Pump up the heat

[silloyd]

OK, so here's a weird one.

Car conked out on the way to the petrol station with characteristics of fuel having run out, even with gauge showing 1/4 full. Feeling a right pillock I topped up using the spare can in the boot, thinking he gauge had gone wonky and I'd run out (I couldn't remember how far I'd gone since the last fill up). But it still wouldn't start.

So, next suspect was the fuel pump. It was really hot (almost too hot to touch) and removing the plastic cap revealed that it wasn't working, essentially because the contacts weren't opening. I fudged the contact blade (Item 22 in the picture below) by bending it upwards slightly and nursed the car the mile or so back home.

A strip of the pump revealed that the black plastic pedestal (item 16) had seriously overheated and sagged with the result that (a) the diaphragm push rod could not travel its full throw and (b) the little ridge on the pedestal (which is supposed to stop the contact blade at the right point) was not even touching the blade and therefore the contacts would not break.

Now, I know it was a hot day (~28-30C) but even with the heat under the bonnet from the exhaust et al shouldn't have that level of effect on the pump.

The pump is temporarily back in the car whilst I order a new (non-electronic!) one, so I'll add pictures when I strip it back out to replace it.

Any ideas of how this might have got so hot and has anyone else had this problem please?

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[bmcecosse]

Can only suggest that with points stuck shut - current would be running constantly through and making the heat...... Change the melted pillars for metal tube ??

[MarkyB]

Any idea about the history of the pump?
It may be that the quality of the plastic on newer pumps isn't as heat resistant as the old ones.

[silloyd]

BMC - The pedestal is completely distorted, not just the pillars, so merely replacing them won't work (I'll post a picture when I strip it down). You may well be right about the points getting stuck or not opening sufficiently, i.e. arcing, and the coil getting too hot, but saying that we all know that 'it's never the coil'


MarkyB - No idea of the history of the pump but it's either old or it's had a bad life!!


As well as a new pump I've ordered a replacement pedestal (Burlen's do all parts separately) for the old one and will repair to keep as a spare.

[bmcecosse]

Well done - didn't realise we could get a new pedestal...... The coil hasn't failed has it ??????

[silloyd]

Piccies as promised. Old melted one on the left, new one on the right.

Note where the washers have sunk into the plastic and the centre section has particularly dropped, which caused the points to remain closed:
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This one gives a better view of how the centre section has dropped down:
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Note the spreading at the bottoms of the legs:
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And the splaying of the legs:
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Will have to rebuild my existing pump for now as the new pump is on 6 weeks+ back order - according to Burlen this is because they've had problems with faulty diaphragms and solenoids (it was the coil!! ), both of which they say have been resolved but there's a manufacturing backlog.

[bmcecosse]

Good pics. My legs are a bit spread and sagged too these days ......... but my fuel pump seems fine !

[silloyd]

... my fuel pump seems fine !

And best to keep it that way!

BTW the suppressor capacitor broke during reassembly, so I replaced it with a diode (see here and here for details on how to do the same). The new pump is apparently not polarity sensitive and as far as I can work out it's because the capacitor/diode has been replaced with a 'varistor'. When it eventually arrives I'll take a gander and see if I can work out the spec for the varistor.

I also found a reasonable video on how to change the points and reset the gaps.

[silloyd]

So, the old pump is repaired and working fine as far as I can see. I followed the destructions to the letter in setting it up. However,it is getting fairly warm in operation (not like it was when it failed, i.e. almost too hot to touch), is this normal or do I still have a latent problem?

How warm/hot do the fuel pumps get after they've been pumping hard, such as when you've just climbed a steep hill?

I'm concerned because the new pump won't be available for some time and I'm not sure if I've just fixed the symptom rather than the cause.

[MarkyB]

They do get hot in service, especially in this weather if petrol is vaporising in the pipe and they are pumping 20 to the dozen to get liquid petrol.

[bmcecosse]

Just pick up a spare from ebay - plenty on there last time I looked........

[silloyd]

Thanks for the confirmation MarkyB. Will keep an eye on it anyway to check for further melting!

[Ufudu]

Not directly answering anyone's questions, but the following link was posted on lrsoc.com by members who's pumps may also not be pumping as well as they should in the British Summer!

Excuse me if you have seen this already.

I found the pdf articles a useful read.

http://homepages.donobi.net/sufuelpumps/

Erwin

[bmcecosse]

Why the diode? Perhaps it's passing current = cause of overheating?

[Ufudu]

The diode referred to in SU Pumps 101?

Diodes are usually used to suppress back-EMF, or to (briefly) dissipate the coil energy through the swamping resistor (I presume) when the points open. Otherwise the energy gets dissipated as an arc across the points. The diode is reverse biased when the correct polarity is applied to the pump, and normally passes no current.

I did not think the "points" type SU pump as supplied by Burlen (AUA66) is polarity sensitive, so perhaps does not use a diode?

[silloyd]

As per my previous post, I think they now use a varistor but will check when the new pump arrives.

[Ufudu]

Makes sense, they are like 2 back-to-back zener diodes, have a symmetric transfer function and are thus polarity insensitive.

[bmcecosse]

But what's the point (no pun intended) my old pump seems to have managed the last 40+ years ok without anything........

[Ufudu]

so it lasts 80 years?

[bmcecosse]

I won't be caring.....