Crank Position Sensor Help

Hi

I have a TD5 (15p engine) and it used to start fine on cold but then running became poor as it got warm, with it really struggling to start. I read on a forum that a failing CPS could be at fault, so I set about replacing it.

I changed it for an OEM one from JGS4x4 (All Makes) and took the old one out (after finding it, and a faff!) and replaced it (no shim on the old one). I could see any issues with the connected and it seem connected ok.

But - it wouldn't start. I replaced it with the old one - and still wont start. Nancomm is showing zero RPM which if I understand it correctly, means the sensor isn't picking up a reading, and this could be 1) spacing, or 2) wiring, or a faulty sensor (although the old one didn't work!).

Any advice?? I think I can take the old one out and check the Ohm between the two, and it should be 1300 ohm I believe. If this is the case, then the sensor is ok, so maybe fit a spacer? If that doesn't work, then is it wiring? And from what I can tell, its embedded in the harness and a pain to fix, so need to replace with more direct wiring ? Not that I know how to do that .....

All help and advice appreciated.

One possibility is that there is a fault in the wiring or the multiplug. The conductors can get brittle or the insulation can come off. I see some people are doing a repair kit for the wiring loom as well as a replacement sensor these days:
https://www.ebay.co.uk/itm/22349427...SkPkGnNB3n2OlNHE-WYGD4WH37NYcmPYaAgIJEALw_wcB
Sensors get less sensitive the further away from the flywheel they are, so if it won't work with the sensor fully home it probably won't work with it spaced away either. The easiest way to try is with a washer on the bolt between the sensor body and the bellhousing.

Another fault that TD5s sometimes develop is that the electromagnetic signal from the starter motor is apt to interfere with the signal from the crank position sensor, hence the lack of an RPM figure. Is it possible to try starting it without the starter motor? For example by rolling it down a slope or getting someone to give you a tow? They're a bit heavy to push by yourself.

Thanks, some good advice. It was working fine when I drove it onto the drive - and replacing the sensor is the only thing I've done - so I'm guessing that would discount Starter Motor interference, but faulting wiring, or position of sensor is a real possibility, I'll dismantle and explore a little more this weekend and see if I can work it out. Landys, don't you just love them !

Well, whatever fault it is, they've all got to start sometime. So the fact that it ran when parked doesn't really narrow it down that much.

The wiring looms of TD5s seem to be rather prone to faults. Land Rover seem to have had a batch of cable that has rather stiff brittle conductors and insulation that is apt to chafe through and flake off in the mid 2000s. A few years ago I got a whole new engine loom (not just the injector loom, but the whole 'red plug' engine loom) and the wires were much more supple. The other thing that's unreliable is the ECU. As most of them are around 15 years old or older now they can fail in interesting ways. It's perfectly possible for an ECU to show up as healthy with the Naonocom (and even when sent to a specialist ECU repair shop) yet fail to start the car. I've had more ECU failures than I've had flat tyres so I now carry a spare. Usually of course they show up fault codes but not always. After all, you wouldn't expect a 15 year old computer to be terribly reliable so it's not surprising that the same happens to the ECUs.

That reminds me - I'm sure you've already looked, but see if the injector loom is leaking oil. As the Defender's ECU is a long way from the engine it doesn't always show up at the red plug, so have a look in the multiplug where it goes in the cylinder head.

Hi, Thanks for the response.

The Injector Loom was something I checked early on a replaced. From all the responses, I've created the following diagnostic sequence, does this look sensible - if so, I'm going to start from the top. Anything missing?

BTW - I wondered about a loom replacement. DIY, or specialist job? I'm a newbie to all this

Root causes to exclude

I. Battery

II. Inertia Switch

III. Immobilizer (where fitted)

IV. Fuel Pump

V. Fuel Return Valve

VI. Starter Motor

VII. Crank Sensor, or Wiring

VIII. Fuse/Relay


Approach

1. Ensure that your battery is in good condition and fully charged at around 12.3-12.6 volts. If it drops below 10v when starting, it will not start. The battery should show 14v when the engine is running.

2. If it’s a TD5 with an immobiliser, try resetting it, which involves a sequence on the key fob on unlocking and locking. **Mine doesn't have an immobiliser

3. Check the Inertia Switch has fired – centre of the firewall in the engine bay, it pops up if fired, just push it down. Its there to cut off fuel in the event of an accident. ** Checked and it hadn't fired.

4. Check there isn’t oil in your ECU (under the driver’s seat, red cable – disconnect battery beforehand). If there is oil, clean it using contact cleaner and reconnect. To prevent it, this is typically a failure on the injector harness (See Replacing Injector Harness on TD5) where oil seeps through the connector and down the wire, which with movement, makes its way into the ECU plug. I’ve seen some raise the ECU into a vertical position to prevent this as well as help with water ingress, if you go mad when off-roading). NOTE: Oil can eventually make its way into your ECU and break it. ** Checked, o Oil. But can't rule out faulty ECU.

5. If could be a fuel issue, Turn the ignition to II position, fully depress the throttle 5 times, the engine management light with flash, then wait until the engine management light stops flashing and crank it then... if it starts right away it might be a fuel supply issue

6. The Crank Sensor (a Variable Reluctance Sensor (VRS)) can stop a TD5 from starting, it should register around 300 rpm when cranking otherwise the ECU wont engage the fuel pump – the starter motor could also be at fault. If you’ve a Nanocom, using the ‘Inputs Fuelling’ setting, you can get an engine rpm reading when cranking/towing. If you’ve a Nanocom, and you see no RPM when either cranking, it could be the sensor, circuit issue or the bad starter motor interference.

Try bump-starting it/towing it –remove the starter relay, and turning the ignition at the same time), if it starts, it’s the crank sensor sensor – if it doesn’t start, then it’s the starter motor.

If you’ve a Nanocom, and you see no RPM when either cranking it from standstill – or pushing/towing, then, the reasons could be one of the following. **Mine is showing zero when cranking still/sometimes with low numbers, under 100

a. The Crank Sensor is faulty. You can test it by measuring the Ohm between the connectors directly on the sensor, and it should read around 1.2 Ohm. ** Tested old and new one and they show resistance

b. The wiring to the sensor could be faulty. The Crank Sensors location is such that it is prone to oil and heat, and this can cause the wire to become brittle – and its not in the easiest place to repair – if you have to, I recommend fitting a new connected, by either splicing it to the old one OR fitting a new connected direct to the ECU (See Replacing Crank Wire(TBC))


Insert a probe into cavities 13 and 36 on the back of the red plug to the ECU and measure the resistance.


See Checking Crank Sensor/Wiring


c. The Starter-Motor could be interfering with the Crank Sensor (they are close, and worn bushes creates interference). You sometimes see a ‘noisy crank signal’ on the Nanocom if this is the case, but not all the time.


7. If the Crank Sensor is working and the Starter motor is working but it still won’t start, it could be a Fuel Issue, either the non-return valve on fuel distribution head).


Checking the Fuel pump


Switch the pump into purge mode, this will cycle the fuel pump. You can now check you a have a charge on the Relay to the fuel pump (R103) which should be energised with Pin 30, 87 and 86 going live, and you can also check this on the fuel pump itself – or listen for the fuel pump priming sound.


8. If its not the crank sensor, the starter motor, or the fuel-pump, it could be the seals on the injectors. Over time these wear thin/corrode and let air/water through into the compression chamber, making it hard to start – if this happens, you often see water in the oil and the oil level rise. If this is the case, change the copper washers on injectors (See Changing Injector Copper Washers) and clean your oil – you’ll need injector pullers, or a small allen key fashioned into a level, to live the injector free.


9. Check your fuses and relays - **TODO



Fuse Box & Replay Information

Fusebox Under Seat (P140)

Fuse 4 (20 amp) – Fuel Pump

Relay 4 (R103) – Fuel Pump


Fuse 5 (30amp) – Starter

Relay (R102) - Starter



Cabin Fuse Box

Fuse 11 (10amp) – Fuel Relay

Relay 31 is the Starter Motor

Fuel Pump Information

Fuel Pump is trigged by C0658-5 on the ECM (Black Plug), when the relay is energized, it will send power to the pump via C0730-30 connected on the fuel pump.

Fuel Pump should push +4 bar of pressure if working

Checking Crank Sensor Wiring


CKP ( 2 x Pins, C1068-1 & C1068-2) are outputs, connected to C0158-13 (pin/black) & C0158-36 (white/blue), with a (positive signal on 13 & and a negative on 36) on the ECU red plug). NOTE: To protect the integrity of the signal, a screened-earth is used, with the earth path going to C1058-16.


It should measure 2-3 volts when cranking, to 6-6.5 volts at 1000 rpm. These readings depend on the correct air-gap between the sensor and the passing teeth of the relator ring (on the flywheel)


The CKP sensor can fail or supply an incorrect signal if one or more of the following occurs:

Sensor assembly loose.

Incorrect spacer fitted.

Sensor open circuit.

Sensor short circuit.

Incorrect fitting and integrity of the sensor.

Water ingress.

Seems reasonable. There are one or two things that are different in my experience. The fuel pump starts as soon as the ignition is on, even if the battery is very low (it just makes a slightly lower note) and isn't conditional on the ECU seeing 300 rpm from the crank sensor. Yes, the injector washers and seals can fail but I'm not sure that this would give you water in the oil, as there's nowhere for it to come from. Diesel from the fuel gallery can get into the sump if the O ring seals have lost their elasticity, and combustion gasses can get past a poor copper washer into the fuel gallery. But if water appears in the oil it may be coming through a head gasket fault or a crack in the cylinder head. Unless of course you've been doing some particularly ambitious wading.

Replacing an entire red plug wiring loom shouldn't be impossible at home. Fiddly and frustrating perhaps but it's not technically difficult. I don't think you can get original Land Rover items any longer but somewhere like Autosparks should be able to sort you out.

Thanks. You're absolutely right, it's Diesel getting into the Oil from the washers, not water

Interesting point on the ECU - it's funny how you read different things across different threads. It made sense when I read it, I wondered how i'd get an authoritative answer. Does that mean the Crank Sensor only controls the timing of the injectors ? and should I see an RPM when cranking?

Fiddly & Frustrating is the story of my life with landys