Smoke on idle/start - 300 Tdi fuel pump drift

Quote:

---

Originally Posted by damienb

I've got a provent oil separator on it, but it's not compression problems. Winding the idle (smoke) torx screw out a full turn (from factory) has eliminated smoke on idle and dramatically reduced smoke on start so I suspect pump or injector. I would have thought though pump lobe wear would result in less fuel, not more. Takeoff and driveability have not changed.

---

Thats not quite how those pumps are built up, its not lobes its ramps and a single plunger runs all 4 cylinders.

pumps slip is the diesel leaking past the plunger so the pressure rises to the crack point of the injector later in the stroke. To compensate for the loss of power the govener assembly injects more fuel, because the fuel is injected later and usually with a lower quality of injection it'll burn like its over injecting or starving for air.

As the engine speed picks up theres less time for the diesel to slip past the plunger and the timing advances. so everything gets back to spec.

you might be able to get away with addind a fraction of advance on the timing to over come the injection delay.

this Torqz screw you wound out, is that the one on the very top of the pump surrounded by 4 nomral screws with a pipe coming from just under the housing going back around the engine and hooking up to either the turbo or the inlet manifold.

also, ditch the hiclone. Even if they did work ,the concept of why they are supposed to work is irrelevant to a diesel, let alone a turbo diesel.


w

Dave,

Thanks for the info. Based on this, you would still not expect fuelling at idle to change due to pump slip since this is not substantially impacted by the governor at idle (and the amount of fuel per stroke is less). Fuelling above idle seems great but I've got a thermocouple on order to check.

Yes, I did wind out (by one turn) the torx screw at the very top of the pump (centered in the pump cover) after removing the cap with a couple of thin screwdrivers.

I don't have a hiclone and never had one. There was some confusion because I mixed up hiclone and provent in my post, and fixed it fairly quickly but bee-utey posted in between.

Damien

the total quantity of fuel delivered I wouldnt expect to change.

when and how its delivered most definitely would change.

the screw you have adjusted is not the idle screw, its the off boost limit stop for the fuel compensator.

With almost all diesel engines you have no direct control over the fuel being injected, thats all handled by the springs, balances and linkages setup by the governor. electronic diesels (very roughly) do it with very detailed look up charts that determine all the aspects of injection.

if backing that off has sorted the pump smoke out then the pump is not tuned/timed correctly and you may have cost yourself a little turbo lag but if its an auto you probably wont notice it.