Thread: What makes diesels smoke ?

Originally posted by DiscoTDI
when you see a brand new diesel pumping smoke down the road its a dead give away

Or it's a GU Patrol That hasn't had the pump and injectors replaced and set up properly by a Diesel expert. A mate just had his done, Nissan reckoned there was nothing wrong with it blowing smoke, Rob had comlained about it from new. It's out of warrenty now so he decided to ring some diesel shops, they all said oh you've got a GU have you and it smokes, yep we know the problem it needs a new pump and injectors, lotts of them do it and Nissan try to fix it by retarding the injection, we can fix it but it costs $3k. He wasn't happy as the car has only done 80k,anyway had it done and it's a different car no smoke, more power less fuel.

Shoulda traded it in on a disco and went on holiday with the 3k. Better fuel economy and no smoke, well a little, but not enough to see it come out the back. Matt

Originally posted by Ace
Shoulda traded it in on a disco and went on holiday with the 3k. Better fuel economy and no smoke, well a little, but not enough to see it come out the back. Matt

yours will put out a haze Ace, check your mirror at night time when there is a car behind you :wink:

Originally posted by VladTepes
I know that smoke (soot) is part of the package, and fortunately mine doesn't smoke - except briefly on startup.

Now I'm not very technically gifted so perhaps someone can explain to me why this happens.

Also is there a (cheap amd easy) way to eliminate / reduce the smoking on startup ?

To get back to Vlad's original question: Tdis (and probably all other mechanically injected diesels, certainly all with Bosch VE type pumps) will always smoke right at start-up and there's nothing you can do about it.

There's a very light spring in the governor mechanism of VE pumps that sets the fuel delivery rate to the maximum when the engine is stopped. As soon as the engine fires and the rpm exceed about 300, this start-up spring is fully compressed and plays no further part in proceedings. If the throttle is left alone, the idle spring now comes into action and controls the fuel delivery to the amount needed to maintain idle rpm (i.e. very little).

So, a short puff of very black smoke as the engine fires is quite normal and nothing much can be done about it. Now, once the engine has fired, other factors can play a part. Whitish smoke after start-up indicates too low combustion temperatures and often means glow plugs not working. (Glow plugs are not just for cold start-up. They're there to keep the combustion temperature high enough for efficient combustion for several minutes, until the metal of the cylinders & pistons gets hot.)

Black smoke at times other than start-up will mean there's not enough air to fully combust the quantity of fuel being delivered. If it's only moderate and for short durations, (like for a few seconds until the rpms get above, say, 1800 in a Tdi and it starts developing a bit of boost pressure) it's nothing to be concerned about. If it's pretty smoky at higher rpm (above 2000 in a Tdi) for any length of time (a few tens of seconds?) you can bet the Exhaust Gas Temperatures will be getting excessive. This can happen if there's any serious air flow restriction, even if the injection pump settings are stock standard. Please have a read of the EGT Information Sheet from my website if you'd like more details.

Thanks Leo (Ian) [img]style_emoticons/<#EMO_DIR#>/smile.gif[/img]