Thread: Startup Failure on 2005 Disco 3 (TDV6 Auto with Euro 2 HPFP)

Dear Abby,
I have this friend ....

A mate of mine with a 2005 Disco 3 is experiencing an issue with getting his TDV6 to start (the issue is that it flat out won’t start!). Sorry but this is going to be a long post - bear with me.

Background
Neil took the body off the D3 to replace the turbo and give it a good clean – the car is 19 years old after all but fastidiously maintained as he’s a retired automotive mechanic. He’s also had the body off my 2015 D4 to replace the 3.0Lt engine which seized at 66,000km (that’s a whole other saga). When we put the body back on mine, it took a while to bleed the fuel system but then it started fine and it now runs beautifully. So let me reassure you - Neil’s not a novice at this.

The Problem
Having carefully out it back together (paying particular attention to earth connections and to bleeding the low pressure fuel system thoroughly) it cranks well but refuses to fire. The only code coming up points to the High Pressure Fuel Pump (HPFP) – P0001 VCV Open. The Volume Control Valve solenoid measures 2.7 Ohms which is within the normal range. It's a Euro 2 pump and these pumps have the reputation of being very reliable so we were reluctant to replace it without being quite certain it was the culprit. So he had it tested (on a test bed) and the test report shows it to be good. This bears out our own belief that the pump itself is OK and is not the cause of the non-firing issue.

A Key Problem
Initially there was a problem with the 19-year old battery in the key having died, but I replaced the battery with a charged up new one (I’m an electronic tech and this is not rocket science believe me). The key was recognised by the RF charging circuit OK and the security light on the dash extinguished so the car could then crank. Initially the remote door locking wasn’t working but I held the key under the steering wheel console and operated the buttons and the key fully resynched and the remote locking now works fine so I’m confident that the immobiliser is not active – and if it was, I believe it would prevent cranking.

How it Should Work (briefly)
The P0001 code points to an open circuit around the VCV. It receives 12V from the ECM relay (R116) and 10A fuse 13E, and this is fed to one pin on the connector to the VCV. The other pin is fed to the Siemens ECM which has a switched output to ground (presumably via an open collector transistor) and the ECM modulates the valve to adjust the fuel supply from the supply (vane) pump inside the back of the HPFP (bypassing excess fuel back to the tank) to the 120 degree triplex high pressure pump which feeds the fuel fail at about 150 bar. There’s also a Pressure Control Valve on the output of the high pressure pump to compensate for pressure variations in the rail caused by the injectors opening. Both VCV and PCV are controlled by the ECM of course.
The Diagnostic Trail

All indications, but especially the P0001 code pointed to the likelihood that the VCV is not opening to admit fuel to the high pressure pump – one would expect that initially on cranking it should fully open and once the engine fires it should begin to be modulated by the ECM to regulate fuel flow.

The Diagnosis (so far)
First step was to try and establish that there wasn’t a problem with the VCV itself and then move to the wiring. So we have proceeded as follows:
• Check VCV solenoid coil resistance – OK at 2.7 Ohms
• 12V present at VCV from relay R116/fuse 13E – all correct
• Wiring continuity from ECM connector C0411C (the brown one) pin J4 to the VCV – all correct
• Continuity from C0411C (the brown one) pin J4 to the VCV through the solenoid and out towards fuse 13E – all correct
• Continuity from ECM power ground C0872L pins M1, M2, M3, M4 to battery ground connector – all correct
• 12V on the ‘top’ side of the VCV when the engine is cranking – correct
• Voltage developed across VCV solenoid when engine is cranking – not happening
• Current flowing through VCV solenoid when engine is cranking – not happening
Conclusion being that the ECM is not grounding the ‘other’ side of the VCV solenoid

The next step might seem a bit agricultural but we were desperate at this point:
• Disconnect ECM from VCV and apply 12V directly across the VCV
• Engine starts beautifully and idles smoothly, but there is no response to accelerator (not surprising I feel because the ECM knows it can’t control the VCV to regulate fuel supply in this condition

This last check has mostly allayed my fear that the Crank Position Sensor or the reluctor ring on the crankshaft may have failed (they’re original) and the 58 short pulses with 2 double-length pulses inverted may not be correct. I don’t have access to an oscilloscope right now (and if you want more info on checking this go to Christian and Vera’s LR Time YouTube channel) to check the pulse form but live data on the SnapOn code reader indicates 500RPM cranking and the smooth idle suggests all is well in this department but until I check with a scope I can’t guarantee this.
Conclusion

Conclusions (so far)
I have concluded now that the ECM is not opening the VCV and I can only think of two possible reasons for this:
• The driver transistor in the ECM for the VCV has failed
I think this is unlikely given the robustness of the Siemens ECM and the fact that there is nothing in the body-off procedure which is likely to have caused damage to the ECM. Also the ECM appears to be working perfectly in all other respects
• There is an input to the ECM which it needs before it will turn on the VCV which is not present
This is the more likely problem in my opinion, but I’m open to any suggestions at this point.

Questions
• First, does anyone have any useful idea of where I should take the diagnosis from here – have I missed something perhaps?
• Second, what is the startup process in the Disco3 as the engine is brought into operation?

I assume that it goes something like the following (but I'd be grateful for any corrections / amendments):

Key to ON
- Low pressure fuel pump activates and provides low pressure supply to the input of the HPFP (-0.3 to +0.5 bar required at the HPFP input)
- Glow plugs activate for appropriate interval then dash light extinguishes

Key to START
- Prerequisites: Transmission in Park or Neutral
- Starter motor engages (can be prevented by the immobiliser module) and engine turns over and the crank position sensor delivers pulses to the Engine Control Module (ECM)
- The Internal Transfer Pump (ITP) takes fuel from the filter and presents it to VCV thus on to the High Pressure (HP) pump
- ITP now delivers fuel to the HP Pump and the HP Pump delivers fuel to the rail

The HP Pump builds pressure in the fuel rail to at least 1500 bar (and the pressure sensor in the rail conveys this information to the ECM)
- The ECM now has the prerequisite information to commence activating the injectors
- The ECM opens the injectors and (hopefully) the cylinders fire and the RPM builds
- The ECM cuts the starter motor (or the driver releases the key) and the engine commences running on its own

The ECM uses the VCV to regulate fuel supply from the ITP to the HP pump and thus regulates supply to the rail. The Pressure Control Valve (PCV) controls pressure in the rail but its primary task is to even out fluctuations in rail pressure due to the injectors opening and due to the fluctuations caused by the pulses inherent in the operation triplex HP pump.
And SUCCESS – the engine is now running!

Is this an accurate sequence of events or have I missed something?

In order to cause the engine to run, the ECM must see:
- Immobiliser not active ie not preventing cranking
- Transmission in Park or Neutral
- Valid pulses from the Crankshaft Position Sensor (58 pulses then a double-length pulse followed by an inverted double length pulse (thankyou Christian of YouTube channel LR Time!)
- At least 150 bar in the HP fuel rail

If any of these is missing, the engine will not start.

Can the immobiliser allow cranking but not allow the ECM to open the VCV I wonder?

Thanks everyone for any information you can provide which might help – Neil and I will be very grateful

Originally Posted by DiscoJeffster

I disagree with a failing pump. It’s not the symptom of one. You are not getting power to the positive side of the vcv which based on the diagram and how they work, means I believe you’re not satisfying a start prerequisite, which is why it’s not powering the relay to drive the vcv.

Why? You’re on the right track. Are you confident the code reader you have is seeing all the possible codes??

Thanks for the vote of confidence there! Yes, I am convinced that the pump is OK. The early ones have a reputation for not failing (unlike the later ones), and this one is an early one and has been tested and it performs to spec.

I'm absolutely sure the issue is around the switching of the VCV from the ECM (this based on my experience as a electronics tech with quite a lot of knowledge of car engines and automotive electronics - well high power broadcast transmitters, car electronics it's all basically the same stuff really just the power supply voltages are different! LoL)