Is this normal ?
Hard to tell from the photo, are you concerned about the rust or something else?
concerned with the gray areas , thinking maybe an exhaust leak .
I’m not sure if the colors shown in the pics are accurate, but yes, its very common to have two tones on the manifolds.
mine is kinda two tone but no rust, AZ car 
My manifold is that colour too. I think you would easily hear a leak from either of the joints if it was leaking, and it would also probably trigger a CEL because it would affect the lambda sensor readings.
You could ask an assistant to block each tail pipe for a couple of seconds while you listen at the manifold or hold your hand close to the joint, if it is leaking you will hear it forcing out, or feel it blowing on your hand.
Casso , yep , I have sensor problems , have been getting the ff4 code , first real chance to work on it a bit later today , 1988 car by the way , so no CEL like on later cars . Local Jag mechanic has suggested that i check all nuts and bolts on the intake and exhaust for leaks , hence the photo , just thought it may be a leak in that area . Exhaust tips at the rear are quite sooty , so yes running rich . Will get at it and see where we end up , gotta love technology .
OK played the ever popular Jag owners game today , "chase the gremlin " can’t find an air leak anywhere , so another area eliminated , o2 sensor fitted , now we are at the spark side of things , with engine running i remove each plug wire from the plug , 1,2,3 engine stumble becomes worse 4 ,5 no change in revs ,6 stumbles again , OK this tells me that 4 and 5 are not doing what they should , Could this be a coil or ignition amp problem , pulled the number 4 plug wire and put a plug on it to see the spark , it didn’t look strong kind of an orangey red , will do the coil and amp strip down and clean tomorrow , also put the mechanics stethiscope on the injectors and they all sounded as if they were working OK ,measured the OHMs across all of them and they are within the range , i also removed the plugs from them as i did with the spark plugs , this had the same result . What does anyone think , i am almost at the "beat your head against the wall " stage. Please help .
Just keep going through it methodically.
When you get to the beat your head stage, pick a soft wall like a mattress, and take a break.
Just check the insides of the plug leads. I had a 2.9 that fired on 5 1/5 until it warmed up, turned out that the No1 plug cap was internally coated in verdigre, once cleaned it was back to 6
Mark, start the engine, let it idle then remove the plug from the mass airflow sensor. If the engine doesn’t die, than it’s malfunctioning.
Mark,
Check the firing order and the correct orientation of the plug leads
The correct firing order is 1:5:3:6:2:4 and the distributor rotates clockwise as viewed from above.
Check also the ignition timing in relation to TDC #1 cylinder on the firing stroke.
Mark, did you notice if the spark plugs from 4/5 were a different colour to the others around the tips ? are they all the same brand and number ? try swapping a spark plug from 4 or 5 with a known good one from 1-2 or 3 and see if the fault moves to that cylinder. It could be the plug that is faulty and it is failing to spark when under compression.
The HT leads may be perished or worn where 4 and 5 touch each other causing ‘tracking’ between them.
You can check for this with the engine idling when dark, look for little blue flashes as you move and flex the ht leads.
Check the inside of the distributor cap for any carbon trails or signs of it shorting out and compare the faces of No. 4/5 contacts to the other four to see if they have worn more or look different in any way.
If you have a test meter measure the resistance of each ht lead from the inside of the distributor cap to the tip of each spark plug, they should all read virtually exactly the same, flex each lead about to see if the reading fluctuates, it may show up one that is breaking down in use, or a bad connection inside the plug caps.
Only when you have a nice blue spark at every plug should you start looking further for the misfire if it still persists.
If that is the case and you are certain the injectors are all ok I think you should then do a compression test.
Casso , when you say measure resistance of each ht lead from the inside of the distributor cap to the tip of each spark plug, do you mean leave the plug in the HT lead ?
Hi Mark
I have a 1988 Jaguar xj40 and have a few spare part you are welcome to borrow incl the parts in the photo plus a distributor cap and leads. My issue was a misfire when driving turned out to be the coil. I believe I am based in the same city as you…
Regards
Hi James , i’m in Adelaide at Tranmere , where are you ?
I would be very grateful if i could borrow what you have , i am at my wits end as to what is going on with this car ,one minute it was working fine the next , massive misfire , to the point of not being able to drive it .I think i’ve narrowed it done to either or all of the following bad leads , bad dist cap , bad coil , bad ignition amplifier, maybe the MAF sensor ( 1) in the photo .Only problem being i have no way of getting to you .
i will give you a call , and thanks , might be an hour or so .
Hi Bryan , firing order is correct . are there any tests i can do to test the ignition amplifier ,i trust your opinion highly here on J-L .