Pre fuel pressure circuit fault, anyone have experience?

Hi All,

got an issue which my local landrover specialist is stumped about, hoped someone might be able to help.
Went out in the RR and the car went into limp mode, tried it couple more times out and whilst it might not go into limp mode from the word go, it does after half a mile or so. No clue what was going on I gave it to the local RR specialist.
My local specialist plugged in the OEM RR diagnostic equipment and returned the above fault code "pre fuel pressure circuit fault", the mechanic said it did not return a code number, so he could not refer it to anything.
1st thing he tried was the gauze and filter in the tank (I think), he said it was gunged up and thought this might cure the issue, however, no joy, next he thought that the blockage might have caused one of the pumps to overload and fail, so he tried changing out the fuel pump outside the tank, which apparently is the normal one to fail, however, he though this did the trick, drived it with new pump and seemed to be okay, however, 2nd drive and it did the same, into limp mode.

Now, the mechanic thinks it might be an electrical fault but cant find anything obvious.

Anuyone have any ideas or suffered the same fault?

What about the in tank pump maybe?

Hi Saint, its a valid point, the mechanic is struggling to know if the fault is mechanical or electrical from the diagnostic.
Problem is that I have already spent £400 on parts and labour replacing the outside tank pump without any progression. So I am trying to keep cost down and was hoping someone might be able to shed light on the diagnostic fault.

When my pump went it didn't bring up a fault code atall. You can still get a small amount of pressure from the transfer pump so might seem like you getting fuel. But not at full pressure

so was it the in tank pump that went on yours? Seems strange it is pulling up this diagnostic fault if its a pump issue. Still think it may not actually be a pump issue? any method of checking pump pressure in the line?

rwilki said:

so was it the in tank pump that went on yours? Seems strange it is pulling up this diagnostic fault if its a pump issue. Still think it may not actually be a pump issue? any method of checking pump pressure in the line?

Click to expand...

Yes intank fuel pump had gone.

Turn you key to position 2 for a couple on min, this primes the fuel system.

Then turn the engine off.

Remove the engine cover and on the fuel rail ther is a shraeder valve

With a rag around it press the valve in. If you have pressure then you will get a jet of fuel out. But use a rag as it's under pressure (or should be)

If no jet of fuel you have no fuel pressure.

Deasy said:

Yes intank fuel pump had gone.

Turn you key to position 2 for a couple on min, this primes the fuel system.

Then turn the engine off.

Remove the engine cover and on the fuel rail ther is a shraeder valve

With a rag around it press the valve in. If you have pressure then you will get a jet of fuel out. But use a rag as it's under pressure (or should be)

If no jet of fuel you have no fuel pressure.

Click to expand...

(his is a Diesel.....from what I can gather - due to the external pump change on the tank!!)

Saint.V8 said:

(his is a Diesel.....from what I can gather - due to the external pump change on the tank!!)

Click to expand...

:doh:

Would help if he had given that info lol

When you say gunk in the tank, I take it your vehicle is a diesel! If so are you using bio diesel or ULSD fuel in your tank.

Alan

Gunk in diesel can often be bacterial growth, nightmare, clogs everything.

Hi

sorry I forgot info, yes its a diesel, standard, no fuel modification.

mechanic has still had no joy, they traced back the wiring loom to see if there was an issue with it but to no avail.

I don't think he has even nailed it down to knowing whether it is a mechanical or an electrical fault

rwilki said:

Hi

sorry I forgot info, yes its a diesel, standard, no fuel modification.

mechanic has still had no joy, they traced back the wiring loom to see if there was an issue with it but to no avail.

I don't think he has even nailed it down to knowing whether it is a mechanical or an electrical fault

Click to expand...

Sounds like you need a different mechanic who knows how to use a DVM.

If you still have "gunk" in your fuel tank it will need cleaning out, I had the same issues with biodiesel several years ago now, the remedy was as follows;

1. Drain the fuel tank out completely, and remove any deposits of gunk.
2. Remove the fuel filter and change, the refill the tank with normal diesel (not bio or ULSD). Then add biocide to the fuel, this will break up and start to cleanse the fuel system.
3. After 3 days of running, follow step 2 again, but on the refill do not add biocide.

At work I still cleaning my ground fuel tanks and adding a weak measure of biocide twice a year.

As Data said it is a sod and darn expensive to get rid of this bacterial growth, also it sounds like your mechanic hasn't had a lot of experience.

Alan

in all fairness nobody on the forums has been able to give any further advice as to what a diagnostic result of "pre fuel pressure circuit" fault might be, so cant exactly say the mechanic isn't doing a good job.

Latest update is that the advance pump and auxillary pump have both been changed and tested and have not cleared the fault.
They have also checked the LP fuel pressure sensor and changed out the fuel pump relay.

I was incorrect, it was not the fuel filter which was blocked, it was the gauze which goes around the advance pump which they cleared, the fuel filter was changed at the service with no blockage, so I think we can dispel a tank bacteria problem.

The next think they might look to try is the High pressure pump, however, this will cost quite a lot of money, so am hesitant for them to do this.

It would be nice is someone could clarify if "pre fuel" relates to either the low pressure or high pressure side of the system.

its usually just one of the pumps that have given up.

you don't usually here anything else that causes issues

From your other thread about the gearbox issue I eventually found that this is a 2004 TD6....
I have to question your "Specialists" knowledge and diagnostic equipment.If he is using Testbook,(The official tool - NOT Autologic or Nanocom etc) then he is not using it properly,the fault codes give P codes and a description in words on Bosch systems like this one.From live data displays he also should be able to monitor the low side fuel pressure which should stay over 250kpa when revving hard,and up to about 400kpa when idling.He can also view the high side pressure in the rail,stability of pressure being more important than the actual pressure.If he was really up to it he would also be scoping both the low side pumps for speed and current draw,rather than just replacing expensive parts.

Thanks eightinavee, a very comprehensive and educated response, I will ask on Monday what type of diagnostic equipment they are using and ask the questions you have asked relating to live pressure monitoring, I did wonder how they could measure fuel pressure on both the LP and HP sides of the fuel delivery system.

I totally agree that changing out parts for new parts without further testing wont get me very far.

I have thought about taking it to a main Land rover dealer, but wasn't sure if they would be able to do much better.

Do you think a main dealer might be able to diagnose this type of fault in a couple of hours? I am trying to stem costs as I have already racked up about £400 without, never mind the other £800 I have spend in preventative maintenance in the last month.

A main dealer should be able to sort it,but its all down to who they have working for them.To many main dealer techs now the BMW TD4/6 engines are old hat and they are now concentrating on later TDV6/8 units.
A decent LR indy is probably a better bet,finding one by recommendation is usually best.Most indies tend to look after cars that are a little older and have more miles on them.The faults we find and fix are often quite different to the ones main dealers see,as things are tending to wear out,corrode or die of old age,wheras dealers get the main of the parts that need upgrading early on.
Most TD6 fuelling faults are well known,and the common rail system on your TD6 is just the same on many other makes of car.It shouldn't be too hard to find someone to fix it.

Put your location in your profile, will help others to recommend an indy who would be close to you...

If you are close to me - I have used Rangers of Guildford, all ex-LR staff who got fed up with the Main Dealer politics and wanted to give a better service to their customers so split apart and set up on there own...decent guys too.

Slyfield Industrial Estate, Guildford, Surrey....

good point, north west based I am afraid, but thanks