I am an idiot.

I spent the day checking out ground points, without any success.

I removed the exhaust manifold shield and voila! Big crack right in front of my face.

Damn Jag Specialist didn't even check.

It all makes sense now. I blew a spark plug a few months back. Guess where the crack is...right by the spark plug well!

So what do I do now? Get a used part? They don't sell new ones anymore, do they.

 

Hey VEE, any chance of seeing the offending split in a photo?
Hope this is the end of your search!
Thank you.

 

Vee,

Do you mean the exhaust manifold is cracked? Front or Rear? The front one is still available new.

Paul

 

Ask and ye shall receive!

I threw in a shot of the interior of my manifold cover. The black smoke was my first clue...

How difficult is this to do myself? Seems straightforward enough...

 

On the X300 sedans replacing the manifolds is a cake walk. You don't even need to get under the car !

Probably similar on XJSs

I found good used manifolds on Ebay

Hope it solves your problem. When I had some weird misfire issues replacing the cracked manifolds didn't change anything....not that I regret having changed them, mind you

Cheers
DD

 

Doug,

What was your problem?

This one seems to make sense. Everything changed after the spark plug explosion. The ECU is definitely sending signals out to all of the coils stumbling the idle.

The grounds are good. It would make sense if the O2 sensors are getting unmetered air.

I am confident this is the cause of the problem. Everything just lines up making it painfully too obvious.

I'd be curious to know how similar your issue was to mine.

Thanks for the interest in my problem.

Other than a new gasket to the block, would I need any other parts?

 

In my case it was a misfire .. driving or at idle....that occured quite consistently but only after running 15-20 minutes.

Cheers
DD

 

You might wanna get a new donut seal for the pipe-to-manifold joint. Might not need it ...but if the original crumbles apart you'll have a new one on hand


Cheers
DD

 

Thanks for the advice. I have added that seal to my order, as well as the two studs, just in case...

I do t have any misfires. No codes. Just an ECU that adjusts the firing direction every 32 seconds. I think this is due top the O2 sensors trying to deal with the unmetered air coming in through the crack.

 

Vee,

Its annoying that its the unavailable rear one. You could ask your dealer to do an all-dealer search on the system to see if any Jaguar dealer has one sitting on the shelf. They are quite capable of doing this search but probably won't advertise it.

I have seen people weld the manifolds after drilling a hole at the ends to stop the crack running. But the lower end of the crack seems to have travelled a long way on yours so could be difficult.

When I changed mine, I replaced gaskets, manifold-to-downpipe studs, nuts and also ended up replacing one of the head studs that got damaged.

Can't remember if you've done this before, but O2 sensors are easier to change with downpipes loose.

One thing you really should be careful of is causing any strain on the joint of the downpipes at their lower end if they are not connected to the manifold. It's a really poorly designed pipe where the 2 sections are crimped together at the end and a short single collector sleeve welded over them which provides the joint to the next exhaust section. This weld always eventually splits. It's covered by the downpipe heatshield. However, you can carefully cut off the last 5" of heatshield and get to the join and, if you're lucky, reweld it back. It's that or a £1000 downpipe!

Good luck, Vee.

Paul

 

I looked up the part number at JDHT and it seems that the
manifold has been superseded by NBC2903AC

That part is much easier to find. I guess I'm going to
find out if it really is interchangeable! (Still for sale
on JDHT, the front manifold is not)Thanks for the advice on the rest of the install. The straightforward looking projects are always the killers. I have downpipe studs ordered as well as that round washer. I'm thinking the bolts can be purchased anywhere if I ruin one.

 

Vee,

Sorry, I misled you, it's the rear one that is available. If I were you, I would buy a new one rather than a 2nd-hand one. They all crack in the end and a 2nd-hand one will be no newer than your own one.

I might be wrong but I don't think you'll find anyone making these except Jaguar, so I'd just go straight to Jaguar Heritage Parts now and order it (whilst it's still available!)

Good luck with the install!

Paul

 

Vee, sorry to say, but I don't think the crack is causing a miss due to the 02 sensors failing to deal with unmetered air coming through the crack. No air is entering the exhaust manifold, it is exiting instead. Keep soldiering on and soon you may solve this problem. It is, in my opinion, being caused by a sensor in the fuel infection system, as mine was.
Cheers, RagJag

 

Thanks for the photos VEE.
Very useful. (I am learning more about XJS's than I thought was possible for a dim-whit like me).

 

I sure hope you're wrong...

I have changed every sensor there is in the fuel injection system. If this doesn't solve the problem, I will spend the spring comparing values between what the sensors are sending out and what the ECU is receiving.

Hopefully, I won't need to buy any new testing equipment. I am armed with only a mid level multimeter...

Either way, I will be sure to post back the results...

 

You could always pack the crack with exhaust repair putty or metal epoxy for the
purpose of testing.

It should hold long enough to find out if the leak has any effect.

 

These are mine::




I think every AJ16 car has cracked manifolds. Mine has been like this for a while and no 32 second drop in idle. Unless your theory is that the oxygen sensors got damaged as well by the plug explosion, which I imagine may be very likely.

 

Mark,

Very disencouraging post you just made, on two accounts.

One, I bought a new manifold and apparently it's not something I necessarily need? Car runs fine with a crack in the exhaust manifolds?

Two, it won't solve my idle issue.

At this point, it looks like I need to get ready to check wire integrity between the ECU and all sensors in the Engine Management System.

I will set up a plan and start moving methodically through the process.

I intend to do an impedance test at the ends of each of the sensor connector as far back to the ECU as I can. I will need help to make sure that my plan is sound, so once I draft up a plan, I will post for review and comment.

After the impedance checks out, I suppose I will need to do voltage checks that line up the readings with the ranges the service manual provides.

 

Well we won't know for sure until you get that new manifold in place. Have you removed the old one all the way? Maybe yours has a even bigger crack than normal on the back side that we can't see.

 

No. Haven't taken it off, however I have managed to loosen all the bolts except for the two that connect the EGR to the rear manifold. Those are soaking in PB Blaster right now. I needed to make sure that all the parts would come off in case I needed to purchase some new pieces. Looks like the two studs I've ordered will remain spares, but for $3, I'm happy to have them.

The bolts all came off easily, considering the amount of rust on them. Took some effort, no doubt, but not as scary as I thought. I will be sure to apply some nickel antiseize when the new piece goes on.