Thread: CIS fuel head
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Alan L Alan L is offline
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Join Date: Apr 2006
Location: New Zealand
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Thanks for the info guys, I had come to the conclusion this extra part does not belong. The orientation of the union fittings is wrong. The WUR really neeed to be on the other side of the engine. They have rotated it 180 deg.
It had no vac hose hooked on it. So, I'm trying to figure if it is there for the enrichment purpose you talk of, or trying to get rid of this cursed air plate spasm.
I will try and dispense with it and see if we do better. But this will mean getting new fuel lines made up - which will take a while. There will be no union fittings close at hand.
I suspect the WUR is correct - altho I cannot find a part No on it now that it is back in car. Is it on the bottom? It does have the vac nipple going to the plenum chamber - and looks different to my SC one.
I dropped my system pressure by taking all the shims out (there were plenty).
Given it was off scale on my 100 psi gauge, this seemed logical. It seemed to have the effect of dropping the WUR pressures too - more into the range they should be in.
Relax Goran. I am no longer afraid of the fuel head - but there are a couple of tricks to putting it back together. I will post them here - as they are worth mentioning. Do not be afraid to pull it apart - but really most people will probably never have to unless you have a critically badly functioning fuel system. In which case for an hour or two investigation, it may well prove to be useful.
There is an O ring sealing the base of the unit to the air box. This is one of the potential vac leak areas that few probably check. You have to prise the head out of the air box. When I next pull my airbox out, I am going to rechamfer the entry for this unit. The O ring was cut to pieces. I discovered this 10 minutes before the shops closed for the w/end. Rushed into town and managed to get an O ring right on closing time. When I reinstalled mine, I ended up having to pull it off. Again, it has sliced the O ring. So, if you have a vac leak you cannot find - here is one potential spot that would be hard to find. I am going to rechamfer this hole.
I had no leaks after reassembly. The two halves are held together by many torquex? screws. I used the ratchet setting on my cordless drill to evenly tighten them down. I used no sealant. But I also noticed there are no filter screens in any of the inlet banjo fittings. I suspect this is a mistake and they have been removed. Any crap in the system will go straight to the injector, or worse, block one of the tiny metering slits. Good luck on cleaning them - they look about 2 thou wide. I intend to source some banjo screens. They can be fitted with the head in place later.
I had one issue that caused me to pull it apart again, apart from the fact the plate flutter still exists. It pissed fuel out to one cylinder. I could detect the cylinder, so when I lifted the two halves I knew which injector meter system I was looking for. I thought one of the ceramic caps must have dislodged off the spring when I put the two halves together. (Line it up perfectly - do not rotate it later , at all, to get the screws back in housing). But it had torn one of the elongated O rings around the metering slot - on the internal chamfer as you push the barrel back into the housing. It is impossible to see this - the diaphragm gets in the way. I had put one drop of oil shared between the 8 O rings to help it in (This head is made to do 8 cylinders - but for us Porschephiles they have not cut the slits on two of them. Make sure your orientation is right when you put the barrel back or you really will have fun - not sending fuel where it is needed and sending fuel where it is not wanted). I had torn one of the elongated O rings. Luckily I had a spare O ring of the right dimension, so hopefully back OK now. 2 nd time lucky. Other than that, it is not too difficult.
But this unit does function differently to the 911 and textbook CIS scheme. They rely on a constricting orifice between the WUR and the metering piston head for damping. This unit has no such orifice and is in direct full contact with the WUR. It does however have a light spring which sits on top of the metering piston - you can see it in my pic. It sits in the recess in the top of the piston.
I still have no idea why the plate vibrates so bad. It may be this extra piece - because it is a spring regulated diaphragm - so maybe it is setting an oscillation up. My other thought for this Sunday was to make up a clearance fit piece I could push into the union fitting for the WUR at the fuel head. I would drill a small hole in it, thus introducing a restrictor orifice like the CIS manuals normally show. If it did not work, I have destroyed nothing, and could simply remove it. It would not tell me the cause of the problem tho, but may fix it. It may have the effect of slightly slowing the airplate /piston response tho.
But I m struggling with this one.
Thanks for the thoughts. And the Google - saved me trying to deal with Bosch.
Old 12-01-2007, 10:59 AM
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