In this entry about two basic situations:
1. the injector leaks (drips at closed state) at the moment of diagnostics;
2. the injector has leaked before, but at the moment of diagnostics – everything is fine.
Note: in this post, the most attention is kept to the DME algorithms of fuel management. We assume correct atomization of leaking injector. Unfortunately, leaking (dripping at the closed state) is not the only one defect of injectors. Poor atomization will cause different symptoms – for example: reduced mechanical efficiency of affected cylinder despite increased injected fuel amount.
But, before we take a look at both situations, a short conspectus what happens if any of injectors start to leak. If the injector leaks (spills), the largest problems in this situation are caused in idle – in idle the amount of fuel injected is the smallest, the effect of each leakage – the largest. Due to this reason, we will talk about idle – the most critical mode in case of this damage.
Let’s assume, that the engine N53 has to be inspected. The problem is in its first bank, right after the engine is started (engine performs Homogeneous mode). Cylinders, which are in the first bank: A, B, C (I will name them in such a way, so there would be no link to the placement order).
The injector of cylinder A sometimes leaks; injectors of cylinders B and C work properly.
First situation: the injector leaks at the moment of diagnostics. How does the DME react?
1. the amount of fuel, injected in in the whole bank, increases unexpectedly because of the injector of cylinder A leaks;
2. if the injector of cylinder A don’t leak such strongly, that misfires start in the cylinder A, all cylinders continue to work;
3. Fuel mixture menu indicates a rich mixture in the bank of the damaged cylinder;
4. when DME sees, that the fuel mixture of the bank is rich (it don’t correspond Lambda 1.00; Lambda is <1.00), it starts to reduce the injector openings for all injectors of affected bank (using Correction and Integrator), to reach a correct Lambda (1.00);
4. situation in the damaged cylinder gradually improves (the fuel mixture is not so rich anymore), but in the good cylinders B and C it becomes lean;
5. the damaged cylinder A continues to work with a full “return” – but the healthy cylinders B and C loose mechanical efficiency, because they lack the fuel to burn;
6. the Rough run menu indicates relatively increased mechanical efficiency of the damaged cylinder, but the mechanical efficiency of the healthy cylinders – relatively reduced;
7. if DME reaches a correct Lambda (1.00) using only Integrator (they don’t reach -30,0%), DME considers that the situation is “fixed” and the engine continues to work with a persistent vibration; if it’s not enough with resources of Integrator, when it reaches -30.0%, DME deletes the old LTFT offset type value and tries to save the situation, overwriting the offset type LTFT to the negative value – also with an offset LTFT to reduce the amount, given to the whole bank;
8. if also the resources of offset type LTFT is not enough (its value reaches -1.00mg/stk for N43 series engine or -1.50mg/stk for N53 engine), DME records the error message regarding fuel mixture (too rich) and the situation is critical – despite all possible tools:
a) offset type LTFT is set to min;
b) Integrator reduces the fuel, injected in the bank for -30.0 %, the fuel mixture in the bank still is rich (Lambda is <1.00);
9. if the problems with the injector continue for a long time, DME gradually reduces the length of the first (“invisible”) injection impulse of damaged cylinder, trying to minimize the problem – it corrects the adaptations, applied to injectors in idle.
This is a typical situation in case of leaking of the injector. Below – a small table for a synopsis.
 critical values for a damaged cylinder: offset more than -0.800 fo N53 series engine; more than
-0.050 for N43 series engine;
 typically: -30.0%; after modifying offset LTFT – could normalize (if the defect is for a long time);
 only after warming up the probes: strongly below 1.00 (to 0.80); if the defect is for a long time – could normalize;
 if the defect is for a long time, could be (usually are) rewritten to min: -1.00mg/stk for N43 series engines; -1.50mg/stk for N53 series engines;
 for the damaged cylinder: offset more than -0.50mg/stk.
Taking into account, then in case of the problems of the injector DME will try to do everything to correct the situation (initially – in a range of all bank, later – also correcting the data of adaptations of the injectors), try to observe the situation max operatively, before DME has minimized the problem. If you allow DME to minimize the problem, it could be hard to detect it. In an example mentioned previously, during the time DME will significantly reduce the opening time of the injector A in idle. Also – the first (of two) injection impulses will be reduced. Unfortunately, INPA ../F5/Shift+F6/F1 live data indicate only the second impulse – its length will be correct. Accordingly – if we don’t know the background, the situation can appear – the total opening of the injector is significantly reduced (because it was leaking), but INPA shows as if correct data!
So – if the injector leaks directly after starting the engine (it’s a typical situation), start the diagnostics immediately!
If the injector regularly leaks in exact conditions (in a range of temperature), the typical symptoms after starting the engine will be:
a) offset type LTFT are recorded min possible;
b) Integrator of the bank, in which the defect appears: negative value, Lambda: below 1.00.
Second situation: the injector previously (in exact conditions) has been leaking, but at the moment of the diagnostics is not leaking. What does DME do?
If the previous leaking of the injector was long-lasting, DME has reduced the length of the first (“invisible”) impulse – reduced the total length of the injection time of the injector, also the offset type LTFT is modified to min possible value.
1. in the whole bank, the total amount of the fuel is suddenly reduced, because of the injector of cylinder A is not leaking anymore;
2. fuel mixture menu indicates a lean fuel mixture in the bank of the damaged cylinder;
3. when DME sees, that the fuel mixture of the bank is lean (don’t correspondsLambda 1.00, Lambda is >1.00), DME starts to increase the opening times of all injectors of the affected bank (using Correction and Integrator), to reach a correct Lambda (1.00);
4. the situation in the damaged cylinder A is gradually improving (the fuel mixture is less lean) but in the healthy cylinders B and C the fuel mixture gets rich;
5. the damaged cylinder A continues to work with a reduced “returns” – it doesn’t have enough fuel to burn, but in the healthy cylinders B and C work with a correct mechanical efficiency, and they have a fuel left-over;
6. the Rough run menu indicates relatively reduced mechanical efficiency of the damaged cylinder, but the efficiency of the healthy cylinders is correct;
7. if DME reached correctLambda (1.00), using only Integrator (it don’t reach +30.0%), DME considers that the situation is “fixed” and the engine continues to work with a persistent vibration; if it’s not enough with the resources of the Integrator, when it reaches +30.0% DME deletes the old value of the offset type LTFT and tries to save the situation, rewriting the offset type LTFT to more positive (correct) value – also with an offset LTFT increase the fuel amount, allowed for the whole bank.
Also in this situation, you have to act quickly – if DME will succeed and fix the situation, Fuel mixture menu can also not indicate any persistent problems. If you will be late, also Rough run menu can “fix” the data of the injector adaptations – nothing will indicate the problem, which was before.
Also for this case – a table of synopsis.
 critical values of the damaged cylinder: offset larger than +0.800 for N53 series engines; larger than +0.050 for N43 series engines;
 typically: +30.0%; after modifying the offset LTFT – could normalize (if the defect exists for a long time);
 directly after warming up the probes: above 1.00 (up to 1.30..1.50); if the defect exists for a long time;
 if the defect exists for a long time, could be rewritten to the correct values;
 for the damaged cylinder: offset larger than -0.50mg/stk.