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| Separate quick release coupling -A- (black or black marking) of fuel supply line. |
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| Connect pressure tester -VAS 6550- with cables -VAS 6550/1- and -VAS 6550/2- to open ends of fuel supply line. |
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| Switch on pressure tester -VAS 6550- by pressing On/Off button. |
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| Open shut-off taps „A“ and „B“ of pressure tester and close shut-off tap „C“. |
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| Start engine and run at idling speed. |
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| Read pressure on pressure tester -VAS 6550-. Specification: min. 0.5 bar. |
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| Place pressure tester -VAS 6550- onto windscreen so that it can be read from inside vehicle. |
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| Increase idling speed to 2500 rpm and read the pressure on pressure tester -VAS 6550-, specification min 0.25 bar. |
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| If the delivery pressure temporarily drops, renew fuel delivery unit → Chapter. |
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| If the specifications are attained, check tandem pump to ensure the fuel filter is not blocked → Chapter. |
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| If the tandem pump values are OK, check fuel pump delivery rate → Chapter. |
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