Injector pump microswitch

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Chris Peddie
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Injector pump microswitch

Post by Chris Peddie »

Hello all,
Does anyone know the purpose of the microswitch on top of the injector pump which is opened/shut by movement of the accelerator arm - it's on a 1996 1.9TD, without any of the electrickery control gubbins. The book of dubious truths lists it as a throttle position switch or something, but makes no reference to its function.
After the car has been sat in the sun all day, the aircon compressor cuts out at the slightest touch of the accelerator, but engages when I lift off the power, and also stays engaged when at idle but cuts out if you rev the engine before engaging back at idle. This all seems to correspond with activation of the microswitch - if I tie it closed (at the idle position) the car seems to drive perfectly normally, but the compressor stays engaged and hence the aircon then works properly.
So, what's the purpose of this switch, and could I just unplug it until I have another switch to try (it feeds down to a blue plug mounted on the front of the pump)??
Thanks in advance!
AlWilliams
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Post by AlWilliams »

Ah,
I had this quandry, and I think I have the answer.
The micros switch de-activates the pre-heating system which would normally stay on for a couple of minutes after starting, to help the engine run smoother when cold. I kicks in when you apply about 25% throttle, at this level of right foot use, the assistance from the pre heat system is not needed.
Hope this helps.
I belive this feature is only on certain XUD engines as it was on my orignial ZX engine and not on my replavement pug one. Therefore, maybe it's a later feature thats not essential.
Chris Peddie
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Post by Chris Peddie »

Thanks, seems like a reasonable explanation and as you say, I don't think swmbo's 306 has a similar mechanism, though it doesn't have a bosch pump.
Will leave it tied shut for the time being, till I find it on an electrical diagram!!
AlWilliams
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Post by AlWilliams »

You could try Haynes, that's where I worked it out from.
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Kowalski
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Post by Kowalski »

Does that microswitch have anything to do with the EGR? I remember somebody saying that on the 106 diesels, thats what it does.
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Post by Peter.N. »

Probably, on the 2.1td XM that's what it's for.
rotodiesel
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Post by rotodiesel »

On the later 106 diesels, the microswitch on top of the pump, actuated by the fuel control lever definitely controls the EGR via a vacuum pilot valve. I believe the post heat disable was fitted to some earlier XUD engined vehicles, but the latest Beru plugs seem to be tough enough to withstand full post heat to time-out, irrespective of engine speed.
On our "runabout" 106, I have replaced only 2 plugs in 102k miles, and in cold weather, the post heat can be for 5 minutes. With a pre-heat of 5 secs max. in the coldest weather, these latest Beru plugs (10 mm AF hex) give a remarkable performance in an IDI engine.
rotodiesel.
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