Right, after making literally 17 attempts to register with Mazda6 forum, only to be accused of being a 'bot' each time, and then posting what seemed like an essay at HonestJohn, only to find that was a waste of time...I've ended up here!

Let's see if I can make some progress.

HI ALL!

I recently purchased a Mazda 6 diesel 120hp on a 56 plate. After around a minute of driving, almost like a switch, it runs on half power for the rest of the journey. If I stop for more than a few minutes, I can get back in the car and it will drive fine for another minute....then it'll be pants! When it is running at half power, there is no smoke....it runs smoothly, and there are no untoward noises.

Whether or not this will be the cause, i do not know. The previous owner has clearly fitted some kind of tuning box. It has a yellow wire that goes to what I think is the fuel pressure switch on the end of the fuel rail, and three others that join to a part of the loom which has been disconnected from some kind of sensor on the bulkhead. Can anyone tell me what this is?

Anyone have any ideas on the running issue?

 

Hey and welcome to the forums!

First off what is a 56 plate??? Just curious.

If it changes power that fast it could be your wastegate is sticking open when the exhaust is hot which would free up when it cools down when it sits (shot in the dark with this though). Also if the PO messed with the computer it could be reading the fuel pressure wrong and cutting your fuel, best thing to do would be to rip the suspect modifications off or disable them and return the car to stock, its difficult to troubleshoot an issue when there are components that only you have an idea what they might be doing. Also try reconnecting that sensor, who knows maybe it came undone Any pics of these by chance?

 

Cheers for that, but there has been a bit of a development....

the guy i bought it off said the dpf had been removed. Mazdas are new to me so i was unsure how this was done. I plugged my obd2 reader in and it came up with a fault for the oxygen sensor. I took a look under the car and notice there were several sensors going into what i thought was the cat. the wires to these sensors had all been cut and the loom was all reconnected into some kind of black box (part of the dpf removal process??). The o2 sensor was still connected but im wondering if it has been damaged due to the way the dpf has been disconnected?

Ideas?

Oh, and 56 plate is a registration number in UK for 2006 models.

Cheers

 

I was going to say that if this were a "petrol" engined car, it sounds like the catalytic converter was clogged. After a few minutes of running the exhaust gasses would build pressure in the cat/exhaust not allowing them to escape as they should, thus reduced output power.
It might be similar with the DPF? If its clogged and not allowed to burn off the excess particulate matter you may just be experiencing this similar situation.

Who ever you bought it from should put it back the way it's supposed to be for you. Or give you your money back.


*edit* And MazdaTirol, what if you exchanged the word "dangerously" in your sig to "diligently?"
Just a suggestion, not an order.

 

But if the DPF was removed and the wiring has been hacked into could it be one of the now "phantom" sensors that is registering the DPF is plugged even if its not there? I do agree though of returning the car back to stock, I also bet you wont pass the next MOT when it comes due when they look under it.

Virgin1......thats a good one, didnt think of that LOL, but I just thought of another one

 

RE: MazdaTirol - Ah, but that (Dependably) only works if you haven't bought a diesel powered 6 that's been hacked by a moron. LOL!!!

'Sorry, and nothing personal, sumaspikey. 'Had to do it. It was just too easy.

 

Thats where the Mostly comes in to play