UKC

Whenever I accelerate hard, e.g. joining a motorway, overtaking etc, a nasty cloud of black smoke appears behind my car (Diesel 1.7 Vauxahll Astra). Anyone had any luck with those injector cleaning chemicals you stick in your fuel tank? Do they make any noticible difference or just snake oil? Is the black smoke a sign of anything wrong?

In reply to bigbobbyking:

No Smoke No Poke... Usually.....

The smoke isnt anything to worry about (normally, unless its a blue colour cause that's oil burning and not great news) Its just deposits burning off, these are now caught in Diesel Particulate Filters (or DPF) on more modern cars.

I was talking to a mechanic that deals exclusively with DPF, he says all the redex type additives do is make the engine burn slightly hotter, burning of the deposits, which is basically what you're doing when you accelerate. He said that they were ok but he really advocated doing long runs every now and the with a higher grade fuel like BP Ultimate or Shell V power and these coupled with the consistent high temps of a motor way journey would help clean out the engine and the DPF (not that you have a DPF). So next time your driving to Hoy or Font, try a more expensive fuel for a tank and it should clean it out.

SO I'M TOLD

In reply to bigbobbyking:

injector cleaning chemicals didn't make any noticible difference with my car - injectors may need refurbishing/replacing ?

In reply to bigbobbyking:

The smoke is due to your injectors being taken beyond the point where they efficiently atomise the fuel. The droplets get bigger and they don't burn properly: smoke. To get the headline power figures out of a modern diesel they do this, it get referred to as "over fueling".

Some experts suggest you use full throttle and redline a diesel periodically to "self clean" the injectors. It might be nonsense.

Restrain your right foot and change up earlier and you won't get the smoke, unless the injectors are knackered. Injector performance falls away as the miles increase on them and they wear (they are wearing from mile 1 as they come out of the showroom). I suspect this meas the smoke will come at lower throttle openings but I could be wrong.

You can get a specialist to inspect them for wear which shouldn't be too expensive but the recommended repairs afterwards might be.

In reply to petellis:

It's just an effect of rich fuelling at high throttle on a pre-dpf engine. Quite normal and nothing to worry about.

In reply to bigbobbyking:

A slight amount of smoke is normal, a nasty cloud is a sign that some servicing or maintainance is needed.

In reply to John Simpson:

fit a new air filter first. is the current one black?

In reply to bigbobbyking:
My brother has worked on large diesels for quite a number of years for some big engineering firms and he suggested I use these when he heard I got a diesel car - think he suggested using every 5 or 6 tanks.


He also said that most people don't run their cars at enough revs to burn the diesel efficiently and I should use the gears to prevent low revs as this would reduce the need for maintenance.

In reply to john morrissey:


I don't know it's not mine, but I do this job at least every week or so:

This is generally what gets checked.

1. Change oil, oil filter, air filter if needed, and check basics like engine breathers, crankcase pressure by running engine with oil filter cap off for blow by, check turbo and inter cooler hoses,check for wear in turbo shaft, and waste gate or nozzle assembly function, maybe check or clean egr valve, plug in scanner and run diagnostics.

If all checks out give it a good full throttle run for a short trip to see if it clears.

2. If still smoking too much, find and replace faulty part/parts.

In reply to bigbobbyking:

before you add anything try the air filter or a intake hose which is possibly collapsing when you put your foot down (will only happen when you accelerate as it is trying to suck more air) black smoke is excess fuelling but normally thats down to lack of air in the mixture ,more noticeable if you have a turbo ,we always check intercooler hoses /intake hoses and air filters before getting into the fuel system ,hope this helps
stuart

In reply to bigbobbyking:

If its an old astra two stroke mineral oil in the diesel (1:200 ratio) can help, clean the injectors and make engine run smoother, quieter and help low rev pull. The logic being it replaces the lubricating properties lost in newer low sulphur diesel.

In reply to bigbobbyking:

Thanks for the input. It's a 2005 model btw, if that makes any difference to the DPF or not features. From my limit research I don't think it has a DPF. I do quite a lot of long motorway drives so I think the engine has plenty of opportunity to heat up and burn stuff up. Had a service just a few weeks ago, so should be a new air filter.

In reply to bigbobbyking:

2005 models wouldn't typically have a dpf, no.

In reply to bigbobbyking:


If it visibly smokes when you rev it it then it probably doesn't have a DPF.

But that is irrelevant anyway: its a diesel so it will smoke at full throttle/high revs (If it is doing it at ~4000rpm/foot to the boards then its normal for a car of that type).

If it does it on a part throttle then have a look at the air filter and hoses then get the injectors looked at but at the moment you are not describing anything out of the ordinary.

How many miles has it done?

In reply to bigbobbyking:

Done 107,000 miles.

For the hoses, am I best to physically look under the bonnet while someone revs the engine for me?

In reply to bigbobbyking:
just give them a squeeze youll soon notice the difference if they have gone soft
forgot , also make sure they aren't holed and that they are secured properly at each end (no pun intended with "give them a squeeze"