2012 Disco 4 Just wont start.

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New Member
Morning guys.

I've been lurking here a while and often have a read up, but I seldom post if at all.
I am posting today because I cannot find a relevant thread concerning my issues and I thought that it may help others once I get it running.

A tiny bit of history as I know this isn't the "introduction section" but I have built / repaired / fixed many Lion engines and I do have a clue what I am doing, but I am missing something here and it has stumped me, so I am asking for any clues to help me get it running or at least point me in the right direction.

I bought this car through the trade not running, The water pump was hanging off, literally, and it cooked.
One of the heads was fubar along with three pistons, but the crank was OK,

So, Three new pistons, new rings all round, hone the bores, new set of tappets, good used head, two skims and valve reseating and new shells all round, perfect. New water pump, two new belts with bearings, new trigger ring, new oil level sensor, new crank sensor, gaskets etc and a rebuild, perfect. Yes I have the timing pin kit and the trigger ring tool.

It spins over and it sounds like it has compression as it should, but it wont fire. if I give it a squirt of easy it will run for a second or two, but I dont want to keep doing that, I now know that it is fundamentally right internally, but it wont start.

I checked the low pressure fuel flow and that is good, the tank pump is kicking in and it is using the right amount of power to run. I have bleed the low pressure fuel feed to the schrader valve.
I crack open one of the injectors and I get a leak, so fuel is getting to the injector, and my snap on is not bonging up a low fuel rail pressure fault.
So, I assume the fuel feed is ok, but I am not totally convinced of this yet, I have a fuel pressure testing kit but the way these injector pipes are routed it is impossible to connect to them, The Snap-On is giving me a high pressure reading but to be honest I cant make head nor tail of these readings, I am not getting any numbers that correspond to the workshop manual, but I am getting a reading, so I assume it is ok enough to start.

So, mechanically it is all good, and it has fuel, that only leaves four options and these are, electrical issues, injector issues, pilot error and something I have not yet thought of, and that is why I am asking on here.

Having a read up on here, someone mentioned a broken / corroded wire, hmmmmm, I dunno, but best to check, so I took the body off again pulled the engine and removed the engine loom and did a continuity check on every single wire to the plugs and all were good, I also double checked the valve timing and replaced the crank sensor and fitted a new trigger ring.

I have a noid test kit, I used this and got nothing at all, so I tested the kit and the led's worked, but I was putting 12 volts to them and I do not know what the voltage of the injectors are so if they are 5 volts as I suspect, then they wont light up anyway, so I failed there, I have a ( far too advanced for me) MAC electrical tester but I cannot get a reading from it once connected to the injector wire when spinning the engine over, I dont know if it doesn't pick up a milli-second pulse, or if there isn't one ???

My thoughts are now heading down the ECU route, I removed it and there were none of the tell tail signs of corrosion and it looked ok, plus I dont see how it could go bad just sitting there, but ?

Whilst on the electrical page, yes I can confirm the earth lead on the drivers side wheel arch is good, so is the smaller one on the passengers side, the main plugs under the passengers head light are good as is the main one under the rear passengers side wheel arch. all these have been checked, removed and re-checked.

I am now down to three real options, the ECU, the fuel pressure and the injectors.

I am ruling out the injectors as I dont see how all six could have failed.
I am not sure on the fuel pressure issue because it all "seems" ok.
This leaves the ECU.

I looked on here to find any threads on TDV6 ECU failure and I couldn't find any, so either there are none because the issue doesn't exist, or, I can't find any, can you please let me know if this is a possibility and if so I will send the ECU off for a rebuild.

If you are still awake :) can you think of anything I may have missed that might be the cause of this non starting saga ?

Sorry for the ramblings, but this saves you asking "have you checked this".

Oh, there are a couple of error codes on the Snap-On, but these are the obvious ones because not everything is connected, like ambient temp sensor on the front bumper, Mass sensors ( but these have been fitted, but not at the moment) and normal stuff like oil temp / pressure ect.
There are no serious fault codes present.

I thank you for your time.


Thank you for the video above, I have seen this video before as this is about the trigger wheel, as I have said in my post, I put the original trigger wheel back on, and it would not start, not knowing why it wouldn't start I took the engine out and checked everything again including the cam timing, I also checked the whole loom, I then replaced the trigger wheel with a brand new genuine land rover part, and I changed the crank sensor for a new one too.

This issue is definitely not something obvious, or maybe it is ???.
Most common rail need 200 bar in the rail to start?
Maybe take one injector out of the head and plumb it in, but have it firing into a tin/jar etc to see what it is really doing.
Pop the leak off pipe off an easy to get to injector and see if any fuel is being returned.
Thank you Lynall, I have had similar thoughts.

I can have the body off in about an hour, so I am thinking I'll do that and join directly onto the pump, I've parked it up for the minute to give me time to see what you guys might come up with and to consider what to do.

I have started working on something else and it is like a breath of fresh air to work on something else, I am beginning to really dislike this car.
Update on this POS.

The body has been off and on more times than I can remember.

I bought a "supposably" good used high pressure pump, it is giving the same readings as my old one, there is pressure at the rail, and there still isn't any fuel related faults on the Snap-On. I removed number 4 injector and spun it over and there is loads of fuel both from the rail and bleed off pipes from the other injectors.

If I give it a sniff of easy it'll fire up immediately and with a continuous flow of easy it'll run and purr as it should.

So, it isn't mechanical, and it does have fuel, so, I am now going with the ECU.

I called a company that I have used in the past for the Toyota's and they dont do these ECU's, Hmmmm, this is odd I thought.

Is it because normally they don't fail, or is it because they are not coded and it is cheaper to swap them out than it is to have them checked and repaired ? I have 5 Disco 3's here and a Disco 5, but not another disco 4 to check, so I need to ask, are they plug and play ?

There are many for sale on ebay, and non mention re-programming, so it looks like they might by plug and play, also, there are so many for sale that surely sellers wouldn't list them for sale if the buyers kept sending them back because they needed to be coded at a cost of "too much".

So, now I am convinced they are plug and play but I would like to be assured on this, so please let me know if you have any knowledge on this.

Just a reminder, I am getting no error codes on the snap-on for ECU fault, other than the normal things that have not been connected yet. no codes for sensors, or timing etc.

I am pushing this POS out again now to get on with something easy :)


They need to be coded, but can be 'virginised' so the process is the same as replacing a defective one with new.
Are you seeing engine rpm as a valid value?
Thank you for this, is the coding a main dealer job, my problem would be getting to a dealership.

As for rpm, The rev counter does fluctuate on the dial, so I should think it is getting a pulse, I cant understand the multimeter fully but I am getting a continuous measure of readings when I spin it over whilst connected to the injector plug.

If you have any idea or suggestions on what to try next please email me [email protected].
Is there some sort of immobiliser fault telling the car ecu not to fire the injectors?
Have more than one key?
No, it doesn't need a dealer to code, unless you have a relatively 'high level' diagnostics kit, (personally I wouldn't attempt with a 'cracked' version of SDD) I'd look for one of the mobile diagnostics type of outfit and talk to them first to assess their level of confidence & competence to do the work.
I don't think it'd be a security issue (if it was, you'd have a relevant DTC) as it's cranking, the start authorisation is one of the functions that needs a valid security seed in the ECM, along with running the LP fuel pump.
When you say there's DTC for stuff you haven't connected yet, can you list them? there may be a relevant code.
What you have said is exactly what I thought - understood it to be.

If it spins over with the ignition on, then immobilizer is off, plus the low pressure pump is working, so the basic security happiness has been achieved.

The codes I have were, Coolant level - because the header tanks was not fitted so no water.
Outside temp - because the bumper was not fitted.

Air flow meter X2 as it also wasn't fitted.

One other that I forget now, and I ruled that out as it too was of similar ilk.
I will check tomorrow.

Thanks for your help.
Air flow meter won't help as it also provides the air intake temperature - which is relevant to injection quantities and rail pressure. You don't necessarily need there to be measured airflow for it to start and run at tickover, but having them connected will rule out reduced fuelling as the cause.
I have had the air filter on, and filled with water, but I have had the body on and off so many times that I don't bother with these any more. It simply will not fire at all, not even a splutter. but the slightest sniff of easy and it jumps into life.

I don't think the air flow meter connection is the issue :)
Good news.
There is no bad news, but that is all the good news I have.

I pushed this POS out and parked it up after my last post in Feb.

I have regained some assemblance of enthusiasm to have another go. So it will be back in the workshop later next week.

I have a super duper sparks who does our work for us and I am going to get him to come and test it all, hopefully he will find something, or at least give me something to look at.

I shall report.