1 Attachment(s)
Resolution - The D3 is Alive and Running
Well I'm delighted to report that Neil and I have finally tracked down the cause of this fault and, as you might expect, it was quite simple and very easy to fix.
You might recall that the ECM was reporting "VCV Open" and our detailed investigation confirmed that the Volume Control Valve on the high pressure fuel pump was not opening to admit fuel to the triplex high pressure pump from the vane type supply pump. We had also confirmed that the low pressure in-tank pump was supplying fuel up to the HPFP and the system had been thoroughly bled (several times). We had confirmed that there was +12V available at the appropriate terminal of the VCV when the ignition was live, but that there was no sign of a ground on the ECM side of the VCV, hence no current was flowing through the solenoid coil. We were able to confirm that the wire from the connection on the ground side of the VCV coil leading to pin J4 on the brown connector on the ECM, C0411C was intact. We also confirmed that the ECM's four ground wires (C0872L pins M1, M2, M3, M4) were indeed grounded and Neil had specifically cleaned the grounding point on the right front guard.
The way I saw it was that the ECM knew it was sending a signal to the driver transistor to turn on (probably an open collector arrangement as is common in such situations) and supply a ground to the VCV. But the ECM also knew that there was no current flowing through the driver transistor (I assume that there's an emitter resistor and the ECM monitors the voltage developed across it when current flows) thus the ECM reported that the VCV circuit was "open-circuit".
This all lead me to suspect that the driver transistor had failed for some inexplicable reason. Having run out of other options this afternoon I left Neil to remove the Siemens SID203 Engine ECM from the vehicle while I went home and emotionally prepared myself to perform surgery on it. This is not the sort of undertaking you approach lightly, even as an experienced electronics tech, and I knew that I could easily brick an otherwise perfectly good ECM if I got it wrong. We did however have a recovery path planned out which would have involved using a second hand ECU, swapping the EPROM with the VIN data, reading the old ECM and flashing it to the replacement ECM. But none of that was needed!
And the prize for correctly guessing the true cause of the fault goes to ...
**** PerthDisco! *****
Neil pulled out the ECM and then inspected the connectors in full daylight and square on. We had checked the pins carefully with a light in situ with it mounted on the firewall and we believed that we had seen everything satisfactorily. No so my friends!
On C4011C pin J4 was leaning from the vertical.
When Neil had first replaced the brown connector onto the ECM after putting the body back on the chassis, he had somehow caught pin J4 and instead of inserting itself into its socket, it had bent and ridden up the outside of the plastic moulding, fortunately into a void in the connector body. If there had been solid plastic there it would probably have folded the pin at 90deg and it would likely have broken when Neil straightened it. But luckily it was only slightly bent and he was able to straighten the pin successfully.
After replacing the three ECM connectors, and resetting the fault codes, the engine started and it now responds to the throttle as it should. At that point Neil broke out a beer to celebrate and phoned me.
So there you are. If you have occasion to remove the connectors on the Siemens ECM for any reason, you need to be very, very careful indeed about reinstalling them, by mating them squarely on top of the ECM. In fact, the safest way of doing it is to release the ECM from the firewall and leaning it forward so that you can see what you're doing because they are something of a PITA to get lined up. Then bolt the ECM back in position.
Neil now has his faith restored in his beloved "Hercules" (so named because of the load it carried when set up for major trips). However Hercules has been relieved somewhat of his burden over recent months as Neil has done a reappraisal of what he needs to carry, and the kitchen sink, along with a number of other accessories, will now be left in the kitchen.
Thankyou all for your suggestions, and encouragement. This has been a frustrating and prolonged investigation. But it has confirmed that if you look at the evidence, especially the fault codes, and proceed logically, you will find the resolution. Just don't make assumptions, and don't overthink it.
And now as I put this thread to bed, Neil and I wish you all good luck with resolving your own D3 and D4 issues.
