Mazda BT-50 Engine Problems

This sounds like another one of pesky electrical problems which occur but don't really create havoc beyond making you wonder why it's happening. In many cases, this sort of problem can be caused by a poor earth somewhere on the car or even a chafed wire that is short-circuiting and turning random lights on and off.

But it could also be a symptom of something more serious with the car's electrical systems, so an electronic scan of the vehicle should be your next move. That will rule out a lot of things and also possibly pin-point the problem.

The clue here might be in the fact that this problem occurs when you drive slowly for an extended distance. This could suggest that something (engine or transmission perhaps) is becoming hot and the vehicle is switching to limp-home mode to avoid damaging any components. Also, it could be a dodgy sensor which is simply making the vehicle 'think' it's getting hot.

It sounds counter-intuitive, but driving slowly can lead to overheating as there's less air flowing over the radiator and/or oil coolers to whisk temperature away. When you stop the car and re-start it, the on-board computer goes back to its default settings and away you go again until the sensors detect more heat build-up.

With that in mind, I'd be checking the radiators and oil coolers for a build up of dust, mud, leaves and other rubbish which could be blocking airflow. But before you start replacing sensors and other components, have the car scanned (by a mechanic) to see if any fault codes make themselves apparent.

The rule of thumb states that if the engine fires on starting fluid sprayed down the intake, but won't run on the fuel in its tank, the first thing to check is the fuel pump. Just because there was some fuel present when you cracked the seal on the fuel injector, does not necessarily mean that there's enough of it or the fuel pressure is sufficient to start the engine.

Modern common-rail diesel engines use very sophisticated fuel systems which use super-high pressure. Without a pump to build up to this pressure, the injector won't deliver the right amount of fuel for successful running. But you should also check the operation of the glow-plugs as well as the condition of the fuel filters. An electronic scan is also a good idea at this point, before you start replacing expensive bits and pieces.

Be extra careful fiddling with engines like this one, especially if you're messing about with the injectors and fuel system. The inherent pressures are so high, that a leak can act like a water-jet cutter; sufficiently powerful to remove a finger.

The rule of thumb states that if the engine fires on starting fluid sprayed down the intake, but won’t run on the fuel in its tank, the first thing to check is the fuel pump. Just because there was some fuel present when you cracked the seal on the fuel injector, does not necessarily mean that there’s enough of it or the fuel pressure is sufficient to start the engine.

Modern common-rail diesel engines use very sophisticated fuel systems which use super-high pressure. Without a pump to build up to this pressure, the injector won’t deliver the right amount of fuel for successful running. But you should also check the operation of the glow-plugs as well as the condition of the fuel filters. An electronic scan is also a good idea at this point, before you start replacing expensive bits and pieces.

Be extra careful fiddling with engines like this one, especially if you’re messing about with the injectors and fuel system. The inherent pressures are so high, that a leak can act like a water-jet cutter; sufficiently powerful to remove a finger.

Anything is possible if you have enough money to throw at the project, but at some point, each project begins to cost more than it will ever be worth.

The real mystery, though, is how you came by a petrol-powered BT-50. In Australia, the BT-50 was sold only with a range of diesel powerplants. Petrol-powered BT-50s were made and sold in regions such as the Americas, South Africa and parts of Asia, but not here. Either that or you have a Mazda fitted with a Ford Ranger engine, as Ford did offer 2.5-litre petrol engine on Rangers from 2011 to 2015, but only on base-model, two-wheel-drive versions. That option was then discontinued.

So maybe you have a privately imported Mazda, at which point, it’s very hard to know what diesel engines will and won’t fit. The bottom line is that if you want a Mazda BT-50 with a diesel engine, the simplest thing to do is simply buy one. Chances are you’ll spend less overall than converting an existing car from petrol to diesel. Swapping a petrol engine for a diesel could involve everything from a different fuel system, wiring, transmission, differential ratios and even things like the radiator and front springs. It’s a big job.

Even though this is a light commercial vehicle aimed at working folks, these later utilities are quite sophisticated in terms of their drivelines. Which is another way of saying that there are dozens of sensors and electronic control modules, all of which can give trouble. The powertrain light is trying to tell you that something is amiss under the bonnet and the lack of power is the symptom that goes with it.

An electronic scan of the car’s on-board computer is the first step in determining precisely what’s wrong and, as well as throwing up the root cause of the problem, is very likely to save you a lot of time and money in the long run. Replacing random parts in the hope that you’ve identified the correct one is a great way to waste hours and hours and lots of dollars.

You can probably rule out anything like a split turbo hose as this would cause the vehicle to lose power all the time, not just after prolonged use. Modern turbo-diesels like the one in your car use a range of electronic sensors and controls to keep everything running properly. It could easily be that a sensor is sending erroneous messages to the computer. An electronic scan of the vehicle should offer some answers.

The other possibility is that the fuel system is not keeping up with the engine over time. This could be due to a blocked filter, a blocked fuel line or return line or even a fuel pump overheating. A check of the fuel system would also be in order.

It sounds like you’ve tried pretty much everything here, but I have a few suggestions. Have you cleaned out the inlet manifold? The combination of soot and oil mist that gets recycled back through the Mazda’s engine (and a lot of modern turbo-diesels are the same) can cause all sorts of poor running conditions including surging and mis-firing. I know you said you’ve disconnected the EGR valve, but this build-up could already have occurred.

What about the fuel system? You said you’ve replaced the injectors, but have the fuel pumps been checked for flow and pressure? What about the fuel return line? Is it blocked and causing an obstruction to the fuel flow below 80km/h? What about the fuel pick-up inside the tank? A split or damaged pick-up can allow air into the system and cause all sorts of grief.

Also, this generation BT0-50 used throttle-by-wire. Many owners didn’t like the operation of the standard set-up and changed to an adjustable system that allowed them to soften (via a dial on the dashboard) the throttle action for off-road use. Has your vehicle been modified like this? Even if it hasn’t, the standard throttle set-up could be faulty and causing the problems you’re seeing.

The fact that the vehicle operates perfectly in some situations leads me to suspect an electronic or fuel supply problem. If it was a major mechanical issue such as a burned valve or a major mechanical glitch, the engine would likely not run properly at all.

We contacted Mazda specifically on your behalf, and its response is that only some grades have an engine cover. Ones that do not are the base XT, while the XTR and GT versions do have a cover. We hope this helps.

Without being able to view it and hear it firsthand it's hard to suggest what might be wrong. It could be a bearing in the turbo, but that's only an educated guess. I would have a mechanic check it.