ACSD whilst it's popular. Removal or Replacement.

[frank rabbets]

There is a timer piston inside the pump. This is kept in the standard timing position by a spring. One standard timing hot or cold. However it is overridden and dictated to by the much stronger spring on the ACSD lever spindle which has the ACSD on it. This allows the ACSD to advance the timing when cold. If the assy is removed and a blanking plate fitted the pump returns to it's standard timing by the action of the timer piston spring. Completely correct for hot engine but slightly retarded for cold engine. (The ACSD also idles up the engine when cold so this item will be lost).

When the ACSD assy is fitted the thermo wax contracts as the engine cools. This causes the thermo piston to withdraw allowing the ACSD spindle to rotate. The spring on this spindle is much stronger than the timer piston spring which therefore fails to keep the timing standard and it becomes advanced to suit a cooling engine.

The spindle has a small lever on the inside acting on the timer piston. When cold the lever will be touching the piston and overriding the piston spring so the piston will be forced into a more advanced position. When the engine gets fully hot the lever will move so as not to touch the piston. When fitting a new thermo wax it's important to make sure this gap is created by sufficient action of the thermo wax. First the timing should be measured and recorded ( in accordance with the WSM overriding the ACSD ). Then the engine should be warmed up and the ACSD lever clamped in position to keep the hot position and then the engine be allowed to cool. Then the timing should be measured again (without override) and if the thermo is adjusted properly the timing should be the same. In fact the spindle retard lever just leaves the piston at 50 deg c to be absolutely correct. If the gap is not maintained it could lead to failure of the mechanism as it is not designed for constant use.

 

[Firewout]

Nice write up.
so no timing adjustment is needed when the acsd is removed?

 

[Towpack]

I'm sure I've read somewhere that the timing does need adjustment (for normal hot running) after ACSD removal but maybe not after all. http://youronlinemechanic.com/ve-pump-options-acsd-automatically-controlled-cold-starting-device/
The loss of idle up with the unit removed can easily be compensated for with the hand throttle but the timing advance cannot, probably at the expense of more laboured starting in cold weather and less efficient fuel burn leading to increased bore wetting and oil dilution over a period of time. The device isn't there for nothing, right? JMO

 

[frank rabbets]

It's a "device" so it does something to the fuel pump i.e. advances it. So if you take it off it won't. Some cars are fitted with the same type pump and the car manufacturers opt out of the ACSD because they don't need it. There is just a blanking plate. I might have posted in the past that you need to adjust the timing but you don't. I've been reading the VE Fuel Pump manual and it explains how the ACSD works. The ACSD advances the timing to obtain more efficient fuel burn but I don't think diesel wash, if there were such a thing, would wear bores. It's more of a lubricant than petrol. The ACSD also causes an increase in idle revs to decrease warm up time, perhaps for regulations. If you rev the engine when cold the ACSD cancels so it only advances at low revs when cold. I have the PDF VE manual but don't know how to link to here but I'll try and then readers can work it out but it takes some studying.

 

[Towpack]

There's nothing really overly complicated about it. The timing advance when cold is to give the fuel a longer burn period as it burns slower when cold. I think the increase in idle revs by holding the throttle open slightly is more to give a stable idle rather than speed warm up. Diesels produce comparatively little heat without load compared to a petrol engine. The ACSD doesn't really 'cancel' when the engine is revved. It holds it's fast idle setting until the coolant temp rises enough to operate the wax plunger. It's really no different in operation to an auto choke on a carburettor petrol engine. JMO

 

[Dave2000]

I know just before I removed mine and checked the timing it was as near perfect for the hot running. So it does seem when it is 'off' the timing is correct for the warm/hot engine. I assumed (wrongly) the cold start would retard fuelling to allow the engine to get to some cranking speed before firing, in a similar way if the ignition is retarded in a petrol engine. Given mine was removed over fours years ago and it never fails to start immediately hot or cold, I also do not have the benefit of 24 volts/4.5kw to spin the engine. I suppose the coldest mine has seen is -8? I only removed it when a guy had his fail and it damaged his pump in IIRC Morocco, this with an annoying 'tick' which I put down to general wear.

The slow cold idle again is no big deal in a manual, it is perhaps 50 rpm lower? In an automatic this may be more of a problem? I have in preparation for a winch fitted a switch to the AC idle up to give the batteries some help when winching, worse case scenario I could use this if need be to up the revs.

regards

Dave

 

[frank rabbets]

According to the manual if you rev the engine when cold the timer piston moves to it's standard position so although the wax themo is not hot nor moved there is no ACSD advance.

My old Land Rover diesels had no ACSD but used to smoke when cold. I'm just wondering if the ACSD and cold idle up are to do with pollution requirements, together with the egrs's and intake heater. The manual says the idle up is to reduce warm up time. But I don't know who wrote it lol.

 

[frank rabbets]

Yes Dave the manual says to disable the ACSD to check the timing. You could just take the whole lot off.

 

[Dave2000]

Yes Dave the manual says to disable the ACSD to check the timing. You could just take the whole lot off.

I did Frank about 5 years ago.

regards

Dave