How To test the Diesel High-Pressure system

[Jules]

FrenchMike

Another observation from me is that the 0.5 volts rises to 0.7 - 0.72volts (rail sensor) before cranking.

This equates to 350kPA (3.5 BAR) which of course is the LP fuel pressure.
The HP pump and rail pipes should see this pressure prior to cranking.
That test can bypass most other tests and time wasting and it proves fuel is being fed from the tank.

Incidentally a CDT will start with rail sensor disconnected (but won't rev)
Be careful doing this as the ECU goes to safe mode
(the open circuit rail circuit actually sends a reading of 400,000 kPA to ECU!!)

[FrenchMike]

Originally Posted by Jules

FrenchMike

Another observation from me is that the 0.5 volts rises to 0.7 - 0.72volts (rail sensor) before cranking.

This equates to 350kPA (3.5 BAR) which of course is the LP fuel pressure.
The HP pump and rail pipes should see this pressure prior to cranking.
That test can bypass most other tests and time wasting and it proves fuel is being fed from the tank.

Incidentally a CDT will start with rail sensor disconnected (but won't rev)
Be careful doing this as the ECU goes to safe mode
(the open circuit rail circuit actually sends a reading of 400,000 kPA to ECU!!)

Thanks Jules,

Interesting to know ,
so with only one measurement,one can learn lot of things ...

[john493]

Had a problem with my 2003 CDTi this afternoon - started normally, drove for about 15 minutes, stopped the engine. About 2 mins later tried to re-start & it turned over but would not fire.
I left it for 5 minutes, then it started normally. The UB fuel pump sounds a bit noisy, not sure if it's noisier than normal. I can hear the IT pump running now, although when I first listened, I couldn't hear it.
Where do I start testing ?
BTW, I looked at the pressure sensor on the fuel filter, it has 3 wires, yellow/blue, green/purple, green/black - these colours appear different from those listed for testing.
Thanks
John

[FrenchMike]

Originally Posted by john493

Had a problem with my 2003 CDTi this afternoon - started normally, drove for about 15 minutes, stopped the engine. About 2 mins later tried to re-start & it turned over but would not fire.
I left it for 5 minutes, then it started normally. The UB fuel pump sounds a bit noisy, not sure if it's noisier than normal. I can hear the IT pump running now, although when I first listened, I couldn't hear it.
Where do I start testing ?
BTW, I looked at the pressure sensor on the fuel filter, it has 3 wires, yellow/blue, green/purple, green/black - these colours appear different from those listed for testing.
Thanks
John

There are 3 wires

+5volt from ECU purple/green (the middle one)
earth from ECU Black
signal sensor output blue/yellow

If you get around 4 volts on the signal wire, all the low pressure side is OK

Mike

[john493]

Thanks Mike - 2 questions:
Testing on the fuel rail sensor, I see the 0.5v with ignition on, I see the 1.2 volts when cranking. When exactly should I be seeing 0.7 volts ?
The 4 volt signal on the fuel filter sensor is OK.

So I'm thinking my cam sensor is suspect, (temperature-related), though today the car is starting with no problems - I've taken a gamble and ordered a used sensor off eBay.
However, I did try to test for the 9 volts at the sensor when cranking, but the wiring colours again are different to those pictured on this thread. I was thinking the right hand red/white was the signal line, but it's still at 12 volts when cranking. So which one is the signal wire ? (as car starts, am taking it the sensor is not faulty at the moment.) See picture of my sensor wiring:

[FrenchMike]

Originally Posted by john493

Thanks Mike - 2 questions:
Testing on the fuel rail sensor, I see the 0.5v with ignition on, I see the 1.2 volts when cranking. When exactly should I be seeing 0.7 volts ?
The 4 volt signal on the fuel filter sensor is OK.

So I'm thinking my cam sensor is suspect, (temperature-related), though today the car is starting with no problems - I've taken a gamble and ordered a used sensor off eBay.
However, I did try to test for the 9 volts at the sensor when cranking, but the wiring colours again are different to those pictured on this thread. I was thinking the right hand red/white was the signal line, but it's still at 12 volts when cranking. So which one is the signal wire ? (as car starts, am taking it the sensor is not faulty at the moment.) See picture of my sensor wiring:

1.2 volt while cranking seems correct (around 300 bars) allowing ignition.

About the camshaft sensor,the signal is the middle one.
earth (Brown) in the right .
Power +12 volt on the left (red/white)

Obviously ,it's when at fault ,that you have to take the measurements.

Carry out a injector leakback as well

Good luck

Mike

[john493]

Well I changed the cam sensor 2 weeks ago & had no further problems until today, when after a 2 mile drive, the car was parked for 10 minutes then would not restart. Turned over but does not fire. Left it for another 5 minutes, then it started straight away. Clearly the original cam sensor is OK so I'll re-fit it. (The misses was using the car at the time, she did tell me that the electric windows would not work when this happened, though I didn't verify this myself ! Is this a clue ?)
Fuel Tank was 75% full.
Not much chance to do any proper testing with such an intermittent fault.
It's a CDTi, 2003.

What's the most likely cause of a heat-sensitive fault like this ?

Thanks,
John

[FrenchMike]

Try to carry out a injector leakback test while warm or hot :

see:
http://www.the75andztclub.co.uk/foru...84#post2006584

[john493]

Thanks Mike I've not got the kit to do a leak back test, I'll see if I can borrow one !
I've seen DIY kits with small bottles & pipe, but I'll need the connectors to fit on the injectors too.

[FrenchMike]

Originally Posted by john493

Thanks Mike I've not got the kit to do a leak back test, I'll see if I can borrow one !
I've seen DIY kits with small bottles & pipe, but I'll need the connectors to fit on the injectors too.

You don't need a special equipment ,only buy one meter of vinyl tube:

(sorry for the french !)

Leak back 3.jpg


Mike