knocking diesel engine

[mick1961]

hi
my engine has started to make a knocking sound ,i have also noted that the idle is eratic i think this is causing the car to shake when stood and the gearbox is in drive.i would be gratefull for any advice thanks.

[James.uk]

Have a good listen and see if you can get at least some idea of where the sound is coming from.. ...
...

[Phil]

Also, if possible, have a look at your crank pulley, they are known for failure.

[the fool]

If the idle is erratic it might be wise to check the MAF sensor - it can cause idling problems if it is faulty, just unplug it and see how the engine idles without it. That may then help you to further diagnose your problem.

[Roverron]

Originally Posted by mick1961

hi
my engine has started to make a knocking sound ,i have also noted that the idle is eratic i think this is causing the car to shake when stood and the gearbox is in drive.i would be gratefull for any advice thanks.

As has been suggested, it could be a fault maf, but also a dribbling injector.

If the maf test proves inconclusive put a couple of bottles of injector cleaner in the fuel and give the car a thrashing (to speed up the cleaning).

If the mileage is well over 100k, have the injectors serviced. (preferably not just given an ultrasonic clean)

Ron

[COLVERT]

Originally Posted by Roverron

As has been suggested, it could be a fault maf, but also a dribbling injector.

If the maf test proves inconclusive put a couple of bottles of injector cleaner in the fuel and give the car a thrashing (to speed up the cleaning).

If the mileage is well over 100k, have the injectors serviced. (preferably not just given an ultrasonic clean)

Ron

You don't have to " Thrash your car ". The injectors don't work any harder at 3,000rpm whether the car is rolling or stationary !!!!
(Those old wives tales !! Pmsl. ) Better to do a leak test on the injectors and give your car some TLC.


Colvert.

( Why does "thrashing your engine " and treating one part of it badly help cure another part ??? ) Totally beyond understanding !!!
Wouldn't want to be your dog. Lol.

[kissifer1972]

I would suggest you follow Ron's advice.

Unplug the MAF sensor and see if performance improves, if so then the MAF may have gone out of spec or totally failed.

The injectors being out of balance can also certainly lead to the problems you have encountered. So a good dose of injector cleaner, as suggested, may well sort that.

Also I believe a blocked PCV valve can lead to lumpy running. So replacing the filter in the PCV, available from Jules on here, might also be a good idea.

Chris

[Roverron]

Originally Posted by COLVERT

You don't have to " Thrash your car ". The injectors don't work any harder at 3,000rpm whether the car is rolling or stationary !!!!
(Those old wives tales !! Pmsl. ) Better to do a leak test on the injectors and give your car some TLC.


Colvert.

DON'T AGREE.

So the injectors aren't working any harder - well they're opening alot more often, and experiencing higher fuel pressure the higher the rpm and torque demand. That suggests they are indeed under more stress.....

You've missed the point anyway so I won't be taking you advice - your'e fired.

The whole point of thrashing the engine is to get as much cleaner through the injectors as vigorously as possible to clean them. Some owners have had a result by filling the fuel filter with neat cleaner.

A leak back test is no use if its just partially clogged nozzles.

He hasn't mentioned starting issues so I've no reason to blame leak back, though it can affect the idle, but not knocking noise which is due to dribbling.
(if not maf related).

If it was me, I'd send the injectors to lynxdiesels.com for complete overhaul.

Ron

[Gate Keeper]

From your experience Ron I have 2 questions which I believe you will know the answers to.

1. Which is the best MAF sensor. A Bosch or a Pierburgh?

2. Is there are particular Fuel Injector Cleaner you can recommend?

On checking the MAF sensor, I cleaned it using an air can but the mirrored surface still had white spots on it which would not shift but did not use any cleaning fluid as I felt too nervous to do this.

If I did order a replacement I would do it through yourself for obvious reasons.

Thanks

[Roverron]

Originally Posted by Gate Keeper

From your experience Ron I have 2 questions which I believe you will know the answers to.

1. Which is the best MAF sensor. A Bosch or a Pierburgh?

2. Is there are particular Fuel Injector Cleaner you can recommend?

On checking the MAF sensor, I cleaned it using an air can but the mirrored surface still had white spots on it which would not shift but did not use any cleaning fluid as I felt too nervous to do this.

If I did order a replacement I would do it through yourself for obvious reasons.

Thanks

I cannot argue with the fitting of the Bosch maf and switching off the Synergy2's maf compensation other than on the grounds of cost.

So if you have a Synergy 2, then a Pierburg maf is £71.65 inc vat & postage. Otherwise a Bosch one is £174.75 inc vat & Special Delivery - the best price I can do and about £20 less than Eurocarparts delivered price.

I hope you didn't use compressed air? This often ruptures the fragile sensor which is inside the cavity at the end.

I always add Millers Ecomax (formerly Dieselsport 4) to all my diesels at every fill up as it contains a cleaner and lubricant as well as a cetane booster to improve combustion (quieter, smoother and more efficient).

The cost is negligible (under £1.00 per tank of fuel) and probably pays for it self in better mpg. I bought a 5L can of dieselsport 4 and just finished it off recently.

If possible get the Dieselsport 4 (still sold on ebay) because I suspect the latest Eco-max is more dilute and needs a double dose.

I haven't tried any of the one-shot cleaners but I'd let the tank get well down before adding it to make the concentration as high as possible or even add 2 bottles if I didn't want the hassle of filling the fuel filter.

Its always worth trying the cheapest and easiest 'fixes' first on a 'nothing ventured, nothing gained' basis. The results or lack of can also aid diagnosis.

Ron

PS For high mileage engines I can also recommend Forte engine flush. It is very effective at removing gums and varnishes, freeing off sticking piston rings and gummed up valve stems. Available on Ebay - follow the instructions exactly.