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| High Fuel Pressure | |
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| Tweet Topic Started: Oct 11 2011, 08:25 PM (1,963 Views) | |
| RogerC | Oct 11 2011, 08:25 PM Post #1 |
Newbie
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Hi I've just joined this forum while looking for ideas with a non start problem. We've been converting a 54 plate 35 Daily to a horsebox . The motor was started intermittantly & then wouldn't. Checked various fuel issues & discovered excessively high pressure to rail. - It turned a 400 bar gauge inside out! It tries to fire up & then I think the excess pressure causes ecu to cut. How is the pressure regulated ? Am I thinking on the right lines ? Appreciate any thoughts / guidance. Thanks Roger |
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| sunbow | Oct 12 2011, 10:05 PM Post #2 |
Member
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Hi, Pressure on common rail is regulated by a solenoid valve positioned in the rear of the high pressure pump and controlled by the engine's ECU. Normally the pressure can be as high as about 1600 bars... Depending on the required load (gas pedal position) and engine parameters (rpm essentially). The ECU calculates a required fuel pressure, compares with the measured pressure (from common rail pressure senor) and acts on the solenoid valve signal (PWM) to make both pressures equal. If this fails, it will signal an error and light up the injector's warning light. The measured pressure on the common rail is used as reference for the ECU to determine the injector's opening duration. Timing is dependent on camshaft position sensor, rpm sensor and gas pedal position. In your case, if the engine fires then stops, the pressure sensor is more likely to give a wrong information (high pressure) to the ECU which in return reduces the injector's opening, cutting the engine out... In this case, the ECU will also act on the pressure regulator to lower the pressure... And decrease further the fuel flow through the injectors... Diagnostic is easy if you can check the ECU parameter with a diagnostic tool. If the measured pressure (through the sensor) is very different form the required one, the ECU might stop the injector's opening to protect the engine... On any case the injector's warning light should light up or flash... In your case, any of the mentioned sensors (camshaft, rpm, pressure) can be defective... The electronic diagnostic tool will tell you which errors are diagnosed by the ECU. Errors history can tell you which one was the first... To go by steps, without a diagnostic tool, the first thing that I would check and replace is the pressure sensor, then the pressure regulator. Cheers Luc |
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| RogerC | Oct 13 2011, 07:22 PM Post #3 |
Newbie
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Thanks for that. Will check as far as I can & see how far I get . Very useful response. Roger |
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