TD Bosch Injection Pump - question

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TD Bosch Injection Pump - question

Post by BX Bandit » Mon Sep 04, 2006 7:16 pm

As I understand it there are two devices associated with cold start on the Bosch Turbo pump.
1) Waxstat which increases revs until warmed up: Located in thermostat housing with cable going to rear of pump
2) A timing (advance i think) device with its own coolant supply. Uses expansion of the unit when hot to push a cable linked to a small arm located at front of pump.

My question is about device 2 above: How much travel is there supposed to be between hot & cold? And how should adjustment be carried out to ensure correct operation? Anyone know what the effect would be of disconnecting it?
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Post by Vanny » Mon Sep 04, 2006 9:35 pm

I believe for adjustment, the cable from the little magic box (which is jsut a different wax stat) should be slack and thus not affecting the fueling when hot. And from this, removal will simply mean the timing isn't advanced when first started.

Dave Rutherford (who seems to have bags of experience with the blighters) reckons they don't work almost from the day they leave the factory and thus removing them will make no difference, and based on this i removed the one from the 1.7td and it made absolutely no change what so ever (except perhaps shedding a few grams!).


I've also noticed that many of the wax stats that screw into the thermostat housing dont ever seem to move when going from hot to cold, however the old 19rd had one that worked and DID make some noticeable difference first thing on a cold morning (but only to engine note and not anything else!).

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Post by jeremy » Mon Sep 04, 2006 9:41 pm

The cold start deviceoperates on the engine timing (advances) to reduce emissions. That system replaced a simple fast idle.

The waxstat devices seem a touch inconsistent - having replaced one on my TD BX and finding it has failed again within 25,000 miles whereas our ZX has done 32,000 miles in our ownership on the same one and it didn't look as though it had been tampered with before then.

On the Roto-diesel they work rather nicely - giving an increase of idle speed of 150-200 RPM and a nice smooth engine when cold - and no visible fumes!

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Post by Brian » Tue Sep 05, 2006 8:36 am

I have collected quite a few dud waxstat devices over the years, the ones that screw into the thermostat housing.

Of these, I have two types, and one can be carefully dismantled, and the waxstat bit can be replaced.

From a collection of water thermostats, I removed a working bit and grafted it into a dud one, this has now been working fine for more that 2 years now.

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Post by DavidRutherford » Wed Sep 06, 2006 10:34 am

Some varieties of the Bosch TD injection pump have two waxstat systems, and it sounds like you have one of them. Instantly recognisable by the small diameter coolant pipes widing their way across the pump to supply the second one.

The first waxstat, screwed into the thermostat housing (and common to almost all XUD, TUD and U25/M25 engines) adjusts the engine idle speed only. These almost never work, and it doesn't matter. If you're feeling adventureous, then you can adjust the anti-stall screw (accelerator bottom stop) and the hot idle speed screw to compensate, but very very rarely is this needed. I've only ever had one engine with a working idle waxstat, which was a 40k mile old 1.4TUD engine.

The second waxstat (the one on the front of the injection pump) adjusts the injection timing only. These also almost never work, and again it doesn't really matter. The point of them was to advance the injection by a few degrees, only when the engine is cold, to reduce emissions a little bit. (to ensure complete combustion within a cold cylinder). You can hear the effect by moving the lever it operates on with the engine running. The slightly deeper growl, with more diesel clatter indicates advanced timing.

The 17TD engine was the only engine to recieve this second waxstat, as N/A models don't have it, and 1.9TD engines use a completely different system (which appears to operate using an electric solenoid buit into the bottom of the pump.)

I'd say if your engine is running well, and doesn't shake the car to bits on a cold morning.... don't worry about them!
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Post by AndersDK » Wed Sep 06, 2006 10:43 am

David -

The single waxstat type does not just raise the coldstart idle revs. It does in fact modify the injection timing to decrease the risc of a cold engine stall.
You will learn that when the winter temp gets below 0degC (like most of the time around here) - it is definately needed to avoid constantly stalling of the cold engine.
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Post by DavidRutherford » Wed Sep 06, 2006 12:30 pm

AndersDK wrote:David -

The single waxstat type does not just raise the coldstart idle revs. It does in fact modify the injection timing to decrease the risk of a cold engine stall.
Anders.... are you sure about that?

From my experience of diesel injection systems, and having pulled a number of these injection pumps apart, as far as I can tell, the lever that the single waxstat pulls on is a "pure governed*" speed control, and not a timing control.

(*as opposed to a combined fuel volume & governed control, such as the accelerator lever)

You can tell by moving the little lever that it pulls on... the governed idle speed will change, but other than the naural change in injection timing due to engine speed change, the timing remains the same. (and I've checked this with an electronic timing sensor on 2 different XUD's... )

But then your injection pump set up may be different for scandinavia, given how chilly it can get up there.

.... but then I've also had reliable starts and cold running from XUD engines with failed waxstats, even on -20°C mornings.....
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Post by BX Bandit » Mon Sep 18, 2006 7:19 pm

Thanks for the info:

I finally got round to disconnecting this cold timing advance device - the engine does not like cold starting any more....so it clearly made a difference. However, I there is very little difference between hot and cold so I'm thinking it may be a dud...anyone know how far it is supposed to move and where I can get one (save for Citroen.....)?
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