I am struggling to find a direction to go on this one. The car will occasionally cut out completely under hard acceleration. The glow plug light comes on & it shuts down totally. The fault code is P0234 & here is the snapshot from IDS....
I have managed to re create the fault in the workshop with the scope connected, although it doesn't seem to suggest an overboost condition. From cold it will rev perfectly, but when its hot, it will start to misfire at maximum revs & randomly cut out again.
Here are the captures (details in the notes at the bottom)
Looking at the captures, it appears that the rail pressure goes a little erratic as the misfire occurs. The inlet metering valve can be seen to shut the fuel off moments after a peak in fuel pressure.
The DTC seems to point toward an overboost situation, but the captures seem to show that the boost pressure remains constant as the fault is logged. I have heard about problems with the intake flap causing similar problems, but this car hasn't got one.
Any experiences anyone?
Cheers for now.
Dave
Re: Ford Focus 2004 P0234
Posted by Tony Ludford on January 7, 2009, 11:29 pm, in reply to "Ford Focus 2004 P0234" Tony Ludford
I hadn't really considered EGR too much to be honest. It feels more like a single cylinder misfire when the fault occurs & not like the general all cylinder power "flutter" that you would usually associate with an EGR problem.
Well worth a look though!
Thanks
Fixed #
Posted by Dave Hill on January 19, 2009, 8:48 pm, in reply to "Re: Ford Focus 2004 P0234" Message modified by board administrator January 20, 2009, 8:10 am
Evening all.
Cutting a long story short...
After replacing the crank sensor, the stalling fault never returned. I was left with a horrible "stumble" under hard acceleration at high revs.
With some road testing with the scope hooked up there was some evidence to move forward....
It can clearly be seen that the MAP sensor nor the MAF are generating a signal that might cause a PCM response. However, the rail pressure sensor signal (in blue) is seen to be the first to show any shift from the norm. The increase in the inlet metering valve current is the PCM taking counter measures, to keep the rail pressure in check.
So with that in mind, I decided that a new inlet metering valve would be a sensible move. Sure enough, several days later with many extended road tests done, it has been faultless.
Just as a matter of curiosity, I noticed something in the CKP waveform that gave me cause to inspect the 18th gap in the flywheel reluctor ring. sure enough there is an odd shaped hole punched, as seen in the following images.......
.....
On another scope capture I have taken, it can be seen that the 18th hole lines up quite nicely with the firing event on injector one (cylinder one ). Can anyone shed any light on what the purpose of this is?
Anyway it is fixed.
Thanks for reading
Regards
Dave
Re: Fixed #
Posted by JOHN COOKE on January 20, 2009, 8:08 pm, in reply to "Fixed #" John Cooke
THANKS DAVE AN EXELENT POST FULL OF GOOD INFO CHEERS JOHN COOKE
Re: Fixed #
Posted by Martin Kelly on January 20, 2009, 9:55 pm, in reply to "Re: Fixed #"
Hi Dave, thanks for the interesting post. I am fairly new to CRD so could you explain the finer points of the inlet metering valve fault please. But if if I was to get shot down in flames...is it because the metering valve is slow to react to the fuel pressure change, is the metering valve sticking?
Thanks, Martin.
Re: Fixed #
Posted by Dave Hill on January 21, 2009, 5:53 pm, in reply to "Re: Fixed #"
Hi Martin
I am by no means an authority on this topic, but here is my understanding.
The inlet metering valve controls the low pressure flow into the high pressure pump. It is a frequency modulated (modulated is a posh word for controlled) device that when fully energised will strangle the fuel flow into the pump. Conversely when it is unpowered (or you unplug it) the valve opens fully to allow maximum fuel throughput.
If you look at the third image down in my first post, you can see a sharp rise in the red signal, briefly after a small peak in the blue signal. This red signal, is the inlet metering valve current & what you are seeing is the effect of the management system fully energising the valve, so as to strangle the fuel flow. This is done as a response to the peak on the blue signal, which is fuel rail pressure.
As for what is actually wrong with the inlet metering valve, I am not sure, but I suspect it may have been sticking or maybe operating at the extreme end of its working tolerance.
Another common type of pressure control solenoid seen on various systems, is a unit that will regulate the high pressure outlet from the pump & these work in the opposite way to the inlet metering valve. By that I mean that when they are fully energised by the management system, the fuel pressure is increased to maximum. A bit like sticking your thumb over the end of a garden hosepipe. The harder your press, the higher the pressure developed. When this type of solenoid is unplugged, instead of developing maximum pressure, it will default back to approximately 50 – 60 bar. This default pressure is created purely by a small spring that presses a ball onto an orifice, to stem the flow. (Remember the inlet metering valve works the opposite way & strangles the fuel flow when fully energised).
There are other types too, but I don’t want to bore anyone to death (any more than normal anyway )
I find the oscilloscope very useful for helping me understand how each system operates. By looking at the controlling current, duty cycle or even frequency I can tell how the fuel pressure is regulated on the various setups. This doesn’t make me an expert, but it certainly helps me understand what is going on & makes things a little less mysterious. The one thing that does leed to much confusion I think, is the varied terminology & abreviations used to describe these control valves. MPROP, VCV, IMV, FPS etc etc.
HTH
Dave
PS If I have any inaccuracies in my comments, please feel free to take the pi**
Re: Fixed #
Posted by Tony Sefton on January 21, 2009, 6:21 pm, in reply to "Re: Fixed #"
Hi Dave. I don't know if This System is Different, But The Bosch Systems on most popular cars works the Opposite way to what you Describe, i.E No current flow = no pressure, full current = full pressure, i would expect this to be the norm ( fail safe ) as otherwise if the system got a bad connection, the pressure could go sky high. ??
I know this to be fact on peugeots as i have Applied 12 volts straight into the DRV and got full pressure. ( Regularly )
Could the Lift in Rail pressure slightly after the raise in current flow be the result of the ecu turning the power up. ?? and then the drop off in pressure be caused by the fault IMV. ??
Tony.
Re: Fixed #
Posted by Dave Hill on January 21, 2009, 7:40 pm, in reply to "Re: Fixed #"
Hi Tony
>>>Hi Dave. I don't know if This System is Different, But The Bosch Systems on most popular cars works the Opposite way to what you Describe, i.E No current flow = no pressure, full current = full pressure, i would expect this to be the norm ( fail safe ) as otherwise if the system got a bad connection, the pressure could go sky high. ??<<<
Yes the inlet metering valve on the Delphi system that most Fords have, works in quite the opposite way to the Rail Pressure Solenoid that you mention. The second example in my post, refers to the Bosch type that you are commenting on.
I agree that it sounds odd that a circuit failure on an inlet metering valve will drive it to full system pressure, but trust me it does! (hardly fail safe hey ) But in reality the PCM will see any excessive pressure & respond, by closing the inlet metering valve (by powering it up)
To clarify....
Delphi Inlet Metering Valve with full current applied = no fuel flow.
Bosch Rail Pressure Regulator (DRV) with full current applied = max fuel pressure.
The simplest way to confirm these strategies is to quite simply unplug the valve in question, (with engine idling) whilst scoping the rail pressure sensor & observe the response. If you unplug the inlet metering valve (Delphi system) with the engine at idle, the rail pressure goes sky high.
As a side note. On the Delphi system that Ford employ, when the engine is turned off, the inlet metering valve is energised fully, to strangle the fuel supply to the high pressure pump, then the injectors are fired rapidly to "vent" the fuel pressure away. This is the high pitched buzzing or whining noise that can be heard when you switch a Mondeo TDCI off.
Cheers
Dave
Re: Fixed #
Posted by lee mackintosh on January 21, 2009, 8:34 pm, in reply to "Re: Fixed #" Lee Mackintosh
Thanks Dave Hill,
this topic has been an interesting one and with a good description of how each type of pressure limiting valve works. It has certainly helped me out as the bosch common rail diesel book i have is a little vague in its description.
Re: Fixed #
Posted by Dave Hill on January 21, 2009, 11:07 pm, in reply to "Re: Fixed #"
Thanks Lee
But don't place too much credence in my comments. If the likes of "Sir" Tony Sefton can question what I am saying, then it needs to be debated, before you should take my word for it.
Cheers for now
Dave
Re: Fixed #
Posted by keith geach on January 22, 2009, 8:06 am, in reply to "Re: Fixed #" Keith Geach
IMV will fail open ie no current = full pressure Mprop will fail closed ie no current = around 80 bar denso and siemens can vary. Later bosch mprop systems can work either way. So in other words you need to know which one you are working with.
Re: Fixed #
Posted by Ben-Zion Zarfati on April 30, 2011, 9:09 am, in reply to "Fixed #"
Dave,as all were satisfied with your diagnose and solution -also, I must say - Thanks a lot! I got the same DTC with Skoda Octavia II 1.9l TDI BXE engine with the DSG AT - and I replaced the all things that were involed - like Engine ECU,Vacuum Box included,(N75 N18 & N345),vacuume lines,Turbocharger with the all EX manifold - and after every road test I got it again - it's start well,drove in first gear,second gear VSS - about 80Kmh and no more gear changes - but when I leaved the gas pedal it's change the gear to D3 but the ECU was in this time in limp on... I searched around the world for such an experience - but nobody put it's finger and said more than I wrote - when I read your experience and with your Ford Scan tool - I saw the last line...and for me it was the Fixed - as we all are saying...I replaced the Mechatronic and done the road test about 3-5 times and - no more P0234!!!(the gears were change correctly and in time...). Always I said as FORD/MAZDA sub dealer(in the past) - the WDS and the new scan tools - were very friendly in such DTC's - more lines with possible causes!!! Thanks again - Dave
Re: Fixed #
Posted by james McCallum on April 30, 2011, 1:50 pm, in reply to "Re: Fixed #" James McCallum
Hi, Dont know if this helps understanding. The new Hyundai system is using Bosch 3, it has inlet control only, which means a voltage is required to give full pressure and no voltage shut down. The bosch 2 system had inlet control which was open with no voltage but the rail pressure regulator controlled the finer tuning, so this was teh failsafe. Frnak massey gives a good example in one of his videos when he is using s bit of kit to control pump pressure indfepend of PCM. Hope this is of help. Jim
on January 7, 2009, 11:29 pm, in reply to "
.....
). Can anyone shed any light on what the purpose of this is? 
) 
can question what I am saying, then it needs to be debated, before you should take my word for it.