Hi All,

Jaguar XJ8 4.0 Sovereign. No issues before drive.

My day off and I thought I'd have a drive to the neighbour town. After driving 50 kms, I was on cruise at ~90 kmh/55 mph in a steep mountain climb and really heavy rain. Out of nothing the "Restricted Performance" in display and yellow "Check engine" came on. The car lost rpms and vibrated roughly on acceleration. Stopped the car at first possibility and let it cool down. I have a obdII reader, but thats in garage.
With no garage near I had to turn and drive home. RP and Check engine came and went during ride home, heavy rain all the way. It eventually felt a bit better when riding a lower speeds in the city and it stopped to rain, but felt some "drops" in idle at traffic light stops - not rough idle but noticable rpm "drop" every 5-10 seconds between.
Came home, let the car sit a couple of hours, fired engine up and no drops in idle. Used my iCarsoft 930 obdII reader and it gave no error codes. Went for a spin and no engine light or RP. Idles fine and accelerates with ease.

Oh, these are the worst ones... I have searched forum, and MAF and coils are the first suspects. But since everything is ok now and obdII would have given error codes, it can not be coils? The fault would be permanent? Same with MAF sensor or air leaks, wouldn't that also be a permanent fault and give odbII readings?

Are there any sensors/connectors that need attention, since the heavy rain may have caused the limp home? I don't dare to take on longer trips before this is solved.

Any suggestions? Thanks a lot in advance.

 

Ok, of course, after a day it happened again. This time I had the iCarsoft 930 with me. No dtc under engine module, but:

Under the Body Control Module: U1041, u2012 and B1794

Under the "Security module": U1135, P0100 and P20e2

So I guess it is the MAF after all and a injector error. Is the sensor blown or can it still be air leaks?

 

It's been said many times on this forum, since it first happened in poring rain I'd suspect the ground connections first. I don't know what kind of weather it was when it happened again but if there are dirty or corroded earth connections it really doesn't matter.

That would be my starting point before I throw a bucket load of money into it to solve a problem which doesn't really exists. Meaning, caused by something else but will show up as a fault on your reader.

 

Thanks Nick,

Yes, I tought the heavy rain may had something to do with it, but today it's nice and clear, and I still have the issue.

I removed the entire air flow system from air filter to Throttle housing. Cleaned the entire air duct and air flow cleaner on sensor. Cleaned contacts and connections I could reach. Made sure (well, 99%) that there is no air leaks. Now I have an intermittent "restricted performance", but no check engine light in rpm meter, just yellow lamp over display. Today the idle is rough and car vibrates gently all over and no difference when RP is lit or not. Yesterday car was ok when RP not lit, and rough when lit.

My deduction is that something has happened during cleaning, and sensor most likely is bad? (Will also check coils when I have the time, reminds me of the same symptoms I had with my XJ40 when one of the plug cables was defect. No dtc for cylinder error though)

Any other toughts?

 

If you have no engine codes, then I would suggest it is not a problem with the engine, when the computer throws restricted performance, it meddles with the engine. I would also ignore the CAN bus errors, that is usually an artefact from connecting an OBD reader. That leaves you with body and security modules. In three years of following these forums, I have never seen a post connecting those to RP. So I agree with a Nick Wood, one of the previous posters, that it is an earthing problem. There are a couple under the bonnet, one that comes to mind is on the right hand side near the radiator. Check the earth strap underneath the car, connecting engine to chassis. Also check that the boot is not leaking, there are a couple of modules there.
good luck

 

Thanks Fredd60.

Yes, I also thought this was strange, but due to the cars behavior I was sure that something wrong with engine. Earthing issues would hardly behave like this. I early suspected coils or ignition problem, but no dtc's distracted me.

I started to doubt that my newly purchased iCarsoft 930 (Land Rover/Jaguar specific) OBDII reader was reading correctly or even be faulty. It should have thrown a code. I have spent the day on internet and in some obd2 forums I read the importance of regulary update firmware for the iCarsoft.

Downloaded update tool and sure there was new sw version available. Updated the iCarsoft to latest version and tried reading the car again. Yes, I now got a "misfire cylinder 8" code (P0308)

So I guess you was right having no "Restricted Performance" without an engine issue.

Inspecting coil for water intrusion or if it needs replacing later today.

Thanks again, guys.

 

Try swapping the number 8 coil with another and see if the code follows it.

 

The lesson here is: DON'T WASH THE ENGINE!

 

Resolved!

Close inspection of coil cover revealed that the top two screws was loose, making a small gap (1 mm) over cylinder 8. Not apparent on first sight. Removed coil cover and moist was clearly present around cyl 8. Took coil 8 off and plug hole had a small amount of water and coil end very moist. Dried up, cleaned connectors, cleaned area and reinstalled coil cover thoroughly.

After 200 m on test drive RP display was gone and car is responsive as allways.

If any lessons learned: ;-)

- Do not blindly trust obd2 tools and have latest firmware installed :-)

At least, my air duct is as clean as new ;-) Thanks to you all.