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Fuel Pressure Sensor – find it and fix it!

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Fuel Pressure Sensors –

what is it, where to find it, how to fix it if it goes wrong.

The fuel pressure sensor is a crucial part of the modern common rail diesel system.     The fuel pressure sensor sends information to the engine management unit informing it of the present pressure in the common rail reservoir.
The fuel pressure sensor is probably the weakest component in the electronic control loop. It has to do a lot of work and is prone to failure.

What are the symptoms of fuel pressure sensor failure?

Cutting out.
Failing to start
Running in limp/ get home mode
Erratic running
Engine will run when sensor is dis-connected but will not rev
Engine runs but lacks power

Are all fuel pressure sensors the same?

No there are quite a considerable few differences. There are different makes e.g. Bosch, Siemens/Delphi and Denso.
Different types of Bosch sensors
Mercedes and BMW versus other vehicles
There are differences in the Bosch types fitted to Mercedes and BMW on the one hand and the bulk of other diesel vehicles. Mercedes and BMW Bosch sensors have a different plug design to other sensors fitted to vehicles like Peugeot, Renault and Iveco for example.

Siemens and Delphi
There are a considerable number of variations in the types of sensors fitted on vehicles running the Delphi and Siemens systems.
On the one hand the sensors can have a different pressure rating and on the other hand they can have a different plug configuration. By this I mean the male plug on the vehicle’s wiring loom is specific to the type of sensor fitted. Subtle differences on the male plug have to coincide with the same configuration on the female plug which is part of the sensor.

Denso sensors are fitted to a wide variety of vehicles particularly those originating from companies like Nissan, Toyota and Mitsubishi. They are difficult to source and at time of writing the price from main dealers has tended to be high. Like the sensors already discussed plug configuration does vary from one type to another. In other words the sensor can look identical to another but cannot be used because the plug is different.

Can fuel pressure sensors be repaired?

The typical fuel pressure sensor is a sealed and integrated unit so it cannot be dismantled. In a word they cannot be repaired. Replacement is necessary. Please view   for more information. Contact person Andy Hewing

Where will I locate the fuel pressure on my vehicle?

The fuel pressure sensor is usually located on the end of the common rail fuel reservoir. It is screwed into the rail in a conventional way and is easy to remove and replace. Unfortunately the rail is located in many different places on the many different vehicles. Sometimes the rail is at the front of the engine, sometimes behind. Follow the fuel pipes back from the injectors to locate the position of the common rail fuel reservoir.

Is the fuel pressure regulator different to the fuel pressure sensor?
Yes the sensor is different to the regulator. Some vehicles are fitted with a regulator on the rail. Usually at the opposite end of the rail to the sensor. One easy way to tell them apart is sensor is 3 pins, regulator is 2 pin.

Biodiesel – Friend or Foe?

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Biodiesel: Friend or Foe? Is it good for your car and can you avoid it?

Biodiesel and biofuel are substitutes for diesel and petrol respectively.

They are produced from different types of biomass.

This article will focus on biodiesel, which is commonly made from rapeseed oil and used cooking oil.

Biodiesel can be made from bacteriaE. coli bacteria ‘can produce diesel biofuel’……read more here

In theory, they will run in every diesel car, though it is normal for biodiesel to be used in a blend with actual diesel, though the proportions of the blend may differ significantly (from 5% biodiesel to 100% biodiesel!)

Get more of the chemistry…

Benefits of Biodiesel:

The most appealing quality of biodiesel is that it is carbon neutral.

During combustion within the diesel engine it releases exactly as much CO2 as was absorbed by the plant during its life. In this era of concern for our carbon footprints, it feels great to be able to drive diesel cars without the guilt of adding substantially to pollution.

Furthermore, biodiesel is a completely biodegradable and non-toxic substance.
Any spillages that might occur will not be a problem, and not endanger wildlife in the way that oil and its refined diesel could.
On top of this, the flash point of biodiesel is higher than that of diesel, making it safer to transport and use.

The Dark Side of Biodiesel:

The problem with the idea of carbon neutrality is that it does not take into account the carbon costs of its production.

If combustion releases exactly as much carbon as has been absorbed, then it follows that any amount of carbon in the production of this diesel substitute will mean a larger amount than has been absorbed.

However, even with this emission surplus, biodiesel is still estimated to produce between 50-60% fewer emissions than its diesel counterpart.

The Trouble with Biofuels ……read morethe downside of biofuels

Another big issue surrounding biodiesel as a replacement for diesel oil lies in the need for land to grow the plants that can be turned into them.

This results either in the destruction of natural habitats or switching from the production of food plants; both of which are far from ideal.

This also increases the costs associated with the production of biodiesel, which are already significant.

One bright side, however, is that the government has introduced incentives to switch to biofuels, and so the cost is not borne by the drivers.

An additional problem that can be associated with used cooking oil as a biodiesel is that in the cold winter months, it has been known to freeze within the tanks of cars.

Obviously, this is a major drawback to replacing diesel, particularly the further North you travel.

Biodiesel in Cars:

The use of biodiesel is on the rise, and no small part of that is due to the UK’s Renewable Transport Fuels Obligation (RTFO) which necessitates all road transport fuels to contain a proportion of biofuels.

From April 2013 that has been a minimum of 5%. Biodiesel production increased by a factor of four between 2000 and 2005, although in recent years there has been a trend towards the biofuel ethanol compared to biodiesel.

The following car manufacturers have approved their diesel car range to run on 100% RME biodiesel (which is biodiesel made from rapeseed):

  • Volkswagen

  • SEAT

  • Audi

  • Skoda

The Green Car Website is here



Despite its lack of complete carbon neutrality, it cannot be argued that biodiesel is not advantageous to the environment, with carbon emissions being substantially lower than their fossil fuel counterparts.

As an added benefit, you may find it is cheaper to run your diesel car on biodiesel, due to the government incentives to do so, resulting in a win-win for both the planet and you.

Wrong fuel in your diesel car?

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Wrong fuel in your diesel car ?

older diesel engines were more tolerant,  modern diesel engines don’t like petrol but
DON’T PANIC –  this is going to be the hardest advice of all for you to accept –

Yes really do not panic.

Do not drive the car. If you have started it stay calm and switch off
Call a specialist for help to drain the tank and refill with clean, pure diesel.

In this article my advice is based on what I have heard and read about misfueling diesel cars.

If you have never misfuelled (wonderful smug feeling) good!

If you have, try to console yourself that 150 thousand people (and you) per year misfuel their diesel vehicles in the UK!….now read on

Nozzle size matters and yes they are different!

Try to avoid putting the wrong fuel in your diesel car or van by noticing some basic things about the fuel pumps on the garage forecourt.

take the time to look at the difference nozzles that you see on fuel pumps on the garage forecourt

the petrol nozzle (on the end of the filler)  is narrow,  the diesel one is much wider

Yes size does matter.

Usually you cannot fit the diesel nozzle into a petrol car filler;  unfortunately the petrol  nozzle will fit into your diesel car.

What to do if you misfuel

If you do put petrol into a diesel car it is unlikely to cause  any damage if you have only started the engine for  a few minutes
do not top up the petrol with diesel and try to drive. it might end up causing expensive damage.

if you have put in say 40 litres of petrol get a specialist to help you drain the tank….. this is not a diy job

Don’t phone a main dealer – you might get rinsed!

Beware of scare stories some people will tell you. Some dealers have been accused of doing work that wasn’t  necessary…
“If you have misfueld you will often phone your dealership, who will most likely ask you to have the car recoverd to them for “extensive repairs”….. this is normally unnecessary.”

The First thing to do is…….
always consider getting a fuel drain first then decide if any damage has been done

What about alternative fuel?


Biofuel is an excellent idea once again it seems to work better in the older type of diesel engine.
biofuel seems to work better in some engines than others. some diesel specialists claim that it damages injectors and pumps  as well as things like rubber hoses and seals

Red diesel

beware of red diesel it is illegal its leaves a trace in your tank if you are stopped by customs and excise the fine is likely to be heavy.

Stolen diesel

beware of stolen diesel it is often contaminated with water

Diesel engine problems

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Solve your diesel engine problems with these easy checks!

Make Your Car Start and Run Better and Go Further


diesel engine“My car is difficult to start and it seems to have lost power!”

DIfficult starting and loss of power are among  the most common  diesel engine problems people get with their cars.


Check for:

  • Air leaks in pipes and connectors.
  • Pay close attention to air intake pipes, mass air flow meter and turbo connecting pipes.

Check for:

  • Dirty or clogged filters.
  • Diesel fuel is contaminating so regular maintenance is important. diesel engine air filter
  • Main filters to change are Fuel, Air and Oil. Fuel contains impurities so fuel filter maintenance will minimize this.
  • Change oilf filter on a regular basis to reduce engine wear to a minimum.
  • Diesel engines rely on compression to function ; clean top quality oil will keep the engine running at it’s best.

Some engines have extra filters (eg BMW diesel ) check service manual for these.

Check for:

diesel engine injector nozzle

  • Worn and/or sticking injector nozzles. Diesel injectors  give very good service overall but will eventually require replacement.
  • Common rail diesel is quiet and effeicient but is operating at very high pressure so expect to change injectors when mileage passes 100k mark (this figure will vary depending on maintenance, driving style etc. )

Check for:

  • Electrical connexions. Modern diesels are electronically controlled so electrical connexions are very important. Always check for electronic faults if you have diesel engine problems.

Check for:
Problems with the turbo.

  • Modern turbos are under pretty savage operating pressure.

Due to increasing demand for more power from smaller and smaller engines and ever  stricter emission controls turbos are spinning at high revs.

  • They are also under electronic control and this can give problems.

Diesel engine problems often involve faulty sensors or regulators.

Check for:

  • Common symptoms of sensor or regulator failure are engine cutting out regularly and unexpectedly. It will usually start OK.
    Also engine will usually run OK when under load but cut out when no throttle.

If car fails to start EOBD check is best course of action.
Diagnostics will often show fuel pressure sensor/regulator problem.

Diesel engine problems  in older cars involving difficult starting 

Check for:

  • Defective glow plugs. Indirect diesel engines are fitted with glow pluglow plug diesel enginegs for cold start. Difficult starting may be down to one or more defective glow plugs.


Check out

(c) Andy Hewing B.Sc. February 2010

"Don't buy a car fitted with a DPF – diesel particulate filter

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Dont buy any car fitted with a DPF ( diesel particulate filter )

I recently read this on a car forum and it got me thinking……

What is a DPF?diesel particulate filter

Are there any new diesel cars without a DPF?

Why are car manufacturers fitting diesel particulate filters?

If your car has one fitted will it block up or can you prevent that from happening?

Is it possible to remove the DPF and for the car to continue running properly?

What is a DPF?
If your car has one fitted will it block up or can you prevent that from happening?

A DFP is a trap which catches the sooty particulates in diesel exhaust fumes. It’s a filter like a vacuum cleaner’s filter – you have to change or clean it regularly for it to work efficiently.

The modern ones are cleverly designed so that they are self- cleaning ; the soot is burnt off at a very high temperature; above 40 miles per hour (64 km/h)

electronic control unitThe ECU (the car’s ‘brain’) detects when the filter is 45% full and subtly alters the engine timing to make the exhaust hotter and thus burn off the soot.

If not (and high enough temperatures have not been reached ) and the warning light stays on you will need to try and clear it by simply driving for 10 minutes or so faster than 40mph.

If soot levels continue to rise in the filter (mainly due to slow driving) a costly  replacement filter may be necessary

This high temperature is mainly achieved when motorway driving.
What happens to the accumulated soot if you drive mostly in town?
The car has to driven at speed to create an engine temperature high enough to burn off the accumulated particulate.

Are there any new diesel cars without a DPF?
Why are car manufacturers fitting diesel particulate filters?

A difficult question to answer.  According to Wikipedia most 1st world countries have introduced tighter and tighter emissions  controls but no-one has made DFP’s mandatory. But all vehicles will be fitted with them eventually!

Is it possible to remove the DPF and for the car to continue running properly?
Yes it is possible to remove the DPF but you will probably need to have the ECU reprogrammed to compensate.