Rough start & not firing on all 12.

[Flappers]

Hello again, I'm about to exchange the plugs on my 89 Double Six (103000 mls) after its dropped a cylinder again on the same bank. I did replace an injector about 6 months ago and that coupled with a new AAV had the engine running smoothly. I'm hoping swapping the plugs out will fix it. If it does and I find soiled plugs, can anyone suggest how I adjust the mixture to get it to start without the need to step on the accelarator of a morning ? ... I mean I know thats nothing of a hardship, but after having Jags that havn't needed it I'm wondering if its in need of a tune up ? Im using the NGK BR7EFS plug, is this the best I can get for my car please ?

[Brakebuster]

sounds strange,
and being an injection system you shouldn't need to stand on the accelerator to start the car , I just lean into my car and she starts with no pedal required ( 1989 marelli V12 )

also , you are not able to adjust the mixture, it is electronically controlled by the ecu ( ecu link in engine bay for different RON fuel )

that said, what is your car, a Lucas or Marelli ignition system ? either should be in tip top condition for optimum performance ( dizzy cap , rotor arm , coils , plugs leads etc ) but more importantly the injector loom does go brittle and fail , this is a tricky one to diagnose and rectify as the wires break inside from being ' cooked ' as well as the injector plugs coming off due to broken tabs on the bosch connectors

the injector power resistor is also a prime candidate for causing issues, not that it fails but its multiplug for all the injectors gets corroded and causes running issues, pull the plug and clean the contacts ( on both resistor and plug ) , and ensure its seated correctly when plugging back in , ( the injector loom goes directly to this power resistor unit ) injectors are always live and fire by being grounded through the power resistor to the ecu

if Marelli , then there is also a vacuum pipe going to the injector ecu ( in the boot on my XJS ) if this is not holding vacuum then the ecu doesn't know the engine is running, and the load on it , there is also a modification of a vacuum holding reservoir than can be fitted by the ecu to give smoother idling and pickup etc.

hope some of this helps

BB

[Flappers]

It says Lucas on the black box near the throttle linkage ?

[Flappers]

So, we have power to the injectors, sparks to all plugs. When the plug was removed from the offending cylinder it was wet through. It was cleaned, replaced and now its firing on all 12 again ... So Im thinking is this the lucas box ? The dizzy cap , rotor arm, plugs leads were all serviced by Bob Bate within the last 12 months and the car has less than 2k on it since then. The coils, I wouldnt know where to start Where does the injector loom clip to the injector power resistor please ? And thank you for taking the time to post Brakebuster, much appreciated.

[Brakebuster]

cool

the injector loom is plugged into a large resistor behind the front right headlight in the engine bay , its an 8 pin plug that goes into the bottom , this area catches a lot of road dirt, and the contacts become corroded , only a small amount will cause issues with this low power system , regular inspection and di-electric grease will ensure trouble free motoring

hope this helps

BB

[davidr]

The base idle mixture is adjustable. There is an adjustment facility on the side of the fuel system ecu. BUT that is a last resort. If you feel that your engine is running lean then I wouldn't adjust the mixture until you've thoroughly checked for air leaks or other issues.
There are a few things that come to mind as to why you may be dropping a cylinder in addition to what BB has mentioned.
You may have an air leak in the injection manifold. If it's near enough to the cylinder in question it may be leaning out that cylinder and causing it not to fire. It may be the inlet manifold gasket or the injector seal for example.
You may have a sticking injector that is putting too much into that cylinder.
You may have a valve that's not seating properly - have you done a compression test?
Just a few thoughts!
Regards
David

[oldtimer]

All the above is good stuff but I don't believe these engine like long periods of in activity. Less than 2000 miles within 12 months is not a lot so a good run might warm things up and blow out the rubbish. What is it called - an Italian tune up.

[Brakebuster]

always time for an Italian tuneup , lol

BB

[Flappers]

Apologies for not replying sooner. Had some issues trying to log in via mobile to the site. Seems fixed now. Well good news on the misfire, it was the corroded loom connection block. Fires up on the turn of the key without help from the accelerator. Once warm though, needs a little help. Many thanks

[Brakebuster]

good news

hot start issues could be

vapour lock on the engine fuel lines,

bad pressure regulators, both flow and return on the engine fuel system

badly set up TB butterflies ( or worn components )

dirty TB intakes around the butterflies ,

BB

[Flappers]

Hi folks, I know it's been a while but this has reared its head again, same issue. Can you tell me how I set up the TB butterflies and replae the pressure regulators? She had a pressure (sniff?) test and is fine on all cylinders.

[Flappers]

I forgot to add, it's on the other bank this time but has been starting roughly for over 12 months.