12v switched feed for electric fuel pump (for carb Spider)

[mangocrazy]

I was undecided whether to put this topic in Fuel System Carb or Electrical, but on balance decided this was the best place. Anyway...

As many will know, my Spider has been in France for quite a few years and has had an 'eventful' life. After replacing the original engine with a 2 litre donor, it was quite a surprise when (back in April) the car fired up almost first turn of the key. It completed a couple of slow laps of the village and then got put away until our next visit.

We're back in France again at the moment, doing more house-bothering, and I'm keen to get rid of the oil that's currently in the engine and replace with fresh. The plan was to start the car up, get it up to temperature and then drain the oil and change the filter. The plan fell at the first hurdle when the car refused to start (fully-charged battery, no changes since April). A good spark was present at the plugs and the transparent fuel filter was conspicuously absent of fuel, so suspicion centred on the Huco electric fuel pump. Connections were checked and cleaned, but with no improvement.

I should state at this point that the Huco is effectively an electric replacement for a mechanical pump, and is designed to 'pull' fuel and as such lives in the engine bay. I wired it up to take a live feed from the coil mounted on the offside inner wing, and this seems to have worked OK for several years. More out of curiousity than anything else, I decided to test the voltage it was getting with my multimeter. The result was quite a surprise - 5.5v with ignition on (and very similar when cranking the engine). The battery was putting out a healthy 12.6v.

So it would appear that I need to reconsider my 12 supply to the pump. Hardly surprising it didn't want to rouse itself for 5.5 volts. What would people suggest as a the best way to supply switched 12v power for a fuel pump? I'm thinking of lashing up a supply from the battery with an inline manual switch in the short term, but will clearly need a safe and functional permanent solution.

All suggestions welcome. Even more so if they have a diagram attached - I'm a bit rubbish with electrics...

[jreacock]

Hi. Maybe the pump is seized or faulty in some way, and the voltage is being pulled down to 5.5V due to the current draw? It would be worth taking the feed wire off the pump to find out what its voltage is when not connected to the pump.

[HFStuart]

That's not a bad idea.

For a feed to the pump you should run a direct feed from the alternator / battery to the pump and switch it via a fused relay from something ignition controlled. Ideally you need to include an inertia switch or an oil pressure switch to make sure it cuts off in an impact or otherwise when the engine isn't running.

[WestonE]

I agree with Stuart that a fused feed from the alternator or battery should be used with an inertia switch in line to provide crash safety. But it should be switched via a relay from an ignition switched live.

Any non change over 30amp relay will do, but you can get them with a fuse built in or with a plug block that includes places for fuses.

The internet is full of how to wire a relay diagrams.

Good luck

Eric   

[HFStuart]

Ummm, I'm pretty sure that's exactly what I said !

[WestonE]

Hi Stuart

It has been a long weekend with the social able Montecarlo Consortium sorry.

Eric

[mangocrazy]

Hi. Maybe the pump is seized or faulty in some way, and the voltage is being pulled down to 5.5V due to the current draw? It would be worth taking the feed wire off the pump to find out what its voltage is when not connected to the pump.

Good idea... I just went down to the garage, disconnected the fuel pump live lead from the coil terminal, switched the ignition on and measured the voltage between live terminal and earth - just under 6.9v

So an improvement over 5.5v, and the difference can probably be explained by the current the pump was pulling, but probably not enough to convince the pump to get out of bed.

Tomorrow I'll jury-rig a supply direct from the battery to the pump and see if that energises it. But long term I'll definitely be doing what Stuart and Eric recommend.

[HFStuart]

Hi Stuart

It has been a long weekend with the social able Montecarlo Consortium sorry.

Eric

That's a pretty good excuse! I take it you drunk a fair amount of 'sociability' ?

[WestonE]

Hi Stuart

I seem to remember drinking the bar out of beer, but I could be wrong 

[mangocrazy]

I'm impressed that Eric could even pen a reply to my query after drinking the pub dry... 

I've lashed up a 12v supply direct from the battery to the pump for testing purposes, and as soon as power was supplied the pump jumped into life and rapidly filled the transparent fuel filter. So it's pretty clear that the issue was an undervoltage supply. I'll assemble all the necessary bits for a permanent solution and bring them down the next time we visit the moneypit...

[peteracs]

Hi

Is that the house or the car which is the money pit?

Peter

[mangocrazy]

Hi

Is that the house or the car which is the money pit?

Peter

Haha - it's definitely the house. The Beta has had money thrown at it, but nothing like the amount the house has...

[peteracs]

Hi

Is that the house or the car which is the money pit?

Peter

Haha - it's definitely the house. The Beta has had money thrown at it, but nothing like the amount the house has...

I guess we have been lucky, though we did buy top of the market in 2006, we only had to spend modest amounts to get it to how we wanted it and now should last us for the next 20 years without too much expenditure even though it is an old building. Always amazes me how much tradesmen cost in France compared to the UK.

(Apologies for hijacking thread....)

Peter

[mangocrazy]

Hi Peter, I bought it knowing that were large amounts of work needed, so I can't really complain. We're doing most of the work ourselves to keep a lid on costs and are only calling in specialist help when needed. Jackie (my wife) has become a dab hand at rendering and plastering and I'm in the latter stages of completely replumbing the house (H&C) and incorporating solar thermal and a wood burning stove with back boiler. I've used a local electrician, as French electrics are very different to UK, but he's Irish and lives in the next village. He's happy to get paid in increments as work gets done, and that suits me as I can keep an eye on costs. He uses my payments as his Christmas savings... 

No problem with thread hijack at all...