I'm in the process of making back to life the xj12 5.3 HE with Lucas amp...


I'm testing all continuity wire to wire to ecu pins...and I have one doubt. (I'm doing this test just to the ecu connector, not to the ecu itself)


All wires has right continuity BUT....


PINS are always earthy... I mean, I put digital meter to test continuity, and if I put earth to the pin 1 for example it goes to "beep" ( sound from the voltmeter that confirm there is continuity)... As well as on the pins 16, 34 and 35... All of them must have continuity between the pin and earth , as they are earth...

The BUT is that I also have earth in the following pins...

3
17
18
23
26
Can someone let me know if its normal? I guess for sure is not... But...

 

All this check with out battery, just looking for continuity....

 

I would never test for that with the ECU actually plugged in. It is after all, and earth means for some circuits and not for others.

Always unplugged, thus testing each wire from there to its destination.

Pin 18 is the Pulse Wire FROM the AB14 Amp TO the ECU, informing of Ignition Pulse (like a Tacho Signal), and the ECU interprets that as active, and pulses the Injectors, simple.
VERY COMMON failure item on the HE.

Attached is a Pin Out chart I wrote a very long time ago, maybe help you some.

I suggested before to add your Home Market and your Cars details to you SIg, via the CP tab at the top. My memory, haha, had yours as an 88 HE, but others have NO idea.
Help us to help you,, give us a clue, its simpler.

 

Thanks for your reply....

So I have the 18 pin to earth... How can I fix it? Because if I put the pin 18 to earth, it beep.. without touching the wire...

My car, as I already fill.my profile, is a 5.3 HE with Lucas amp

Your list (founded in another post) was very useful as I did all the checks posted in this thread.

And here I'm I... After checking all, I discovered what I have posted here.


My pin 18, is grounded... As well , as the 1, 3, 16, 17, 18, 23, 26 ,34 and 35.

If I put my voltmeter in continuity, it's beep when testing this pins to earth...


​​​​​​

 

OK, lets sort the terminology first.

You say "my pin 18 is grounded".

Do you mean the Pin of the ECU, or the wire in the Multi Pin plug???

The latter is the most common, as mentioned earlier.

In the engine bay is the usual failure area, Somewhere between the Ignition Amp and the grommet in the RH inner guard, near the bonnet catch. All the ones I have had issues with have been in that length, usually near the heater tap, but not always.. I splice in new wire, and all is good. It is NOT special wire, standard TV Coaxial Cable is just fine.

Like 99% of the wiring IN the engine bay, which will be old and crispy, hence the numerous threads to bacically rewire the engine bay, ONE WIRE AT A TIME. Not as hard as it sounds.

 

thanks again...

​​​​​​I Will try to be more specific...

Wire has continuity from the amp, to the pin 18.
Also the wire has continuity To the ground
And the last, if I put the voltmeter to the pin 18 to ground, it also beep. (so pin 18 is grounded with out connecting the wire itself)

 

To test that shielded wire you need to have it disconnected at bothe ends.

So, unplugged from the ECU, NOT removed from the Multi Pinplug.
Unplugged at the Ign Amp.

If you have continuity, \\ of the thin signal wire, good.

BUT

Then you need to check for short to the shield, as that is more common than a broken thin signal wire.

The shield is ONLY earthed at ONE end of the Coax. Some are at the ECU, but I have found some earthed at the Amp.

I have NO idea of what happens when you probe the connector AT the ECU, never bothered with that, as ECU failures could counted on one hand, and what happens inside them is all Smoke and Mirrors to me.

 

Fixed! Engine runs!

My problem was that the coax cable going to the amp, has also a black cable, that I climped together when I was doing the new wires...