In recent months I have seen an overwhelming number of 2000-2001 Ford Focus DOHC engines coming in for repair with the service engine soon light on. After scanning the ECM (engine control module) most will find that they are getting diagnostic trouble code PO304 Cylinder 4 misfire. The vehicle idles fine but after driving a while you will feel a misfire under acceleration.

Well as you would guess most repair facilities will say you need a tune-up. I can assure you this will not correct the problem. Then you will be told you need a fuel injector,ignition coil and you will be shown a TSB ( technical service bulletin) that will say this could be due to carbon build up and causing a valve to stick. Which is true all of these could cause this problem. But through extensive testing I have found that if your mechanic hooks up a fuel pressure gauge to the vehicle and takes the vehicle on a test drive he will notice a drop in fuel pressure. If the fuel pressure drops below 55psi you will develop a misfire in cylinder 4. Now 95% of all mechanics will say if it is a fuel pressure problem it will be affecting all 4 cylinders. Well on this particular vehicle the fuel pressure is not strong enough to give cylinder 4 (the last cylider in the engine) it's full blast of fuel.

If my steps are followed it will save you hundreds and hundreds of dollars if not well over a thousand dollars if you are convinced by the mechanic that it's carbon build up. Which they will have to replace the cylinder head with a new an revised one as recommended by Ford.