Iran Khodro EF7

Iran Khodro's 1.65-litre four — developed with FEV in Germany and known domestically as the national engine — fitted to the Samand, Soren, Dena and Runna, and produced in naturally aspirated, turbocharged and bi-fuel CNG forms.

It replaced the licensed Peugeot XU and TU engines that Iran Khodro had built for decades, and that transition is the first thing to establish on an older Samand: an XU-engined car and an EF7-engined car share a body and almost nothing else under the bonnet.

The CNG variant is the one worth understanding, because it is common in its home market and changes the diagnosis: running on gas alters combustion temperature and valve-seat wear, and a misfire or valve-clearance complaint on a bi-fuel engine has causes a petrol-only engine does not. Independent technical documentation is thin outside Iran, which raises the value of community write-ups attached to this node — and is precisely why the engine has one.