This is for my 1990 Jaguar XJ12 Series 3 with Lucas ignition. I've been battling a running issue.

1. Replaced 10 of the 12 plugs (will need to order two more which were cracked a the ceramic).
2. Replaced the cap and plug wires.
3. I can hear all the injectors click with a stethoscope

It still has a miss at idle from the passenger side bank (LHD car) that you can hear in the exhaust but at least the cats are not turning red.
It's now developed a hunting idle that I did not notice before.

See video

 

Misfire on one bank could be an injector problem (working, but not working optimally) or an ignition problem (will one of your new plugs be installed on this bank?).

Idle hunting in this case sounds like a left-right mismatch on the throttle blade settings and/or linkage holding one side open a bit more than the other. In the later case try simply disconnecting the linkage rods and see if anything changes

Cheers
DD

 

Thanks, all the plugs were replaced on that bank and so were the plug wires. I tested each cylinder before installing by verifying both old and new plugs before I installed and can confirm that were not firing beforehand. I will disconnect the rods and see what happens

EDIT: Checked by removing the linkage and it did not make much of a difference. The cats are still running red hot on the passenger bank, just taking longer so it's still running rich. I will try replacing the temp sensors as it may be running full rich.

 

If the cats are red hot on a Lucas car, the problem must be that one of more injectors are not closing properly. This may be crud in the injector, a faulty one, or as likely, the loom is shorting out.

 

Thanks Greg, I can hear the injectors clicking open and shut with an automotive stethoscope. It does not mean that they're not leaking but they are opening and closing for sure.

 

Does anyone know where this vacuum line goes? It's on the passenger side bank

Thanks in advance


.

 

It might go to that blue dump valve.

I see a broken plastic nipple in the end of the hose. Look for something nearby with a broken-off nipple

Cheers
DD

 

It shouldn't make any difference. You might have a left-right discrepancy in throttle blade adjustment. This is easily sorted but my gut tells me you have other problems as well. Most likely some faulty injectors.

Sometimes a surge or oscillating RPM can be the Oxygen sensors making big adjustments in an effort to correct a mixture problem.

Until and unless you know the injectors are 100% is pretty hard to do much else. With injectors at 100% and ignition at 100% you can then go after the finer points of getting the engine running correctly.

Also....what about the injector harness? A fault here (very common) can cause injectors to stay open too long. It's another "must be 100%" item

Cheers
DD

 

Thanks, the blue dump valve has a vacuum line attached so unless it's supposed to go elsewhere, I can't see where this one goes. I'm going to have to break down and join the jaguar owners club so that I can beg a local member to look at their car.


I'm beginning to think the same thing and am leaning towards replacing them. I read somewhere that these injectors interchange with mid 80's Nissan 300ZX (this particular injector) https://www.summitracing.com/parts/smp-fj696 and I should be able to get a set of rebuilt injectors for under $400 (two sets of six). Any thoughts?
As far as the wiring harness, the connectors are all broken but the wiring seems okay. I have them zip tied to the injectors so that they make a good connection and I can hear all the injectors firing with an automotive stethoscope. I did have to replace the pintle caps and if any of the nozzles are stuck, might still be able to hear the injectors clicking, but still be open at the same time. I wish there was a better way to check, I hate throwing money at parts and hoping it would solve things.

As far as spark goes, I cranked the car to test each speak plug and made sure it fired before installing it.

 

Send your injectors to David. He'll fix you up

Jaguar Fuel Injector Service


I can tell you from experience that "seems OK" isn't enough. For reduced hair-pulling go thru each sub-system and make it 100%. Then move on to the next. Do it all, do it once, do it right. Then you can forget about it for years to come. :-)

Cheers
DD

 

100% agree with Doug, this is the only way to own a classic Jaguar. No half-steps ever pan-out for long...
Rgds
David

 

I appreciate it both. My issue with having these redone is that I already cleaned them with a heated ultrasonic cleaner, replaced the pintle cap and filter and flow tested them to where they would balance out using the injector cleaning rig. I bought this rig about 10 years ago when I converted my 75 XJ12C from propane back to gas and have used it several times to clean failing injectors. Unless there's more to it then what I did, it may make sense to just go with new ones

 

Under those circumstances I think the most likely cause of your problem is a shorting out injector loom.

 

Greg, thanks. I'm not averse to rebuilding the wiring harness. I had to do the same on the 75 XJ12C but I don't think that's the issue because the injectors were firing fine before I took them off and ran them through the cleaner. The smart money right now is to replace them or least remove them and find out of they're leaking by themselves. That should be an easy test as I can just throw them back on the rig and dial the pressure up without turning on the current to actuate the injectors.

As it stands right now, all I know is that i'm getting spark, i'm hearing the injectors pulse and the engine is dumping fuel into the cats which are turning them red hot

 

OK, read all this over 4 coffees, and my only "siggestion" at this point is:

Is the bast fitted with Cold Start Injectors???

Jaguar messed with fitted/ not fitted, throughout the 5.3 life span.

I remove them mechanically and electrically from any V12 that darkens my door.

THey dribble, spray spasmodically for no apparent reason, the relay and other triggering system bits and poeces are Lucas (nuff said), and just dont behave as expected.

In really COLD 1st starts, I operate the loud pedal, Ign ON, twice (idle to floor), BEFORE going to start, works every time. This activates the Injectors twice, and moee than enough Bang Juice to start it.

Remember, the Cold Starts were only designed to spray whilst in Cranking Mode, and Engine Temp dependent.

 

Grant, thanks. I'm very familiar with the problem a cold start injector could cause as I've owned several Mercedes Benz from the 70's and 80's where these would be my first go to for resting (it's easy to test on an MB). The only thing I can say at this time is that this stuff only started happening after I replaced the injector hoses and cleaned the injectors so i'm focusing on what I would have disturbed which would have been the ignition wires, injectors and wiring harness.

I've ordered 12 new injectors. Let's see what happens.

 

The EFI system on a V12 hunts like that when the EFI ECU sees the TPS as closed (idle) BUT for some reason the engine goes above around 1200 to 1400 RPM. Essentially the EFI ECU thinks you're coasting down a hill so the overrun fuel circuit is triggered cutting fuel and re-instating it when the RPM falls to around 800 or so. Usually this is because the AAV is stuck open providing way too much air for the system at warm idle but it can be for other reasons like the throttle blade adjustment or leaking throttle bushings (or other air leaks). Rarely fuel or timing related....

~Paul K.

 

Thank you, this makes sense. I'll see if I can remove the AAV and clean it.

 

Test it in boiling water like a thermostat. It is rebuildable (there are threads here and on Jag-Lovers about it) and Jonas Loda out of Estonia does rebuilds for people on exchange with better SS internal parts (if it needs it). You can also try blocking off the AAV inlet to see IF it is bypassing air when it should have closed.

~Paul K.