On any car if you get a check engine light or other fault light this typically means one or more of thesensors has failed or has a faulty connection.
The fault can be something quite simple and nothing that’s going to stop the car to something quite major that will reduce engine power and possibly stop the engine
The ECU senses this and may put the car into 'limp home' mode which typically limits the revs and the amount of power available.Usually the car is safe to drive for a short distance as the mode is intended is intended to get you home without incurring any engine damage
The quickest route to repair is to have the car plugged into a diagnostic machine which will read off the fault code stored in the ECU (providing the light is still on at this point) and indicate which sensor has failed or whether the fault is more serious.
You can do a very rough and ready check yourself by unplugging sensors one at a time and seeing if any of them change the driving condition which would indicate the most recently unplugged sensor is the faulty one.This method is not foolproof though and reading a fault code off is the better method.
however there's some basics you can check
This could be a lack of fuel pressure from the electrical pump at the tank.If the connections to this are corroded or damaged then the pump could stop at any time or could not be running at full speed. Check that its relay switches in and out and the relay contacts are clean and bright – replace the relay if in any doubt and do the same for the fuse, Ideally measure the pressure at the inlet to the main engine fuel pump and if this is low check the pump as described and also consider changing the fuel filter as if this partially blocked this too will reduce pressure.
If both of these are OK then also check the connections to the EGR valve, if either the vacuum pipe of electrical connection are damaged / corroded then the EGR can be on all time which certainly will hurt performance. Its also possible that its a fault with the EGR valve so its worth removing the valve and cleaning it out with brake cleaner, if it looks particularly clogged then replace it.
If this is OK then check the small vacuum lines to the turbo and its connected control solenoid on the bulkhead, any cracks or leaks can give turbo issues and its best to have the boost pressure measured actually measured with a boost gauge to check that the turbo is healthy and that the sensor is reading correctly
If its a variable vane turbo (they’ll be an actuator on the turbo body - but not a wastegate) then check its vacuum pipework as above and check the connections to the diaphragm / solenoid valve
Also worth checking that the glow-plug relay is switching off as they can stick on and leave the glow plugs also on - on some cars this can force it into limp home
Also worth considering adding a bottle of injector cleaner into the tank as a clogged injector nozzle will reduce powerand give poor combustion - the next stage on from this is to remove all the injectors and have them ultrasonically cleaned and flow checked
Also check all the high pressure hoses post turbo/s for any split hoses or cracked metal pipes, also check the ends of the intercooler as its not unheard of to pop the end caps off under high boost.
do you still need help with this?
The Audi has been in garage for 2 weeks!
They have found a lot of oil in tank-now all cleaned out
Had injectors cleaned professionally and put back on
The particulator filter cleaned thoroughly and put back on
fuel filter really oiled up -now cleaned and back on
Replaced the something pump?
cleared everything down on computer
They started it up and took it for run
Started fine and went OK for a while but then the glow plug came on and the car went into limp mode
Oh dear-- please give me something for garage to try!!!
Yes indeed, they have checked that out.
The problem is they cannot locate how or where the oil was coming from in the first place to clog everything up
Everything through the system is now apparently clean but the car still closed itself down after starting OK and running OK for a while(initially it would not even start)
The proprietor believes it could be the oil is getting in via the seating of the injectors which, on this model Audi, do not have copper/brass washers seating them onto the cylinder head
What do you think?
Grateful for your comments