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Thread: MFI problem in mid range

  1. #1

    MFI problem in mid range

    Help I need some advice with a 72S MFI problem.
    The car has been put on a dyno and it has been concluded that there is a problem with the injection pump. Basically at lo and high rev's the CO levels are ok but in the mid range ~3000rpm it leans right out but the graph is all over the place. The problem has come up fairly suddenly (over a couple of hundred miles but over several months ) so I hope and don't believe that it is a wear problem. About 2000miles ago I had the car on the same dyno and the CO graph seemed fine at the time and the car has been fine until this problem. I have changed the fuel filter and had the fuel pump checked. We have richened the pump right up but it is still lean in the middle. I have been through the links here and found quite a lot of info on MFI's but nothing specific to my problem so if anyone could help I would appreciate it.
    Another question I should ask is about having the pump rebuilt. I am in Australia and one of Pelican's articles mention Walz diesel injection (in australia) as one of the rebuilders of these things. Has anyone direct experience using them?, I have not got positive feedback locally about them and have heard that the recommended coarse of action here is to send the pump to the States to Pacific Fuel Injection. Can anyone give me an idea how much it cost's to do this?.


  2. #2
    Shane, this may seem an odd question, but what kind of muffler are you running? My car had a "flat spot" at around 3700-4000 rpm during my brief fling with a modified "sport muffler". When I returned to stock, the flat spot vanished, the car got a bit quicker.
    Paul D. Early S Registry #8 - Cyclops Minister of West Coast Affairs
    "Now, to put a water-cooled engine in the rear and to have the radiator in the front, that's not very intelligent." -Ferry Porsche (PANO, Oct. 1973)

  3. #3
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  4. #4
    I am running a standard muffler and this has not changed since when the car was running fine. Also my problem is more than a flat spot more like a totally dead spot!


  5. #5
    Hmmm. In that case, I'd suggest checking everything else before pulling the injection. Do compression & leakdown tests to search for internal problems, check ignition & timing, other words, assure yourself that the base engine is fine. This because even the best MFI guy on the planet can only work on the system based on an otherwise good engine. Everything is interrelated when it comes to an MFI engine. As far as shipping & other costs related to Pacific Fuel Injection? They'd know best. Sorry I couldn't be more help. Paul (edit) Here's a link that may give more help...
    Paul D. Early S Registry #8 - Cyclops Minister of West Coast Affairs
    "Now, to put a water-cooled engine in the rear and to have the radiator in the front, that's not very intelligent." -Ferry Porsche (PANO, Oct. 1973)

  6. #6
    I have done all the other stuff except compression and leakdown but the car had a top end done a couple of years ago - pistons and cylinders were in good condition so new valves, guides, rings and the car ran well after that and as mentioned this problem has happened too quickly for me to believe it wore out over a short time unless I have had some failure that I was unaware of that made it wear out quickly. Can anyone tell me if the symptoms I am having can be a sticky rack? I'm not sure how the pump works but could it be that through a certain movement it is getting stuck and maybe trying the carb cleaner trick mentioned in some post's could help me? Also I may be able get my hands on a pump from an 2.4E though I don't know how good it is so can anyone tell me the implications of using an 'E' pump on an 'S', will it work ?

    Shane (is'nt the internet wonderful !!!)

  7. #7
    Everything I've read suggests that the pump internals must be matched to the engine's cam profile. So I don't think bolting an E injection pump to an S engine would be a good idea. Did you visit the link given above? I know it's a LOT of reading...but it's good reading!
    Paul D. Early S Registry #8 - Cyclops Minister of West Coast Affairs
    "Now, to put a water-cooled engine in the rear and to have the radiator in the front, that's not very intelligent." -Ferry Porsche (PANO, Oct. 1973)

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