Surging Ranger

I have a 2005 Ford Ranger with the 4.0 liter V6 petrol engine that has done more than 300 000km.

The vehicle runs well until it reaches 3000RPM and then it occasionally starts gradually losing power until it gets to approximately 2000RPM. Then it suddenly kicks in again and the revs run up to 300RPM again.

I say occasionally as it seems to happen when the vehicle is under load (e.g. going up a hill or when I am overtaking). I have had it with a number of technical people including Ford. The diagnostic computer doesn’t seem to pick anything up.

I have replaced the fuel pump, spark plugs, fuel filter, plug leads, etc. I have submitted this query to the Ford Ranger forum and the best idea thus far has been that I need to clean the Mass Airflow Meter (MAF). I will be trying that this afternoon.

The problem I have is that this appears to be “linked” to the revs and at first I suspected that the fuel supply couldn’t cope. If that was the case then the revs should have stayed at 3000RPM and not have dropped to 2000RPM before kicking in again. This is a potentially dangerous especially when I am overtaking.

This sound like an intermittent problem, and as you have started the elimination game, I know its not easy to find. Murphy strikes when least expected. It could be anything from a connector that has got moisture into it and makes and brakes intermittently. You need to check all your connectors even the least important ones. Unplug and replug computer box and inspect to see if there isnt any corrosion anywhere on any connectors. Sometimes due to vibration you might also have a component that has come lose on computer board in computer box (if this is not a sealed unit, I had this in remote fob) Also with high kilos on vehicle check to see if there is no spot where harness rubs on body or engine and possibly rubbed through and confused computer. Another place to focus on might be your immobilizer alarm unit, there might be a loose component. From your query you say it happens at around 3000rpm, seems this is a point where something resonates to bring up condition though not always. Hope you find the gremlin.