Smoke on Acceleration A4 2.5 tdi Avant

[Phil G Watson]

Hi all

I'm new to the forum and joined to ask this question.
I've owned my Audi A4 1999 2.5tdi Tiptronic Avant for 8 years and it now has 166,000 on the clock. It's been main dealer serviced all it's life with more or less no expense spared to maintain and repair it. All round a brilliant car, still goes like stink and returns 40mpg if you can force yourself to stay below 80mph.
Question is this, it smokes on acceleration (looking in the rear view mirror at night, following cars disappear in a'fog'.)
I know older diesels smoke (Taxi's) but it's a characteristic I usually associate with unloved heaps, rather than well maintained vehicles.
Can anyone tell me if I can improve the situation (other than with a rebore!). Would new injectors make a difference for example. Is it simply a symptom of bore wear and old age?

Thanks for any input

Phil

[spartacus 68]

The 2.5TDi isn't exactly an eco-friendly engine. The manual 6-speed version (AKN) engine (with quattro drive) produces 216g/km CO2. By today's standards that's still pretty high. Rather than going to the expense of new valve stem seals, try a couple of cheap fixes first. It's obviously getting the through the MOT on the fast idle run, and you're still managing 40mpg - so it can be too bad. Assuming it doesn't use oil then try this first.

When were the glow plugs last changed? Supposed to be every 40k. Replace with Bosch plugs. In addition, dispose of the standard air filter element and fit a K&N oiled air filter. Lastly, but most importantly, drain the fuel filter and add a can of Forte diesel conditioner straight into it. On start-up, drive her hard and watch the smoke in your rear mirror. As it's a auto-box you'll need to start-stop for best effect. On a manual box, it can be driven hard in 2nd and 3rd gear. Replace the fuel filter and top up with fresh diesel.

[Phil G Watson]

Thanks for the insight Spartacus, thats great,
To my knowledge the glow plugs haven't been changed at all. I'll try that and the filter / additive route first.
Regards
Phil

[HomerSimpson]

Hi Phil,
Welcome to the forum, is it black smoke when you accelerate? If it is then it would be worth checking the hoses going to the intercooler, I had a split hose on my 98 A4 TDI and it would belch out black smoke on accelerating.

[teccyjim]

Changing the glow plugs will make no difference, they are an ancillary item used to assist starting the car from cold. When 'warm' the natural cycle of the engine (compression/diesel effect) takes care of combustion unlike a petrol engine which requires a precision spark, timed correctly in order for combustion to occur.

If its black smoke, it basically means too much fuel, not enough air. This could mean worn injectors or as mentioned, blocked air filter or an intercooler leak. Your EGR valve may be cocked/gunged up as this device allows some exhaust gasses back into the inlet manifold to assist with combustion and is effectively, a method of emmisions control.

I agree, the Forte diesel system cleaner is THE ONLY diesel additive to use that works, forget anything on the shelfs at Halfords. The method of filling your diesel filter is perhaps a tad extreme but will no doubt work. For the £8 or so off ebay, i'd add a whole bottle to your tank as you fill up next, especially if you're not keen on getting the spanners out. My mum's old 106 diesel smoked badly but after the Forte treatment, no probs. The MOT tester was also shocked at how low the diesel particles were on the test.

regards,
Jim

[mrjolly]

another tupenys worth , ive known cars that have filled the intercooler/pipes with oil and it has started to get its way into the engine with the air. you tend to get a bit of oil in your boost pipework especially if the motor has done a few miles and it can build up.