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Fitting a custom air filter/induction system to a 1.6 HDI...

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Author Post
alfsgc4p   
Mon May 01 2017, 08:59am
Member No: #31280
Joined: Jun 19 2013
Location: London, UK.
If you have a C4 Grand Picasso fitted with a 1.6 HDI at some time or other you will have no doubt shared my frustration with the ridiculously hard to reach air filter and housing, which for some reason known only to Citroen has been sited right behind the engine! 
To greatly improve access to the filter and help keep the going into the Turbo cooler to increase efficiency, I wanted to try fitting my own "after market" air filter to make changing the filter a doddle.  I purchased a nice looking cylindrical air filter housing made entirely of Carbon Fibre.  The filter inside has a built in central cone to help "ram" the air in and it is also washable and reusable.  The inlet and outlet bores are 3" (76mm)...Larger than the standard Citroen air ducts which are about 60mm.  This gives an opportunity to increase performance, whilst reducing fuel consumption.
All I needed to do was to decide where I would fit the new filter housing and what Silicone and Aluminium induction pipes I needed to buy to allow it to reach that location.  I decided to use blue Silicone induction tubing, as it looks great.  There is a perfect place for the filter down by the passenger side of the engine bay, between the battery and the radiator, so that is where I decided to fit it.  (NOTE:  To enable this operation entails the relocation of the MAF sensor.).
The plug on the loom that fits the MAF sensor is connected to very short wires right at the top of the engine...clearly I would need to find an easy way to extend these wires. 
I rang an auto electrician who told me the only way to accomplish this was to cut the wires going to the plug and solder in longer ones...A very tall order when you factor in where the MAF sensor plug is located!   So I decided a plug-n-play option would be best.
  To accomplish this I bought a second hand Ford 1.6 TDCi MAF sensor (It has exactly the same sensor) from a local breakers yard for £20, to provide the socket and I bought a used plug with about 10 inches of loom attached from a breakers up North, on ebay, for about another tenner. 
I carefully cut around the base of the socket by hand with a cordless angle grinder (a hacksaw could be used too, I just couldn't find mine at the time.).  The socket and the sensor block inside then slid out sideways.  I cut most of the sensor "block" off with the angle grinder, about 20mm from the inside face of the socket.  After breaking off some bits of plastic with a pair of pliers, I eventually ended up seeing 11 tinned electrical connector pins embedded in the plastic.  These are what I would solder the wires from the plug onto.  First I had to use my cordless drill and the side of a drill bit to carefully remove as much of the plastic on either side of the pins as possible (A Dremmel would have been better but like the hacksaw I couldn't find mine at the time.).  Some skilful plier and screwdriver use later and I had isolated all 11 pins. 
The MAF sensor plug is only connected to four wires, therefore using a continuity meter I discovered which of the 11 pins corresponded with these.  I then broke off the remaining pins just leaving the four pins required.  I scraped them, re-tinned them and then soldered the plug wires to them.  Finally I wrapped socket connections and the cable with rubber self-amalgamating tape for waterproofing.  I now had my plug-n-play extension cable! 
I wanted the new induction tubing to be largest at the filter housing (76mm bore), tapering down to the 45mm, to fit onto the turbo inlet, as this would help increase the airflow into the Turbo due to the Bernoulli effect. 
The MAF sensor is oval in section with an inlet and outlet size corresponding to round tube of 70mm OD, so needs to be fitted into the system with the ends of slightly "squashed" 70mm bore Silicone tubing and the original oval Jubilee clips.
Between the turbo and the MAF sensor there is the need to provide a connection to the oil mist take off pipe at the side of the head above the turbo.  This was accomplished with a 63mm bore ASH Aluminium T-piece, which has a 25mm OD side branch.  To connect the side branch to the head I used a short length of 25mm Aluminium tube (with the end going into the head wrapped to the correct diameter with rubber self-amalgamating tape) and about 60-70mm of 25mm bore Blue Silicone tube.
I should add the tubes and fittings required have cost be from about £6 up to about £16 each, so fitting this custom filter has not been cheap, but even so, I still feel it was worthwhile as the fuel savings will eventually pay for the conversion.
The fittings I used were as follows:  a 63mm - 45mm 90 degree blue Silicone reducer, a ASH 63mm Aluminium T-Piece with 1" (25mm) side branch, a 70mm - 63mm 90 degree blue Silicone reducer, the original MAF sensor, a 70mm 135 degree blue Silicone elbow, a short, straight through, 70mm Aluminium pipe coupler and a 76mm -70mm 90 degree blue Silicone reducer.
To maximise the airflow at the filter inlet I bought a 3" bore air cone.  I fitted this to some flexible and extendable 3" bore tube (which came with the filter housing).  This enabled me to move the inlet source into the side of the front wing, as with the original setup, this providing a source of cool air.
https://flic.kr/p/UoiMjR
Alf.
 

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