+12v on both sides of injector connectors? 😕

1993 4L

So the old girl had been running fine, but one day I started it, she ran for a few seconds, and then cut out. Cranks, but doesn’t start. I checked that the fuel pump was running as that has been an ongoing issue with this car, and it was. Also getting spark. Cranking seemed to be a bit more sluggish than before even though the battery is in good shape.

I checked the injector harness, and it is showing +12v on both sides of injector connector. That’s not right is it? On other injector systems I’ve worked on, one side is +12v and the other is grounded through the ECU. Is that the same on these cars? Anyone have a wiring diagram for the ECU?

How’s the rotor and cap? Don’t overthink the problem would be my call.

Hi Dan …

Here’s the wiring diagram for my '89 XJ40. I’d be surprised if your '93 is much different

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Spark doesn’t seem to be the problem.

Thank you! I’ll take a look…

Have you tried the key cycling trick? Turn the ign. key between off and the 2nd position 5-6 times then try to start the car. You might have a low fuel pressure. You can also check the ignition relay.

Never worked on an XJ40 but on the V12s and older XJ6s, with KOEO, both sides are 12v “+” until the ECU grounds one side…which obviously isn’t happening in your case.



Thanks DD on the tip about +12v on both sides of the plug. Focusing my attention on the apparent lack of power now. Ruled out the battery… Could be a bad cable somewhere, and I’ll start doing drop voltage tests to isolate that. I also plan on testing the resting current draw. I have an icky feeling that a module somewhere is shorted out and putting a load on the system.