Low voltage at fuel pump?

Discuss Electrical problems here.

Moderator: Moderators

KeithL
Minor Fan
Posts: 117
Joined: Mon May 24, 2010 9:06 pm
MMOC Member: Yes

Low voltage at fuel pump?

Postby KeithL » Wed Aug 08, 2018 9:09 pm

For the first time ever our Traveller refused to start today. It was turning well on the starter and there was a strong spark at each plug. However the fuel pump didn't seem to be pumping as there was no clicking. It is a relatively new electronic SU pump which has given no problems up until now so I checked the voltage between the cap and the earth and it was only 11.9V. The battery was a healthy 12.4V.

Is such a low voltage to be expected and should the pump work at this voltage? If not would it suggest the regulator is faulty as I assume the power to the pump comes via the regulator?

I'm not a motor technician but since I need to get the car started before it goes anywhere (i.e. a garage) I am going to have to sort this myself. What tests should I now be carrying out to try and isolate this problem? The regulator is a Lucas RB106/2. As a start I will tomorrow disconnect the fuel pipe to the carburettor to see if it is in fact pumping anything.

Thank you in advance for any help.


StillGotMy1stCar
Minor Fan
Posts: 304
Joined: Wed Jun 07, 2017 11:37 pm
MMOC Member: No

Re: Low voltage at fuel pump?

Postby StillGotMy1stCar » Thu Aug 09, 2018 12:05 am

The voltage at the pump isn’t that low, you get voltage drop though connections the ignition switch and the wire itself, also the circuit is partly shared with the ignition coil that if isn't electronic ignition will draw current through the points that will most likely be closed.
If you can’t hear the pump ticking there is a good chance it has failed and may be drawing current causing an additional voltage drop. No need to touch the voltage regulator.
So your next step is correct to remove the pipe at the carb and see if it is pumping preferably into a suitable container.
Good luck and take care.
Regards John

Nickol
Minor Addict
Posts: 505
Joined: Fri Apr 18, 2014 2:40 pm
MMOC Member: No

Re: Low voltage at fuel pump?

Postby Nickol » Thu Aug 09, 2018 6:39 am

The fuel pump has a set of contacts which switch themselves off and on as it pumps. That is the clicking sound you normally hear. Sometimes the points stick. Give the pump a good hit ( do not overdo it) with a spanner or small hammer whilst it is switched on.
Gott schütze mich vorm Sturm und Wind und Autos, die aus England sind.
download/file.php?id=4822[/sig]

ManyMinors
Minor Legend
Posts: 1502
Joined: Tue Nov 11, 2014 9:41 am
MMOC Member: No

Re: Low voltage at fuel pump?

Postby ManyMinors » Thu Aug 09, 2018 7:25 am

I also had an electronic SU pump fail inside 12months and reverted to the traditional contact type after that........

KeithL
Minor Fan
Posts: 117
Joined: Mon May 24, 2010 9:06 pm
MMOC Member: Yes

Re: Low voltage at fuel pump?

Postby KeithL » Thu Aug 09, 2018 1:46 pm

Thanks everyone.

I checked with Burlen and the pump should work between 9.5V and 13.5V so the voltage isn't an issue.

I have disconnected the fuel pipe from the carb and the pump is pumping as expected. I didn't measure flow rate but I very quickly filled a 1/4 of a large coffee jar with petrol.

Just for fun I tried jump starting the car in case it was the battery. That made no difference either.

Under normal operation the carburettor obviously tells the fuel pump to stop pumping at some stage so has that mechanism stuck / broken / failed in my carburettor?


Nickol
Minor Addict
Posts: 505
Joined: Fri Apr 18, 2014 2:40 pm
MMOC Member: No

Re: Low voltage at fuel pump?

Postby Nickol » Thu Aug 09, 2018 6:53 pm

If the pump is working as you say when disconnected from the float chamber but otherwise not then suspect the float needle in the float chamber and that the float itself is working properly. The needle (valve) may be clogged with dirt or broken .....
Gott schütze mich vorm Sturm und Wind und Autos, die aus England sind.
download/file.php?id=4822[/sig]

KeithL
Minor Fan
Posts: 117
Joined: Mon May 24, 2010 9:06 pm
MMOC Member: Yes

Re: Low voltage at fuel pump?

Postby KeithL » Fri Aug 10, 2018 10:18 pm

I took the top off the float chamber and gave everything a good clean. It is the newer type with the plastic float which presses directly onto an aluminium plunger with a rubber seal on the end. I gave Burlen a call and their technical department said that if the car has been sat unused for a while, like ours has, then lacquer can build up on the rubber seal and make it sticky. As instructed I gave it a good clean with petrol and it seemed to move much easier. Once everything was put back together the car fired up. Result.

Thanks Nickol.
Attachments
DSC07050.JPG
DSC07050.JPG (1.15 MiB) Viewed 627 times


ManyMinors
Minor Legend
Posts: 1502
Joined: Tue Nov 11, 2014 9:41 am
MMOC Member: No

Re: Low voltage at fuel pump?

Postby ManyMinors » Sat Aug 11, 2018 7:43 am

That's a good result. You hadn't mentioned that your car had been standing unused.

KeithL
Minor Fan
Posts: 117
Joined: Mon May 24, 2010 9:06 pm
MMOC Member: Yes

Re: Low voltage at fuel pump?

Postby KeithL » Sat Aug 11, 2018 9:14 am

ManyMinors wrote:
Sat Aug 11, 2018 7:43 am
That's a good result. You hadn't mentioned that your car had been standing unused.
It's only been 2-3 months since it was last driven but it hasn't been driven must since October so I guess that was enough to cause this problem.


myoldjalopy
Minor Legend
Posts: 1142
Joined: Tue Jan 29, 2013 10:32 pm
MMOC Member: Yes

Re: Low voltage at fuel pump?

Postby myoldjalopy » Sat Aug 11, 2018 2:11 pm

Nice easy fix - we like them! 8)


Who is online

Users browsing this forum: No registered users and 3 guests