So I have been working on my 78 xj 12 I'm getting there slowly. After sitting for 15 years I have it turning over and spark and with a little starting fluid it will fire and run for a second. Sometimes with the key on for a few seconds it will fire for just a second but I don't hear the injectors clicking. I found a new trigger board on ebay and so not so sure what to do next. If any one has a thought for me I would love to hear it.

Thanks Tom

 

Tom,

You are near on top of it I reckon.

The original trigger board was 3 wire and had "reed switches: imbedded in the sticky stuff. They were a pain from new, and were updated to a 4 wire unit with "hall effect" switches replacing those older switches. The trick is to ensure the 4th wire is connected to a 12v ign supply. The rotor was also changed to trigger the newer switches, round magnet was the early style (reed) and rectangular was for the later (I think) it has been a while. I never understood the magnet change, coz magnets are magnets and shape should not change what they do.

Failing that the injection amplifier (big alloy thing on top of the radiator panel) is another culprit, BUT, they are not known to fail.

With the ignition ON, and engine OFF (it wont start so not an issue), turn the throttle capstan, you SHOULD hear the injectors "fire" (click) as you open the throttle. If you got clicky going on, the amp is OK, If you no got clicky, either the throttle switch (under teh capstan) or the amp is playing up. The throttle switch is a known item to reek havoc.

In all my years with these beasts the trigger board is the main injection failure issue.

 

Thanks for the quick reply, I will look at those things when I get back to it latter today.

 

Hi Grant, I had to walk away from this project for a while but, I'm back at it. After fallowing your advice I check a few things and yes when i turn the the throttle wheel I do hear the injectors click not sure what ones. I still have not injector fire when try to start the car. I pulled out the distributor and hooked up the wires and spin the shaft and still nothing. When I check the plug for the trigger board at the fire wall with a test light I hear click and then the other side a click, I go back an forth and it clicks. With the test light on the injectors both side of the injector lights up, is that right?
So any more thoughts.
Tom

 

OK, reading you findings a number of times to soak it in.

Sounds like you have the early "reed switch" trigger board with only 3 wires, and if you can hear the switches clicking as the magnet passes over, that is deemed OK. It appears as if you are NOT hearing them click. The rotor has a magnet in the heel, make sure it is still a magnet??. If in doubt, get a small magnet (universal magnet on a stick is what I use) and wave it over each end of the trigger board and listen for the switches, they may NOT be operating, and on a 3 wire board that is COMMON. No need for ign ON for this test.

If by some chance you have a 4 wire board, you still need a magnetic rotor, but you wont hear those switches, very different design. Just make sure the 4th wire is connected to 12v ignition supply, IF you got 4 wires that is. Ign ON is required for testing a 4 wire board.

The "clicking" as you turn the throttle capstan is also deemed OK.

Unplug one injector and probe the actual plug. One side will/should be 12v (ign ON), the other zero. The EFI amp is an earth switching device, so one side of that plug at each injector has to be zero (earth via the amp), as the trigger board switches. If you got volts at both terminals in the plug/s you got a loom issue. VERY common as it sits in the bottom of the "V" and gets fried, and shorts out. Time to lift it out of there and make a new loom, quite simple really, a little time consuming, but not difficult by any means.

There is wire (White/Black) I think from the -ve terminal of the coil that is EFI pulse supply. Make sure it is connected and not broken at the terminal.

 

Thanks, and it is a four wire. I will give all that a try and get back to you

 

You would happen to have any wire diagrams of this?

 

I did just check at the injector and both sides have 12v with it unplugged.

 

OK, you got an EFI loom issue as I said before.

There are NO shortcuts here, lift it out of the "V", and listen to it "crackle and pop" as it basically falls apart.

I have a diagram and will search it for you.

I have tried in the past to "upload" them on here for all to use, with NO success, so PM me with your email address, and I will scan and PM it to you as soon as I know that address.

Or, post the email here, as I have done in the past, and I have had NO issues with silly emails, we Jag people are past that behaviour I reckon, haha.

 

Hi Grant, my email is
Tom@perfectphoto.com

 

Got it Tom.

I forgot to look today, I do that a lot now a days, then the Merlot takes over, or is it that Rover P3 restoration that goes on forever, damn I forgot which already.

I will delve into the library in the shed tomorrow, PROMISE, and scan and email it.

 

Hi Grant, well I got the loom out and it was cooked and melted together. I'm in the process of rebuilding it all (loom,injectors and ignition harness). I will keep you posted.

 

Hi Grant, Well I got the harness rebuild and I still have the same problems. I'm not sure what to do at this point. The injectors still have 12v at both sides of the plug. What I'm i missing? Any thoughts would be great.

 

As I remember it, it is the Lucas-Bosch D-Jetronic system and it works by grounding a group of injectors and thus causes them to fire. So if this grounding is not working, you will get 12 volts on either side of the injector plug.

You can buy tester bulbs that plug into an injector plug and glow on and off as the pulse is generated, I have one in my toolbox. There is a lot more on this site: -

JAGUAR V12 FUEL INJECTION 1975-1980 - D Jetronic / AJ6 Engineering

 

I have a update, I just figured out that I have the wrong rotor, since I have the four wire tigger board, it would appear that I need the rotor with the bigger magnet. I will track one down and get back to you all.

 

MMMMMM, so maybe rotors do matter in this case, still learning after all these years.

As Fraser said, one side of the injector plug should be 12v ignition ON, and the other side earth switched, so a backfeed from the amp is ticking in my brain. however, not knowing how they activated that earth, I may be wrong. The HE is simple in that area, and I reckon that the PreHE is as simple.

Look for a "white/black" wire from the -ve post of the coil. It is the EFI pulse wire, and if it is missing, the system will not get a pulse indicating ignition activity, hence injector pulse, and a running engine follows quite quickly.

 

I thought I might not get here, but it runs. I have spent a lot time to get it to run. The missing link is I needed a different rotor with the four wire tigger board 54400048. I still have long way to go but it runs. It sounds pretty good too, no funny sounds.

 

BLOODY HOORAH.

Well done on all areas.

A sweet sounding V12, sends shivers up the spine, mmmm.

You are obviously having FUN.

 

So cam towers are leaking oil, so how hard is that job?

 

Unfortunately the cam covers are "covered" by the inlet manifolds on each cylinder bank, so these have to be removed to get to them. Once this has been done, it should be pretty easy. The gaskets will be cheap, it is the labour time, but as you are paying yourself, it will be a cheap job !