460GLE running problem

[andykg]

I have a K reg 460GLE 2 litre injection, 82000 miles on the clock. It doesnt idle smoothly and also when I accelerate hard it bogs down and lately it has great trouble getting past 4000RPM, it coughs and splutters going through the 4K mark. Fuel consumption is also terrible. I have roughly worked it out and am getting 20 mpg.On a recent MOT it failed due to appalling emmisions.

I have changed all the spark plugs and made sure the HT leads are all ok.

I am at a complete loss to what could be causing this so any help would be greatly appreciated.

[Peter Milnes]

Does your car have an Idle Control Valve fitted to it? It should be on a bracket below the inlet manifold with a couple of pipes and an electrical connector. If you have this piece of equipment then it probably needs a thorough clean-up with copious supplies of carb cleaner.

All the best, Peter

[Dan F]

Hi Andykg.
Sounds awfully like your 'cat' is breaking up and clogging up your exhaust.

This gives all the symptoms you are talking about. Especially the not really able to get past the 4000 rpm mark!

I suggest you get someone to check it out and if necessary change it.

If it is not that then I am at a bit of a loss, but having experienced the symptoms you are describing and the fact that it was the 'cat' that needed changing in our case, I would bet that is what it is.

Hope that helps a bit.
Dan.

[andykg]

i have cleaned all the connectors but this didnt make any difference.
Very strange as this morning driving to work I could get past 4000rpm ok, im wondering if the car was still too cold when I tried to do it last time. then again this shouldnt make much difference.

As for the erratic tickover it makes the whole dashboard shake. Another thing i noticed is if you rev the engine it doesnt drop back to idle quickly it kind of revs up stays there for a second then drops back down again.

Is the cat very expensive to change or get looked at?

The search continues,

Thanks for all the advice.

[Dan F]

Hi Andy.

The Cat won't be expensive to get checked....same as a brake check I should think....not sure.
Obviously the cat will be quite expensive to replace, but it is a necessary, and required by law, evil.

If the car feels like it goes slower the harder you push the pedal and it is doing a really low mpg then the cat definitely needs checking.

Cheers,
Dan.

[andykg]

Just had my car at the garage for them to check over. Good news the cat is ok, bad news they done a compression check and no 4 cylinder has 60 pounds pressure where as the other are between 175 and 180 :(

The new plugs i put in the other day were all oiled up and the HT leads were shorting out!!!!!

They believe its a valve. So the expensive option is to check that so they suggested running some feul system cleaner through it for a week to see if that sorts it...

fingers crossed

[Bungee]

Be careful with the fuel system cleaner if you have a cat. I've heard that it can really mess up the inside of the Cat, the same goes for oil treatments. How true this is, I dont know. Might be worth investigating though.

[ChrisB]

Valve, head gasket, or broken piston ring (yes they can break and it not smoke).

A wet compression test can be used to eliminate rings. Teaspoon of fresh engine oil into the cylinder before doing the test. It if the compression improoves then the rings are the fault.

Head gasket is more likely than a valve. But a garage that has a cylinder leakdown kit can test for this.


With all three the head has to come off. No amount of fuel system cleaner is going to sort that.

[andykg]

my car is finally at the garage, favourite is a valve followed by the rings and 100-1 is a head gasket...i'll know tomorrow

As for the cleaner I knew it wouldnt sort out the major problem it was a £15 shot rather than the hundreds its gonna cost to take the head off...It did actually improve fuel comsumption a little too