XUD Bosch VE Pump query

[Geoff Lebowski]

On early (circa 1990) Bosch equipped xud turbos there was a timing advance mechanism on the front side of the pump. Whilst some were mechanical and some were hydraulic (on later models circa mid '90s) they were there to advance the timing a few degrees for cold starting.
On later models, but before the TPS and ecu were involved (P plate 96/97), this timing advance module disappears.
Does anyone know why?

[citronut]

didnt they just have a cable operated by a wax stat which released the cold start lever which just let the revs drop to normal tick over,
and later one's had a servo but also the wax stat that opened and closed a set of contacts, which fed the servo with a negative/ground connection,

[spider]

I think most turbo's had the advance unit with the contacts on the fast cable as Malcolm has said, earlier NA units did not have this unit fitted as far as I can tell.

Having removed one from a (mechanical advance pump) and fitted the blanking plate, it made no real difference to its cold running as the fast idle cable did all the work in effect. I'd assume they deleted it from some models (warmer climates maybe) as it did not really need it.

[CitroJim]

The later mechanical VP20 had electrical cold advance. What looked vaguely like a stop solenoid on the side of the pump the front timing device plate activated it..

Otherwise all others had mechanical cold advance...

[Geoff Lebowski]

That's the later type Jim, yes, the ones that look like a stop solenoid.
It's the Lucas pumps that use the wax stat combined with an electrical contact to both advance timing and increase revs.
The Bosch, uses the same waxstat for increased cold idle, but had a separate 'device' for timing advance, be it coolant/mechanical or electrical/hydraulic.

My query rises from repeated cold start lumpiness. I have checked/renewed the glow plugs, all contacts are nice and clean/sound, the battery is only a couple of years old and the alternator is good. The glow plug relay is also sound. I've even advanced the pump a degree permanently to no avail.

Injectors maybe, buy they aren't normally associated with poor starting (AFAIK). Economy is good. I've not checked compression but I've had the engine from new and it's been regularly maintained.

Spider, I'm inclined to agree with you - that the manufacturers deemed it a 'redundant' (expensive???) device, but that goes completely against the grain as far as Euro emissions are concerned.

I wondered if PSA changed the camshaft timing, or the VE pump timing was altered. Either more advanced or possibly an internal change.

I have to say I think CAV pumps are better starters, hot or cold.....

[Peter.N.]

Most of the ones I have had didn't work anyway, the waxstat doesn't seem to last for very long, I did replace one but it didn't make a fat lot of difference.

Peter

[Xaccers]

That's the later type Jim, yes, the ones that look like a stop solenoid.
It's the Lucas pumps that use the wax stat combined with an electrical contact to both advance timing and increase revs.
The Bosch, uses the same waxstat for increased cold idle, but had a separate 'device' for timing advance, be it coolant/mechanical or electrical/hydraulic.

My query rises from repeated cold start lumpiness. I have checked/renewed the glow plugs, all contacts are nice and clean/sound, the battery is only a couple of years old and the alternator is good. The glow plug relay is also sound. I've even advanced the pump a degree permanently to no avail.

Injectors maybe, buy they aren't normally associated with poor starting (AFAIK). Economy is good. I've not checked compression but I've had the engine from new and it's been regularly maintained.

Spider, I'm inclined to agree with you - that the manufacturers deemed it a 'redundant' (expensive???) device, but that goes completely against the grain as far as Euro emissions are concerned.

I wondered if PSA changed the camshaft timing, or the VE pump timing was altered. Either more advanced or possibly an internal change.

I have to say I think CAV pumps are better starters, hot or cold.....

Have you ruled out air ingress by replacing the leak off pipes, and replaced the filter to pump pipe with a clear one?also blown down the fuel return to make sure it is clear?