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MG MGB Technical - Solid State conversion on SU pump

Has anyone done the solid state conversion to thier SU fuel pump? I see it is available from Burlen Fuel Systems. If so, is it easy and is their anywhere else to buy it from?

Thanks,

Tim
tim

Tom,
I think you may find that the jury is out on SU electronic pump reliability at the moment. My own experience has certainly not been convincing. At £33 this conversion seems expensive. Bearing this in mind I'd be inclined to replace the points and perhaps the pump will live for another 30 years !!
Iain MacKintosh

Unfortunately, the pump is only 2 years old and has 5,000 miles on it. I'm not sure why it is acting up. Maybe just a bad set of points. I'll be checking my wires to make sure I'm getting proper voltage to the pump.

Thanks,

Tim
tim

A two year old pump should be fine. Check to make sure you have the vent pipes installed otherwise dampness will get in and the internals will deteriorate.
Iain MacKintosh

I put one on ( bought an exchange pump with it fitted) about 4 years ago, (maybe longer we were on our way to an AWC event in the Morelands Brewery , and thats been a housing estate for four years.) So far , so good.
S Best

I agree with Ian that the Burlen Fuel Systems conversion kit is rather expensive. That said, I put on on the pump in our MGB to see how well it works. If it is properly installed and adjusted, it works very well and is somewhat quieter than the points style pump. It (or any solid state conversion) is especially useful on pumps used in cars that are not driven year around in that there are no points to film over and stop conducting current from disuse. Cheers - Dave
David DuBois

Hi all.

In my personal opinion the ultimate solution may be transistor assisted contacts.

If the original points are used to drive a transistor (a power MOSFET would be even better) it removes the current load from the points while leaving them in place so that the pump could be switched back to 'standard' should the transistor / MOSFET fail.

A three-way switch (conventional points / transistor assited / off) could even provide theft prevention.

Has anyone tried this ?.

Don
Don

Don - Many people have used transistors controlled by the points. I did it for many years until I realized that, with the new alloy used for the contacts on today's points hade a greater propensity to develop an insulating film. This has always been a problem with the points on pumps in cars that are seldom driven, but as long as the cars are driven and the pump is operating, the current through the points keeps the film burned off of the contacts. The problem that I was experiencing was that the base circuit of the transistor draws so little current that the film didn't burn off and eventually stopped the pump from running (a case of unintended consequences). I finally resorted to replacing the upper points with a magnetic reed switch and a magnet glued to the lower toggle in place of the original contacts to drive the transistor. This has eliminated all problems associated with the points either burning or filming over. Interestingly, on some of the original pumps that I transistorized nearly 30 years ago and just filed down the original points are still operating just fine today. It is this information that has led me to believe that the points today use a different alloy in the contacts, one that is more prone to film over. Cheers - Dave
David DuBois

The thought of all those extra connections and wiring into the pump fills me with horror.

People *have* used the fuel pump as an 'immobiliser' simply by adding a switch in the white circuit where the main harness joins the body harness by the fusebox. Quite a good idea, as in most cases it will allow the car to be started and run a few yards before it conks out. A tea-leaf would have to be pretty brazen to then try and get it going again with the car probably causing an obstruction or at least in public view.

I can confirm David's findings, Telcos have (or maybe had) special circuits to pass a significant current through contacts that otherwise would switch only a microscopic current or they developed an insulating film.
Paul Hunt 2

Tim,
http://www.mgccq.org.au/tech4.htm
article on page 4 of tech tips
this might be of interest not sure if its what you want - DIY.
Gordon

GORDON

Gordon - That article is my original article from about 25 years ago, published in our local newsletter. That is the transistor modification that I spoke of in my earlier post. Can you put me in contact with the webmaster for that web page, I would like to get that article either removed or changed as the directions have some errors in it and the final result is that the modification may or may not work as intended.

It has been interesting to me that this article has appeared in so many different publications over the years. Thank you - Dave
David DuBois

Dave, could you send to me or direct me to the updated instructions. I don't have a date on the instructions I used and keep in my car but they appear to be from a site called "The Sacred Octagon". I didn't make a note of when I made the modification but probably 10 or more years ago on a car that sits undriven/unstarted for obscene lengths of time and never a problem with pump since the modification. I did make a note that I had to use a 27 ohm resistor (Radio Sack number RSU 11344587) as they did not have a 25 ohm one.
Thanks for coming up with a modification and instructions so simple that even I could perform it with success and a fantastic sense of accomplishment.
Rick

Rick - You must have reused an old set of points to have the modification work so well (a friend, whose pump I did about 25 years ago has had the same success). Yes, the original article, after being published in our local register's newsletter, went to the New England Register and was published in The Sacred Octagon. The change that I made since the original article was published is that I eliminated the resistor, replacing it with a straight piece of wire. The resistor was originally used when I had outboarded a great huge power transistor and needed the resistance to limit the base current. I later found that the TIP 31 or TIP 41 transistors worked better without the resistor (some of them wouldn't work at all with the transistor). I would say, that if your pump has worked all these years without giving you any problems, don't mess with success - leave everything as it is. Cheers - Dave
David DuBois

To be honest, I don't remember if I used the old points or replaced them but even if I did replace them it is very likely the new points would have been old spares and not of the type subject to the problem you mention.
I have made a note of the resistor elemination.
Thanks again for your guidance.
Rick

Hi all.

I have (in my professional capacity) seen problems of an insulating film developing on contacts that are very lightly loaded and don't have a 'wiping' action.

A 'wiping' action is achieved by having the contacts rub over each other slightly as they close / open.
If memory serves, the points on a correctly adjusted SU pump should have a wiping action anyway, but it is no problem to arrange for a resistive load to increase the contact current to a level that keeps the contacts conducting but still with a much reduced (and, possibly more to the point, non-inductive) load.

A wiping action (in relays or similar) usually involved the moving contact continuing to move after contact is made with the 'fixed' contact. The 'fixed' contact (which is actually capable of movement as it is mounted on a spring) is then pushed in the same direction as the moving contact, and the two contacts slide against each other as the 'pivot' points are dissimilar.

We need David's article !.

Don
Don

The contacts I have seen wetting currents applied to *do* have a wiping action but still filmed over when the wetting current failed.
Paul Hunt 2

Dave, I just noticed that it was you posting about using magnetic reed switching. Could you send details to me for doing that.
Back when I first found and used your instructions we have been discussing, I was dealing with 3 different SU pump failures and in all 3 I noticed raw fuel getting into the points area of the pumps due to failed diaphrams (presumably from MTBE in fuel at the time) and wondered why they did not detonate from the fuel being present and the spark of the points. That may have even been the reason I started using the internet, to see if anyone had actually had "an event".
It seems to me that your reed switch conversion would eleminate that concern.
I also see that you have used the Burlen solid state conversion that this thread started with. Of these choices, and with that "spark" in mind, which would you advise.
Again, I can not thank you enough for your guidance in these things electrical.
The mechanical aspect of the English cars comes naturally to me, the 12 volt hot/ground, clean connection, even relays, I understand,... but whatever all that electron/transitor/resistor stuff is just baffles me, so I look to you and others for instuction.
Rick

As originally set up, the pumps have some kind of an arc suppression circuit in them. for the very early pumps, this circuit consists of just a swamping resistor internal in the coil. Later, a capacitor was added and the latest, non electronic pumps have a resistor diode in the circuit. These various arc suppression circuits work to hold the arcing of the points to a level where minimal erosion of the contacts take place. Unfortunately, the stalling of the pumps in a current on condition, such a when there is a clog in the inlet side of the pump occurs, or is the points get old and stick together, the swamping resistor burns out and the arc suppression goes away. This usually happens after many years of reliable operation and the owner looks at the results and determines that new points are in order (which is usually the case). But replacing the points with a compromised arc suppression circuit results in the rapid burning of the points and a short lifetime. This is why a new pump will last many years, while a "repaired" pump lasts only a short time. The answer that I have opted for is to convert to the magnetic reed switch and magnet. The down side of this conversion is that it is difficult to set up and needs a test stand to be able to properly adjust the gap for the magnet to the point where it will work properly and still be within the confines of the lower point trunion travel that will sustain good operation. For that reason, I have opted to not publish instructions for others to do the modification (plus the fact that I was once accused of ruining the pumps of someone who put the original transistor modification together incorrectly by not following the instructions that I had published. The magnetic reed switch modification also has a propensity to stalling out if a large piece of ferrous metal is in close proximity to the end cover. It takes a bit of fussing around with lower trunion adjustment and placement of a magnetic shielding piece to minimize this effect. In this regard, the all electronic kit that Burlen Fuel Systems is a better approach, in that it is easier for the layman to install and adjust and it doesn't suffer from close proximity of ferrous metals due to the placement of the magnetic components internally. That said, once my method is properly adjusted and the magnetic shading piece is properly positioned, my modification will operate equally as well as the Burlen Fuel System's modification. Both modification have the advantage of no points to film over if the pump is left idle for long periods of time, such as the car being placed in hibernation over the winter months.

Normally, a fuel leak through the diaphragm does not cause a problem with ignition of the fumes under the end cover because the resulting air fuel mixture is too rich to support combustion. There are conditions, with the later pumps used on the MGBs that have a vent on the end cover, where the air fuel mixture can ignite, but is normally confined to the area beneath the end cover and doesn't cause a problem. This condition can be avoided by having a piece of tubing attached to the vent that is sufficiently long that the column of air in it will only be pushed back and forth rather than actually drawing fresh air into the area under the end cover. Cheers - Dave
David DuBois

"the column of air in it will only be pushed back and forth"

As a matter of interest that is the sole purpose of the vent(s) i.e. to avoid air pressure from damping or opposing the movement of the diaphragm, and not for getting rid of any fumes to the atmosphere. The tubes on the vents prevent dirt and moisture being drawn into the pump.
Paul Hunt 2

Paul - I agree that the purpose of the vent is "to avoid air pressure from damping or opposing the movement of the diaphragm", but if there is no tubing on the vent, or the tubing is too short, it will draw fresh air into the space below the end cover. If the tubing is long enough, now fresh air will be drawn into the space, but venting will still occure. Cheers - Dave
David DuBois

PS to the above post. The last line should read ..., no... rather than now. Also I need to give credit to Daniel Wong for getting the concept through my dense head, of the long tubeing resulting in an oscillating coulmn of air rather than an exchange of fresh air. Cheers - Dave
David DuBois

This thread was discussed between 17/10/2005 and 21/10/2005

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