How to analyse injector correction data

[Baz in Kent]

Hi, I had the injectors on my Ducato x290 replaced about 3k miles ago, I’ve just done some diagnostic runs and noticed the injector correction values intermittently exceeding 2 and sometimes up to 4 on 1 or 2 cylinders. The total correction remains around 0.

These relatively high values occur half a dozen times for only a matter of seconds in a run of 45 minutes, there don’t seem to be any other parameters that are out of line or any specific rpm or temperatures that look different to the “norm”.

My question is, should I be concerned about transitory measurements like this when for most of the run the figures are fine and often showing 0s?

I can supply the .csv data sheet if needed.

Thanks in advance for any help.

Baz

[s130]

When the injectors were replaced were they correctly coded into the ECU. If not the ECU could be providing incorrect injection values to the injectors.

[Baz in Kent]

Thanks for your reply.
Yes, this was done by a Fiat main dealer and I have confirmation.
In a test run today the values were out of spec (+/-2) for about 25 seconds in an hour run, this doesn’t seem much?
Cheers,
Baz

[s130]

I'm no expert on this but from what I have read elsewhere values of +/-2 are typical. The fact that you are saying they basically average out at 0 then this suggests to me that everything is fine and that the engine management system is only occasionally stepping to make on the fly corrections.

My understanding of the correction system is that it is to generate a smoother running more balanced fuel ignition explosion.

Unlike petrol engines (which don't have these corrections) which have a smooth progressive flame combustion and resulting gas expansion the diesel engine relines on a more explosive combustion. If one cylinder explodes more violently than another then that cylinder will be noisier and produce more thump than another. The injector correct is to try and balance the fuel/explosion/etc. across all the cylinders thus leading to a smoother and quieter (less knock) running.

Well that is my basic understanding.

In an ideal world every injector would deliver the same amount of fuel for the same fuel pressure and opening time over the entire possible range of opening times and speeds. But they don't that is why they have codes to quantify their fuel delivery which you code into the ECU so the ECU can correct it's timings to try and ensure every cylinder gets the same amount of fuel to burn. Once this is done there are going to other factors that would possibly require individual injector correction.

I don't know but I suspect engine "knock" by cylinder is a major factor the ECU takes into consideration. It knows the timings it uses on each steady state (say constant 2000rpm moderate load) and can see the knock magnitude on each cylinder so it then tries to level these up with minor corrections.

[Baz in Kent]

Thanks.

My understanding from the Fiat forum is that values above +/-2 are indicative of a problem, what I’m trying to establish is exactly to what extent the frequency of these out is spec values is acceptable and to what extent it means there’s a problem.

For example, on a run of 15 minutes I might record “out of spec” (>+/-2) values for, say a total of 1 minute (assuming 1.5 secs for each instance), is this acceptable? If it is, what percentage time out of spec on a run would be unacceptable? Conversely if it isn’t acceptable what percentage would be ok?

Cheers,

Baz

[s130]

If values were always over +/-2 then that would indeed suggest a problem that the engine ECU is trying to correct.

Your are saying that on average the correction is 0.

Also a read elsewhere that to check correction values you run the engine at a steady fast idle of 2000 rpm (which would be a mid/optimum rpm value for a modern diesel engine).

If the car is running fine, performance is good, no error codes, etc. then I would not be concerned or worried about any specific values on any parameters.

Sometimes (I'm guilty of this as well) we go looking for problems etc. where none exist and we may have been influenced by values/data etc. where people are having problems and then apply their data to our normally functioning vehicles.

[Baz in Kent]

The reason I’m monitoring a number of paarameters is that I had to have all the emissions control system components replaced when my van had only done 13k miles (but was out of warranty). I was quoted £7.5k for the repair but eventually persuaded Fiat to supply the parts (£6k) FOC - essentially I don’t trust the vehicle despite having had it repaired by Fiat.

The combined injector correction values sum to 0 but this doesn’t mean the individual injectors are 0, injector 3 is the one most likely to show higher values but only on a temporary basis, sometimes as high as 4 (this has been rare). I can run the van at 2K rpm and on some occasions will get values >+/-2 but more often well below. Hence my question - when are these values ok?

Thanks.

[DaveDevon]

I have just replaced a set of injectors after real problems diagnosing the faults.

Fuel pressure was low but engine started and ran. Later it would go into limp mode when the accelerator pressed to move the car. It would rev fine at no load.

I replaced the pressure regulator and sensor. Engine would not start. I un-plugged the sensor and it started. This was proof I had a weak pump.

The injection pump was replaced and fuel pressure issues were gone. But I was getting black smoke, revs hunting and sometimes injection knock. Symptoms that indicate a dribbling injector. I pulled the set out and found #1 was wet at the tip. That injector also had a high negative trim setting from the ECU. They all have similar miles so I decided to replace the set.

I fitted an exchange set of four Bosch remanufactured injectors (silly money) and I now have MES refusing to change the code numbers. MES works perfectly on everything else.

Oh what joy.