How to Diagnose Jaguar XJ6 X300 Series Non-Start/Poor Running Faults

ADDENDUM:
Keeping in mind this video is far from a comprehensive guide, and more to give you pointers, I recommend visiting the Jaguar-related website by Jim Butterworth (link below) for more details. It is an excellent resource. In the future I may do a part two video covering more non-start/poor running issues on the X300 XJ series.
jimbutterworth.co.uk/8jagstart...
This video is for Jaguar XJ6 X300 series owners who have problems with the car either running poor, or not running at all. There is some crossover of these issues with XJ40 and XJ12 also. Here we do a whistle-stop tour around the car pointing out most of the common culprits leading to running issues on these old Jags. The AJ16 engine itself is a magnificent unit and unlikely to fail mechanically, unless severely neglected. However there are a number of modules and sensors that can be an issue, as well as fuel delivery problems. Diagnosis of these running problems revolves around four main areas: fuel, air, spark and electronics (as with most cars with an internal combustion engine). One omission in the video is cleaning the throttle body, which is different for the XJ6 and XJR6. If the throttle body itself gets very dirty, you may get a sticking throttle and rough idle.
This video is a strictly a DIY guide, not professional or sanctioned by Jaguar Cars LTD. Undertake any vehicle repairs purely at your own risk.

[@djonfonsteen6331]

Excellent!! This is one of those "return to video, as and when needed". Cheers

[@Biggles]

Thank you!!

[@exoticprairie]

This was great help in my diagnosis.

[@tonyburford421]

I thought the silver cylinder was the gearbox interlock switch and it was the linear switch that causes the non starting issues (which I have on my 95xjr) not helped by a lot of parts being unobtainable new.

[@kmdifo]

Love this color!!!

[@noyaboyfleett2701]

So crazy because I watch this video to go outside and check and discover that my car was turned off in drive 🤣🤣🤣🤣🤣 you saved my stupid little life

[@thirdworldassassin]

mad skills homey , i am familiar with all those things but didnt know the names of them lol i found your video very helpful , i didnt know about the rev thing with the position sensor , thats cool , im hoping its just my fuel filter lol

[@tonyblackie3277]

Hi, awesome summary thx. One more that immobilised my x300 for literally months (busy cheap backyard mechanic) was a relay BASE (not relay) under bonnet near the air filter. All relays CHANGED, no fix, but the base itself had to be changed. I think the ignition positive relay BASE was faulty.

[@Biggles]

Tony Blackie Thanks for the comment. A bad relay base is a really insidious fault. Sorry to hear you had to struggle with it. Please consider subscribing if you can. It really helps the channel out!

[@superApollo2012]

Hi Tony, I am having same issue as well: ECM Immobiliser Circuit Malfunction; Out of range voltage for diagnostic line'. I wonder if any mechanic around Bedford area could help me, pls

[@chefbrody]

Great video thank you very much! I often need to start my 1990 xj40 twice. And there is gas smell. I suspect a failing fuel pump. (It’s under the car easy to get to). Would you suggest looking into the fuel pressure regulator before changing the fuel pump? Thanks again for your video

[@Biggles]

RickParis Thanks for the feedback, much appreciated! Definitely change the fuel pump as a matter of course. I had one that would overheat and then the car would just die. The spec for the fuel pump is not brilliant on the XJ40. Somewhere there is actually a service bulletin noting that the car can die in very hot weather and that having two pumps in line is a fix, typical Jag! You can take the fuel pressure regulator off easily to inspect, clean, and replace but usually the problems is the fuel pump. Don’t forget to change the fuel filter too!

[@chefbrody]

I’ll do that Thanks !

[@billymint1]

Very helpful thanks

[@markmathews6876]

thanks mate

[@talmadgebutts4766]

Great video! My jag is currently giving me a crank no start issue after about a half dozen starts that took progressively long turnovers to finally start. I just replaced the CPS and it almost started a couple times after that but now back to nothing but the engine turning over. Any guess as to what I might have going on or could check? I’m seeing no rev counter movement even with the new CPS so I wonder if I have a short in the wiring harness somehow?

[@Biggles]

Thanks for the comment. That is an annoying fault indeed. If your rev counter is not moving then there is no signal from the CPS for whatever reason. Have you checked the condition of your ECU? I would imagine any water ingress there might cause this issue too. Other than that I would proceed by inspecting the wiring and the plug connector from the CPS to the main loom.

[@talmadgebutts4766]

@@Biggles Really appreciate the reply. I’ll check that out.

[@richardshort3914]

Thank you very much.

[@fitzroyarmour7391]

Excellent thank you

[@tonyblackie3277]

Hi, excellent video, thx so much for making the effort :) I had a no start issue with a relay HOLDER or BASE in the engine bay. It's in the small engine bay fuse box front left that contains but one (brown) relay also. Whatever that says it does (horn etc) in the end it stopped the engine from starting. Once we replaced the BASE it was away. Took ages to find out the base was at fault. Just realised that I have already posted this repair solution earlier. For the $1,500 it cost to diagnose the $10 part, probably worth mentioning twice!

[@Biggles]

Tony Blackie Absolutely! Thanks for adding that to the list. Very important info. Indeed that is the danger paying non-specialist mechanics lots of money for diagnosis. They simply lack insider knowledge, which we enthusiasts can share! Keep subscribing people if you can! So close to 1000 subscribers now thanks to your help!!

[@JAMESBOND77778]

Wonderful!.Thank Sir.

[@Biggles]

JAMES BOND Don’t forget to subscribe if you like the content. It really helps the channel!

[@joshthepropertyguywiththeh4130]

Could you do a video on how exactly you put a live wire to test the fuel pump? Would be much appreciated!

[@Biggles]

I’ll keep that in mind for future videos!

[@grimlock2676]

Hi. You said "use only RC9YCC Champion plugs" You mean XJR or normal R6? Many people recomended RC12YC.

[@Biggles]

What a coincidence you mention this now, because the other day I took delivery of a set of RC12YC plugs to test this idea out. In my case it is to see whether they will resolve a lumpy idle on a 1995 XJR manual. After a quick test it seemed to do the trick but I don’t know whether it was really just the previous set of RC9 plugs going bad (they were not old, but the car has had lots of work and messing around recently). Reading the RC12 plugs after a run they seem to be a hotter plug so I’m not sure whether I would stick with these plugs or not. I will also try another set of new RC9 plugs soon to see the difference. As many say though these cars basically run lawn mower spark plugs!

[@markunderwood7079]

I have this exact problem. Getting the inhibitor switch out was not fun. Once out I tested with multi meter and it reads 50.0 ohms resistance. Is this a good switch or should I replace it, current they are 400.00$ US. Also would you know the size of the indicator light bulb, might as well replace that if I can find the right one. Thanks.

[@Biggles]

Before condemning the inhibitor switch, I would have a careful look at the microswitch that activates the park light. This is the more common failure point, rather than the inhibitor switch. Furthermore it's usually just the metal tongue part of the microswitch that gets bent out of shape. You can carefully bend the tongue outwards to help the gear level come into contact. I'm not sure about the light bulb for the park P. A lot of small bulbs on the X300 are the 286 T5 type.

[@markunderwood7079]

@@Biggles the micro switch definitely has good contact and it doesn’t look like it’s replaceable as it is riveted to the bracket

[@Biggles]

@@markunderwood7079 You could try spraying electrical contact cleaner into the microswitch. Not easy since there isn’t much of a gap anywhere to spray into, but still worth a go.

[@javierdieguezaperador8361]

Hi, I'm having trouble starting a jaguar x300, the fuel pump works but the ignition system doesn't produce the spark to the spark plugs, the phase sensor works

[@Biggles]

Have you checked the condition of the ECU?

[@javierdieguezaperador8361]

@@Biggles The ECU has not been revised before

[@Biggles]

@@javierdieguezaperador8361 I would recommend checking the condition of the pins and connector blocks going into the ECU.

[@mpwr27]

👏👏👏

[@jamesbest9741]

Only have a hot start issue any thoughts??

[@Biggles]

It could be one of a few things, but start with this simple check first. When the car is hot and not starting, crank the engine (assuming it will crank). Look at the rev counter while you crank. While cranking you should see around 200 rpm on the rev counter. If the rev counter is at zero when cranking the fault will be the crank position sensor (with about 95% certainty in my opinion). The crank position sensor is the cheapest (£25) and easiest part (5 min job) to replace if it is faulty, so we’ll worth a check.

[@pauldavies9464]

My X300 does pink now and then and the power is not as good as my previous XJ40 any suggestions, interesting Video

[@Biggles]

Paul Davies I think you just have to be systematic in investigating such an issue. The three fundamentals are fuel, air and spark. Before throwing lots of expensive parts at it, check the spark plugs, change air and fuel filters. Check appropriate fuel flow at the fuel regulator. Mass airflow faults cause lots of running issues. Throttle bodies get quite dirty and are easy to clean. Then you could check the condition of the coil packs, check for burns or signs of arcing. There are old cars now and exhausts can be in pretty poor condition. Spare a thought for the catalytic converters. The can collapse on the inside, blocking flow of exhaust gasses. One way to investigate is to get an IR thermometer gun and check how hot the exhaust is getting. Bad oxygen sensors cause problems as does the coolant temperature sensor to the ECU. Finally check the condition of the ECU. It sits upright next to the driver’s foot and is notorious for getting wet and corroded.

[@pauldavies9464]

@@Biggles Thanks that's a comprehensive list, I do have a IR thermometer gun hadn,t thought about the catalytic converters I think I will start with all the checks first and clean the throttle body as well I do have a 98 XJR V8 and because that is so lively that it may be making me think the X300 is sluggish but having said that it does pink on a big hill under load,thanks once again for the reply and all the useful info in the videos.

[@Biggles]

Paul Davies Happy to share the knowledge. If you haven’t already, please consider subscribing as it really helps out the channel!

[@pauldavies9464]

@@Biggles I will yes no probs, I like the colour of your XJR works well.

[@jacobemanuel5758]

I got a 1997 Jaguar xj6 but whenever I attempt to Crank it uphe will not crank up but he won't even shift out of park with the key on and my foot on the brake the dash lights work but the headlights interior lights brake lights and blinkers hazard lights none of that works can somebody please tell me why

[@Biggles]

Jacob Emanuel You seem to have multiple unrelated problems there at the same time. Whenever I hear of this I recommend looking at the ECU for corroded and broken pins. Many people have strange electrical issues/non starting when the ECU gets wet, the pins corrode and break.

[@Belief88BM]

what the crunchy noise at 0:57 ? I also hear that sound in my xjr6 when engine starts, this sound is annoying.

[@Biggles]

Well spotted. My current XJR6 also does the same, intermittently. I’ve been trying to catch the sound with my mechanic’s stethoscope but when I want it to make the noice, it won’t. I think the culprit is a worn upper timing chain tensioner (i.e. the one sticking out the side of the engine block). My current XJR is still on the original tensioner so I’m assuming that is the problem. The replacement part is updated from the original design and more reliable. If I pin the sound exactly, I’ll post my findings here.

[@Belief88BM]

​@@Biggles i hear that sound at every cold start, or when the car is parked after a trip about an hour and i start the engine again. Thanks a lot for a your video and fast feedback! =)

[@Biggles]

Belief88BM No problem. Please consider subscribing if you like the content as it really helps the channel.

[@Belief88BM]

@@Biggles already subscibed =)

[@tonyblackie3277]

It may well be a loose lower front pulley! Took mine in to get an intermittent ABS light sorted and mechanic noticed a loose front lower pulley about to fall off!! I had thought for ages a noisy A/C clutch, but as A/C working fine, I had sort of ignored it. Prob not the same sound, but give your big lower front pulley a good wiggle from time to time :)

[@busche1]

Danke ! Grüße aus Berlin.

[@Biggles]

Danke schön!

[@stunnaman9745]

Hi i got a jaguar x300 xj6 and it still does not start i got it out of park mode but nothing any help??

[@Biggles]

STUNNA MAN Does the engine crank at all?

[@stunnaman9745]

@@Biggles no nothing plus got no reverse lights

[@Biggles]

STUNNA MAN I would definitely check the battery in that case and all fuses/relays. Have you checked the condition of your ECU? Sometimes the pins corrode and snap, causing lots of problems.

[@stunnaman9745]

@@Biggles I will get a new battery tomorrow and we'll check the rest of the ECU and the relay

[@stunnaman9745]

@@Biggles no nothing at all

[@paulshook7611]

Looking for a computer box for a 2002 type x Jaguar

[@Biggles]

Paul Shook Sorry, this video is for a different model Jaguar. Not sure what you mean by computer box for X-type, there are many. If you mean ECU then I recommend trying to find one from a specialist spare parts supplier.

[@paulshook7611]

I need a computer box for a 2002 Jaguar

[@thirdworldassassin]

that car is not a 94 its a 95 , unless they released the xjr 95 a year early in europe which im guessing must be the case

[@Biggles]

In this case by 94 I mean built 1994, but registered 1995. There were some cars on the U.K. roads in 1994 also like prototypes and press cars.

[@thirdworldassassin]

@@Biggles aah thats hwo my 97 is , built in 96 but is a 97 , i wonder if my 95 is like that too ?

[@Biggles]

@@thirdworldassassin One possible way to tell if it’s an early car is whether you have a glovebox or not. No glovebox = early car. It should be possible to contact Jaguar Heritage to get more info on when your Jag was built. You can get a heritage certificate for your classic Jaguar from them.

[@thirdworldassassin]

@@Biggles you mean that little spot by the steering wheel where i put my united states constitution in case i get pulled over and have to be like bitch you abide by this lol

[@Biggles]

@@thirdworldassassin No I mean the hatch in front of the passenger.