109 Fuel Boost Diaphragm

Diaphragm-splitThe RRC already had an issue with the fuel injection pump not responding to turbo charger output before it came off the road.  that was recently sorted out, as per a previous post (stuck pin at the base of the boost plunger).  Well, the 109 has had similar symptoms since before the turbo failed; a progressive reduction in performance and a cleaner exhaust under load.

200-boost-diaphragm-(2) While I had initially suspected the turbo itself as the cause, given its complete bearing failure and significant rotor and casing wear, the new turbo only partially restored performance.  While it was driving generally satisfactorily, acceleration seemed a little sluggish and it was having trouble maintaining speed in top gear on long, steep hills.  It also lacked any trace of black smoke at full throttle, which in itself is no bad thing, but is an indication of under-fueling.

200-boost-diaphragm-(3)200-boost-diaphragm-(4)The cause was very simple to find, as it had to be boost related and I could easily hear the new turbo spooling up.  First inspection of the boost pipe to the injection pump passed muster, so the next candidate was the boost diaphragm , which turned out to have a small hole.  A temporary repair with Tiger Seal PU adhesive did the job perfectly until the new diaphragm arrived.  Swapping them is relatively simple – the top cover is removed by undoing the four slotted screws, the diaphragm and plunger lifted out after noting the position of the stamped dot on the top washer, and the plunger diaphragm stack disassembled for replacement before putting everything back in the same orientation.  At least the plunger lifted out easily this time, unlike on the Range Rover’s pump, where the stuck pin was locked on the bottom lip of the plunger.

At just over £20, I’m a bit surprised at the cost of the diaphragm, but at least I avoided any labour costs.

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  1. Hi Nick,

    Happy to hear that the Tiger Seal repair held up until you got the new diaphragm fitted. I love that stuff, so versatile!



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