Hi All,

been on a bit of a saga in the last few weeks with the car spending a lot of time at my local specialist. I will preface this with a defence of the specialist I have used as I believe him to be trustworthy, if a bit out of his depth at times with a rare car (XJR6 manual) which doesn't benefit from the latest onboard diagnostic equipment. I am mainly looking for advice on where I go next, as I am competent with basic home mechanic work, but I suspect this may be beyond my ability. The car has 136k miles

The problem:
I took the car to the specialist about 6 weeks ago now presenting with a small misfire at idle only when hot. The engine ran fine otherwise, or at least I think so, as I only bought the car about a month before and have limited experience with XJR6. Either way, the misfire was what I would class as liveable. The only other issue, which I assumed was related, was the engine cutting out when dropping down to idle. as puling up the lights and putting the car briefly in neutral or holding in the clutch I was finding the engine sinking below idle and cutting out sometimes. I eventually was able to drive around this as it seemed to be load dependant, IE, don't go in too hard on the brakes with the foot on the clutch. Anyway, the car was dropped off to the specialist with these 2 problems. I will emphasise this felt like a couple minor faults and was broadly liveable when you knew how to drive around them.

The tests performed:
below is a list of work that the specialist carried out and my second hand account of the results.
- Checked coil packs - checked the recently fitted (within last year) non-jaguar coil packs for function, these proved good, but also swapped with known good jaguar units to see if any difference was made. This made no difference
- checked idle control valve - Checked for blockages and cleaned idle control valve and throttle body. slightly gummed up so cleaned and replaced
- checked for sensor faults - no clear sensor faults and traced all lines and signals back to ECU. He did notice an aftermarket crank position sensor bracket (presumably a timing advance bracket) but this was swapped to a standard bracket to no positive effect, so was eventually swapped back on.

At this point, the mechanic felt it was out of his knowledge base, and reached out to Jaguar technical. They suspected an ECU fault and the work was a bit sporadic here around trying to confirm or deny whether it was down to this.

Jaguar Technical diagnosed the issues as ECU related, and recommended replacing the ECU. This didn't sit well with the mechanic though, so he carried on and performed a cylinder leakdown test to show if there were any engine internal issues detectable

The cylinder leakdown test showed 30% leakage on cylinders 5 and 6, the mechanic advised this would be down to a couple valves not seating correctly

The car now:
The car has a severe misfire at idle, to the point where it is hard to keep the engine running while manoeuvring. I do not necessarily blame the mechanic, as if this is a stuck valve misfire, I would fully expect it to get worse and worse as the engine is run. I was hoping to run the car for a few months to research and save up some money for an eventual head rebuild, but the running problems are not what I would term liveable now.

So... what is next? take it to a shop that knows these engines better for a more comprehensive diagnosis? assume the worst and book in a head rebuild (to my wife's great displeasure I am sure) and hope this cures all its ails?

I guess I want to know what is next and roughly what to budget. The mechanic reckons it would be around £1500 for a cylinder head rebuild, which obviously smarts a bit on a car I just bought and was told run perfectly, and there's the added concern this won't cure all the issues.

 

MMMMM, my thoughts on my car when I had it, although an Auto.

That mileage at that age is LOW, so a lot of short trips, etc etc, NOT good a Supercharged engine of any brand.

Mine was also low kms, and 2400+kms from me. On the drive home, similar misfire about an hour into the trip. Never mind, its a Jag, we will be fine. Dosed it with Injector cleaner, and DROVE it as designed the remaining kms to our fleet home.
Well, the stuff that came out the exhausts was YUK, and about 400kms later, SWEET AS.

When home, spark plugs replaced, they were OK, but at $7 each why not.

During this task, I noted some cracked wires in that wiring loom, the one that is folded back against the windscreen when changing the plugs. Repaired that as a matter of "why the hell not". My 3.2 had the same cracked loom when I first got it.

That leak down is possibly valves nit seating properly, and a good long hard drive, will either fix it, or it will stay as is. That price for that head build is a tad low to me, that would be my expected for an NA engine, not a blower engine, the amount of bits to R & R is nearly double.

I do note its worse, after fiddling, and that has me thinking that coil loom is at play, as is spark plugs. Coils??, NAH, not a real issue in my time with them, but OZ be different in many ways. It does have some Alien coils fitted. My only experience with coils of this type is with both the S Types, and like you, only when hot. I tested them on the bench, cold, all good. Old age kicked in, grabbed the hair dryer, heated the coils up, that sorted the men form the boys, 2 doing odd things, NEW NGK coils, warranty claim, all good.

Head off at the mileage would be a LAST resort to me.

It needs a good long, hard run, Glasgow and back for example.

 

Misfire at idle when warm is a classic lambda issue, but actually cutting out sounds a bit more serious.
Do you have a jaguar club close by with other XJR's? you could try swapping over the ECU quickly to see if it fixes the problem - automatic ecu's work just fine on a manual car for testing the issues you are having.
i would also inspect the ECU plug/connector for water ingress and corrosion, as that's something that happens from time to time.

i also agree that italian tuneups do work, so using some injection cleaner and taking the car on some long trips will often lead to a nicer running engine if its mostly done short trips.

 

Ian,
A few observations;
Idle related issues abound on these cars, as you will see from other threads.
Cylinder head problems are rare
Engines needing rebuilt are even rarer
ECUs can be problematic, but usually only when they have been affected by water ingress, when it tends to become rather uglier than your initial symptoms would suggest.
Cleaning the IACV on a supercharged car is not a trivial undertaking, and involves disturbing the throttle body, which can of itself be a source of problems
X300 diagnostic capabilities are indeed primitive by modern standards, but they are not non existent. A scan of available codes would be very useful.

Were it my car, I would change the plugs and crankshaft position sensor without giving it a second thought, and play it from there, starting with a code read. Put cylinder head work out of your mind

 

Ageed with the above replies, head/valve issues are rare.

I also think something has been disturbed to go from slight misfire to major misfire. One long shot to check is the 5 and 6 coil connections. Will take 5 mins and it's free. It's not unusual to get these reversed for those not familiar with the engine. They should be like this

 

Agree with all of the above and would humbly suggest draining/replacing fuel and/or checking system.for dirt/water.
Have had mine run like a hairy goat, with a gutful of crook fuel.
cheers,
Steve
Orstralia.

 

Let me revise my earlier suggestion, and Do what Brendan suggests first. Mixing up number 5 and 6 coil connections is almost easier to do than connecting them the right way! I would think it would only take 4.5 minutes rather than 5 though!

 

Thanks all for the replies, I will have a look today at the coil plugs and condition of the spark plugs if this is not it. I am hopeful it is something in the sub £100 order of magnitude. Can throw some plugs and crank position sensor at it along with a dose of fuel system cleaner and a long hard drive.

I will post my progress later if I can steal an hour or 2 to investigate

Cheers,

Ian

 

Pulled the plugs today and all of them are pretty sooty. I also noticed that one of the coils was mismatched (looked 2 shades darker in colour than the others)... cylinder number 5. This leads me to believe the mechanic forgot to swap one back to my matching set I had on the car before and this may be exacerbating things.

New plugs to be fitted tomorrow and I will pop down to the specialists next week and check out whether one of the coils in his parts bin is a better match.

I have also thrown some fuel system refresh in the tank to see if that helps, but I am hopeful its a spark given how dirty the plugs looked.

 

Just had another thought too... Have any of you guys experienced stripped coil bolts? my coil packs do not seem to pop into place like I am used to with other coil packs and so the only thing holding them in is the bolts, but the bolts are stripped. I can't imagine this is helping matters, and wondering whether to helicoil them to tap them out bigger to get a better seat on the plug...

 

OOPS.

Stripped coil retaining bolts = Rock Ape Fool has been in here.

They only need to be just a tad firmer than finger tight.

The lack of hold down of the coils will have an affect on things in my opinion.

If you have the means, helicoil to use the original bolts. The tap out for bigger, might not suit the holes in the coils, I dont remember the amount of clearance there.

I made and fitted a separate earth wire, standard 4mm Black wire, nothing fancy, from the rear coil bolt to a firewall bolt close by, just to make 100% sure that camcover was earthed. It is fairly well insulated from the rest of the engine, and it gave me that "warm and fuzzy" feel, HA.

Good luck.

 

As the bolts are ‘only’ just over finger tight, maybe, for a test, just use a bit of plumbers tape (or electrical insulation tape) around the bolt to just give it a bit more grip and see if that helps the misfire?

 

Hi All,

Had a bit of time on it at the weekend, and you wouldn't believe it. It was a set of blickin' plugs!!

I ordered some plugs from euros to test my theory it was the sooty and badly gapped plugs. The ones that were in there were gapped far below the recommended 35 thou or 0.8mm, probably half that in some cases. Either way, cheapie NGK plugs set up to the right gap and it seems to have alleviated matters greatly.

There's still a barely detectable misfire there at idle, but the cutting out seems to have resolved itself, albeit the occasional rev dip when selecting neutral pulling up to the lights with all accessories on. I am guessing there's still a small vacuum leak somewhere as my cruise control doesn't work, and hasn't since I bought it.

Anyway, I am now putting the small misfire down to the valves being a bit gummed up, the coil that the mechanic forgot to swap back and potentially the stripped coil bolts. I am putting a dose of fuel system treatment through it and hoping this coupled with a spirited tanks worth of driving clears any gunk.

I did walk around with a pokey stick to apply some pressure to each of the coils (5 and 6 where the misfire was at its worst) before I replaced the plugs, but didn't notice that it cured the misfire. That said, the misfire is so mild now that the coil retention it is another variable that shouldn't be there, so I will helicoil them in due course. I plan to use the car in all (summer) weathers, so doesn't sit right with me, no pun intended, that the seal isn't reliable between the coil and the plug wells.

There's a lesson in this somewhere, but needless to say, I am fairly shocked (dodgy puns all over the place) that is was something so simple. The mechanic shall receive my feedback for his future learning.

Cheers all

 

Sounds like you need to find a new mechanic - failure to address the absolute basics right away means he really shouldn't be working on cars at all.
the occasional misfire could be the bad connection to the loose coil, so i would get that addressed as soon as possible - pressing the coil down from above with some foam between it and the cover might be an ok interim solution until you can get the helicoil.
If the idle misfire is still there after the coil-fixing and hard running, i would check the lambda values with an obd reader - on mine, i didnt get any codes from a failed lambda, but changing them fixed my occasional idle-misfire (that happened after the car had warmed up)

 

There ya go.

WELL DONE .

Mostly the simple things, and we humans tend to overlook that item, being smart as we are.

That other stuff would "possibly" sort out with a good long hardish run, especially with sooted plugs, the rest of the combustion chambers will be sooted up also.

Beer O'clock I reckon.

 

While we are still on the subject of rough running I thought I would bring to everyone's attention "Jaguar Technical Bulletin 03.1-10 for my XJR sedan " which basically says cars which are only run around town will develop
rough running which is attributed to build up on the exhaust valves. It advises there are two ways to fix this problem.
1. Change the valves to a different "cutter valve"
2. Take it out on the highway and give it a hard run
I acquired a 1996 X300 from a deceased estate earlier this year. It had 200,000 ks (120,000miles) on the clock. It was in beautiful condition but had a terrible idle and ran roughly.
On a compression test four cylinders came in at 160 PSI but two were around 110.
A very experienced Jag mechanic friend advised me to take it out on the road and "give it a good flogging".
At the same time I discovered the Jag.Technical Bulletin.
I gave it a 40K (25 mile) run at highway speed limit 100kph or 60mph, brought it home and compression tested it. the two "crook" cylinders had improved to 130PSI.
Once again out to the highway but held it in lower gears keeping it around 4000rpm for the 40K
It then ran beautifully and another compression check showed all cylinders around the 160 mark.
This just for information on what appears to be a not uncommon problem with the AJ16 engine.

Bill Mac
MK1
MK2
XJ6S3
X 300 (x2)
14 previous Jags MK5 to X308

 

Sounds like a nice excuse to get out and drive! I think the fuel treatment and about 50 miles of driving over the last weekend made it noticeably smoother, so here's hoping the leak test results would be much better if measured again.

 

See the Coil Pack Testing in the thread above

Not all supercharged AJ16 engines have a EGR valve

There is a EGR position error signal that can be seen on a 327 treader as a PID ..........EGR_error

Someone recently found the EGR coked over

The ECU connector pins have been found to have corroded or on mine 4 broken socket tabs that pinch the sloted pins on the ECU

Parts avail online

 

Same here Bill.

When we got the R in Sydney, North side shopping car. Awesome condition, but not exciting on the Grunt section, or teh smoothness.

Dosed it with Injector cleaner, and headed for Adelaide, via the Hume. Time we got past Wodonga, the thing was bloody scary, so one eye on the speedo at all times, the cruise had a female moment.

Time we got home, sweet as, and stayed that way till we parted company.

The 3.2 was similar when we left Canberra with it, but you basically had to wring its neck to get out of the carpark, so easier to "tune up".

Interesting Bulletin: Change the valves, NAH, drive the wheels of it, HELL YES.

 

Grant
Actually I had a similar problem with an XJ40 3.2 litre car. Was in excellent condition body and paint wise and was a 'one owner".
The original owner was a fairly senior partner in an accounting firm in Brisbane and used the car as a daily driver in city traffic.

However it lacked power and played up on the idle. It turned out that the oxy sensor was shot and a new one sorted out some of the idle and odd engine stopping problems but otherwise it was a "WUS"
It definitely did start to improve the more it got used on highway driving. I drove it for a couple of years prior to getting into X300 cars.
I sometimes wonder why Jaguar persisted with the 3.2 engines. I never saw much difference in fuel economy between the 3.2 and 4.0 litre engines. I suspect it had something to do with the pommy road tax/registration system.

Bill Mac
MK1
MK2
XJ6S3
X 300 (x2)
14 previous Jags MK5 to X308