CDTI Smoking and rough running @ 1.5 Revs,

[zaph]

The smoke makes the answer obvious, it is over fuelling. The question is why?

I know you want to dismiss the sensors and injectors after all that work but to my mind it is highly likely the two are linked. Either a bad component or something damaged when they were fitted.

[SteveThackery]

Originally Posted by zaph

The smoke makes the answer obvious, it is over fuelling. The question is why?

I don't get this - could you explain more? We're talking about a diesel here, so you get more engine speed and/or power by injecting more diesel.

I don't see how you can over-fuel a diesel which is sitting at 1500rpm with no load on it. If there's too much fuel going in then it will simply rev higher, until it reaches its governed rev limit.

Obviously you can over-fuel a diesel while you are out driving it and the engine is under load. What happens then is that there is more fuel going into the cylinder than there is air to burn it (shouldn't really happen with ECU-controlled diesels). The incomplete combustion of the diesel results in black smoke from the exhaust.

Alex30013k reports white smoke. As far as I know there are only two causes of white smoke from a diesel: fuel which hasn't been ignited (such as when it's not firing on all four cylinders, or any cylinders during a prolonged cold start); secondly, when water is entering the combustion chamber (for example from a blown head gasket), in which case at least some of the smoke is actually water vapour.

So my understanding is:

black smoke = incomplete combustion, usually from over-fuelling

white smoke = unignited fuel, or possibly water vapour

Am I wrong about this?

[Mike Noc]

Originally Posted by trippple

I used to have an old and old school vw lt van with a manual injection retard function - pull the lever to retard to help cold starting, bit like a choke. Guess the idea was to inject later at max compression and heat, this would produce impressive clouds of white smoke if you used it when hot and not all the fuel was being burnt. Wonder if your injection timing has somehow slipped?

Can't see the timing slipping in relation to the pistons as the injection timing signal, once initiated by the cam sensor, is taken from the crankshaft sensor, which picks up directly from crank itself.

Originally Posted by zaph

The smoke makes the answer obvious, it is over fuelling.

The OP mentioned smelly white smoke, so sounds more like incomplete combustion of the diesel. So, often injector related, low compression or low fuel pressure. The injectors have been replaced, so hopefully are working correctly, and to check the fuel pressure and low compression you really need a T4 diagnostic check or a multimeter and a diesel compression test gauge. As mentioned, the comms need sorting before doing that.


Mickyboy can test the injectors properly to completely rule them out.






.

[SteveThackery]

Originally Posted by Mike Noc

..... and to check the fuel pressure and low compression you really need a T4 diagnostic check or a diesel compression test dial.

Mike, could you explain what the T4 does to enable checking the compression? I've done hardly any work on diesels, but with petrol engines I've just put a pressure gauge in the spark plug hole and spun the engine on the starter.

[Mike Noc]

Yes Steve, you can enable the compression check from the T4 engine management menu, and then when you crank the engine T4 disables the injectors and measures the speed of the crankshaft from the crank sensor. It can then determine the crank slowing down as each piston comes up on compression, which is relative to the compression in each cylinder.

[SteveThackery]

Originally Posted by Mike Noc

Yes Steve, you can enable the compression check from the T4 engine management menu, and then when you crank the engine T4 disables the injectors and measures the speed of the crankshaft from the crank sensor. It can then determine the crank slowing down as each piston comes up on compression, which is relative to the compression in each cylinder.

Ah, nice!

I fact I've found it quite easy to hear uneven compressions by listening to the starter motor before the engine fires up. That's with petrol engines, though - I've never heard uneven compressions on a diesel. But it's cool that the T4 can do the same thing, only much more accurately.

[brianw]

Regarding T4 not communicating with your car.
I had a similar issue with T4 communication not being able to be initiated with my CDT a few years ago.
When I got home i tried communicating using Toaf. Same result it could not complete Scan. On mine i found that when i disconnected the Hiline system in the boot it would connect. It may be worth trying to eliminate items and trying again. Another favourite to stop comms is a faulty FBH so if you have one it may be worth trying with it unplugged.

[Alex30013k]

Toaf now can comminate with all the ecus in the car, don't know if this due to a new lead or the replacement ecu i have had fitted,

No fuel burning heater,

Thinking of trying the t4 session again,

need to do something as to get out of my road in the morning as due to the road my car is @2000k and it just smokes all the way.

[SteveThackery]

Originally Posted by Alex30013k

need to do something as to get out of my road in the morning as due to the road my car is @2000k and it just smokes all the way.

Can you remind us of what colour the smoke is when you are driving it?

[Alex30013k]

It's white smoke, not black. I get a miss fire or when driving I get white smoke and you can feel the hesitation, I get the same when the de accelerating in the in the 2K rev range too.