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Discussion Starter · #1 ·
been having problem with my 2008 crd srt design
engine management light comes on also etc light ...car was going into limp mode used code reader and code p0088 high fuel rail pressure fault came up
cleared codes comes back again and car shuts down ..when i check fuel rail pressure it goes all the way up to 47000..anyone any ideas or know what the fuell rail pressure should run at.or what part could be faulty..is there a regulator or solenoid .........:17:
 

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43000 pressure is much too high.

Fuel pressure will typically be just below 4000 psi at idle and about 23000 psi under max acceleration.

Could be:
Fuel Pressure sensor giving wrong info to ECU
Contaminated Fuel
Air in Fuel
HP Fuel Pump
Fuel Pressure Quantity Solenoid
Fuel Pressure Solenoid

Its a long list and a case of deciding which way to go.
If you have a code reader or access to a code reader you could start by reading the fuel pressure when the ignition is set to "Run" but without starting the engine. This will allow the electric pump to prime the system before the mechanical pump runs. The code reader would then be able to read the fuel pump pressure which should be around 150psi (or thereabouts, not critical). This would basically prove the Fuel pressure sensor is not giving out a permanently high output.

Would probably be worth checking for chaffed wiring in the engine compartment in case the fuel pressure sensor wires are chaffed and giving a permanently high output. 43000 is very high though so I would suspect chaffed wires or a faulty pressure sensor.

Just read that you have a code reader.
Connect it up and read pressure without starting engine. Should be low (about 150psi)

Jack
 

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Discussion Starter · #5 ·
thanks ..tried conecting code reader when ign on gives a reading of 5710kpa or 828 psi so it looks like its giving a high reading before mechanical pump kicks in ...any idea where the sensor is there seems to be a sensor on each fuel rail front of rhs and rear of lhs looking from front of car ..please can anyone help...does anyone even know what mercedes engine this is so i can source parts
 

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The Fuel Pressure Sensor is on the RH fuel rail at the end nearest the windscreen (RH when sitting in the car).

If you have a voltmeter you could check that the 5Volt supply on pin 3 is actually 5V and not something greater.
Also check pin 1 has good continuity to chassis or has zero volts on it.

See drawings attached.

You have to be very careful working on the fuel system on modern diesels the pressure can get extremely high.
Engine is an OM642 but not sure which version.

I would not be certain its a faulty sensor though because the reading has not stayed at the very highest value measured. The fuel pressure solenoid would be worth a check. Ideally the fitting of a temporaray mechanical pressure guage would confirm if the pressure sensor is faulty or not.

Jack
 

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Discussion Starter · #7 ·
thanks jack...certainly will try that ..one last thing i tried..i unplugged the fuel pressure sensor this gave a reading of 33000 kpa when unplugged took the car for a drive and drives fine not going into limp or shutdown and shows no fault codes......any further thoughts would much appreciated
 

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thanks jack...certainly will try that ..one last thing i tried..i unplugged the fuel pressure sensor this gave a reading of 33000 kpa when unplugged took the car for a drive and drives fine not going into limp or shutdown and shows no fault codes......any further thoughts would much appreciated
 

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thanks jack...certainly will try that ..one last thing i tried..i unplugged the fuel pressure sensor this gave a reading of 33000 kpa when unplugged took the car for a drive and drives fine not going into limp or shutdown and shows no fault codes......any further thoughts would much appreciated
You could have left the code reader plugged in to monitor the fuel rail pressure while driving.

Have someone in the passenger seat looking at the reader and shout out out the pressure. Drive at a steady speed and have them write down the pressure. Accelerate hard and write down the pressure. (This is assuming your reader hasn't the capability to draw a graph)
As said before should be about 4000psi at idle and 23000psi accelerating hard.


There is an APP for Android phones called Torquepro but you also need an ELM ???? electronic device to plug into your OBD socket to get the readings to the phone. This app is very good and gives you graphing capabilities.

I would definitely check wiring for chaffing as well though. But to get your problem the 5V supply would have to short to the sensor wire on Pin2 which is unlikely. The shorts on 300C's are usually to chassis.

Jack
 

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Discussion Starter · #10 ·
thanks again jack im going to try fuell pressure sensor and fuel pressure solenoid ...just waiting for delivery ...thanks for your help will let you know how i get on
 

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thanks again jack im going to try fuell pressure sensor and fuel pressure solenoid ...just waiting for delivery ...thanks for your help will let you know how i get on
The Fuel Pressure solenoid is only supplied as part of the LH Fuel Rail. Could be expensive ?? Did you get a price ?


Jack
 

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How have you proved the pressure sensor is OK ?

You do need some means of monitoring the fuel pressure and analyzing the results.
Problem can sometimes be caused by:

1) Air in the fuel system causing spikes in pressure
2) Fuel Pressure sensor
3) Fuel injector or injectors
4) Fuel pressure solenoid
5) Fuel Pump
6) Fuel system contamination causing spikes in pressure.

You should also checked for chaffed wires round engine bay, especially at the RHJ rear of engine when viewed from front: around the air conditioning pipes.

BUT you must have some means of measuring the pressure. Even if its just an OBD reader.

jack
 

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Its difficult to tell, and I am no expert, but the video does not help much because the accelerator is being pressed too often and it doesn't give a chance to see how stable the pressure control is.

I assume there are no other error codes ?

The ECM sends a signal to the pressure control system and tells the system exactly what pressure to deliver. If the pressure spikes by more than about 7Kpa it will set the code P0088 which you have.

The pressure range on your video looks about right so it is just the specific pressure that is not being regulated accurately enough for some reason. Its difficult to check the control on the video because the accelerator is being operated too much.

It could possibly end up being the:
Fuel Pressure Solenoid or the
Fuel Quantity solenoid.

These are usually checked by replacing them as they are difficult to prove.
 
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