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Fuel Pump causing lights to flicker

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dterhune Avatar
dterhune Silver Member David Terhune
Cleveland, TN, USA   USA
My MGAs fuel pump seems to be causing my lights to flicker slightly.. all lights including the dash. I noticed this a couple weeks ago when driving back from my clubs monthly meeting.. on the drive home my alternator belt began squealing and i stopped to see what was going on under the hood.. this is when I noticed my tail lights flickering as it was very obvious. Here is what I know.

When the car is not running, and the key and lights are on, when the pump clicks the lights flicker noticeably .. this is why I began to look at the pump.

When the car is running, and the lights are on, the lights faintly flicker randomly .. pretty often, it does not match the pump operation.

I can disconnect the power from the pump and the flicker stops immediately.

I can run the pump from a separate battery and lead and there is no flicker.

I measured the voltage drop on the pump with the lights on and its drops from 13.88 to 13.56.

Here are the non standard items on this car.. I am running a CS130 alternator and the LED cluster tail lights. The harness is about 15 years old and not modified.

I have no idea when this started but I do drive the car pretty often and have returned home from events in the dark many times.

Anyone seen this before?



David Terhune

My Blog http://mymgcars.blogspot.com/

1970 MGB-GT, 1974 MGB and 1957 MGA Coupe

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Tveditr Eric EN
Indianapolis, USA   USA
1962 MG MGA
1971 MG Midget
I would start by checking All the grounds beginning with the engine ground strap. Also make sure all connections at fuse box are clean and secure.

ghnl Avatar
ghnl Silver Member Eric Russell
Mebane, NC, USA   USA
1961 MG MGA "Calvin"
First thing I suggest is to make sure all grounds are 100%. By make sure I mean to remove, clean & reconnect. This may not cure your issue but it is good preventative maintenance and will allow you know for sure the issue is not iffy grounds.

(great minds - with great names - think alike!)



Eric Russell ~ Mebane, NC
1961 MGA #61, 1981 Alfa Romeo GTV6, 1984 Alfa Romeo Spider, 1991 Honda ST1100



Edited 2 time(s). Last edit at 2019-02-08 05:46 PM by ghnl.

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RJBrown Avatar
RJBrown Randy Brown
Queen Creek, AZ, USA   USA
Check this connector in the right rear corner of the car. It should be attached to a bumper bracket.It is the ground for both the taillights and the fuel pump.


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dterhune Avatar
dterhune Silver Member David Terhune
Cleveland, TN, USA   USA
“I would start by checking All the grounds beginning with the engine ground strap. Also make sure all connections at fuse box are clean and secure.”

All grounds checked and fuse block cleaned and wires reattached ..



David Terhune

My Blog http://mymgcars.blogspot.com/

1970 MGB-GT, 1974 MGB and 1957 MGA Coupe



Edited 1 time(s). Last edit at 2019-02-08 09:56 PM by dterhune.

dterhune Avatar
dterhune Silver Member David Terhune
Cleveland, TN, USA   USA
“First thing I suggest is to make sure all grounds are 100%. By make sure I mean to remove, clean & reconnect. This may not cure your issue but it is good preventative maintenance and will allow you know for sure the issue is not iffy grounds.”

Have checked .. thanks



David Terhune

My Blog http://mymgcars.blogspot.com/

1970 MGB-GT, 1974 MGB and 1957 MGA Coupe



Edited 1 time(s). Last edit at 2019-02-08 09:57 PM by dterhune.

dterhune Avatar
dterhune Silver Member David Terhune
Cleveland, TN, USA   USA
“Check this connector in the right rear corner of the car. It should be attached to a bumper bracket.It is the ground for both the taillights and the fuel pump.”

Checked .. cleaned etc thanks



David Terhune

My Blog http://mymgcars.blogspot.com/

1970 MGB-GT, 1974 MGB and 1957 MGA Coupe



Edited 1 time(s). Last edit at 2019-02-08 09:57 PM by dterhune.

Bolney Coupe Avatar
Bolney Coupe David A
Haywards Heath, Sussex, UK   GBR
1960 MG MGA 1600 Coupe "Iris"
Make a new ground from the fuel pump directly to the battery?

dterhune Avatar
dterhune Silver Member David Terhune
Cleveland, TN, USA   USA
Tried that .. no change .. thanks!

In reply to # 3888343 by Bolney Coupe Make a new ground from the fuel pump directly to the battery?



David Terhune

My Blog http://mymgcars.blogspot.com/

1970 MGB-GT, 1974 MGB and 1957 MGA Coupe

barneymg Avatar
barneymg Barney Gaylord
(Somewhere in USA), Pick one (or more), USA   USA
1958 MG MGA "MGA With An Attitude"
My "guess" is that all of your electrical connections are fine, and it is a failing regulator inside the alternator. Disconnect the alternator wiring, switch on lights and ignition, and see if the flicker is gone, engine running and engine not running (with key on). You might have to disconnect a fuel line to let fuel flow to get the fuel pump to tick when engine is not running.

The small electrical load of the fuel pump affects system current draw, and the regulator has to "modulate" to keep voltage constant. When the regulator fails it can overcharge, like up to 20 volts momentarily, which is likely to make the drive belt slip and squeal (and you may see very bright headlights). Or if the regulator is just a little flaky the voltage may fluctuate slightly to make lights flicker a bit.



Barney Gaylord - 1958 MGA with an attitude - http://MGAguru.com - barneymg@mgaguru.com
(Please email me direct, do not leave a PM on the public server).

Don MGA 1600 Avatar
Don MGA 1600 Silver Member Don Tremblay
Rutland, Rutland, USA   USA
1960 MG MGA "My Oldest Friend"
1962 Jaguar E-Type "Rich Bitch"
Dave,


Your comment that the dash lights (and others) dim more with the engine not running than with the engine running to me, eliminates a grounding issue.

My opinion is that with each cycle of the fuel pump contacts making or breaking, you have a voltage drop due to a short internal to the pump resulting in an increase of electrical resistance within the pump, dropping the voltage thus flickering the lights at each cycle of the pump.

Let us know what you find.

Don

dterhune Avatar
dterhune Silver Member David Terhune
Cleveland, TN, USA   USA
Thanks Barney .. I actually swapped the alternator for a new spare I had in the garage as the first remedy and it had no effect ...

In reply to # 3888410 by barneymg My "guess" is that all of your electrical connections are fine, and it is a failing regulator inside the alternator. Disconnect the alternator wiring, switch on lights and ignition, and see if the flicker is gone, engine running and engine not running (with key on). You might have to disconnect a fuel line to let fuel flow to get the fuel pump to tick when engine is not running.

The small electrical load of the fuel pump affects system current draw, and the regulator has to "modulate" to keep voltage constant. When the regulator fails it can overcharge, like up to 20 volts momentarily, which is likely to make the drive belt slip and squeal (and you may see very bright headlights). Or if the regulator is just a little flaky the voltage may fluctuate slightly to make lights flicker a bit.



David Terhune

My Blog http://mymgcars.blogspot.com/

1970 MGB-GT, 1974 MGB and 1957 MGA Coupe

dterhune Avatar
dterhune Silver Member David Terhune
Cleveland, TN, USA   USA
Thanks Don .. was trying not to buy a new pump but I am thinking you’re probably on the right track ..

In reply to # 3888416 by Don MGA 1600 Dave,


Your comment that the dash lights (and others) dim more with the engine not running than with the engine running to me, eliminates a grounding issue.

My opinion is that with each cycle of the fuel pump contacts making or breaking, you have a voltage drop due to a short internal to the pump resulting in an increase of electrical resistance within the pump, dropping the voltage thus flickering the lights at each cycle of the pump.

Let us know what you find.

Don



David Terhune

My Blog http://mymgcars.blogspot.com/

1970 MGB-GT, 1974 MGB and 1957 MGA Coupe

dterhune Avatar
dterhune Silver Member David Terhune
Cleveland, TN, USA   USA
I wanted to close this thread by saying this.. I ended up creating a new separate circuit to run the fuel pump(s) from a relay, and I still have a slight flicker when running the stock SU and the back up "AirTex" like pump I finally installed permanently as a might as well from this project. I wonder if the slight dim flicker is just a product of the LED cluster tail lights I have. Anyway, it is much improved and I got the backup fuel pump installed finally.



David Terhune

My Blog http://mymgcars.blogspot.com/

1970 MGB-GT, 1974 MGB and 1957 MGA Coupe

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