- Citreon C5 HPI 2.0 2001.Excessive lean mixture Archived Message
Posted by Trevor Grigg
on October 10, 2008, 6:10 pm
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Hi all. We have in this citreon C5 hpi that suddenly runs very lean:lambda reading 1.850 combined with 02 level around 12-14% and reduced co2 level.After conducting usual tests we have localised the problem to fuel pressure reducing from approx 85-90 bar to 65-70.at the same time the delivery pressure from the in tank pump remains steady and in spec at 5 bar.To prove that fuel reduction/lean mixture is the cause we have installed a 1.5k resistor in the coolant temp circuit, which has the effect of fooling the ecu into 55deg C constant,thus not allowing the car to fully come out of warm up mode. The results of this are perfect emissions and restored driveability,the fuel pressure remains a steady 90 bar which would rule out a mechanical problem with high pressure pump. We cannot leave the resistor in as a quick fix because the cooling fan and temp gauge becomes inop. With the resistor still in series we have monitored the voltage from the fuel rail pressure sensor, which at idle is stable at approx 2.65v,after removal of resistor car is started, and both pressure regulator and rail pressure are monitored by using two multi meters and both change values together when the fault occurs, which makes it difficult to make a decision on which component could be faulty.We decided to opt to renew the pressure regulator,but this has failed to resolve the problem,I should mention that every time the problem is acute a fresh restart will bring things back to normal for a few minutes. No fault codes exsist,we have also blanked off the egr valve at this stage,does this sound like a possible spurrious signal from ecu to pressure reg,or have we not considered some sensory input signal.Any suggestions would be welcome. Many Thanks. Trevor. |