Engine smoking after cold start
QI have an Isuzu 35hp engine in my narrow boat that has only done 900 hours. It gives off white smoke when first starting up cold that goes after 1 to 2 minutes. When hot it starts up without smoke. Do you think it has fuel injector problems on one cylinder? I have replaced all the pre-heaters. BARRY CAMP
ATONY REPLIES: In theory it should not smoke but white smoke on cold starting is not particularly uncommon. The smoke is normally just vaporised fuel that has not ignited on the first compression stroke. There can be several reasons but at this time of year it might be low ambient temperature or a poor quality fuel problem. It seems incidents of smoke from poor fuel are increasing.
Have you measured the voltage at the glow plugs when they are operating? If it’s lower than 12V then there is probably some sort of electrical resistance on the glow plug circuit that is preventing them getting hot enough to start on the first cycle. In no particular order, this could be undersized cables, dirty or loose connection (often in the big multi-plug that is in the main harness), or resistive ignition switch or glow plug relay if a relay is used.
Once you are sure the glow plugs can get hot enough I would change the fuel filters then drain and cut the old ones open to see what they have caught - if anything. That may give the first indication of a fuel quality or contamination problem.
If the compressions were compromised you would get this sort of symptom but at 900 hours internal wear is unlikely; however a valve clearance may have closed up so check the valve clearances.
After doing the above I would give the tank a good dose of injector cleaner from a motor factors or Halfords type outlets and let it work through the system. Then see what happens at the next refuelling. If the problem goes away it is likely to be poor quality fuel being more difficult to ignite or dirty injectors but at a true 900 hours I do not think an injector problem is likely, but who knows.
Anything that makes the fuel more difficult to ignite can cause this symptom. So if an injector is not closing properly or streaking rather than atomising the fuel it will cause unburned fuel to lay in the cylinders and exhaust at cold start, hence the white smoke.
If the injector pump rack is a little sticky it may not rest at maximum fuel, which is the cold start position so try starting it with full throttle, but slow down as it fires.
Air might be getting into the fuel system somewhere so if your engine has an electric lift pump turn the ignition off for a minute or so before using the starter. That should purge any air. If it’s a mechanical lift pump try spinning the engine with the stop control in the stop position. That should do something similar. These are diagnostic tests rather than regular starting procedures.
If all else fails you may have to get the injectors serviced but at 900 hours that seems unlikely unless you have had water in the fuel problems.
You may even find the problem goes away once the ambient temperature rises a bit.