Erratic running at around 1000rpm

[radiumrob]

I hope someone may be able to offer some help with a tricky diagnosis...

I have a 2007 S80 D5 185bhp (Geartronic). Driving on a motorway last week, I noticed that the car felt that it was marginally underpowered, not a lot but enough to be noticable. Later on the same journey there were a couple of slight judders that could have been mistaken for a spurious gear change. When returning home, the judders/misfires became more frequent, and when turning into the drive at crawling pace and low revs the car stalled. It restarted instantly, but the engine ran unevenly.

RAC diagnosed three faults - glow pug 1 not functioning (apparently not related); fuel rail pressure sensor high input, and crank sensor reference voltage low. A local garage replaced the crankshaft sensor, and cleared the fault. The car seems to run ok at idle and at high revs, but is very uneven at around 1000 rpm. The rev counter jumps a few hundred rpm in a discrete step when accelerating through 1000rpm.

Local independent garage is talking about injector replacement now. Does anybody have any opinion or experience that may confirm or refute this.

Many thanks

Rob

[GJB]

Originally Posted by radiumrob

I hope someone may be able to offer some help with a tricky diagnosis...

I have a 2007 S80 D5 185bhp (Geartronic). Driving on a motorway last week, I noticed that the car felt that it was marginally underpowered, not a lot but enough to be noticable. Later on the same journey there were a couple of slight judders that could have been mistaken for a spurious gear change. When returning home, the judders/misfires became more frequent, and when turning into the drive at crawling pace and low revs the car stalled. It restarted instantly, but the engine ran unevenly.

RAC diagnosed three faults - glow pug 1 not functioning (apparently not related); fuel rail pressure sensor high input, and crank sensor reference voltage low. A local garage replaced the crankshaft sensor, and cleared the fault. The car seems to run ok at idle and at high revs, but is very uneven at around 1000 rpm. The rev counter jumps a few hundred rpm in a discrete step when accelerating through 1000rpm.

Local independent garage is talking about injector replacement now. Does anybody have any opinion or experience that may confirm or refute this.

Many thanks

Rob

Has the fuel filter been changed recently?
May be partially blocked

[radiumrob]

Well, the injector was replaced today but apparently the lumpy tickover at around 1000rpm remains.

The car was serviced around 3k miles ago (total mileage is around 44k) and the fuel filter was replaced.

[radiumrob]

The tech has tried swapping the removed injector with the other injectors in turn (on the assumption that it wasn't faulty), but there was no change and the uneven running remains. There's quite a bit of vibration with it too.

Under load, the running seems smoother and the rev counter needle doesn't jump.

Grateful for any suggestions...

Rob

[gazza12345]

I would start by looking at all the vacuum hoses for leaks. Then look at the egr valve. That would make it run ruff if it was stuck open at low revs.

[radiumrob]

Thanks for that. Is that something I could do easily at home, or does it need a trip to the garage?

Cheers