Hi, i’m hopeful somebody will be able to advise me on a starting issue I'm currently having with a skoda octavia 1.6tdi (2016). 
 

Essentially, the car when driven under load was throwing up a p0087 - low fuel pressure fault, and went into limp mode, this reset when the car was switched off until the next time under heavy load. 
 

Now, this seems to have progressed to the extent the car cranks and wont start, i have on occasion got It to start, following which it reverts to the above mentioned symptoms. 
 

Plugged the diagnostic in - when cranking and not starting, the fuel rail pressure ranges from 70-120 bar, commanded value is 350.

 

when it starts and is idling, the commanded value is 270 bar and measured pressure is also 270 bar. 
 

The low pressure side up to the filter and Hpfp is good. 
 

i have worked through the electrical circuits while following the haynes repair manual, and have come across the following discrepancy which i hope this forum will clear up.
 

for pin 1 of the fuel pressure regulator valve, with ignition on, it advises voltage should be around 12v, however I'm measuring 2.7v.
 

the next step would be to measure somehow at ECM output, which i think will be difficult as its enclosed using shear bolts. 
 

Would anybody have a Skoda wiring diagram for this, are there any other connectors before ECM or should the indeed be 12v? 
 

my concern is that the 2.7v may be normal and the ECM route is a red herring.. 

 

any comments on the above greatly appreciated..  

39 minutes ago, Matthew6743 said:

for pin 1 of the fuel pressure regulator valve, with ignition on, it advises voltage should be around 12v, however I'm measuring 2.7v.
 

the next step would be to measure somehow at ECM output, which i think will be difficult as its enclosed using shear bolts. 
 

Would anybody have a Skoda wiring diagram for this, are there any other connectors before ECM or should the indeed be 12v? 
 

my concern is that the 2.7v may be normal and the ECM route is a red herring.. 

 

Measured connected to the regulator or disconnected?

 

Is pin 1 the supply voltage to the sensor or the output?

What is your engine code?

Hi, thanks for the replies... 
 

Pin one is indicated as supply voltage, pin 2 Gnd.
Regulator resistance was 2.1ohm. 
 

voltage when disconnected was 2.7v

when connected, its dropping to 0.25v. 

solenoid operated ok when actuated from the battery.. 

 

engine code is CCXB

Have you tried measuring this voltage while cranking to see if you get the supply then?

Voltage when cranking is 1.7v

Well, assuming the Haynes manual is correct, I agree with you in that your next step is to measure directly at the ECM and bell out the wiring if required.

 

One more thing, are you measuring the voltage to the ground pin or a chassis ground?

A sensor reference voltage will be a regulated 5v (connector removed), I havn't trusted Haynes manuals for decades and am very suspicious of that extract because it speaks of testing the solenoid.

Its a difficult one as the Haynes manual indicates pin 2 to be a brown although mine is black/green, so I'm not 100% convinced just yet. The feed wire colours are correct (red/blue) and the rest of the checks carried out around other circuits all make sense.. 
 

I’ll try getting the shear bolts out to access the ECU, looks to be a closed plug tho so may prove difficult to measure, cable resistance from ECU plug to regulator may be my only option.

 

All measurements have had negative lead directly to negative battery terminal.

the regulator is a solenoid, not a sensor

 

I too am suspitious of the Haynes advice though as I havnen't seen muh detailed information from them in a long time

 

I am a little sceptical you will find anything wrong with the wiring, but it rules something else out and thats what fault finding is all about.

 

Have you measured the fuel pressure given by the lift pump? Is this the engine with or without the extra auxiliary fuel pump?

Edited 3 January, 20251 yr by SuperbTWM

Thinking about it, if you haven't got any fault codes for the regulaing valve, then electrically it should be alright.

 

I think more than likely the fuel pressure regulator has failed mechanically, if you don't find anything wrong electrically there is quite a detailed test procedure for the regulating valve which involves metering the return fuel into a measuring jug