Good Day all.

Still haven't found the fix to my '95 XJR.
running on 3 Cylinders(4, 5, and 6).
And the tach is all over the place. It will range anywhere from about 800 to 3000 RPM when idling(actual RPM doesn't change).

Any help would be appreciated.

 

Have you checked/replaced the crankshaft position sensor? That sensor controls spark timing and feeds the tachometer signal.

 

Try swapping the front three coils with the back three. If that doesn't change anything, get at the Engine ECU in the RF lower "A" pillar and check it good for moisture ingress.

Gotta start somewhere.

Good luck!

 

Thanx for the direction. New to the jag's.(and love it when its running)

Using a Noid Light, which plugs into the fuel injector terminal at the injector, it appears i am not getting signal to the #1,2, and 3 injector.

I pulled the ECU off and there are signs of corrosion at the connection.
I will clean the terminals up. And coat them with Dielectric grease?

Do I dare open the the covers on the ECU?

 

At this point, sure, open it up. Maybe you can tell for sure it is damaged beyond repair, or can possibly be cleaned up with electronics cleaner and dried out. Sometimes you are lucky, sometimes you're not. If it's not too bad, hunt down some stuff called DeoxIt D5. It's an electrical cleaner that works wonders at dissolving corrosion in electronics. It's pricey, but it can save an ECU, too.

Good luck!

 

I know when I was getting misfires due to signal loss at the coils, it was due to wire damage in the main harness where it exits the firewall.

 

I opened up my ECU only to find someone had made some mods in the past.

I have 2 wires that are broken that someone soldered onto the inside and joined into the harness.

I will do some soldering to patch this up.

The " black side" wont open unless i release the clips on the heatsinks, correct?

 

That's correct. There are several spring clamps keeping pressure on the power transistors, and most are stuck to some special heat conductive adhesive material that conducts heat to the aluminum. I wouldn't separate those unless I absolutely had to.

Good luck!