Howdy all!

Well, this is my first foray into the seemy and bizzare world of late '70's fuel injection technology. I've done a ton of reading on the topic and thanks in advance to anyone who can help add to my "schooling."

The Case: A Canadian-market '78 XJ-12L with 56K Kilometers. In great shape. Tons of service records. It's now in California where the "snowbird owner" drove it to Palm Springs. He sold it to me in disgust because it wont stay running (or sometimes even start well.)

I've checked all the usual culprits: fuel pump, sensors, relays, temperature senders with an ohm meter even at temperature, etc. The local British shop is no fuel injection expert -- more of a Stromberg expertise -- but he did confirm all of my initial testing and believes it's the ECU.

My ECU is: Lucas 3CU 83477B

Questions:

1.) Is this ECU unique to a Canadian Market Car vs. a US given the difference in smog requirements?

2.) How does the thing disconnect? It's got a fat black cable that goes somewhere through the backseat "firewall," but unsure where. All the "Ebay" ones just show cut wires -- that doesn't look fun to splice, hoping it's "unconnectable"

3.) Any advice here on what to do next? It's a great car and a shame to cast it aside over this ECU, but I can see why it drove the previous owner to fury.

Anything I'm missing?

Thanks so much!

Brian

 

OK, going purely on memory here.

Mainly from S2 experience, and I see no real change with the S3.

The Bosch D Jetronic system is robust, bordering on bullet proof, and I have never seen a 3CU die.

Inside the boot, up against the steel panel that shuts off the cabin, is a Fibro trim panel, with a "bump" in it, sort of on the RH side of the centre line. This is where that ECU is.

Memory again:

The wiring loom is secured to the casing with a "half moon" clamp, and a small threaded screw securing that clamp to the casing.

The actual loom plug is held into the mating socket with 2???? long threaded screws, and (nightmares now) as those screws are undone, the 2 sections of the multi pin plug seperate. Refitting that plug also requires the 2 sections to be "pulled" together evenly and CAREFULLY, using the threaded screw method.

The biggest issue with the D Jetronic is the EFI trigger board inside the distributor, and the magnet in the heel of the rotor.

Early versions had a 3 wire trigger board, SAD item indeed. Replacement trigger boards are a 4 wire unit, and as solid as things come.

The Opus ignition amplifier, originally situated in the V, behind the a/c compressor, has a very short life, and goes AWOL for no apparent reason. Really, the damn thing fried. This amp was relocated in a TSB to a cooler area under the bonnet, hahaha.

Sooo, if the erratic behaviour is spark, then the Opus is suspect. If its Injection pulse, the trigger board is 99% the pest.

As for ECU market compatability, NO idea.

 

Grant, THANK YOU.

I should add, it's got a Pertronix Ignition conversion. As such, this would rule out the "trigger board" issue, correct? I do notice the car has an ignition amplifier -- a metal ridged box -- it's located in front of the radiator on top of the mount.

1.) Does the Pertronix work in conjunction with the amplifier? Or is this amplifier now not connected subsequent to the conversion?

2.) That's nice to know about the 3CU. Other things seem easier to source and fix than that unit. They seem rather difficult to find.

Again, much appreciated!

Brian

 

Brian.

The Ignition system and the EFI system DO NOT talk to each other as such.

A simple ignition pulse signal is all the EFI needs to keep injecting "go juice".

The trigger board is still needed to "trigger" the EFI functions.

Mine had a Crane system, and that ONLY took care of the spark. The D Jetronic stuff stayed as is.

This might help a tad.

D Jetronic Jaguar info.doc

 

The trigger board that triggers the fuel injection is inside the distributor directly under the rotor. There is a magnet in the back end of the rotor that triggers hall effect switches, or if you have a very early trigger board, reed switches, that provides an input to the ECU for engine speed. this is totally independent of the ignition system! It just shares real estate innside the distributor. If your trigger board has 3 wires it is reed switches, and probably iw worn out by now. If it has 4 wires it is a hall effect board.

 

on my 78 XJS, after you disconnect the screw securing the half moon clamp at the ECU, there is a gray plastic cover that will slide out, allowing you to unplug the ecu. Mine does not have any additional screws that need to come out, the plastic slide piece keeps the plug from coming out

 

Thanks Doug.

That confirms my memory sucks.

Its been 25 years since I unplugged a 3CU, and now I do remember that plastic slide.