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Steve4012

Fuel pump problems 85 turbo

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My fuel pump seemingly failed. I had an old spare that was functioning when removed so short term I put this on and all was fine for a bout 2 days before this did the same thing. I had voltage at the pump terminals but just got a 'thump' at the fuel pump when ignition turned fully on. Thinking I was unlucky I bought a new pump. Same one as I put on my dry sump which works perfectly. All fine for a couple of weeks but now it's done the same! It can't be 3 faulty pumps inc. one new one. 2 of the fuel pumps were noisy before failure inc the new one. Looking more closely I have found I only have 7v at the pump terminals. So far I've tried and failed on disconnected rev limiter, beefed up ground by adding jump cable to negative of battery, the trip switch seems fine and this also trips ignition but the car still has spark and fires on the fuel left so I think rules this out too. Engine has been out and fuel tanks too which are spotless inside. New fuel filter 300 miles ago and all new fuel pipes at same time. Any suggestions on why the voltage drop to just the fuel pump (battery fine and cranks car easily) and can this be confirmed as to why the fuel pump just thumps instead of whirring and were noisy before failure? I don't think there is a relay(?) and fuses in glove box all look fine but these would surely be good or bad not 7v

Thanks for any help in advance, 

Steve. 

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Crazy Idea.

You have 7V at the fuelpump?  Are you sure that the positive wire to the inertia switch , or to the fuelpump isn't coming from the + of the ignition coil AFTER the resistance wire? Because in that case you will get about 7V instead of 12V. The resistance wire is there to provide the ignition coil with a lower voltage (7V) with engine running . On starting, that wire is overided by a normal wire coming from the startermotor, to have a bigger spark (12V feed), but once the startermotor stops working, voltage on the coil falls back to 7V (over the resistance wire).

If your + feed to the pump was taken by mistake on the coil after the resistance wire, you get the same voltages to your fuelpump. That is 12V on startup and about 7V while running.

Anyway. You already tried adding a jumpcable to negative. Just try if the pump works normal having a jump cable to the positive .

 

Edited by gvy
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Fuel pump is fed directly from Inertia switch,  I would therefore see if you also get low voltage immediately before & after the Intertia switch.   If voltage still low, trace the white feed back to the ignition switch and recheck there.  NB The CE ignition is not ballasted.

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Apart from the voltage issue this type of pump will get very noisy when the fuel supply to it runs out, then it will stop completely. Might be worth checking the tank outlet is not bunged up with crud.

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There is also a suppression capacitor that runs from the supply wire to earth. Worthwhile taking that into consideration. Seems crazy not to supply the fuel pump through a relay though. Not you, but Lotus factory.

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3 hours ago, ekwan said:

There is also a suppression capacitor that runs from the supply wire to earth. Worthwhile taking that into consideration. Seems crazy not to supply the fuel pump through a relay though. Not you, but Lotus factory.

This was normal practice on older cars, Ignition was never fused and fuel pump usually not. The thinking behind it was these systems need to be kept going if at all possible, even with the risk of some burend wiring.  

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29 minutes ago, Andyww said:

This was normal practice on older cars, Ignition was never fused and fuel pump usually not. The thinking behind it was these systems need to be kept going if at all possible, even with the risk of some burend wiring.  

😢 I am almost coming to the end of restoration work and one of the final jobs is to replace the old "contact breaker" type SU pump with the modern electronic pump. I am still debating in whether to add a relay or not, given the fact I am trying to retain as much factory originality as I can. Also bearing in mind, this also puts at risk, an almost irreplaceable, if NOT ENTIRELY IRREPLACEABLE ignition switch. 😥

Edited by ekwan

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20 hours ago, Steve4012 said:

My fuel pump seemingly failed. I had an old spare that was functioning when removed so short term I put this on and all was fine for a bout 2 days before this did the same thing. I had voltage at the pump terminals but just got a 'thump' at the fuel pump when ignition turned fully on. Thinking I was unlucky I bought a new pump. Same one as I put on my dry sump which works perfectly. All fine for a couple of weeks but now it's done the same! It can't be 3 faulty pumps inc. one new one. 2 of the fuel pumps were noisy before failure inc the new one. Looking more closely I have found I only have 7v at the pump terminals. So far I've tried and failed on disconnected rev limiter, beefed up ground by adding jump cable to negative of battery, the trip switch seems fine and this also trips ignition but the car still has spark and fires on the fuel left so I think rules this out too. Engine has been out and fuel tanks too which are spotless inside. New fuel filter 300 miles ago and all new fuel pipes at same time. Any suggestions on why the voltage drop to just the fuel pump (battery fine and cranks car easily) and can this be confirmed as to why the fuel pump just thumps instead of whirring and were noisy before failure? I don't think there is a relay(?) and fuses in glove box all look fine but these would surely be good or bad not 7v

Thanks for any help in advance, 

Steve. 

Steve, any idea which ignition system your vehicle is running?

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Thanks all for your input so far. It's still not working but an update:

Full 12v from ignition to inertia switch when measured disconnected. When joined to white/ purple wire which goes directly (I believe) to fuel pump this then drops to 8v measured at inertia and 7v at fuel pump. So all good until it gets to inertia. I then ran a temporary wire from here to fuel pump and therefore not using white /purple wire and the voltage still drops. So when the fuel pump is part of the circuit the voltage drops, disconnect this and full voltage. See photo with terminals removed from inertia plug. Thick white cable from ignition, black is temp cable to fuel pump. Disconnected 12v, touched to positive on fuel pump immediately drops to 7v?! Maybe I need to re-examine the earth at the pump? 

rps20190520_104323.jpg

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If this is dropping in this way it could be one of two things:

The pump could be drawing a large current and this means its seized up. This will happen if its starved of fuel. This type of pump has the fuel running right through the motor and lubricates it. If the fuel dries up the pump will at first make a noise then stop as its seized. If fuel is re-added it might free up if it has not been damaged. So this indicates the problem is a blockage in the fuel feed to the pump.

Or

A high resistance in the circuit before the point you are measuring it. Pretty much the only part apart from wiring is the ignition switch. It could be that. if you disconnect the pump, do the windscreen wipers work normally as they are fed from the same ignition switch contact and would draw a pretty high current.

 

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Also do not discount the fact that the positive feed wires could have built up resistance with ageing. 

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Thanks gents. Andy your first suggestion seems to be accurate which is baffling to me. I got the pump to atleast work by connecting a battery charger directly and independently to it. This obviously freed it up and it now comes on with ignition as well. The baffling bit is that it does seem to be starved of fuel. I've had the engine and 'box out for a major service, fix leaks etc and the tanks, crossover pipe and all fuel hoses out too. All now perfect condition in and out but I have no fuel being fed to the carbs even though the car has been running great since completing. I now need to find out what is blocking the fuel. 

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Ok, there is no fuel blockage to the inlet of the pump. I would have been astounded if there was and I am certain that the fuel pump would not have run dry at any point. The pump is now making a noise with ignition on but there is no fuel coming out the other end. If I wasn't on my 3rd fuel pump I would say the pump is bad. Can anyone be that unlucky?! 🤔

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A blockage downstream could cause problems but seems unlikely.

Was the fuel pressure screw on the regulator set by the correct method using a pressure guage?

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I haven't touched the fpr Andy as it was running fine before engine out so didn't see a need to. It also ran fine prior to the fuel pump failures. This new pump was very noisy immediately it was installed and I know it had fuel as I had to use pipe clamps to change it. I've sent a message to the seller to see if they've had any bad ones but it seems a long shot. At this point I can't see any alternative than buying yet another fuel pump.

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Although it might be nothing to do with the problem its vital to check the fuel pressure. Even leaning on the regulator, from working on the engine can cause the pressure to change. Its very sensitive and if the pressure is a lot higher than is should be it can push past the needle valves and overflow the carbs.

The sound of the pump does change when you adjust the regulator but not sure if incorrect setting could cause pump stall.

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Ok Andy thanks, will check that as soon as I have some fuel to measure 👍

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Just a quick thought...... if you disconnect the fuel pump, do you get 12V at the feed wire?

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1 hour ago, Steve4012 said:

Ok, there is no fuel blockage to the inlet of the pump. I would have been astounded if there was and I am certain that the fuel pump would not have run dry at any point. The pump is now making a noise with ignition on but there is no fuel coming out the other end. If I wasn't on my 3rd fuel pump I would say the pump is bad. Can anyone be that unlucky?!

Maybe hotwire the -ve/+ve terminals directly to the battery and re-test?   

Edited by 910Esprit

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Yes 12v if disconnect it from pump and actually I have full voltage with cable connected as well, now the pump is making a noise. It was obviously seized and therefore affecting the current drawn as Andy said. No fuel flow though pump seems knackered. It's just too much of a coincidence for 3 pumps all to fail in the same way and I'm concerned I haven't found the reason they're failing. Apart from running dry and I've verified there is fuel to the inlet how can you damage a fuel pump? 

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You can easily test the fuel pump operation on the bench by seeing if it would empty out a bucket of water.

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4 minutes ago, ekwan said:

You can easily test the fuel pump operation on the bench by seeing if it would empty out a bucket of water.

Possibly the worst advice I have ever seen on any car forum. These pumps have the fuel going right through the motor which is completely immersed in fuel. Filling up an electric motor with water is a really bad plan.

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I've just tested both old pumps off the car with a full can of fuel up high, the pump below the fuel level and an empty fuel can low to assist the gravity feed. Powered up, both buzz but neither move any fuel. Should they move fuel with this set up? The upper line is obviously not primed. 

rps20190520_161916.jpg

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40 minutes ago, Andyww said:

Possibly the worst advice I have ever seen on any car forum. These pumps have the fuel going right through the motor which is completely immersed in fuel. Filling up an electric motor with water is a really bad plan.

Oops my bad 😣

I forgot the Turbo doesn't use the SU diaphragm-type pump but a roller cell type..

Edited by ekwan

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The pumps are not self-priming and wont work unless there is a head to the pump.

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