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308 168gr hornady with IMR 4320 - Optics

Posted by Soon Herbst on


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Tony Parsons

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  • Optics Master
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At Last !!!!!

I have been waiting for someone to say this for absolutely ages ! Well done and thank you.

BTW, what does it mean ?

Posted on Jul 10, 2019


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IMR - Inlet Manifold Runner valve

1.10) IMR- Inlet Manifold Runner valve (actuator)

What is it? The inlet manifold consists of a plenum chamber onto the front of which is mounted the throttle . Extending from the plenum is a series of moulded pipes called 'runners' curve round to the intake ports on the cylinder head. In some instances there are two intake ports for each cylinder fed by slightly different lengths of runner. When the engine is at low revs the longer pipe works well. However at higher speeds the shorter length of the alternative runner is better suited. To cater for this the shorter port, which is normally shut off at low engine speeds by a plate (very similar in operation to the throttle plate), is opened by a motor or solenoid. The shorter runner is usually opened in addition to the longer runner and not as a substitute. The opening of this additional shorter runner is done by the IMR.

Where is it located? The IMR valves are located in the throat of each inlet port and the controlling motor is located at the end of the interconnecting shaft.

How does it work? At a predetermined engine speed (>3000rpm) the ECU sends a voltage to the IMR that snaps open the additional inlet portsto boost power output. It does this by either a) directly with an electrical motor or b) it opens a solenoid valve and allows vacuum, sourced from the inlet manifold, to act on a diaphragm to rotate the valve shafts.

Symptoms of a faulty IMR
Associated OBD2 error codes DTCs: P1500 - P1599

  • Power reduction - If the IMR fails to open in the upper rev range the engine will seem to lack any (power) 'head-room'. The engine will still operate but the usual additional power boost in the upper rev range will be absent.

How to Check? Visually check the action of the action of the actuator in response to increasing engine speed.

How to Fix? Check the wires and connections. If the device uses a vacuum, check the tubing for leaks. If the IMR unit is faulty replace it.

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