Question for Mike and a few other XJS owners
(remember mine is a 4.0 Straight 6 AJ16)
A few times over the last few months (three times I think) I have experienced something rather unnerving, both times after a good long run (at least 1 hour) at speed.
The car develops what I think is a misfire, the sound gets very lumpy, vibration is evident, and acceleration is non existent. If I slow down to a stop, the whole car is vibrating terrible and moving away in 1st gear is hair raising.
On 2 occasions it was close to end of journey, I parked, went about my business, came back, and started the car - all was well
on last occasions (yesterday on way home from Clarkes) the problem developed at a point int he journey where I could not stop (was on the M25), but equally mysteriously it disappeared again and reverted to normal after taking the speed down to about 50mph for 15 mins.
All guages read normal, oil pressure, temperature etc
Ideas? hoping its as simple as a spark plug!
Anyone know an AJ16/Jag specialist in Herts?
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my first look would be a new set of plugs. then new leads etc then if that d oesnt work just open your wallet at an indy and weep a little.
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although the car is 1995, the engine and gearbox were replaced in 2006, only 5 years on them., Hope its sparks, it first happened after a very wet spell, very very wet.
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One thing that can break down with heat on a long or fast run is an ign coil... and as it rarely shows the symptoms in the workshop it can be hard to trace. I had this (not on a Jag) once and it was only proved by running the car with an ign test analyzer laying on the passenger seat and connected to the coil. The readings showed the coil fault as the power fell and it misfired. The feeling was that the juddering was so bad you didn't think you could get the car home.
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Its sounds a sparky problem to me, fingers crossed!
Pop the bonnet open at night, run the engine and spay a light mist over the HV bits with a plant sprayer, you may end up with a fancy light show!
Last edited by: Zero on Tue 12 Apr 11 at 18:08
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It can get pretty hot under there, so fuel evaporation is a possibility.
Allowing the car to cool by stopping would cure that, as could bowling along at low revs at 50mph.
The engine's been in and out, and with the best will in the world, simple items such as heatshields can be left off.
Have a look under the bonnet and trace the fuel line, see if it passes the exhaust manifold and if there's any sign of missing bits of foil board.
If it happens again, stop if possible and lift the bonnet - if that cures the problem you know you are on the right lines.
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thanks
"The feeling was that the juddering was so bad you didn't think you could get the car home"
THat describes perfectly the sensation
Guy
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If the problem happened in cold damp weather it could also be carburettor icing, Is there a heated intake air supply from around the exhaust? The icing will melt if you slow down as heat soaks into the carburettor.
Last edited by: Old Navy on Tue 12 Apr 11 at 18:52
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Missed the edit -
The key statement was the problem goes away after a stop or slow down, the ice melts!
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I'd also have a good look for air leaks, a loose bit of intake trunking shifting around could produce these symptoms.
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Why not take the critter to a dedicated diagnostic centre,
some will even have a rolling road so you can take it up to 95 without getting your collar felt.
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>> Anyone know an AJ16/Jag specialist in Herts?
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1, Wyn Thomas Jaguar, nearish J26 M25, It's Essex (Epping Forest), but well achieveable from Herts.....01992 578555. I've used them for many years on my S Type and then my wife's X Type when it came out of warranty. Very good, but not cheap Jag specialist, cheaper than main dealers though.
2, Jaguarrepairer Ltd, (Paul Vandermolen), premises in Edgware, which is very near Herts. Exceptionally knowledgeable Jag mechanic. Only used him in the past 6 months, but knows his stuff. Don't let his prems put you off (looks like Steptoe and son), he will only park customers cars at his parents large house in Stanmore, when not working on them. Tel: 020 8954 1816 or 07831 755666.
No hesitation in recommending both and both provide Jag courtesy cars. Both give customers advice on the phone.
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If you havent already id ask on the Jag forums as when I had an issue with dropping oil pressure on my XJ6 they went to the issue straight away with just a description online and it was an easy fix.
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most likley coils but there is one thing that gets overlooked on these engines and thats the valve clearances ! May need a check, when they get hot they close up and make them idle lumpy and run a little rich as the vacum drops so the map sensor in the ECU thinks its running on a wider throttle !
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it has happend three times, first was 90 minutes in to an otherwise uneventuf drivem the car had been standing for a couple of weeks undriven and there had been a lot of rain during that period, no ice though around that time.
the last time was Monday this week, lovely warm day, but again the car had been standing for 1 week undriven, this time it was 2 hours in to an otherwise uneventful drive
No I haven;t been on a jog forum, which would you recommend
Guy
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>> there had been
>> a lot of rain during that period, no ice though around that time.
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It only needs to be a cold wet day to cause intake icing, it does not need to be freezing. I agree it could also be heat causing an electrical fault.
Although carburettor icing is usually found in aircraft engines I have suffered from it in a car many years ago.
Last edited by: Old Navy on Wed 13 Apr 11 at 17:05
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thanks, Paul in Edgware sounds like my kind of place!
Guy
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www.jaguarforum.co.uk/
forums.jag-lovers.org/
Both seem fairly brisk.
Last edited by: KosaiIggypop on Wed 13 Apr 11 at 13:34
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Consensus seems to be ignition coils judging by response on Jag forum
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Had them go on my S Type a few times....can be intermittent, if you're lucky the engine management light will show temporarily (in which case there should be a fault code to see). If not it's guess time. The coil packs are not all that expensive in the big scheme of things. Make sure you remember which one you've changed..so that next time it won't be the one to worry about...or do as I did and do all 6 in one hit, so the damned things wouldn't catch me out in circs of gross inconvenience.
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Jaguar XJS 3.6 AND 4.0 - A couple of questions - nyx2k
