Hi all, another round of Jaguar woes from me. So, I managed to get the XJ running in my last post on this forum, and all appeared fine. It behaved itself for a few days of usage, except for stumbling as it came up to temperature. I thought this might be due to low fuel, as it was almost empty. However, after filling up, the problem persisted. The car became harder to start, requiring two or three attempts on the starter to get going and sometimes a little bit of throttle to coax it to idle. I suspected maybe the CPS has failed, as it sometimes fired up right away, and other times took 15-20 seconds of cranking across two or three runs of the starter motor. This was usually when the car was warm, but it did struggle a bit one time when fully cold. So that's one problem.

A more serious problem presented itself, however. The car's stumbling got worse even as it was up to temperature. It would hesistate when accelerating, and felt down on power. As I pulled out to overtake and found it very reluctant to accelerate one time, I manually dropped it into second gear and floored it. It got to 4,000 RPM, then stumbled significantly and backfired a few times, unable to accelerate any further. I did this again as a cautious test, and it then blew a hole in the front exhaust manifold and now sounds like a John Deere X300 rather than a Jaguar X300. Annoying.

So, first of all, why would it be hard or slow to start when warm and experience stumbling as it comes up to temperature and under acceleration? Why would it be unable to get past 4k RPM?

And what's the procedure for removing the front exhaust manifold on a 4.0 car? Is it likely that a smaller exhaust leak caused the stumbling and inability to accelerate, a smaller leak which suddenly worsened? Or was the failure caused by back pressure, or over-fuelling? And would replacing the manifold resolve things? I suspect it isn't so simple.

Thanks for any tips, this car is testing my patience in an already unexpectedly stressful time.

 

Codes ?

P0340 ?

When the engine coolant sensor sees 88 C the fuel mixture will be regulated by the O2 sensors

A leak in the exhaust before the 4 sensors will bias the O2 sensors to make the mixture rich , common

this condition accurse at the idle range only

 

I haven’t checked for codes yet, but no warning lights on the dash. The car seems to idle ok, the stumbling was most noticeable when accelerating gently, or accelerating hard at 4k RPM. I was leaning towards overfuelling being the general issue, but wanted to be sure before I start buying parts. Manifolds are expensive.

 

The exhaust leak / rich mixture issue Parker refers to only tends to show up in the fuel economy (lack of) and fuel trims. Even at full rich trim, the car runs sweetly, just expensively!
Your backfire and lack of power sound more inlet side fuel related.
Exhaust manifold removal is relatively straightforward provided the nuts come off, which mine did. The tricky part is the joint to the down pipes, where you will need an assortment of socket extensions and universal joints to undo them from below. Reassembly requires care to ensure the donut forms a good seal.

 

Thanks for the advice. Would the lack of fuel coming in cause the exhaust to break suddenly? I don’t want to replace the manifold if it’ll just break straight away again due to the other unresolved issue.

I wouldn’t have thought low power and a bit of stumbling would cause an exhaust to fail, but fail it did. Perhaps the shaking of the engine as it hit a ‘limiter’ at 4k caused a crack to open up?

 

You can tighten the 4 down pointing donut gasket studs for free

Best from underneath

13 or 15 mm median lenth socket and separate universal on a long extention , 1 of the 4 has a tight wall clearence

The gasket ( 2 ) if replaced is 60 mm pipe OD so the gasket is 60 mm ID

Jaguar # EBC9388A ( X 2 )

New studs can be obtained , of the 20 sizes of studs at the hardware store the ones needed I had to order from a US vender

Jaguar # EAC3823 ( X 4 )

 

Getting up to temperature just (most likely) means that there's a sensor giving it bad information.

When was the last time you replaced the oxygen sensors?

 

I’ve had a bit of a poke around, and although both manifolds are cracked, they’re only blowing a tiny bit. The main leak which is causing the noise is underneath the car, at the join between the downpipe and the next section, I think. I’ll have to jack the car up and inspect it properly. Hopefully, I can tighten this join up or replace the gasket. Should be easier than the manifolds.

I haven’t replaced any sensors since I’ve had the car besides CKPS. It could be a bad O2 sensor causing the stumbling from overfuelling, but someone (countyjag I think) said earlier that even if running really rich the car still runs smoothly. Does a bad O2 sensor cause rich or lean running?

My feeling is that there is a problem with fuel delivery. Slightly down on power in normal driving conditions, then suddenly worse under heavy acceleration. Could be fuel pump, pressure regulator, or fuel filter? Would bad fuel cause this stumbling?

 

A bad O2 downstream sensor makes the engine run like crap.

You're confusing information. If the ECU remains in open loop, and will run rich, but well, since it's relying on preset data to fuel the engine instead of relying on actual real world feedback and data to figure out the ideal fueling amount. Your car starts out that way everytime you start the cold engine. It waits for certain checks from the sensors, and certain conditions before it is ready to go closed loop and take direction from them. An O2 sensor without an operating heater would do this. A sensor making bad or slow reads on the exhaust would allow the car to go closed loop while feeding it bad information, hence the poor running engine.

I'd start with the oxygen sensors. These things are likely original and about 30 years old. They are a wear and tear part and do not last forever.

 

Hi chaps, took the Jag for a test drive this evening. Annoyingly the stumbling issue didn't reoccur, so I can't test it. Perhaps it is just bad fuel? I accelerated all the way up to redline when she was cold (sorry Jag, it's for science) and at temperature, and no issues with either. Smooth and constant acceleration throughout. Maybe slightly down on power, but I could be imagining that as it's been a while since she was healthy so I might have forgotten what healthy feels like. Fuel economy seemed worse than normal tho, with the car coasting along downhilll it didn't go above 40mpg on the instant fuel reading. It used to go up to around 80-90 when rolling down a hill. So it's probably still running rich, just not as lumpy anymore for some reason.

Exhaust is still deafeningly loud, but I'll get under her to take a look at how to resolve that when we have some better weather.

 

You should check to see if the car is staying in closed loop. Perhaps it’s running well because it’s not relying on sensors for fueling direction. That would make sense if you believe your mpg is in the toilet.

I assume you have an OBD2 reader?

 

I have got one, a very basic one. Do you have to let the car get warm and then check?

 

It depends how it reads whether the car is in open or closed loop. I'm not sure a cheapie will tell you, but maybe it does?

I'd start reading cold and see if it changes when the thermostat gets past 168F. If it doesn't, I would recommend getting a smarter OBD2 reader, or a wireless OBD2 dongle that connects to your phone? (iPhone can only use WiFi dongles, whereas Android users (I believe) can take advantage of Bluetooth or WiFi)

Either way, you need to have some device that can tell you.

 

Is it a supercharged car? They have a secondary fuel pump which is needed to sustain life beyond 3500 rpm, as the engine is demanding fuel at a dramatic rate in that condition, and yours may not be working.
Returning to the exhaust side, cracked manifolds are a common fault, and cause the car to run rich. Sweetly, but rich. They tend to be small and not especially noisy, so if you are sounding like a tractor, look elsewhere.
Dead O2 sensor(s) will prevent the car going into closed loop. Remaining in open loop results in higher emissions (forget about getting an MoT) and higher fuel consumption. She will still run sweetly though.
Failing O2 sensors will tend to push the fuel trim to rich, see above consequences. She will still tend to run sweetly though.
For what it is worth, I only ever had my attention drawn to O2 sensors by an MoT examiner and a marked drop in fuel economy. Performance, idle etc were fine.
Most any scanners will allow you to see output from the O2 sensors, not least as I believe it is one of the legally mandated minimum OBD2 functions. Sometimes you have to dig around in the various menus to find it.

 

Not a supercharged car, just a normal 4.0. The main exhaust leak is coming from underneath, near where the pipe turns to the horizontal after having come down from the headers but I haven’t been able to get underneath and have a proper look yet. Hopefully it’s just a new gasket or tightened bolts needed. Not looking forward to trying to reach up to some of those bolts.

As the car is now running smoothly, just loudly, I can’t work out why it did have the stumble previously. Might have been some bad fuel or a temporary blockage causing low pressure? I’ll have to fix the exhaust, then take it out for another proper drive to see if the issue returns. Can’t be driving it to work at the moment, it’s as loud as the F15s we’ve got flying overhead.

 

I’ve found the leak. It’s a three inch hole in the downpipe, not just a loose connection unfortunately. See below photos.



There are also holes/cracks in both manifolds with minor leaks, but the noise is most definitely the downpipe.





It’s even blown the heat shield apart. Could this be a symptom of a clogged cat further down the pipe? Or just bad luck and an already rusty exhaust. It did occur as I was accelerating hard, and when the car stumbled at 4k RPM and wouldn’t accelerate any higher.

If I replace the downpipe, will the new one suffer the same fate and promptly burst due to a blockage down the line?

What is the process for removing the downpipe? Undo bolts front and rear, and it all drops out? Then, what do I need to replace? Which gaskets, which fittings etc would I need? Thanks.

The last bit of good news is that since this has been parked on my driveway for the last couple of weeks, some *$£# cack-handed delivery driver has managed to reverse into it, leaving a foot-long scuff on the boot and bumper, before swiftly buggering off. I’m sure this car is cursed.

 

On another note, if any of you UK Jag types fancy a slightly scruffy, but generally ok low mileage 4.0 Sovereign, I’m not averse to exploratory offers. Pictures, further details etc can be supplied.

 

Sorry to hear that. I really am.

I don't know what caused that exhaust pipe explosion. I don't think it's a common occurrence, but I would think any exhaust shop could probably spend a few minutes with it to see if the cats are in good shape and give you a quote to replace the pipe. Replacing it without a lift will not be easy. The bolts holding everything together will be rusty.

I should have a previous post where I replaced the exhaust manifolds. That should give you a good list of what to expect there, JDHT should have the part maps for you as well.

 

I was planning on finding a used downpipe on eBay and all the necessary parts, then taking that to an exhaust shop for them to fit. I don’t think my driveway ability will allow me to reach the necessary bolts without rounding them off.

The scuff’s annoying, but nothing can be done about that for now. Hopefully, if the ‘new’ downpipe survives a while, the cracked manifolds won’t then develop further.

Thanks for the tip about your previous manifold replacement post, I’ll have a look for that.

 

Do any of you fine chaps know the parts and part numbers needed for this job? I’ll be replacing the downpipe, so I imagine I need two gaskets at the front, one at the rear (or is it just a clamp?), and then all the relevant fittings. Maybe two O2 sensors too? If you could help me out with the specifics, especially gaskets, I’d be very grateful.

Is this a slip or an olive type connector? Are the two interchangeable or must they be the same on both pipes to mate properly? Whichever this one is, what clamp do I need? I need to order all the bits to get this in for repairs.