How To test the Diesel High-Pressure system

[FrenchMike]

Hi all,

In case of non starting (preferably hot),Camsensor is generally incriminated.
But we have to know the behaviour of the common rail pressure in order to rule out a possible injector leak back.

Here is a easy way to do it:

YOU NEED:

-a lowcost multimeter (DC 2 volt range)
-one or two alligator clips with pin associated (as already describe somewhere)


PROCEDURE

1 Disconnect the camsensor.
2 Pin throught the insulation of the blue/black wire (the other green/brown
is the ground.
to pick up the fuel rail pressure signal.
3 turn the key position 2 (you must read 0.5 volts)

4 Crank for 4 secondes then release the key.

If you get a chart like the green one,then,you have no significant leak.





Camsensor test:



Low pressure test



High pressure test.




In case of low values,an injector leakback test is recommanded.




Check the HP pump regulator gaskets as well.




MAF test




Cranckshaft sensor is easely tested by looking at the tachometer needle during cranking.

Don't forget;if starting with easy start,it's not an electrical issue but likely an injector fault.

Mike

Enlarged Thumbnails.....

[simpsora]

Another simple but very informative diagnostic test. Could save members lots of time and money if unsure about any starting problems.
PS my FBH started yesterday (5 deg ) first time this season !!
Thanks again for all your work for 'the forum'
Regards , Robert

[FrenchMike]

Originally Posted by simpsora

Another simple but very informative diagnostic test. Could save members lots of time and money if unsure about any starting problems.
PS my FBH started yesterday (5 deg ) first time this season !!
Thanks again for all your work for 'the forum'
Regards , Robert

Thanks,Robert

That's nothing , only happy to be useful still !


Mike

[Starman]

How quick and easy.

Mike, forgive me asking silly questions but a) will this show a small leakback if it exists, and b) how much would the voltage change by vs the amount of leak?

Many thanks and well done for posting this up.

Regards Steve.

[FrenchMike]

Originally Posted by Starman

How quick and easy.

Mike, forgive me asking silly questions but a) will this show a small leakback if it exists, and b) how much would the voltage change by vs the amount of leak?

Many thanks and well done for posting this up.

Regards Steve.

Hi,Steve

That's a good question.

The green plot is get from my own car (she runs well)
I guess, if there is some leak (in particular injector),it
must be something like the supposed red plots!

Knowing that a lack of pressure prevent starting the engine

But effectively, if someone with a leak could make this measurement,
It should be interesting!

Mike

[chrissyboy]

Originally Posted by FrenchMike

Hi all,

In case of non starting (preferably hot),Camsensor is generally incriminated.
But we have to know the behaviour of the common rail pressure in order to rule out a possible injector leak back.

Here is a easy way to do it:

YOU NEED:

-a lowcost multimeter (DC 2 volt range)
-one or two alligator clips with pin associated (as already describe somewhere)


PROCEDURE

1 Disconnect the camsensor.
2 Pin throught the insulation of the blue/black wire (the other green/brown
is the ground.
to pick up the fuel rail pressure signal.
3 turn the key position 2 (you must read 0.5 volts)

4 Crank for 4 secondes then release the key.

If you get a chart like the green one,then,you have no significant leak.



Now,you can see the Camsensor side;but before buying one,have a look here:

http://www.the75andztclub.co.uk/foru...ad.php?t=65916

All comments are welcome

Mike

watch out for all the cranking as the cat will build up with un burnt fuel .as your just testing the ecu is sending a 5volt to it and the ecu is recieving a signal back make sure it cant pump fuel ..just pull the pump fusethe best things to use or the snap on hook and tighten ones so you get a constant un interupted flow of currant,check for continuinity if that is there it is working as it should

[al_dente]

I thought I'd give this a try to see if it helped shed any light on my car's cutting out issue.

When I'd connected my voltmeter, I had 0.465 volts on the meter. When I cranked the engine, the reading didn't change.

I thought I'd see what happened if I reconnected the cam sensor. The car wouldn't start with the cam sensor connected. I then disconnected the voltmeter and tried again - the car started.

So, I have two questions:

1) becasue the volt reading didn't change, does it mean I've done something wrong - or could it indicate that my injectors are leaking really badly?

2) is it right that the car wouldn't start with the voltmeter connected to the blue and brown wires?

Cheers

Al

[FrenchMike]

Originally Posted by al_dente

I thought I'd give this a try to see if it helped shed any light on my car's cutting out issue.

When I'd connected my voltmeter, I had 0.465 volts on the meter. When I cranked the engine, the reading didn't change.

I thought I'd see what happened if I reconnected the cam sensor. The car wouldn't start with the cam sensor connected. I then disconnected the voltmeter and tried again - the car started.

So, I have two questions:

1) becasue the volt reading didn't change, does it mean I've done something wrong - or could it indicate that my injectors are leaking really badly?

2) is it right that the car wouldn't start with the voltmeter connected to the blue and brown wires?

Cheers

Al

Hi Al,

A high impedance voltmeter (several Mohms)must not disturb the pressure sensor output ! (low impedance DC signal)
And then of course you can run the engine!

however no use to have the engine running ; It is the pressure decrease
whicht is interesting in that case.

Mike

[Jules]

Originally Posted by chrissyboy

watch out for all the cranking as the cat will build up with un burnt fuel .as your just testing the ecu is sending a 5volt to it and the ecu is recieving a signal back make sure it cant pump fuel ..just pull the pump fusethe best things to use or the snap on hook and tighten ones so you get a constant un interupted flow of currant,check for continuinity if that is there it is working as it should

That wouldn't work Chris.
There will be no fuel pressure to measure if you pull the fuse

[Mike Noc]

Originally Posted by Jules

That wouldn't work Chris.
There will be no fuel pressure to measure if you pull the fuse

Agree Jules but also there won't be any fuel injected anyway because the cam sensor is disconnected.

Mike.