Alternator Load Effecting Idle

Hello,

If I leave my 200tdi to idle and then apply load to my alternator (such as full beam and cab heater fan on full), I find that the idle drops significantly to the point that the idle speed governor struggles to keep my engine idling smoothly. In other words, my engine slows to the point where it is just above stalling, and the injection pump compensates momentarily by giving the engine more fuel. It will continue to hunt / rev up and down until the load is removed from the alternator. I can hear the engine slowing down as I apply more load, starting with main beam, up to everything running, but I can also hear the injection pump adding more fuel to compensate (more injection noise).

Is there a problem with my alternator? I find it very irritating when stopped in traffic or at a junction etc when I have my lights on or any form of load on the engine. Just for the record, it used to do this with my last injection pump, this pump is brand new so the governor is not at fault. I have also found that this problem is less apparent following replacing my alternator brushes, although it is still noticeable enough to irritate me.

Thanks,
-Tom

Its mechanical only, ie no idle stabilisation or load compensating etc? Does the 200TDI have cold start compensation?

Raise the idle speed a bit?

paul_c said:

Its mechanical only, ie no idle stabilisation or load compensating etc? Does the 200TDI have cold start compensation?

Raise the idle speed a bit?

Click to expand...

Pardon? The Bosch VE fitted to 200 and 300 tdi engines does have a load compensating governor yes, it has an idle speed governor too which should inject more fuel to maintain engine speed when load is applied. It does have a cold start advance mechanism too. There is no EDC in my pump, just on the later 300tdi pumps. Obviously there is a limit as to how much extra fuel the governor can provide, and I think the load on my alternator puts more resistance on the engine than the pump can compensate for without increasing the idle speed.

I know the idea of upping the idle speed a bit seems to be bodging your way round the problem, but is the idle speed actually set right to start with? If it has been set a bit low then any increased load at idle would cause the engine to struggle. You need an accurate way of measuring it. Laser tacho or similar.
It could be the alternator but if that is pulling more load than it should then that load has got to be going somewhere. Overcharging the battery perhaps which I would have thought would have trashed the battery by now. Assuming the battery is charged then all the electrical loads don't really amount to that much unless you have a winch fitted.
I would try and check the off load idle speed first and then possibly get the alternator professionally checked.