Hi all! I am new to the forum. I have taken on a non running 1984 xj6 3.2l carbureted. The previous owner had changed the fuel pumps in the tanks. Now every time I turn the key on fuel runs out of both of the carburettors, I have checked both of the needle and seats. Is there two types of in tank pump for this model EFI and SU carb.? I suspect that the fuel supply pressure is far too high.
Two types, yes, but the F,I, pump is externally mounted so there is no chance of inadvertently installing the wrong type.
Cheers
DD
Carbed will click and EFI will whirr, correct? Donât check again without removing the supply line and adding a container. Other possibility, can the SU pump fail and keep pumping?
You are probably looking at this the wrong way around. The âcorrectâ SU pump will keep running if there is somewhere for it to pump the fuel to, but it will slow down ticking/pumping when the float bowls in the carburettor have risen and sealed off the flow.
What you need to do is test the pump by sealing the line and the pump ought to stop ticking/pumping once it fills the line with fuel. If that happens, then it tells you that the carburettor needed fixing and there is probably nothing wrong with the pump.
kind regards
Marek
1 Like
Are the fuel pumps the ones that are fitted into the tank with access in the rear wheel arch?
If so, I have a car with those pumps and I can tell you for certain that the pumps run continuously as long there is oil pressure in the engine.
They do not make a clicking sound like a normal SU pump.
I do not know if any fuel injected cars had this set up, but I donât believe they did, so the first thing to do would be to check the fuel pressure at the feed to the float bowl. Should be about 4 - 5 p.s.i.
If that checks out the the problem is certainly with the needle valve or seat. These are available from Burlen and are dead easy to fit.
Slight possibility that the floats are punctured so test them in a small container of fuel and see if they sink.
The other thing can be dirt under the seat of the needle valve and it only takes the tiniest amount to cause a leak. This from experience.
The other thing is to check the float level itself. If you have the HIF carbs, which I believe you do on that car, then this can be adjusted by bending the arm on the float.
Hope this helps.
Dave
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Sure is, Daniel!
EFI pumps deliver 100+ psi and will overwhelm carb needle valve. The carb pumps are usually rated for 15 psi - though 5 psi is adequate.
Itâs indeed highly unlikely that a PO has fitted EFI pumps in the tanks - but POs sometimes do the strangest things. Unlike Doug; my trust in PO âingenuityâ is unlimitedâŚ
First step; check fuel pressure at the carbs, and indeed, as Marek says; clamp the carb hose to ensure the pumps stop. His point about sunken floats is valid - and indeed; check float levels. Needle valves and seats cannot function with either fault - carbs will floodâŚ
That the pumps run with ign âonâ means that the fuel safety switch is bypassed. This prevents pumps from running unless engine has oil pressure - but will not otherwise interfere with carb behaviour. They should not floodâŚ
Frank
xj6 85 Sov Europe (UK/NZ)
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Ok,
The in tank pumps were fitted to the later series 2 carbureted cars and the series 3 carbureted 3.4 litre cars.
As Doug says the EFI fuel pumps were externally mounted.
There is an oil pressure switch towards the rear of the engine where the fuel pump relay is earthed. This is arranged so if there is no oil pressure there is no earth so the fuel pump will not run.
However, I have seen a few cars where the wire has been removed and connected directly to earth. The reason being that if the car has been standing for a long time and there is no fuel in the float bowl, then it takes ages to build enough oil pressure and fill the float bowls just by operating the starter motor.
The in tank pumps are made by AC Delco.
They do not shut off if you block the delivery pipe. The pumps run continuously as long as there is oil pressure.
Dave
Heh heh. Too true!
However, I said it would be impossible to inadvertently install the wrong type
Cheers
DD
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In âcrankâ the fuel safety relay is bypassed, Dave - the relay is configured to run pumps independent of engine oil pressureâŚ
Frank
xj6 85 Sov Europe (UK/NZ)
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