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Mayfair86
Member Since: 25 Nov 2020
Location: Bedfordshire
Posts: 11
  
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Hi all, I have an issue with my Discovery 3 V8 project, I am so close to completion but it wont start after fitting the engine.
Overview: I have swapped the blown TDV6 engine in my D3 to a 4.4AJV8 from another D3. I bought a complete donor car and have swapped all of the electronics across. The major part of this conversion is that it is now mated to a Manual gearbox.
The engine turns freely by hand. I have swapped the keys internals so the immobiliser de-activates (no red flashing lights on dash). I can turn the key and other than some issues relating to things trying to find the auto box tcu everything works as it should. As I turn the key the fuel pump primes, the throttle butterfly moves with the pedal, the brake lights work as they should, the epb works. However the start function doesnt seem to. I have had the starter out and re-built it, cleaned earths and +ve connections. I have tested the starter relay in the battery fuse box, I have grounded the P/N switch in the tcu plug on the loom. I can get the engine to turn over by triggering the starter relay manualy (with a peice of wire) but even with the key in ign run pos it wont fire. If i try to start it on the key the fuel pump kicks in as it should but no cranking. I have trawled through all the wiring diagrams and as far as I can tell if I can get it to crank over with the relay, the only think missing from starting it with the key is the signal from the ECU to the relay. I have plugged my IID tool in and when I try to start on the key it says that the fuel pump and starter relays go 'active'.
Does anyone know any other reason that would inhibit the starting of the engine with the lack of TCU? From what I can tell from the diagrams the only link the TCU has to the starting system is the P/N switch.
Any help is greatly appreciated!
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 8th Dec 2022 11:00 pm |
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jenseneverest
Member Since: 12 Jun 2017
Location: somewhere
Posts: 769
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the CAN system will be looking for the Auto gear box ECU which is obviously not fitted.
There is also a clutch position sensor, manual gearbox gear indicator. (possibly more stuff ?? )
It is beyond me, but i would imagine that you need to tell the CAN system it is now a manual gearbox.
Im not sure how else the keys affect the system either.
There is a guy on here that did a conversion to a v8 (think diesel )
It may be an idea to ask him for help
https://www.disco3.co.uk/forum/tdv8-retrofit-169498.html
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| 9th Dec 2022 11:11 am |
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Pete K
Member Since: 15 Jan 2016
Location: GL
Posts: 10620
 
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I'd read the fault codes, see if that gives any clues.
The starter relay requires both - and + coil signals to be enabled to crank. Sounds like neither are working!
Trace them both.
there are Significant differences between auto and manual wiring to that relay.
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| 9th Dec 2022 6:19 pm |
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Mayfair86
Member Since: 25 Nov 2020
Location: Bedfordshire
Posts: 11
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Fault codes don't show anything other than the usual passive coil one that every disco seems to have and the TCU Comms error, but this shouldn't inhibit starting. The relay has good power supply to it, good connection to the starter and a good ground (it's grounded via the P/N switch) all of which works when power is given to the ECU side of the relay (demonstrated by the fact that the engine turns over as it should, just not on the key). Indicating the ECU isn't sending it's signal as it should.
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| 9th Dec 2022 6:28 pm |
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Pete K
Member Since: 15 Jan 2016
Location: GL
Posts: 10620
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Have you checked the key crank request signal is getting to the ecu ?
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| 9th Dec 2022 6:37 pm |
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Mayfair86
Member Since: 25 Nov 2020
Location: Bedfordshire
Posts: 11
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On the live values list there are 2 outputs, 1 for fuel pump relay status and one for start relay status, when I engage the start on the key, both of these go from 'off' to 'on', the fuel pump relay kicks in and the fuel pump activates but the starter one doesn't.
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| 9th Dec 2022 6:42 pm |
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Martin
Site Admin and Owner
Member Since: 06 Nov 2004
Location: Hook Norton
Posts: 18537
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You've grounded the P/N output wire from the TCM, but it should be bridged to +12V. Try bridging to pin 9, green/white (ignition supply from Fuse 64)
The PCM/ECU supplies a negative feed for the relay coil as the start signal, so the P/N output must be 12V to allow the relay to close!
Doesn't answer why the engine doesn't run when manually cranked though. 06 D3 SE / 15 LR D90 XS SW / 88 LR 90 Td5 / 68 BMW 2000 ti
Any issues with the site let me know!
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| 9th Dec 2022 7:48 pm |
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Mayfair86
Member Since: 25 Nov 2020
Location: Bedfordshire
Posts: 11
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You sir are a genius! There are actually 2 green/white wires, I chose the thicker one which is pin 6 (pin 9 is a small brown wire) and it now cranks on the key! Didn't start but I think that's now down to the LPG ECU not firing the injectors so an easy fix, fingers crossed! I will study the wiring diagrams again to try to figure out where I went wrong but the main thing is that it works!
Thankyou very much!
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| 10th Dec 2022 9:56 am |
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smithie1623
Member Since: 16 Apr 2014
Location: Rossendale
Posts: 107
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Don't forget that the engine ECU is going to be looking for a Park signal from the gearbox.
you might need to replicate this. on the dash is it giving you the gear number ?
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| 10th Dec 2022 11:13 am |
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