Testing lift and TDC sensors

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Testing lift and TDC sensors

Post by Xaccers »

Jim and I put a few more gallons of clean diesel in my old 1.9TD last night to clear it through a bit more as while the cam belt was off, we had snow which the veg in the fuel system didn't take kindly to.

The engine runs, but is very lumpy and produces lots of white smoke.
If we disconnect the lift sensor, it runs much smoother and the taco stops working.
If we disconnect the TDC sensor, it makes no difference.

Anyone got any experience/hints/tips on how best to check if these sensors are working?

We're also going to double check the timing just incase that's slightly out.
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Post by Peter.N. »

White smoke is unburnt fuel, indicative of either retarded timing or low compression on one or more cylinders. If it starts OK on all cylinders I would look at the pump timing. Presumably it uses an EPIC pump, I have not had anything to do with these as both mine are mechanical, so providing the belt is correctly fitted I would think the problem would be in the electronics.
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Post by Xaccers »

It's a bosch pump, with keypad immobiliser (it's the 1.9TD with the problem, not the 2.1TD :) )
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Post by Peter.N. »

OK, you mentioned a lift sensor, that's why I thought it was electronic. The standard Bosch pump has a normally 'sealed' screw on the back of the pump above the injector pipes, screwing this in (clockwise) will increase the fueling, only do it very slightly though, as a little movement makes a lot of difference.
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Post by RichardW »

Mucho info about this system in this thread, and the ones before it that it references....

Synergie troubles

Have fun :twisted:
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Post by CitroJim »

One thing we noticed with Xac's car is that if we disconnect the lift sensor the tacho stops :? This bothers me a little. It seems a little bizarre to operate the tacho from this signal. It was always my belief that the tacho worked from the TDC sensor (the one on the top of the bellhousing).

The fact that disconnecting the TDC sensor without any change to the running of the engine would suggest the TDC sensor is duff. I notice it has three wires. What principle does it work on? Inductive or Hall Effect? How best to test it without substitution? My first thought would be to look at the output of the TDC sensor (and the Lift Sensor) with an oscilloscope but I'm not sure what the correct output should look like :?

Does anyone fancy trying disconnecting the sensors in turn on a good runner and confirm what effect they have on engine running and the tacho? If anyone could hang a 'scope across them, that would be fantastic?

The engine in question is the 1.9TD with the Bosch VE semi-electronic pump.
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Post by RichardW »

Jim,

I think that's right re the tacho. Sorry - the links don't work anymore in the original post (they're Andyspares), but you can get them here:

http://www.frenchcarforum.co.uk/forum/v ... hp?t=10775
http://www.frenchcarforum.co.uk/forum/v ... hp?t=11055

Dave Burns gave lots of good info in the original thread. Sounds like the TDC sensor has gone AWOL for whatever reason. No idea why 3 wires, nor what it would look like on a 'scope!
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Post by CitroJim »

Richard, Thanks :D Dave Burns Posts are extremely helpful :D

So, the tacho should work with either the lift or TDC sensor disconnected :)

It's looking very much like the TDC sensor now then :wink:

I'm wonder why it became unhappy when the original problem with this engine was a slipped cambelt. perhaps when it stopped suddenly the flywheel just made contact with it and broke it.
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Post by AndersDK »

The TDC sensor is a straightforward wirewound coil sensor, the wellknown magnetic pickup principle.
One wire is one end of the coil, second wire the other end of the coil, third wire is a signal shield (earth) braid in the cable.

Even standard coil sensors are often referred to as Hall effect sensors, as a Hall effect sensor in principle is nothing but a solid state (semiconductor element) counterpart to the coil. In principle and circuit designs they work the same way, but the solid state version must of course have some means of a (small) current feed. Which is exactly why the old fashion (but simpler to use) coil type is still the widespread one.

Simple to test : unplug any connector and check the ohms reading. Something sensible for approx a hundred meters thin copperwire should be expected (200 - 2K ohms).

Lift sensor is similarly a 'Hall' coil sensor built into one of the injectors. Exactly the same applies to this coil. Except its the complete injector that must be replaced on a defective sensor :cry:
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Post by Xaccers »

Is it number 2 injector?
Could I just nab another injector off a scrap XUD9TE?

As I've mentioned, the car had veg sitting in it's fuel system when we had a bout of cold weather and snow, so it's likely to have gummed.
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Post by AndersDK »

The injector syndrome :
Engine type to be obeyed -
Bosch or CAV system to be complete with exact mating parts (no mixing !) -

If fullfilled - YES nab that injector/sensor :lol:

Donno if its injector 2. But obviously you would have a 'strange' (extra) cable going to exactly that injector/sensor - not found on the other 3 injectors :wink:
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Post by CitroJim »

Anders, thanks for the info :D

I checked the lift sensor and that read 110 ohms so it looks OK.

I did not check the resistance of the TDC sensor but seeing as the tacho stops when the lift sensor is disconnected, it really does point to the TDC sensor being the problem.

A scrappy should have one Andy and they're a lot easier to get out than an injector :twisted: By all means do pick up a lift sensor equipped injector though as they're always good to have as a spare. Same goes for the ECU if the breaker does not want a fortune for it.

I'm not sure if the TDC sensor is injection system specific but I'd do all I could to get one that goes with the Bosch pump/ECU.
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Post by Xaccers »

Well I need to go to the scrappy after pay day to pick up two new height levers, so will add a TDC sensor to the shopping list and maybe some injectors/ECU if they're not asking too much for them.
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Post by CitroJim »

Xac wrote:Well I need to go to the scrappy after pay day to pick up two new height levers, so will add a TDC sensor to the shopping list and maybe some injectors/ECU if they're not asking too much for them.
Let me know when you're going and I'll come along :wink: I must make a list as well :lol:
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Post by wheeler »

yeah both of these sensors are of the inductive type & i reckon the only 'proper' way to check them is with a scope. resitance checks are only really showing if its ok at rest,i have seen many resistance checks showing up ok but a scope pattern tells a different story.
the signal from the TDC sensor should be a clean AC sine wave but remember there is a missing tooth on the flywheel so there will be one wave cycle with double the wavelength.
the needle lift should be similar but more jagged,kind of hard to describe.
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