V6 Diesel oddity?

**lencuff** · 3rd November 2010, 18:44

Hard to explain but it seems like once I am up to 'cruising' speed the engine appears not to run as smoothly as I would have expected. Seems to hunt around a bit. Acceleration is fine. Only just got the car so wanted to make sure it's something wrong not just me. It happens when I lift the pedal to maintain the speed after getting there.

**Celes** · 3rd November 2010, 19:54

Mileage? How old is the fuel filter?
I have something similar on mine (sometimes) and I'm suspecting a bad injector. Although mine judders more if I accelerate lightly up a hill in 6th 65mph-80mph.

**diesel dog** · 3rd November 2010, 20:04

Does cruise control work OK?

**lencuff** · 3rd November 2010, 20:21

Cruise control works but still feels the same. Done 72000 and has just been fully serviced.

**lencuff** · 3rd November 2010, 20:22

Forgot to add that it seems to do it in any gear if the pedal is only just down a little.

**lencuff** · 3rd November 2010, 20:23

Also hard acceleration is perfect

**m8internet** · 3rd November 2010, 20:23

Your profile shows a 2007 SRi 150
Can you confirm the MY and engine
If the car is over three years old, is it covered by a warranty?
When was it last serviced?

**lencuff** · 3rd November 2010, 20:28

Whoops sorry Profile updated. Just had full service.

**lencuff** · 3rd November 2010, 20:29

It's covered by AA warranty, parts and labour.

**m8internet** · 3rd November 2010, 22:04

Originally Posted by lencuff

Seems to hunt around a bit. Acceleration is fine

With the engine on idle, it should be stable
Watch the rev needle, does it move at any time?

I suggest you try finding some long, straight, level roads of varying speed limits
On quiet day, typically a Sunday morning, try some tests

The first is at 30mph in as high a gear as possible, either 5th or 6th gear
The revs should be very stable
Look at the revs and see if they drop at any time

The next is at 40mph, in 6th gear
Same again, the revs should be stable

Finally, find a dual carriageway road with NSL
Start off as previous, at 30mph, then 40mph
Accelerate up to 70mph in each
You should then notice a vast acceleration from 2000rpm

Finally, on a long run (10 miles or more) at constant speed
Is there any "surge" from the engine at constant speed? (Normally this cancels the cruise control)

In general driving, do you drive below 2000rpm or above 2000rpm?
For example, at 30mph what gear do you drive in?