Hi guys and girls I have a 2007 xk and have an issue. When travelling at about 70 to 80 mph on a motorway the engine runs lumpy almost feels like something is slipping. It's not revving high or anything just lumpy and not smooth. I am concerned about this as could be a big problem have any of you come across this before?

 

Also thinking this could be some kind of misfire at high speed?

 

No check engine light? It could have codes stored in the computer even if it doesn't throw the light. Only a shop can tell you that.

Does it run rough or cut out when you accelerate? Have you ever changed the fuel filter? It's really easy to do because it has quick release connections on both ends. Otherwise it could be a lot of things.

Govtslug

 

Based in the fact that you've given us almost zero in terms of information on your car, it is my professional opinion gathered from years of mechanical expertise that "it may be something or it may be nothing". Never heard of a description of a car being "lumpy". Provide us with miles, last tune up, what has done or not done at your last maintenance, any code readings, has the car be driven regularly, is ot all stock, etc and maybe we can help or pay a mechanic his fee

 

Does it run rough or cut out when you accelerate? Have you ever changed the fuel filter? It's really easy to do because it has quick release connections on both ends. Otherwise it could be a lot of things

Thanks for the reply yeah no engine management light has come on it's quite odd it doesn't cut out just isn't smooth if it had a cam belt I would say it feels almost like that was slipping but it had a chain hence why I was a bit confused. Has been serviced regularly on time. I don't drive the car every day but not sure if that matters

 

No engine management light as yet and has been devices at the correct intervals currently has 68000 miles. Lumpy running is pretty straightforward it is smooth I.e when travelling at 70 the if I leAve the accelerator pedal in the same position it feels like something is slipping and the engine loses a small bit of power which can't be corrected by just adding more power. I have sent in for the 70k service and also asked for a diagnostic check so will let you know if there are any codes mainly wanted to find out if this was something common or just my car

 

Also lumpy running is a bit of a British phrase so apologies for that but hope you got the idea from my reply to yours and previous comments

 

Please validate that this "lumpy" effect is RPM related, and not Speed related.
Is it "lumpy" at the same RPM in second or third, as it is on the motorway?

Vince

 

Hi vince
So all good the lumpy running is in 6 but assuming that as my XK is and auto. I had it serviced and to solve the problem they reset the power control module adaption and cleared fault codes and didn't share codes with me from what I understand that is like a reboot as I say I am no mech. It seems to have solved the problem but will give it a few more drives until fully convinced. The problem seemed to be related to a specific speed range 70 to 90 mph when cruising at that speed it didn't seem to affect the rpm although it was only a slight rough running so the difference in rpm might be minimal it was more I could feel it through the accelerator pedal I.e. The power dropping of slightly

 

I'd start with the obvious - new plugs (probably not that or you'd get a misfire code), fuel filter, take a look at the air cleaner, run it at high RPM's for a little bit in case it was bad gas or just an anomaly. Being there was no error code that helps a bunch, maybe try some Seafoam couldn't hurt

 

Thanks leeper have changed fuel filter as part of service and am going to do some longer runs in it over the coming weeks thanks for the advice much appreciated

 

This happened to me with both my '08 XK and my ex-wife, both of which were "lumpy". In both cases, it turned out to be bad gas. The XK is fine now.

 

Could be a failing coil or an air leak. Doubt it's plugs.

If it's a coil they often misfire worse at 50mph or so uphill (up slope). Misfire counts may show it but you need a dealer tool.

Watch the MIL as it does it in case it flashes - bad misfires if so.