ASK THE MECHANIC: Why is my BMW misfiring?

Hello Paul, my BMW 525i e39 2001 is misfiring. On doing computer diagnosis, it indicated low fuel. We changed the fuel filter and tested the fuel pump return and all was okay. We also tested the coils and it was discovered that the cylinder one coil was faulty and replaced it but the problem persists. What can be done? Edson

Hello Edson, there are several causes of BMW E39 engine misfire. Ignition coils, spark plugs and fuel supply (pump, filter and injectors), which you have checked are some of them. Ask your mechanic to inspect the vacuum system and the positive crank case ventilation system to rule out vacuum leaks.
Also, check the engine management crank shaft and camshaft position sensors using a diagnostic computer. If they are fine, examine the wiring circuits to the ignition coils and sensors mentioned. If all is fine, you will need to carry out a comprehensive engine diagnosis to examine the performance of the intake valves.
On odd occasions, the E39 engine will experience damage of the timing chain kit due to age and lubrication issues. This can cause a retardation of timing which will cause a misfire as the intake valve opening is not synchronised with the fuel delivery system. This would require a replacement of the timing chain kit and as a precaution, the oil pump.

Hello Paul, I am a recent driver and I am looking for a fuel efficient car to buy. It should be able to handle the Mukono traffic jam and have good height and ample driver legroom. I am considering a 2.4 litre Toyota Kluger online and wondering about its fuel consumption, especially in traffic jam. Please advise. David

Hello David, you should stick to your first choice and buy a Toyota Kluger 2.4 litre petrol. Your decision will be driven by your requirement for high ground clearance to tackle light offroad duty. Ample legroom seems to be another pressing need to make you and your family comfortable while you drive. Fuel economy to manage the Mukono-Seeta traffic jam is equally important.
Kluger’s 2.4 litre, four-cylinder straight engine has better fuel consumption compared to the alternative 3.0 litre V6 shaped engine. In city traffic or traffic crawl ups such as from Mukono-Seeta, the Kluger will give you about 8.5km/litre and on the highway, it will give you about 11-12 km/litre.
You can improve the crawling traffic fuel economy to about 10 km/litre and highway fuel efficiency to about 15 km/litre by driving sensibly (avoid aggressive take offs and harsh braking, use momentum on slopes, switch off AC and switch off engine if not moving), servicing the car periodically with good quality lubricants, using efficiency enhancing fuels and replacing worn out tyres.
If you have to buy a car online, use companies that have local representation or offices. This gives you a solid point of reference in case you need to raise issues about payment and condition of a delivered car.

Hello Paul, I have a Mitsubish L200 which was recently serviced and most components replaced or repaired. A new clutch plate was also put. However, when driving, the gears engage easily but when I start the car after parking it for some time, engaging any gear is hard. What could be the problem? Timothy

Hello Timothy, harsh engagement of gears on a manual transmission are commonly caused by a worn out clutch kit. A clutch kit has a pressure plate, friction disc plate and release bearing. Occasionally, you may need to replace the clutch fork if it is worn out. It’s a mechanism that helps the smooth operation of the clutch release.
From your account, you only replaced one of the components in the kit, the clutch plate. You may need to ask your mechanic to revisit that clutch repair job and replace the complete clutch kit. The condition of the fork should be examined. Also, confirm that the clutch release cylinder works well. Occasionally damaged components in the manual gearbox such as H gate selectors can cause hard shifting. In your case, your description of symptoms points towards a faulty clutch system.