PicoScope 7 Automotive
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STC I have been looking at the low system fuel pressure sensor fitted to this model, its the same as they fit on some of the BMW diesels, the part number of this fuel pressure sensor is Bosch 0261 260 046, I am kind of leaning towards this sensor being a MAP sensor that seems to be able to cope with pressures between 0.3 - 4.0 bar. You referred to the testing of this previously where I advised that the supply voltage was 5V, the ground terminal number 2 was 0V, and the terminal 3 was about 2.5V and dropped to about 1.7V when the engine was revved up. AD advise that the terminal 3 with the engine at idle should read 4.3V, they don't however advise if this reading should increase or reduce when engine revs are increased, but based on MAP sensor understanding the voltage level normally increases at WOT, and this sensor is reducing voltage at WOT, and fuel pressure would normally be expected to increase when the engine is revved up.STC wrote:Andrew.according to auto data injector nozzle opening pressure is 250 bar
I didn't see that on Autodata, I'm under the impression that this is Common Rail ?
Me neither, it is Common Rail version 4.0. The last time I had this vehicle in from the FRP sensor using electronic test equipment, the rail pressure static was 3.50 Mpa, and when engine idling was 36.70 Mpa.
Technician
Wouldn't be a bad idea to test LP fuel flow & pressure before you go anywhere near the HP side.
Once that is confirmed, Are you able to monitor Actual & Desired FRP on your scan tool ? and as above monitor LP with a gauge.
On AD, there are 2 variations for that Reg No, the first one distinctly shows 2 fuel pumps - just 2 add to the confusion.only a low pressure supply pump on the side of the fuel tank along with the filter.
As above confirm pressure and flow on the LP side first, then move on.
I will look in Topix and report back if I find something.
I think that is either a mistake or they refer to Minimum pressure required before firing injectors..??I thought it was common rail as it has a fuel rail pressure sensor but under specs it has nozzle opening pressure 250 bar which i thought was strange
just checked it defiantly states common rail and nozzle opening
That pump is switched by a relay, not Duty or PWM so I would expect it to remain at a constant ~2.6bar at Idle or WOT. Pressure control will be a mechanical regulator within the pump assembly or upstream of it but before the HP pump, perhaps within the filter housing ???they don't however advise if this reading should increase or reduce when engine revs are increased,
That is what is throwing me. (I have only ever seen NTC Temp sensors work backwards)but based on MAP sensor understanding the voltage level normally increases at WOT, and this sensor is reducing voltage at WOT
As above, if anything fuel pressures may drop slightly (on the LP Side) at times of high demand but still within the +/- 0.2 bar tolerance. The IMV and HP pump combination will take care of increased pressure requirements in the rail. As long as the IMV & HP Pump are fed correctly.and fuel pressure would normally be expected to increase when the engine is revved up.
Indeed, that's the way pressure sensors work, certainly the majority I have come across, that would be Air, fuel, hydraulic ...... I believe you do have it correct. Now I think that may be wrong information. I would expect to see 0.5v Ignition On pump NOT running as a plausibility check for the ECU then maybe something in the region of 1.1v to 3v with pump running dependant on how it is calibrated. At any engine speed if my theory on this set up holds water - this is not a demand controlled pump ??if you think of the map sensor as a standard 5 volt pressure sensor
in a manifold its under slight vacuum with throttle closed = low voltage
throttle open pressure rise = voltage rise
Andrew, I understand the above, but my thoughts initially with the pressure sensor voltages thought it was faulty with the voltage dropping, but when I disconnected the three pin plug from the pressure sensor the engine ran OK. The fuel pump at the time of changing the sensor for the second hand one did have just over 2.6 bar as I remember it, but now the fuel pump pressure is running at 3.47 bar, so I don't think I have a low pressure problem, although the low pressure circuit is now operating too high, this is a problem, but not a low pressure problem if you see where I am coming from, and just commenting on STC's point about 4.3 volts setting a fault code, I don't think from resent experiences with this vehicle that would happen, the reason being I linked terminals 1 and 3 together thus providing the ECM with full 5V, the engine produced no fault codes and I did drive it a good distance to see if the code P1260 would return and it never did, not even now with high fuel pressure and the current P1190, referring to the common rail being high pressure. Obviously the link wire was removed.andrewbishop66 wrote:Hi All
if you think of the map sensor as a standard 5 volt pressure sensor
in a manifold its under slight vacuum with throttle closed = low voltage
throttle open pressure rise = voltage rise
in the fuel pump situation
at say 2.5 bar = 4 volts
open throttle pressure drops in the feed system = voltage drop
If that is the situation with this one if the sensor is good and the voltage is dropping I would say the pump cant deliver enough fuel volume to maintain 2.5 bar
Please someone correct me if i have it arse about face
Thanks Andrew
Working on the Td4 tomorrow, will see what happens about the strategy of the code. I never thought about this important point when testing the fuel pressure, but on the low side from the pump can I use my 014800 sykes fuel injection pressure test gauge?andrewbishop66 wrote:It is a strange one be nice to know the strategy for the fault code
good luck
Andrew