Hello, I'm looking for some advice to achieve a more even and consistent combustion across all cylinders on my 90' v12 xjs 140k. I have already done abit of work on the ignition system and now im looking to better address the fuel injection. The things ive done so far include, coils, plugs, dist/cap, and I pulled all the injectors and cleaned them the best I could with minimal resources (pumped brake clean through them under pressure and pulse). I drove it like this for awhile and the engine made a adequate amount of power and woke up nicely under any rpm. It did however have a slight miss at ideal (1-2 cylinders on driver bank). Currently after sitting for abit (~1 year old fuel) the miss is more prominent (2-3 cylinders on driver bank) at idle and low rpm accompanied with low power. It will still wake up with some rpm.

My goal is to restore as much power as possible through a balanced fuel system. Would it be necessary to pull and flow test the injectors? Should I Just attempt to re-clean them as ive done before? Are o2 sensors commonly a issue? Or any other things I should take a look at on this car?


Keeping this car cool has also been a issue in the past and I figured that may be worsened by lean combustion on some of the cylinders on each bank as the car dumbly attempts to correct fuel on a per bank basis.

How beneficial are upgrades to the injector control on these motors? I feel I could make a decent ECU with a Driver/sensor interface and a FPGA (similar to megasquirt like systems).

Best,

 

One year old gas may or may not be a factor. On GP, pump it out and add fresh. That's a good place to start. Then, yes, have the injectors professionally cleaned and graded.
This company...

https://www.jaguarfuelinjectorservice.com/

....will give you a full report and if you have any injectors that are out of range will provide replacements so you have a balanced set.

The harness to the injectors can cause grief. Common failure point. Replace the harness if you have nt already done so. Or make a new one; not that difficult; most here make their own.

You didn't mention plug wires...which can certainly cause odd misfire events.

As to keeping the engine cool please provide more detail. What is happening, when, and what steps have you already taken?

Cheers
DD

 

Following Doug's list:

The Injectors are fired in 4 banks of 3 as per below.

Sequential, it is not.
Port Injected is is, as apposed to newer stuff with Direct Injection, as per Diesel style.

1/3/5A
2/4/6A
1/3/5B
2/4/6B

Stale fuel, hell yes.
Lack of use, hell yes again, as this is the single biggest "killer" of a V12, followed very closely by "sedate driving".

Keeping it cool, again Doug's ask is the key.
My Sticky re cooling systems may be a good read. Then the Thermostat fiasco kicks in.
Down here we get HOT, and none of mine run hot, ever.

 

Change the fuel filter, test the fuel pressure. Clean the resistor pack, for starters.

 

Just curious, what's the elevation where you are?

 

Other work ive done that wasnt mentioned in the first post includes:
Fuel filter (havent checked fuel pressure)
Plug wires
Injector harness and repair to coil wires.
Coolant flush

In the past Ive just thrown fresh fuel into it and blew the cobwebs out. That has restored performance to the same level ive been used to and has resulted in many enjoyed miles. I would love to get it running better as I feel that would make it easier to pass emissions, keep the car cool, and enjoy the full performance of this old jag.

Has anyone used that injector service posted above? I see the link posted in various places but would be curious to how timely and accurate it is. There are few places offering a similar testing service that advertise that they test the flow pattern ect for a similar cost. Ive done a simple volume test with pulses and it was pretty close between all the injectors. I am still assuming one of the injectors is not flowing the same. Are airflow or o2 sensors worth looking into?

The car struggles with heat sitting in traffic or slow drives in hot weather. About at the same time the engine is slightly missing at low rpm. Im able to keep it cool at speed although I do need to replace the front air dam. No idea how accurate the temp sensor is on this car.

Altitude is about a mile. any fun ways to help these cars breath better?

 

Quote:

Has anyone used that injector service posted above?

I have, many times. Great service. And the owner often posts on Jaguar forums with helpful info.

Quote:

I am still assuming one of the injectors is not flowing the same.

Reasonable assumption. In any case, other efforts at improved performance and/or idle quality sorta begin with making sure the injectors are 100%. It's foundation work, so to speak

Quote:

Are airflow or o2 sensors worth looking into?

Lazy O2 sensors can cause some idle quality weirdness

It should be mentioned that 100% glass smooth idle, 24/7/365, is something not often achieved. Even when new magazine editors would report some idle irregularities. Jaguar itself tried a couple different schemes to improve "idle stability".

By the way, don't forget to clean your throttle bodies, set the gap, and synchronize your throttle linkages. It really does make a difference.

Cheers
DD

 

Buy three inexpensive pieces of test equipment. ( can be used on any car ).
1st
stethoscope. Nope, not medical grade. Cheap, I bought mine from JC Whitney in the 1960’s. Try Amazon. Today.
I listen to each fuel injector. If you hear a regular click click click the injector is probably good. You can also use it to hear sounds. Water pump? Bearings etc etc etc.
2nd
Spark detector. Looks like a pen. Has a window on the side and you lay it on the spark plug wire to see if the spark plug is firing. Much faster and easier than trying to pull the wire off the plug. I can check all 12 in 30 seconds. Without risk of pulling the wire apart.
3rd
IR temp detector. Little plastic gun you aim at each cylinders exhaust manifold to see if it’s actually burning. Even temps in all 12 cylinders means everything is right. Lower in one cylinder tells you which one is lazy. That will take you a whole minute to check all 12 cylinders.

 

If you want to have a go at the injectors yourself, there is a pretty good video series from Camp Chaos showing how to clean, test and match your injectors.