'89 n/a 19 diesel (Bosch) black smoke.

[AndersDK]

The good old simple diesel setup

This is my s-i-l's diesel which has gradually become worse in creating black smoke and hesitating in power while smoking. It also black smokes on start-up and idle.
It is definately BLACK smoke like all you guys have seen from an over-fuelled engine any kind. Absolutely no white or blue'ish smoke under any circumstances.

No major service has been done prior to this problem - except for regular oil & filter - including air filter - changes. Timing belt and glowplugs are not even half due yet since last change.

We have tried running the engine with air intake directly from the free - no change to the problem. The car has recently (last autumn) been on a long trip to Greece and behaved 100% perfect on the trip (some 2K miles).

My theory is that its the Bosch pump which is worn and now has reached a state where you need to set back the fuelling - on the fuel volume screw.
I would certainly like to read opinions from you specialist (BX) owners.
I take it the fuelling screw must go OUT to decrease fuel volume (Bosch) ?

Cheers fellow BX'ers

[jeremy]

Anders

I think individual pump adjustments are not the cause of your problems. My reasoning is that black smoke at all revs is a sign of unburnt fuel being present at all times (which I agree is unusual)

Black smoke is as I understand it due either to excess fuel being present (which cannot cause problems at idle or low load conditions as the engine would simply run faster) or insufficiently atomised fuel - with burning taking place on the edge of the droplets rather than smaller droplets burning completely.

So I think your problem is either defective injectors - or pump timing. My ancient fault finding charts suggest advance means a noisy engine, retarded means a smoking engine - which is I suppose a starting point.

If you suspect one injector you can of course test it simply by loosening the feed pipe and eliminate that injector.

jeremy

[Brian]

Hi Anders

Unusual one this...

It has to be too much diesel getting into the combustion chambers.

You have eliminated restiction in the intake, which would have been my first guess..

So it has to be either the pump or the injectors...

My Money would be on an injector not seating effectively, thus letting too much fuel through...

When you have resolved the fault, let us know the result.

Cheers
Brian

[AndersDK]

Tx guys -

The engine has a very sound and "soft" diesel noise scheme - a real nice diesel "purr". Nothing rough or hammer-on-steel like noise. Its always been like that ever since we replaced the HG (and skimmed the head) a couple of years ago.

I'll drop my fuel volume theory then and skip directly to the injectors cleaning & possible replacement job.

[DavidRutherford]

If the diesel noise is very soft, then you may have either retarted injection timing, or weak pintle springs in the injectors. A set of recon injectors and a DTI on the injection pump will definitely improve the running, and should release more power/economy too.

[AndersDK]

Right -

The car now has 4 recon injectors fitted - incl new seal washers and fire rings (coned upwards towards injectors). The old ones barely had anything left on the tips to make a spraypattern ...

... and still weak/smoking
Only difference smoke is less heavy but more steady. Found out that the lousy paper hose to the filter box was collapsing and strangling the engine.
Now running w/o hose to the filter box (quite a bit more noisy then )
... but still unsatifactory power and smoky ...

For testing its now running w/o a cleaning element in the filter box ...
No changes so far ...

Nothing - whatsoever - has been adjusted since it still ran well on the old injectors. All service items are up to date and checked, checked and re-checked. Oil & filter new and same type as used the last couple of years (10W-40).

It starts easy and fast on first flick on the key ...
Both hot and cold, both within the hour and after several days left parked ...
Ohh - and the diesel clatter is a fraction more sharp now, like you would expect it on a sound engine.

Any ideas ?
Thanx.

PS : will be checking the diesel pump timing in near future - when I've made up a "pinking" sensor to get the exact injection timing signal.
(Tom : would the microphony from a standard 100nF decouple ceramic capacitor do as such a sensor ?)

[jeremy]

Sounds retarded to me.

As the pump wears it may not produce quite as sharp a pulse of fuel as it did when new, and so it takes fractionally longer for the pressure at the injectors to be enough to open them. Makes accurate timing with a dial gauge useless but a touch of additional advance may sort things and disguise the problems for a while (like another 100,000km?)

[AndersDK]

Thanx Jeremy -

Thats about my first theory then
Looking forward to mess around with my small electronic project - its been a while my oscilloscope has been up & running ...

BTW : the recon injectors were some £44 each, including seals, fire rings and vat.

[jeremy]

Otherwise you can adjust it the expert's way - mark its position, slacken the mounting bolts a touch and move it say 1mm from the mark (top of body towards engine) - and make sure you leave lots of bruises on the alloy pump mount!

Then test for improvement and if appropriate do it again!

Nice bit of electronics must be better!