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Thread: Type L SU fuel pump

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    Yoda NutmegCT's Avatar
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    Type L SU fuel pump

    Just wondering if anyone here can advise, or point me to a troubleshooting source, for an SU fuel pump "issue".

    Issue: no more steady tick/clicks - just a fast whirring fluttering sound.

    Thanks.
    Tom M.
    Mac & Phyllis Take a Trip: http://nutmegflyer.com/trip-details-daily-updates/
    History: 1976 MGB, 1959 Triumph TR3A, 1960 Mercedes-Benz 190b, 1958 Rambler American.
    Current: 1953 MG TD27318.

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    Yoda
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    Re: Type L SU fuel pump

    The SU fuel pump uses a reinforced rubber diaphragm activated by a solenoid body; i.e. it's essentially a piston, with one-way flapper valves to force the fuel in the proper directions. The most common failure is in the electrical switching mechanism, which is usually a set of contact points but modern versions use solid state switching. I can't imagine how one could make a whirring sound, but they can fibrillate (flutter). They aren't terribly difficult to repair, or you can buy new from the usual suspects. A third option is to send to an expert for a rebuild; Dave DuBois has fixed several for me, and he can install an optical switch which should outlast points: http://userwebs.donobi.net/sufuelpumps/ (NFI).

    But, before you buy or repair, make sure the plumbing is in good nick. An air leak, esp. on the intake (tank) side can cause the pump to run rapidly, and reduce fuel flow.

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    Yoda NutmegCT's Avatar
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    Re: Type L SU fuel pump

    Bob - thanks for the advice.

    It's certainly possible the diaphragm needs replacing. I'll need to remove it to see if it's the 3" long, or 2 3/8" long part.

    Could you advise me how to remove the old one without breaking something? Do I just carefully lift the lip of the diaphragm, and grasp it and unscrew it? Or are there internal parts (bearings, springs, retainers, etc.) that might come flying out?

    Here's what the current diaphragm looks like.

    IMG_0046.jpg

    Thanks.
    Tom M.
    Mac & Phyllis Take a Trip: http://nutmegflyer.com/trip-details-daily-updates/
    History: 1976 MGB, 1959 Triumph TR3A, 1960 Mercedes-Benz 190b, 1958 Rambler American.
    Current: 1953 MG TD27318.

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    Yoda
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    Re: Type L SU fuel pump

    Hoo boy ... that diaphragm is shot. My guess is ethanol got to it.

    Yes, you can peel the edge of the diaphragm away from the pump body. The diaphragm has a shaft--as you say, 3" long, or 2 3/8" long (not sure which pump uses which)--that is screwed into a threaded trunnion on the points throwover mechanism. You can just rotate the diaphragm--counterclockwise--to unscrew it from the points, but you probably would have a bit of trouble getting the shaft and trunnion lined-up for the new diaphragm shaft. I think, given the poor shape of the diaphragm, you should pull the cap off the end of the body and have a look at the points; at the least, you'll probably want to file and adjust them. The adjustment process varies with models, and I only have the procedure for Big Healeys. Also, the quality of aftermarket points sets was suspect--China or Taiwan--last time I bought a set from the Usual Suspects, so you'd want to go to a source for genuine SU parts. There should be a paper gasket between the diaphragm and the pump head (where the valves are).

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    Yoda Randy Forbes's Avatar
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    Re: Type L SU fuel pump

    Unless you're building up your car for concours showing__or you're a masochist__why bother with an original fuel pump at all?

    I fit one of these about thirty (>30) years ago, and as of yesterday when I last drove the car, it's holding up just fine.

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    Re: Type L SU fuel pump

    Although I don't disagree with Randy on the cost benefit of purchasing a Facet pump over that of an SU, I have had my original SU pump running strong for the past 52 years with only minor issues. I am not sure that I agree with Bob and believe your diaphragm appears to show some contaminants from your fuel that may have caused the pump's valve to stick open. Fuel agitation as a result of the open valve could be the source of the whirring sound and could be blocking the tick and eliminating delivery.

    I would clean out the pump and readjust for good flow. Additionally, if you have a points-triggered pump, I would clean the points and remove any electronic component connected to the points (SU placed diodes across the pump points to eliminate point flash but it didn't work all that well). I would then install a Transient-Voltage Suppression (TVS) Diode that will eliminate point flash and burn to make the points last almost forever.

    As most are unaware, the SU pump depends upon a coil for operation. Many have not realized that this coil has the potential of raising voltage across the points to as much as 200 volts and is the primary cause of point flash and/or burn. A P6KE20CA TVS (manufactured by Vishay), at a cost of around $1.00 or so, will allow up to 27 volts to pass across the points and shunt to ground anything above. The 27 volts is sufficient to burn off point corrosion formed during long periods of inactivity and/or storage but well under that needed to cause point flash or burn. As a result, I have found no need to replace points or do any maintenance on my pump since installing

    Yes, if you are going to replace your pump, the Facet pump is both reliable and much less expensive then a new points or electronic SU pump. However, I would first consider seeing if I could service the SU pump back to performance before a replacement.

    Just my thoughts,
    Ray(64BJ8P1)
    Last edited by RAC68; 12-05-2017 at 06:10 AM.

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    Re: Type L SU fuel pump

    Writing just to say that I found Randy Forbes' comments (and accompanying photo/website reference) on using a facet fuel pump to be a good alternative to the SU fuel pump, in the event of failure. There seems to be such a science built around fixing/servicing your old one (note Ray's (RAC68) explanation of the electronics), not to mention the various codes for the multitude of SU fuel pumps out there. Notwithstanding the general reliability of SU pumps, I quite agree that the simplicity and cost of the facet pump makes it a worthwhile consideration, particularly when electronics happens to be your Achilles heel, such as in my case.

    DB

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    Re: Type L SU fuel pump

    From the online patent drawings, both the cylinder and box Facet pumps have no diaphragms so should be most reliable. The one Randy uses is for >150hp. The gold box for <150hp.

    Since I've never run an SU, am not captivated by the "romance" of them.

    My car came with a plastic German aftermarket pump which performed erratically.

    screenshot.1051.jpg
    Steve Gerow
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    Jedi Knight Healey Nut's Avatar
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    Re: Type L SU fuel pump

    Quote Originally Posted by Randy Forbes View Post
    Unless you're building up your car for concours showing__or you're a masochist__why bother with an original fuel pump at all
    Just buy a solid state SU install it and be done with it . Find something else more worthwhile to tinker with .
    "If it aint broke ....dont fix it "
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