Hi i need some advice?

I purchased a 05 plate Renault Modus on the 10/02/2016 i paid £1030 via my credit card from an independent car dealer.

I did take it for a 20 min test drive and the car had some service history. The car had 93k on the clock,on day of purchase the car broke down on the way home(turned out it required a new battery,had it fitted and the cost was shared 50% each way) I also had the car serviced.

On the 18/3/2016 37 days after purchase a fault code occured "Check injection", parked it up over weekend and took it to the local garage,took 3 attempts to start plumes of white smoke on the 21/3/2016 had a diagnostic £20,3 codes that wouldnt clear :DF029 Cylinder 4 injector circuit at minimum limit.DF025 Preheating diagnostic connection and P0170 Cylinder balancing.I phoned and texted the dealer on the same day,he replied it was only a 30 day warranty and the best he could do was have his mechanic do it at cost. Not happy with the reply i sent two recorded letters to the dealer asking to cover the full cost of the repairs under the consumer right act 2015. He replied saying he wouldnt cover the cost,the fault wasnt present at time of purchase,or within 30 days.So next i tried the Credit Card they said they would do a "chargeback" even though i asked for a section 75,i emailed all the details and sent them to the bank. The reply came 2 weeks later :

"Unfortunately on this occasion we are unable to action a chargeback. As the faults with the car have occurred over a month after purchase, it confirms the car was fit for purpose at the time of purchase.When purchasing a car of this age and the mileage on the clock, it is expected that common faults will occur and general maintenance will be needed. I'm sorry we cannot offer a more accommodating response at this time."

So they decided to do the chargeback and then declined it,they didnt procecess my Section 75?

I am taking the car to be repaired this week,but have been informed that i will be quite costly,how much i dont know? Remove Injectors,test injectors,replace Injectors if faulty,replace Fuel pump if required?

But six weeks before it needs major repair i am not a happy chappy to say the least,its spent more off road than on it. Yes its used car,i have had them before most at least see a year out before a major repair or scrapping!

The car has no invoices from the dealer,ie service or Mot,its all from the former owner.

What would you say would be the next course of action? Section 75 or financial ombudsman or small claims?

Thanks for any advice.