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Flickering gauges
JC - 1/7/19 at 07:32 PM

Hi all,

I have 2 (possibly separate?) electrical issues.

My car has the ‘el cheapo’ gauge set from CBS. When I’m driving they are all over the place, giving random readings, sometimes dying, then coming back to life. Sometimes at a standstill, engine running, the speedo winds up to 40-50 mph then returns.....

I’ve checked supply and earths and they seem ok. Is it likely to be interference or dodgy gauges?
Edit to add:
I have checked with the engine NOT running. Putting the indicators on causes the indicated voltage at the voltmeter to pulse between 10v and 12v as the indicators cycle. It also causes the Rev counter to indicate - I unplugged the signal feed from the coil and the pulsing continues... the indicator switch and tell tales are all part of the dashboard. Is this an earth issue???.

The second issue is my water/meth injection pump.... when it cuts in, the voltage drops - you can hear the electric petrol pump slow if the engine isn’t running. Apparently it draws 6-9 amps when it cuts in, 3-6 continuous running. I have an odyssey 25 battery - could it be that it isn’t man enough?


Edit to add:

Ran voltmeter across battery terminals. Stayed at 12v+, even with water injection running.

Measured voltage in to injection pump....just over 10v

Measured voltage between live battery terminal and power to pump (voltage drop?) with pump running and it was 1.45V.

Power distribution is via a CBS easy wiring module, if that makes a difference, and through a battery isolated switch.



Thanks

BTW Car is supercharged MGB powered...

[Edited on 1/7/19 by JC]

[Edited on 1/7/19 by JC]

[Edited on 2/7/19 by JC]

gremlin1234 - 2/7/19 at 12:57 PM

quote:
Originally posted by JC
Measured voltage between live battery terminal and power to pump (voltage drop?) with pump running and it was 1.45V.

a 1.4V drop on a short cable means it needs a bigger cable.

note 1.4v at 5a is 7w so that cable will be getting warm

JC - 3/7/19 at 05:07 PM

Spent the day checking everything. Finally added an additional, thicker earth return between battery and the chassis and all ills instantly cured! Hurray!

mangogrooveworkshop - 4/7/19 at 09:28 AM

This is physical proof that a properly designed wiring loom is the key to making the systems work without fail.

Smoke pipes ......

zilspeed - 17/7/19 at 05:40 PM

quote:
Originally posted by mangogrooveworkshop
This is physical proof that a properly designed wiring loom is the key to making the systems work without fail.

Smoke pipes ......


You're alive ;-)


Hope you're well.

JC - 17/7/19 at 07:57 PM

quote:
Originally posted by mangogrooveworkshop
This is physical proof that a properly designed wiring loom is the key to making the systems work without fail.

Smoke pipes ......


Absolutely! I bought the car from the builder last year.....new dashboard and a rewire on the winter to do list!

r1_pete - 17/7/19 at 08:12 PM

Yup, many folk forget the same current exists round a circuit, not just the +ve feed...

907 - 18/7/19 at 04:06 AM

To account for variations in running voltage some gauges require a voltage reducer, temp, fuel etc.


My Smiths gauges run off 10v to give accurate readings.


Paul G