Hi.
I'm new to Jaguars, so for my first one, I bought a 30-year-old XJ-S with close to 200,000km on it, without getting it inspected.
It has already cost me heaps to get the rear brake discs replaced and the power steering pump and rack rebuilt and the handbrake fixed... so at least those aspects of it are good now.....
I want to ask what to expect from the 3.6 AJ6 engine in terms of idle and startup. I know there are a bunch of variations of this motor, and between their differences and the amount of posts about V12 cars that contain 'AJ6 Engineering' , it's hard to find info.

My engine runs smoothly under load (I had the centre muffler boxes removed so I can definitely hear it), but it doesn't idle as smoothly. It has an intermittent stumble, not a permanent misfiring of one cylinder. You can see the engine shaking when it misses, even if you raise the engine speed above idle. I have the Lucas 9CU engine management, and my cylinder compressions and spark plugs seem okay. Fuel system cleaning pills added to my petrol, cleaning my airflow meter and doing some hard driving have not helped. Is this just how these motors are, or are they meant to be the kind of engine where you can balance a coin on it while it''s running?

I've also noticed (and this may be unrelated) that the car doesn't start from cold in the manner that I would expect. It cranks for a bit long then shambles into life at low RPM, steadying out and climbing to idle speed after a few seconds. I would expect a bit more enthusiasm - a flare of engine revs to build oil pressure, gradually settling down to idle. The car only comes close to doing this if it was started within the last few hours. There's also no air pressure in the fuel tank when opening the filler cap - is that also normal?
I'm hoping that all these things are related to one simple adjustment / replaceable part, and not something horrible like a loose timing chain, worn cam lobes etc.

 

Hello Ben

Another mid 80's 3.6, and another one from NZ. Here I was thinking they only came out as V12 until the 90's. I am still learning.

Anyway - can't help that much except to say welcome to the forum. Your issue does not sound too bad - others way more educated than me will point you in the right direction.

Cheers
Steve

 

Thanks Steve. I think you may have read info for the American market. The AJ6 engine was launched in 1983 (with a 3.6l displacement), but it wasn't available in the US until the 1991 facelift (by which time it was 4 litres). If I'm wrong, as you said, a more knowledgeable person will come along shortly!

 

Welcome to the Forums.

When the beast settles, or teh beer runs out, please do an Intro in the New Members Area.

You will find HEAPS of 3.6 related info in the XJ40 Tech Section.

My 3.6 XJ40 (daughters car really) had issues, and I simply:

Replaced the spark plugs, AND the HT leads.
Cleaned the Green goo out of the coil HT lead socket.
Cleaned the throttle body inner bore, HEAPS of goo in there.
Changed the fuel filter.
Checked ALL the Intake trunking for proper sealing, especially from the Air Flow Meter TO the throttle Body.
Replaced the oil cap seal, it was cracked, and it sucked air, which upset the AFM, and crappy idle reek supreme.
Oil change and oil filter were just part of post ownership common sense.
Air filter element, oops, it was BLACK.

I then added 2 bottles of Injector Cleaner, to "about" 1/2 tank of premium fuel.

Then she took it for a drive, DAMN, I forgot a 17yo, who had NO idea what the Red Line on the Tacho was for.

Returned in one piece, and SMOOTH as you could want.

Cold start issues sorted out after about 1 week, and I reckon the Injector Cleaner finally did its thing.
She still has that car, after 16 years, and now sits at 260000kms, and they be HARD kms, and it is still sooooo sweet.

Simple cars, dont get complicated with them.

 

Hi Ben, you can see I’m from NZ as well and I have a very similar 3.6. I agree totally with Grant. First things I did with my XJ-S was plugs, air cleaner and get injectors checked, You will find the car is not around town runner and hates 50km speed areas in 4th gear, low revs will give you kangaroo jumps, best leave in 3rd, however it’s not a town car, get out on the open road and she will dance to your tune beautifully and give you reasonable fuel consumption. Short journeys around town will see you doing 18l / 100kms. Blenheim to CHCH I achieved circa 11L / 100kms.

mike

 

I reassembled the intake today after taking it to bits to clean it out.
I set the throttle butterfly gap, checked the throttle position sensor voltage, then tried to follow the idle setting procedure. Something must still be wrong because I couldn't quite reduce the idle speed to 600rpm even with the idle adjuster fully closed. The car idles at 800rpm now, still with a little stumble, and I think I can now detect some misfiring at light throttle cruising also. Guess I still have more diagnosing / random parts replacing to do.

 

edit: somehow posted this in wrong thread thanks weird forum scrolling.

mods pls delete.