Air is collected and pumped into the check valve heads by the twin vane air pump into a rubber supply hose that interconnects both air check valves. At the same time the electrical solenoid controlling the check valve vacuum is energised, allowing vacuum to pull open both diaphragm caps. On start up from cold the secondary air pump relay ‘N’ is commanded to close, this applies voltage to the air pump DC motor protected by a 40A fuse, Fuse 31. It is worth noting that it takes faults to be detected on two engine start/run cycles for the engine management lamp to illuminate on the dashboard.īoth control relay and fuse located in right hand fuse board. Here is some info on the conditions that are required to be met for a check to be made by the ECU/ECM. ![]() What happens at a variable point during the drive cycle when certain engine conditions and running criteria are met, is that the secondary air pump is cycled for a short burst, check valves are opened and the ECM monitors and compensates for a change in the O2 levels measured in the exhaust gasses. People have wrongly assumed that the secondary air system only operates at start up, this is not strictly true. It will prevent any electrical current flowing to the secondary air pump and it will also prevent the air check valves on the exhaust manifolds opening with the possibility of allowing exhaust gasses to exit via the disabled air pumps delivery pipe. This will accomplish two things until you get chance to repair the system, although please note it will not extinguish the engine check lamp. ![]() The way to disable the system is to remove and plug the single vacuum outlet (the base of the clear thin pipe to the left in the picture above) from the control solenoid to the air check valves, one either side of the v6,v8 and v12 variants, then simply pull the control relay from the right hand fuse board in the engine compartment. Air pump mounted between the ‘V’ of the cylinder heads at the front of the M113 engine
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