Common rail fuel pressure

[Rapid_Axe]

Hi all

What should the fuel rail pressure be in a common rail diesel?

I've been hunting a surging issue for the last three weeks in my NS Paj and last night decided to get the OBD2 scanner out and watch what the car was doing when it surges in Torque.

- Revs ok and doesn't drop
- Boosts ok
- Temps all ok
- Keeps speed ok
- Auto doesn't flair and shifts ok

The only thing I saw was when I put up the fuel rail pressure, on soft acceleration the pressure would sit at about 4500 psi and not move much, when I accelerated normally it fluctuated between 7500 and 23000 psi (during the surging)

Safe to assume the pump is gone?

[Rapid_Axe]

Also where would I be looking at the engine to see where the pressure sensor is? Can't hurt to look at that either.

[FIS9076]

Im no expert at all, but I think that the common rail fuel pressure is linked to the actual engine speed, as it, the higher the revs, the higher the fuel pressure.

Ive got mine idling around your 4500, and steadily increases with engine rpm up to max (not sure exactly but your 23000 sounds right)

I did have an issue with mine where an extra filter was creating too high resistance to the fuel pump so it would hesitate when accelerating, but I wouldn't have said it was a surge.

Perhaps try throwing on a new fuel filter and seeing if anything changes?

Fuel rail pressure sensor is at the back of the big manifold bit that all the injector lines run off, below the air intake manifold and above/behind the fuel pump

Dan

[Rapid_Axe]

You could possibly be right because it seems with revs that it increases but it shouldn't go to 7500psi, then to 23000psi, back to 10000psi, back up, down, up like that as revs increase.

It's going in for a service next Tuesday (150,000km) so should answer my question there, could also be the filter is blocked.

[ijoe]

Wow, I know this tread has not had any reply for over 2 years,

But..

I'm experiencing the exact same issue..
Just wanted to know the outcome and if there was any way this could of been resolved without taking to a dealer..

cheers

[RUGGA]

Rapid Axe has not been active on this forum for over a year now.


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[ijoe]

Yeah i saw that..
Never know when someone might get a email saying someone replied to their thread.

I'm hoping someone knew the outcome.. As my Paj is experiencing the exact same issues, I too can see the Rail pressure dip up and down using Torque and a IDBII tool..

[wakeboarder]

another 2 yrs on I just had the same problem to the point where car was stalling flat out.
replaced scv, fixed problem temporarily. new fuel filter, cleaned tank , fuel lines and and in tank filter plus added filter to tank vent and its running the best it ever has since I have owned it.

[RUGGA]

another 2 yrs on I just had the same problem to the point where car was stalling flat out.
replaced scv, fixed problem temporarily. new fuel filter, cleaned tank , fuel lines and and in tank filter plus added filter to tank vent and its running the best it ever has since I have owned it.

Well done, did you have a dealer do the work?

[Seigried]

I had this on my NS. Replaced fuel lines filters maf and map clean fixed mine. Still need to do the in tank filter for piece of mind.

Sent from my SM-G900I using Tapatalk

[starjunk]

I had this on my NS. Replaced fuel lines filters maf and map clean fixed mine. Still need to do the in tank filter for piece of mind.

Sent from my SM-G900I using Tapatalk

I'm having a related issue. Not surging as such, but an intermittent flat spot, mostly with engine cold, around 3000rpm. Feels as though it's starved of diesel or missing, but put the foot down and she goes fine and problem disappears. Fuel lines were replaced along with new injectors 2 months ago. Have bought an SCV but not fitted yet, thinking that this problem is not the 'surging' that is normally associated with SCV wear.
Sounds like MAP and MAF clean are the go? When the problem occurs, fuel rail pressure is perfectly stable. Boost pressure also stable. So maybe MAF rather than MAP?
What's the best stuff and procedure to use to clean the MAF? If there a MAF cleaner? Or does one use carby cleaner?
Cheers, StarJunk

[BBP]

Starjunk,
Get a proper maf cleaner. Carby cleaners are too aggressive. Supercheap have one.

Rob

[starjunk]

Starjunk,
Get a proper maf cleaner. Carby cleaners are too aggressive. Supercheap have one.

Rob

Thanks Rob! Will go out and get some today. :-)

[craka]

Reviving an old post, I know.

It doesn't appear that anyone replied with normal fuel rail pressure at idle.

Been towing a trailer around which I know adds to fuel consumption, but my fuel consumption with towing is up around 17L/100km and has me wondering wether something else is going on.

Had a look with torque pro and my fuel rail pressure at idle is cycling between approximately 4000 and 4500 psi. Is that normal, or within tolerance to bounce between those two figures at idle?

[erad]

I have looked up my W/S manual (Russian CD) and it is complicated.


With engine CW temp @85 to 95 Deg C, transmission in neutral and all lights off, the common rail target pressure is 20 - 35 MPa at idle speed. Press the accelerator slightly and the pressure should increase (the amount would vary according to how hard you press).


The rail pressure sensor will bring up code PO191, 192 or 193 if the rail pressure varies by more than +/- 10 MPa.


4000 psi equals 27.56 MPa and 4500 psi equals 31MPa