Another 3.5v8 efi problem

[rincewind23]

Hi all,

I'm just going through troubleshooting my Discovery 3.5v8 efi wiring loom. I found this diagram on this forum:

http://forums.lr4x4.com/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=41513

This shows the wiring for the ECU. I also found a troubleshooting manual, which goes through "check this: if it works, go to step x, otherwise go to step y". I can dig out where I got it from but it's on my other PC in the garage.

I went through checking that I get +12v at Pin 15, and then when I turn on the ignition I get +12v at pin 19, as my guide says I should. The next step is that with ignition on, I should get +12v coming out of the main relay. Pin 12 should activate the relay to pass the volts through to the injectors.

The trouble is, pin 12 is always at +12v even when the ignition is switched off. When I check the volts on the relay, I get:

85: +12v

86: +12v

30: +12v

87/87a: 0v (or as near as makes no difference).

This is whether the ignition is on or off. Now, I am guessing it's one of these options:

a) Bad ground somewhere

b) Relay is b0rked

c) ECU is b0rked

d) I'm using the wrong troubleshooting manual.

Can anyone put me out of my misery? Happy to provide more info if needed, I know enough about electrics to follow wires, check volts, resistance and continuity, but that's about it.

Cheers,

Kev.

[FridgeFreezer]

Looks to me like Pin12 is active low, so it should dip to 0V, grounding that side of the relay coil to energise it (12v one side, 0v the other = on!).

When it's not active, the pin will float up to 12v as there's 12v on the other side of the coil. (12v both sides = off, no volts across the coil)

[Early90]

I had to do this for the first time recently. All the info you need is in the diagram and fault finding routine you found on here. As i understand it, the ecu grounds pin 12 to energise the relay,follow the guide to the next step according to your readings. That is, REMOVE the ecu plug and ground pin 12 on the plug,this should energise the relay...take it from there,good luck.

[rincewind23]

Thanks, FridgeFreezer, Early90. I'm not sure what's supposed to be providing the +12v to +ve on the coil, but when I run a direct test wire from +12v to +ve on the coil, pin 12 works as above.

Well, that's not entirely true... It drops from +12v to about +2v. Is this close enough, or does it indicate a problem somewhere else?

[Early90]

Given the results in your first post you need to do the next step as described above......with the ign off remove the ecu plug and ground pin 12 on the plug,check for battery voltage on pin87 of the main relay.

If the relay triggers you will get battery volts at 87 on the relay,if you do then check the ecu earths,pins 14 40 27. if good earths then suspect ecu.

If you get 0v at 87 then suspect the relay.

Get a Bosch one if it is the relay,don`t buy an allmakes one as they had a batch where the wrong type of 5 pin relay was in the bag.