I recently acquired a 1980 xjs v12. Among several problems I'm beginning to sort out, the worst is the fact that one entire (drivers side) bank is not firing. By that I mean that none of those 6 injectors are pulsing. I've checked this using noid lights at each injector plug of the harness. The harness all looks good from what little I can see of it. What are the chances the ECU is bad? Is there any tests I can perform to check this? Is there a way I can run the injectors to ground from the ECU side of the harness to see if I can get the noid light to light thereby eliminating the actual harness being bad? Any advice would be appreciated. Also, the car will start and run on the one bank, but not very well and not without holding some input on the throttle. It is also very very rich when it does run like this. Also, if it is a bad ecu, what other years are a compatible swap? Any advice or leads would be greatly appreciated, I'd love to get this engine running right.

 

Has your car got a pre-HE engine, or an HE engine? The HE plugs are not easy to see or remove and they are fitted so they slope inwards at an angle towards the centre of the V.

Greg

 

That 1980 should be PreHE.

The D Jetronic system is a good reliable system.

The root cause of the bank being OWOL will be the reed switches in the trigger board INSIDE the distributor.

Two versions of boards:

3 wire has reed switched imbedded in the mastic stuff, and SUPER unreliable.
4 wire has hall effect sensors imbedded, and SUPER reliable. The 4th wire is an Ign 12v supply.

Maybe other stuff, but I really doubt it.

The ECU for that thing is purely analog, and I have NEVER seen one die.

 

Yeah it's definitely a pre-HE. So how do I go about servicing the reed switches? The guy I got it from said he put a new distributor in it, but maybe he lied and only did cap and rotor, maybe he messed the reed switches up when doing that? I do believe it is only a 3 wire. I can verify that in a bit.

 

First things first.

Remove the cap, CAREFULLY.

If its a 3 wire board, proceed with the following.

Obtain a "magnet on a stick", tell everyone to be QUIET, and wave the magnet over one end of the board, and you should hear the switches clicking. Then go to the other end and do the same.

If you got GOOD clicking at both ends, the board is deemed OK. It is still suspect, but deemed OK. The switches are not serviceable that I know of. Any we got waaaaay back with switch issues/suspect, were replaced with the 4 wire board and updated rotor.

Next. Remove the rotor, MORE CAREFULLY, as they break easily, and turn it over. Look at the "heel" (the end opposite the pointy end), and note the magnet imbedded in the plastic. Take a metal item, screwdriver will do, and ensure that the magnet is still a GOOD magnet.

Next. The board is fastened to the distributor casing by 4 plastic screws, and 4 rubbery spacers in the corners of the board itself. Make sure they are all installed. The screws break by simply looking at them, so be warned, and the rubbery spacers are often missing. This is critical for proper alignment of the board with the path of the magnet in the heel of the rotor. Those screws and spacers are still available I think. Try XK Unlimited in San Louis Obispo, thats where I got my last set some 10 years ago.

If its a 4 wire board, the magnet test will still work, but you need the ignition ON, and you will not hear any clicking. I have never seen a 4 wire board go bad. The plastic screws and alignment still count for the 4 wire board.

 

Ok, I took the dizzy cap off today and found nothing like what I was expecting to be in there, as far as the trigger board is concerned. What I found was the rotor had no magnet in it, but underneath it was a circular rotor that has 12 pins vertically in it that pass by a little pickup with 3 different contacts on it, also in a vertical row. Does this car have the right distributor in it, or is this some kind of upgraded version? It is still a 3 wire pickup. I've attached pics to show you what I found.

 

OH DEAR.

Politeness abounds, HAHAHAHA.

That is a V12 CARBY distributor. They dont run a trigger board for obvious reasons. That rotor is a Carby version rotor.

The 4 mounting holes for that trigger board are plugged up, as they are on the later HE dizzy.

The 3 wire you mention is the IGNITION section of the dizzy, and has NOTHING to do with the EFI section.

I am now VERY confused as to how the injectors are lighting a Noid light at all, as without that trigger board there is simply NO pulse for the EFI system to do anything but just look pretty.

I think I have a spare trigger somewhere in the junk outside. I will go look later and snap it and post that snap here so you can see what I am talking about.

Have you got teh OLD distributor??????, or can you get hold of it.

I reckon the engine is running purely on the fuel sprayed by the cold start injectors at ign ON position.

OR.

The EFI management system has been replaced with an aftermarket system, like a HalTech, Wolf3D, Megasquirt etc, but I seriously doubt that.

Back to work now, talk later.

 

Now we're getting somewhere!!! You sir, are going to be my savior! There is definitely not an aftermarket EFI system in place like any of the ones you mentioned. I do not have the old dizzy, as this is how I received the car. The PO told me he replaced the dizzy in an effort to get it running right....Clearly, he was clueless as to what he put in there. So now my question is this, can I drill and tap those holes and put the proper parts in that dizzy, or will I need to get an entirely different unit? I found a new old stock trigger kit on ebay, complete with trigger board, rotor, bushings and the like for a pretty good price I think. Here's the link: Jaguar XKE E Type V12 XJS Distributor Trigger Board Kit with Rotor Hardware | eBay

Please let me know if this is what I need and if it will work or not. Thanks for all your help so far!!

 

OK, we are on the same page, bloody hurrah.

Those holes can be drilled and tapped, no huge effort. The steady hands (not mine) and the correct thread tap will be needed, again not rocket science.

That kit looks just fine. It is the original 3 wire board, BUT, being NEW, should provide reliable service for about 15 years.

Soooo, based on that info, there should be a 3 wire plug of some sort down in the "V" that would plug into that new boards 3 wire socket.

With that unit installed, it should simply "fire up", thats how good these PreHE engines are. Our S2 XJ12, has just topped 500000kms, and is untouched.

Be VERY CAREFUL with that large plastic ign wheel, as they are fragile at best. The 12 ferrite rods in that wheel have a BAD habit of falling out, thanks to gravity, so check them carefully, and a drop of Super Glue is usually all that's needed to secure them.

I have not found that old trigger board as we type, and I will cease looking now, as you have found a new one.

 

Ok great, I'll get that kit ordered up. My only issue now, is I can't find the other 3 wire plug down in the valley. Can you tell me what it's typical route is and what harness and where it ties into? Maybe that will help me trace it down. But it's definitely not sitting in plain view down there. I thought it might be laying where the ignition pickup harness connects but it's not. I really hope the PO didn't cut it out or some other similar foolishness. I swear, that guy had no business under the hood of this car, he had no idea what he was doing! Thanks again, I'm glad we are finally on the path to a running engine.

 

Can anyone tell me where the car side plug of the trigger board harness from the distributor should be at? Or which harness it ties into that I could trace to maybe find it? Should it be toward the firewall or toward the radiator?

 

Time Zones my boy.

Most of us that have any knowledge of the inner workings of a PreHE are Down Here, or some other Zone.

The trigger board wiring goes out via a rubber plug thingy that sits in a groove in the outer circumference of the distributor upper portion.

The exit point SHOULD be facing the A bank #4 spark plug.

SOOOOOO, looking down on top of the distributor, with the vac capsule facing the firewall (sort of), that groove should be at about the #4/#5 A Bank area. Based on that, the wire loom you are looking for will be somewhere down around the REAR "A" side of the engine, BUT, you got a huge ballast resistor block bolted onto the throttle pedestal just there, so eyeballing it will be a challenge at best. The wiring pigtail on the trigger board is about 6" long, so look around, I dont reckon he was clever enough to cut it out.

I need a drink, its 1PM, and "Beer O'Clock".

 

Ah yes, I keep forgetting where you're located.

Well another visual search has turned up empty handed for finding the plug. I'm going to have to remove the distributor to drill and tap the 4 holes anyway, maybe with that out of there I can see better and have success in finding this damn elusive plug!! Thanks again for the help. I'll let you know what I do or do not find.

 

Ok Grant, I think I've stumbled onto something.....bare with me while I try to explain.

I believe my car is one of the about 1000 made that they put the Digital P injection system into between December 1979 to February 1981, when the HE motor was then released. I discovered my car has O2 sensors in the downpipes when if it had the D-jet, it would not have them correct? Also, that plug for the trigger board, is absolutely not on this car. (good thing I just possibly wasted $200 on that new one But lets nevermind that for now.

So, If I do indeed have one of these rarer cars, would that lead back to the ECU being bad and that is why I have the entire B bank injectors not working? My research yielded that when the Digital P injection came out, the injectors were divided at the ECU into the 2 banks of 6 so that it could control each bank according to feedback from the O2 sensors.

Also, having the digital P system would explain how I am able to get noid lights flashing on the A bank injector plugs without a trigger board!

 

BUGGA.

You may well be right??

Those cars are sooooooo rare that they are almost a NO SHOW anywhere.

That means it has the 10:1 comp engine, as versus the 9:1 for the D Jetronic.

Based on that, I reckon the ECU, or maybe the plug at the ECU is giving the grief.

The only people I can think of that would have ANY idea of that system, would be Roger Bywater at AJ6 Engineering in the UK. Roger was at Jaguar for a very long time, and was involved in the development of these systems.

 

Yeah, it's cool to have a rarer car, but at the same time it really limits finding used parts such as the ECU that's basically only good for this one year run on the 10:1 motor.

I've found some info about cold/cracked solder joints being suspect on these ECU's, so gonna give reflowing some solder a shot on the injector portion of the circuits and see if that fixes it. If not, looks like I'll be buying a standalone system or an ECU from AJ6 engineering.