Technical Ducato Still Smoking after changes

[brox]

So My Ducato 120 Multijet 2.3 is still smoking, faulty Lambda sensor changed, Air flow sensor changed, Egr working fine, When I disconnect the air flow sensor the smoke disappears, plug it back in and smoke ploughs out, done this with the old air flow sensor as well, Injector 1 and 3 is showing minus on live tests, but been told that this wouldn't affect it and would probably splutter and such.

2 new Injectors are pricey, so not wanting to buy new ones if that isn't going to solve the problem either, is the Lambda and air flow sensor have already cost a packet.

anyone any ideas, coz the mechanic is stumped:bang: and so am I:bang: and as it stands not much money left to throw at it

Thanks.

 

[digger58]

http://www.nicorette.ie/

Sorry couldn't resist

 

[CDK]

Without more info like fault codes and the circumstances (engine temp., load, speed or idling) it is unlikely to get useful suggestions here. The engine can provide lots of data if you have an ODB-2 device and a PC, tablet or smartphone, pulling plugs is not the proper way to diagnose a fault.

If you remove the plug from the MAF sensor, the ECU substitutes the missing input with a value from an internal table and goes into "limp mode".

 

[brox]

only the codes for when MAF disconnected, when connected only starts smoking when temp starts to warm up and is constant smoke, at first it said it was a faulty lambda sensor, which I got changed, the tested EGR and seemed to be opening and closing fine, injectors were all working away fine, but 1 and 3 was showing minus, MAF disconnected the van ran better, little sluggish when starting but ran better with no load and half load than with MAF connected and no smoke, idling, speed all fine fine nothing limp about it, turbo working fine etc, but as soon as it connected again, smoke heavily.

It just seems to smoke when connected and no smoke when its not

 

[lm04]

Sounds like you have replaced stuff you didn't need to. The reason it runs fine when you disconnect the MAF is it allows more air through - balancing the mixture from the vehicle over-fuelling.

Look at injectors or timing if you have had a recent belt change.

 

[brox]

Apparently Injectors 1 and 3 were running minus on live tests, but no codes, does this mean new Injectors, wasn't wanting to replace them as they are expensive per injector and throwing more money at it when it might not even sort the problem, as I have already done with the MAF and Lambda (although it was reporting faulty)

So I guess the inevitable is change injector 1 and 3?

 

[lm04]

If an injector is starting to fail (in your case two) they will either under or over-fuel.


What this excess fuel will do is send all the wrong information to the other sensors, who will be trying to compensate for the fuel. They effectively think your vehicle is under more load than it is. More fuel, needs more air. Your MAF will throw in more air to try to balance the mixture.


With all this air and fuel going in, the ecu checks that all this is getting out in a controlled manner. The Lambda sensor has two modes; one for cold (an old fashioned choke) and another for warm (lean) When cold it turns off lean and turns on cold, and vice-versa (a switch)


Thing is, you are idling. Lots of fuel going in -ecu thinks you are cruising, throws in air. Lambda thinks your cold and throws in more fuel, and the MAF throws in more air think you are warm and cruising at speed.


As neither sensor seems to be making sense - a fault code for all sensors in that circuit is listed. Meanwhile you are looking at a cloud of unburnt fuel billowing out of the exhaust.


Now you understand a laymans description of what goes on - you get the idea. To avoid an expensive injector issue, you have gone for the cheaper sensors as these are what the codes said - when they are the result of a fault and not the cause.

 

[brox]

That is the best answer I have ever heard, not even the mechanics said it like that, thanks this is the information I have been looking for from the start and I know it's all process of elimination and codes etc, when you don't know how the whole system works deep down, the whole process doesn't make sense and leaves you scratching your head when someone says that's injectors and another says nah its got to be that, computer said so.

So just another quick question which has probably been answered, when connected it smokes due to injectors failing, would it still not smoke when maf is diconnected considering the injectors are failing and should still be firing unburnt fuel out?

 

[corcai]

You can get the injectors bench tested at a Bosch authorised centre if you want to rule those out. It's about £18 per injector

 

[lm04]

So just another quick question which has probably been answered, when connected it smokes due to injectors failing, would it still not smoke when maf is diconnected considering the injectors are failing and should still be firing unburnt fuel out?

When you unplug the MAF the sensor allows all air through - max air, so and over fuelling engine, with an unpluged MAF with run fine. Although will be drinking fuel!

Do what Corcai has suggested above, and get your injectors tested at bosch. Save you a fortune in trial and error mechanics.

 

[brox]

ok thanks for the info guys will get them looked at and see what the damage is.