Thread: What happened to your D3/D4 today?

Almost finished the rear storage setup, carpeted the plywood and welded some loops for using straps to tie it down.
Just need to make the box for the other side.

Originally Posted by loanrangie

Almost finished the rear storage setup, carpeted the plywood and welded some loops for using straps to tie it down.
Just need to make the box for the other side.

Easy to take out? Looks like a snug fit.

after installing and heavily modifying my Traxide 5U DBS I was getting some electrical gremlins. I would notice the aux battery charging from the alternator at nearly 15V while the cranking battery sat > 1V lower. I also had the occasional blip where the cranking battery voltage dropped for an instant and went back to normal but this triggered a couple of low voltage faults with transmission and TC. Other than that I wasn't getting any other issues and as I was camping at the time I let it ride and planned to look at it when back at home.

batteries1.jpg batteries2.jpg

But while out on a rough track I noticed the LED on the in cab module cutting in and out, turning off completely, going into shared mode even when both battery voltages were >13V, going into isolated/off mode.

Popped the hood to find two things:
1) the positive terminal on the aux battery had worked itself loose. On a rough off road track the lateral movement of the power cable from the aux battery to the rear of the car must have slowly unscrewed the terminal. I've secure the power lead to the side of the battery box and tightened the terminal probably a bit too much!

2) the dog leg on the cranking battery positive terminal was hot hot hot! so hot it had started to melt some of the insulation and even mark the battery (luckily only superficial). I found some ?crud? between the alternator lead and the dog leg has been causing some resistance and heating up which got worse with the DBS. I don't know how long it has been there because I've never had a need to remove the lead from the dog leg - it's not necessary when changing the battery and the DBS isolator hooks up to a free spot on the dog leg so it could have been there since new! Took a lot of filing and sanding to remove all the crud and corrosion on both contacts.

Now both batteries charge at the same voltage and no more low voltage transmission faults.

BUT! while I was in there I found the fan on the ECU behind the cranking battery completely seized... would not spin. Seems to be a pretty standard 6cm x 1.5cm 12v DC fan used in computers so ordered one to replace it. Does anyone know what this ECU is for? I vaguely remember reading it was the audio control unit but could be waaaay of!

Originally Posted by DiscoJeffster

Broken down. Push start, cranks, gets going stuttering and stops. Repeat. Runs for about a second or two. Seems to show rail pressures around 6000psi briefly so doesn’t seem to be a high pressure pump issue though unsure. 2010 TDV6 3.0L. No errors showing on GAP.
Look like she’s off to the Indy on a flat bed. Grrr

For what its worth, don't forget about that tiny restrictor in the fuel return line back to the tank. It is external from the tank; sits in the line just before it goes into the tank, and necessary to drop tank to gain access.
If it fails (loosens) it gives all the symptoms of failed HPFP/LPFP as it doesn't maintain the 4-6 psi fuel pressure to the HPFP.
I have a mechanic friend who works on many D3/4's and has had two with this problem.

Originally Posted by Discodicky

For what its worth, don't forget about that tiny restrictor in the fuel return line back to the tank. It is external from the tank; sits in the line just before it goes into the tank, and necessary to drop tank to gain access.
If it fails (loosens) it gives all the symptoms of failed HPFP/LPFP as it doesn't maintain the 4-6 psi fuel pressure to the HPFP.

i know you’ve mentioned it before, but that just makes no sense. A fixed orifice is never going to maintain any form of reliable pressure drop, is going to cause back pressure in the injector spill lines and will cause huge issues under high fuel flow. The 4-6psi is regulated by the regulator in the tank and flow is managed by the volume control valve. Excess is only returned via the crank case on the pump (lubrication and cooling) and spill from the PCV.

Originally Posted by Macadamia

BUT! while I was in there I found the fan on the ECU behind the cranking battery completely seized... would not spin. Seems to be a pretty standard 6cm x 1.5cm 12v DC fan used in computers so ordered one to replace it. Does anyone know what this ECU is for? I vaguely remember reading it was the audio control unit but could be waaaay of!

The engine control module.

Originally Posted by BradC

i know you’ve mentioned it before, but that just makes no sense. A fixed orifice is never going to maintain any form of reliable pressure drop, is going to cause back pressure in the injector spill lines and will cause huge issues under high fuel flow. The 4-6psi is regulated by the regulator in the tank and flow is managed by the volume control valve. Excess is only returned via the crank case on the pump (lubrication and cooling) and spill from the PCV.

I'd post up my photo of the white board where we drew the fuel circuit, but am a bit ignorant when it comes to such things, but, it goes like this: it flows from the LPFP (in the tank) to the regulator (which is in the tank), then to the external fuel filter. From the filter to the HPFP, but excess which the HPFP doesn't need is returned from the filter to the fuel tank via (through) this restrictor which is outside the tank. This helps to maintain the low fuel pressure to the HPFP.

(As well, excess from the HPFP and injectors goes to the cooler and then back to the filter.)

That is the way we worked it out, anyone feel free to disagree.
Where is this volume control valve you mention?

It is not designed to maintain a pressure drop, it is designed to maintain the (low) pressure in the system to the HPFP and, "control" (if you like) the fuel flow return to the tank which is basically the same thing.
In both cases (D3 & D4) a new one was machined up (easier than stuffing around with LR) to identical size and located it so it couldn't move (which had caused the fuel bypass/pressure drop) and it fixed the problem. He got the 4-6 psi back.
Just saying......
PS: off the subject but, maybe someone someday if they feel inclined could post up an Idiot Proof detailed step by step easy to follow.... for idiots like me.....guide to putting up photos etc..? Would be much appreciated.

Originally Posted by Cambo_oldjaguar

The engine control module.

oh so pretty important! haha