDIT: Just a little extra info.

It happens regardless of time of day and whether the engine is hot or cold. It happens in every gear. I can easily get the car to 70mph providing I keep the gear changed below 2000-3000rpm. When the car is kept below these revs it acts as normal.

The car has 113,000 miles (Approx 182,000 km) on it. The engine has been refurbished recently around 10,000 miles ago due to a rod bearing going.

I only noticed the DPF was removed when I had an Oxygen sensor go faulty. It appears there is a straight pipe welded in place of the Cat and DPF. The three sensors that usually sit in the Cat (Beginning, middle, end) have been removed and the wires are in a small box zip tied under the car (Haven't opened the box yet.).

There is a cigarette pack sized black box zip tied by the battery in the engine compartment. Upon opening it appears there is a USB port and a serial connector. The serial connector has been spliced into a wiring loom, with a white wire strung across the engine bay to an electrical connection on the left of the common rail system.

I am in the UK.

Hope this helps.

Thanks,
Pete