Andrew Bessent

Hi im new here but from what i've seen there seems to be a lot of knowledge on here, so im hoping you can help me.

The car kept going in into limp mode when driving and now it wont start at all. Initially there was hardly any fuel getting to the injectors, so i changed the fuel metering valve. I also had the injectors tested and found out that they were faulty so i have replaced them with another second hand set which have been tested and are all good.

I have used ForScan to read the live data and have found that i have fuel pressure of between 450-500 bar when cranking. I have also tried disconnecting the injectors and fuel metering valve to see what the maximum fuel pressure i can get is. This came back as 1600 bar.

I have changed the cam sensor and the crankshaft sensor on the bell housing, but still no joy. I tried connecting an injector up with it sticking into a pot and no fuel came out of the nozzle when cranking. The live data for the fuel correction shows 0 mg on all injectors.

From what i can tell the ECU is not activating the injectors but i'm now out of ideas as to why. Does anyone have any ideas on what else i can try?

Andrew Bessent

Thought id give an update and hopefully increase the chances of someone knowing whats wrong.

I used a noid light to test for injector pulse signal today and sure enough there is no signal from the ECU. I then checked the voltage at the camshaft sensor where i found 12 volts between the middle wire and the right hand wire as you look at the back of the plug. I had 3 volts between the middle wire and the left hand wire with ignition on only, and this reading fluctuated between 3 volts and 4 volts during cranking. I then checked the live data for engine speed which was around 200 rpm during cranking. I then disconnected the crankshaft position sensor and checked that the live data showed 0 rpm during cranking, which it did.

I also checked what the mass fuel demand reading was, which is 39mg when i start cranking and then shortly after it drops to 0 and i get fault codes of p0251 & p1211.

I have noticed that in addition to the crankshaft position sensor the mk3 mondeo has a crankshaft pulse sensor. Does anyone know where this sensor is and exactly what its purpose is? Could this sensor cause the fault that i am having?

Also, does anyone have a wiring diagram which covers the injector circuit?

RichieST

iTrader: (2)

I am presuming you had the injectors coded to the ecu when you fitted them?

Andrew Bessent

Yeah i programmed the new correction codes in using FORScan when i fitted them, and i have read the correction codes since to ensure that they are still correct.

The strange thing is that when the pump wasn't delivering enough fuel it sounded like it was trying to start but since resolving that issue the injectors have stopped getting a pulse signal, so now it doesn't even try to start. It's as though i've disturbed something but i can't find what.

Andrew Bessent

Okay so to give an update, and hopefully increase the chances of someone knowing whats wrong, i've done some more investigating and found the following;

When cranking there is initially no signal to the injectors, but once fault codes P0251 and P1211 appear the ECU starts to send a signal to the injectors. However, it still doesn't even cough.

If i disconnect the fuel metering valve (brown plug on back of pump) i get a signal to the injectors all the time i am cranking. However, it still doesn't even cough.

Live data of the rail pressure shows that when cranking with everything connected fuel pressure increases to around 500 bar, and when cranking with the metering valve disconnected this increases to 1200 bar. If i disconnect both the metering valve and the injectors the pressure increases to 1600 bar. Then as soon as i stop cranking the fuel pressure drops quickly to 8 bar and slowly from 8 bar to 4 bar.

Live data shows that engine speed during cranking is around 200 rpm.

Camshaft sensor has 12 volts between middle wire and right hand wire (as you look at the back of the plug) and 3 volts between the middle wire and the left hand wire when engine is still, which then fluctuates between 3 & 4 volts during cranking.

I performed an injector leak back test and found that each of the injectors has between 10ml and 20ml during cranking for around 1 minute. However, I'm unsure what leak back levels i should get when cranking with 4 good injectors.

Live data shows the mass fuel demand as 39mg when i start cranking and then this drops to 0mg as soon as the P0251 and P1211 codes appear.

FORScan says in the info for P1211 that the throttle position sensor is open circuit.

I have checked the live data of the accelerator position sensor and this is fine.

Andrew Bessent

Hi,

Is anyone able to answer any of the following;

a) What rail pressure should i have during cranking?

b) What pressure should the rail drop to when i stop cranking?

c) Is there a way of testing the fuel metering valve / what should the resistance of the metering valve be?

d) what voltage should i see at the injectors?

e) How much injector leak back is normal during cranking?

Thanks,

Andy

e2e4

I am not a mechanic but...

250bar should be enough for any common rail injector to inject when about 70Vpp short pulse is applied to the injector solenoid. At the constant pressure, the quantity of fuel injected depends on the pulse width. To measure both the pulse amplitude and the width, an oscilloscope's needed.

In addition, it isn't important whether the ECM was told about exact injector specs or not. If not, the engine will work more roughly, with a bit less power, asking for more fuel but, that's all.

It is hard to say about the return fuel flow, I think it doesn't matter much, injectors can't stay new all the time.

Have you checked the vacuum leak at the injector's back leak off connectors? Their rubber o-rings tend to dry out with time. Also their plastic clips that should keep them tight to the injectors comes with pretty bad quality. If there is a vacuum leak at them, the common rail pump sucks the air at one or all those connectors. If need be, use plastic cable ties to tie the connectors to the injectors properly. If you have ever found some diesel on the rocker cover, around the injector seals, those connectors are the culprit.

Disconnect the return hose from the fuel filter and hook a vacuum pump to the hose. There shouldn't be a vacuum leak there at all.