XJ6 S3 hesitancy to rev

Good evening all,

I am 2 months or so in to Jaguar ownership (well, “proper” Jaguar ownership that is, my old XF doesn’t count!)

My girl is a 1985 UK Series 3 Sovereign as pictured below, with 131,000 miles on the clock.

She has been running like a dream since I bought her, however recently a small issue has reared its head.

I noticed it for the first time the other day, that she would accelerate up to a speed with RPMs at 2000 but then would struggle to go on past that.

I thought it was strange, but hoped it was some bad fuel perhaps. I then parked up and drove later and there was no sign of the issue.

Fast forward a week later and the issue has occurred again - a hesitancy and unwillingness to Rev much past 2000 rpms but on an intermittent basis.

A friend has suggested it could be the distributor on the way out, but I would greatly appreciate any other ideas. It might be just my increased awareness as I’m looking for issues more closely but the idle seems to be slightly lumpier than before, too.

Best regards
Jack from Surrey, England

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Welcome! A beautiful example; she looks brand new. I’m not expert with the S3, but many others are and you will soon have some suggestions.

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Any correlation with weather? Arcing plug leads when rain/damp can do this.

No correlation with the weather as far as I can make out

You could try switching tanks whilst it’s acting up–crud can block the in-tank filter intermittently. More common in the early carbed versions though.

-Check elbow for airflow meter, make sure clamps are tight & secure
-Inspect throttle cable, nuts may be undone
-Check ground or loose wire
-Buy tune-up kit, change plugs, wires distributor & amplifier/coil on head
-Fuel Pressure regulator, must change
-Change fuel filter

Set timing after distributor job

Car looks good, no rust, impressive.

Very nice car Jack!
Welcome to the forum.

Did you change to the other tank, Jack - as Robert suggested?

It’s a valid diagnosis test, confirming or rejecting a feed problem - tank crud is a common enough cause of intermittent problems…

Next time; select ‘N’ and see if the engine will rev unloaded?

xj6 85 Sov Europe (UK/NZ)

Hi all

I did switch tanks and it did not change anything so I don’t think it’s tank crud

I have more diagnosis to do, but she seemed to Rev happily at a standstill last night


It’s then one of those tricky ones, Jack - it’s so much easier to work on if the engine won’t run…

Intermittent faults can only be effectively pursued while the fault is present - requiring patience; changing parts willy-nilly is a last resort. There is no pat answer to your problem, but confirm that the tack revs seemingly followed the actual engine rpms. And if the event occurred while accelerating or under load…

That it is long period intermittent, and the engine doesn’t actually quit, implies that most parts are working as they should. You should definitely check the possibility that coolant is dripping onto the distributor lid from a leaking hose. It will cause misfiring, and then disappear as coolant evaporates; wipe the dist lid clean and spray on some silicon…

It may also be some water in the petrol, supposedly filtered out by the fuel filter - how long since it was changed? But the engine will misfire if injectors feed it water, until digested - there is never much water present, but a little may briefly interfere.

Certainly, a bad electric connection may be intermittent; do the ‘wire shaking’ test. With the engine idling; shake all accessible wires - the engine will react if there is a bad connection in the area shaken. With firm connections there will be no reaction…

Welcome on board by the way - sorry that a firm solution cannot be presented…:slight_smile:

xj6 85 Sov Europe (UK/NZ)

In the early V12 H.E., dual ignition coils are used. If the secondary coil is bad or gets disconnected, the engine runs fine at low speed but runs out of ooomph at about 4000 rpm. This sounds similar enough to what’s happening here that I’d suggest looking at the ignition system.

I’m sorry not to be able to add any suggestions to what has already been offered, Jack but I just wanted to say welcome and that is a beautiful looking car!



Four items to check: 1)auxilary air valve 2) ignition amplifier 3) coil 4)distributor cap & rotor
I had the same problem some years ago with my 1986 XJ6. It happened twice. Once, problem solved replacing coil, second time replacing auxilary air valve.
You have a beautiful car, I’m sure it’s been residing in an enclosed garage throughout much of its existence. Pepperpots look great. As you can see, I’m a big fan of pepperpots as well.

Yours is also beautiful! Nice to see such good examples are still around.

I had a broken spark plug (HT) cable giving very similar hassles. Intermittent, of course.
Fuel pressure is the other item to check, under load.

Coil maybe, but the AAV cannot possibly cause this symptom…

xj6 85 Sov Europe (UK/NZ)

Congratulations, what a beautiful car. Does the rev hesitancy happen only with the engine properly warmed up? Does it rev normally again if you select P or N?

OK so a little more diagnosis yesterday evening

Started up fine, drove out of my garage and accelerate up to 2k and it was happening again. A reluctance to keep accelerating much past 2k, and a bit of light coughing, down on power not much more to give.

Pulled over to a stop, put in P and revved up to 3k, very happy to rev. Went to a shop and returned, drove a bit more, gently, until she had warmed up again and then tried to accelerate harder again.

Wow she came back, happy and purring and ready to take on the world. Locked the trans into 2 and she was very eager, really happy to go right to 4k and beyond. As if nothing was ever wrong.

So, it looks like when she heats up the problem is gone. Does this help with the diagnosis?


She‘s too lean and you need a new coolant temperature sender?

Not sure about that, the temp gauge is working perfectly