Thread: D2a TD5 loses power at WOT on hills

I wouldn't worry about it, even it it runs for 30 secs, if it doesn't cut out it is not reaching full pressure cut-out or I assume the pressure sender/regulator must be faulty.

If the vehicle has travelled more than 100K, then suspect the fuel pump. The symptoms you are experiencing are quite common when facing a low output fuel pump. Pressure is a function of volume and vice a versa, the engine will run quite well at half pump output even, on the flat, but ask for more supply when climbing hills or overtaking and that will be a certain result.

I have seen many last to 200K, but most half way between IME

JC

Originally Posted by justinc

If the vehicle has travelled more than 100K, then suspect the fuel pump. The symptoms you are experiencing are quite common when facing a low output fuel pump. Pressure is a function of volume and vice a versa, the engine will run quite well at half pump output even, on the flat, but ask for more supply when climbing hills or overtaking and that will be a certain result.

I have seen many last to 200K, but most half way between IME

Thanks Justin.
The vehicle has almost 180,000km on it now. I receipts for the work carried out on it for most of it's previous life and will check them later out of interest to see if the fuel pump has ever previously been changed.
I guess that there is only two ways to confirm that it is fact the fuel pump:
Connect a fuel pressure gauge in line and drive the vehicle monitoring the fuel pressures - I assume the vehicle would have to be driven in order to simulate the issue so that the fuel pressure could be monitored while it is occurring.
Remove and replace and if the problem goes away, it was the pump.

I just had a look at it seems that a new pump can be purchased from the UK for under $200.00 AUD delivered, which in my books is reasonable (it's not much more than a Falcon fuel pump retails for here). So the replace test method might be easier than trying to hook up a pressure gauge in line.

Originally Posted by mturri

Fuel pump and fuel pressure regulator usually go hand in hand, if one fails expect the other one to follow.

What is the symptom of a failed fuel pressure regulator? Does it usually cause too much fuel pressure or not enough or does it vary? I'm wondering if there is any means to identify whether the cause is the fuel pressure regulator or fuel pump?

I have actually just replaced the flexible fuel line that runs underneath the inlet manifold from the front of the head to the fuel pressure regulator as this sprung a leak on me where the rubber hose is crimped to the metal line.

Originally Posted by mturri

Regulated fuel pressure (downstream of fuel pressure regulator and engine, just before entering fuel cooler) should be 4 bars steady when idling, down to 3.5-3.6 bar at full boost. Never out if this range.

What is the purpose of testing this? Surely downstream of the engine makes no difference as this is the excess fuel after the engine has taken and used that which it required? Isn't this just excess fuel that just runs back into the fuel tank to go around the cycle again?
I understand testing the fuel pressure from between the fuel pump and the engine as this is the fuel that feeds the engine.

Originally Posted by twr7cx

What is the symptom of a failed fuel pressure regulator? Does it usually cause too much fuel pressure or not enough or does it vary? I'm wondering if there is any means to identify whether the cause is the fuel pressure regulator or fuel pump?

I have actually just replaced the flexible fuel line that runs underneath the inlet manifold from the front of the head to the fuel pressure regulator as this sprung a leak on me where the rubber hose is crimped to the metal line.




What is the purpose of testing this? Surely downstream of the engine makes no difference as this is the excess fuel after the engine has taken and used that which it required? Isn't this just excess fuel that just runs back into the fuel tank to go around the cycle again?
I understand testing the fuel pressure from between the fuel pump and the engine as this is the fuel that feeds the engine.

some fuel should go back, if not enough then indicates that not enough getting to engine from the delivery side of the pump

Fuel pressure regulators can fail in a number of ways, one of which being them not steadily holding the required pressure (4 bar) but less, and less pressure means less volume so the engine starves (especially in full boost conditions as it appears to be your case).

As for engine starving, it can be due to a failing FPR or fuel pump (or why not both...). The way to identify this is to measure each pressure individually, idling at first, then if not conclusive at incremental loads.

Here's a schematic of the fuel delivery system on the Td5:


High pressure or "raw fuel pump pressure" line marked in red, "system" pressure lines in blue.

Fuel pump sends diesel at 6-7 bar which enters the FPR, gets regulated to 4 bar and exits the FPR from its backside directly into the fuel rail. Part of the diesel is taken by the injectors and the rest returns to the FPR (internally in EU2 engines, and externally in the later EU3 ones). From the FPR "spent" diesel is sent to the fuel cooler and then back to the filter housing.

This is the fuel pressure regulator assembly:



Fuel pump pressure can be measured by either removing the temperature sensor and screwing in (or getting the right "T" adapter) or by disconnecting the line entering the FPR marked (4) in the above schematic and inserting an in-line device.

Also from the above schematics it can be deduced that regulated fuel pressure can only be tapped into once diesel leaves the FPR, in practice by disconnecting the hose going into the fuel cooler. The Td5 fuel sender pumps about 180 lts/hr thence even on a fully loaded engine the injectors only take a minimum volume of diesel therefore not reducing pressure significantly.

After years of struggling with Td5 fuelling problems (on both own as well as other peoples) I put together a gadget to this effect. Using parts from a failed FPR devised what in essence is an extension fuel hose with a side outlet where an electronic pressure sender was mounted. Built a long enough loom as to reach the cabin and adapted a cheapo suction cup type cell phone holder to which the electrical gauge was fixed to. The Autometer kit I used was a costly item and yes I could have gone analog (standard mechanical pressure gauge), but I wanted to have the ability to drive the vehicle, eventually flooring it, without the presence of a live diesel hose in the cabin, or say a mechanical gauge hanging from the windscreen wipers. No fancy looks but does indeed help, here's a few pictures:






Having not only used it for diagnosing fuel pump & FPR troubles but also for day to day drives I have come to learn the following:

Raw fuel pump pressure (sender installed upstream of FPR):
- Runs between 6 and 7.5 bar
- Not a steady value, even when idling permanently oscillates in a 0.5-1 bar range
- Decreases slightly as fuel heats up (can be observed when starting from cold)
- Decreases as fuel consumption rises

Regulated fuel pressure (sender installed downstream of FPR and injectors, i.e. upstream or downstream of fuel cooler)
- Runs at 4 bar (58 psi) steady
- Decreases more noticeably when consumption rises (down to 3.5 bar at full boost)

In conclusion:

1- If fuel pump is busted raw pressure will be either too low or all over the place (specially on a fully boosted engine)
2- If FPR is busted regulated pressure will be either too low or waving up and down
3- Both pressures can look good at idle speed but start misbehaving as fuel expenditure increases

Other own conclusions (that could well be wrong):

a- Fuel pump is cooled by diesel within the tank, as fuel level drops fuel pump works hotter, then not recommended to run on an low tank as a habit
b- Fuel pump and FPR work in association, when one malfunctions the other one suffers, then when one goes down the other will soon follow
c- Partially clogged fuel filters do fuel pumps no good (one can sometimes get rid of fuel pump whining by replacing the fuel filter), too bad fuel pressure upstream of the filter cannot be monitored.


...I'm exhausted... hope this helps!

Cheers

Matt

That's an absolutely sweet setup Mturri, but probably far more effort than I intend to go through! I think my fuel pressure test gauge is an ABW low pressure unit for carburetor vehicles.
At $450.00 for a new fuel pump and pressure regulator I'm probably better off just purchasing both and installing them than forking out a couple hundred to setup a gauge to test/monitor them - if I get 100,000kms out of them after replacing then I'll be happy!

just a thought, the first outlet hose from the turbo delaminated inside on mine and created power loss under hard acceleration / high boost. Have you checked the inside of this hose? if yours is delaminating causing a bockage in airflow than it could cause significant power loss under load but not under moderate load / boost. Changed my hoses to silican and problem was fixed for me.