Fuel Pump Problems
Discussion
I've had some fuel pump problems of late.
Done the obvious and cleaned all connections and earthing but was not convinced this was the problem.
Any way now the pump is dead as a door nail when you turn the key there is no pump noise at all.
I've put a meter across the supply terminals and I get voltage.
To the point of the post:
1. I get 5volts across the terminals. Is this normal or should I see more like 12v ?
2. I see 5v for about 5sec then you hear the relay click off and the voltage drops to 0v. Is this normal ?
3. If the pump is dead has anyone got any recomendations for a replacement?
Cheers in advance.
Done the obvious and cleaned all connections and earthing but was not convinced this was the problem.
Any way now the pump is dead as a door nail when you turn the key there is no pump noise at all.
I've put a meter across the supply terminals and I get voltage.
To the point of the post:
1. I get 5volts across the terminals. Is this normal or should I see more like 12v ?
2. I see 5v for about 5sec then you hear the relay click off and the voltage drops to 0v. Is this normal ?
3. If the pump is dead has anyone got any recomendations for a replacement?
Cheers in advance.
On mine, the pump runs for about two seconds when the ignition is switched on, then stops. It runs continuously while the engine is actually running, of course. This sounds similar to yours.
I would normally expect 12v at the pump. I understand that on some cars a dropping resistor is used to extend the life of the pump, so it may be lower on these cars. I wouldn't expect the normal running voltage to be as low as 5v. However, if the pump has seized it will draw the full stall current, and if you have a dropping resistor fitted the voltage would drop more under these conditions.
If I were you I would hotwire the pump with a fused 12v supply and check the pump actually runs. If not, that is the problem right there. If it does run, you may have a resistance somewhere in the supply causing the voltage drop. Candidates would the fuel pump relay, immobiliser, inertial cut-off, and all wires and connectors.
I would normally expect 12v at the pump. I understand that on some cars a dropping resistor is used to extend the life of the pump, so it may be lower on these cars. I wouldn't expect the normal running voltage to be as low as 5v. However, if the pump has seized it will draw the full stall current, and if you have a dropping resistor fitted the voltage would drop more under these conditions.
If I were you I would hotwire the pump with a fused 12v supply and check the pump actually runs. If not, that is the problem right there. If it does run, you may have a resistance somewhere in the supply causing the voltage drop. Candidates would the fuel pump relay, immobiliser, inertial cut-off, and all wires and connectors.
RAW-SEWedge said:
If the pump is knackered, then I know they can be got for about £40 off Ebay brand new.
Got mine off there and it works a treat.
Ta, never thought about that
This is the guy I bought mine off, he's legit and is as described - he's raised his price slightly but still a bargain compared to the £166 a TVR dealer wanted.
I’ve been having intermittent hot start problems, which has turned out to be the immobiliser going t**s up. Thing is the immobiliser works on three circuits, the fuel pump being one of them. If as previously mentioned the pump works when hot wired then this may be the place to check next.
Cheers,
Simon.
Cheers,
Simon.
Thanks for all the suggestions on this one. Thought I’d give a quick update for sake of reference.
Problem is now fixed but I’m not 100% sure what the fault was. I know there was only 4-5volts at the pump and as soon as I hot wired 12 to it then it burst into life.
I checked for resistance through all the wiring and no problems there.
Checked the inertia switch, again no problems there.
Had a good 12v feed to the fuel pump relay but only 4-5volts out.
So I took the relay apart and had a look, no obvious signs of a problem and when putting 12v across the coil sure enough it closes. So I plugged it back in with the top of and manually closed it, bugger-me 12v out and the pump works!
Cleaned the relay contacts and put it back together and the dam thing fires up.
Looks like it was probably the relay after all so I’m going to pick up a new one and replace it. We’ll see how it goes from there but it’s looking like another passenger foot well gremlin
Problem is now fixed but I’m not 100% sure what the fault was. I know there was only 4-5volts at the pump and as soon as I hot wired 12 to it then it burst into life.
I checked for resistance through all the wiring and no problems there.
Checked the inertia switch, again no problems there.
Had a good 12v feed to the fuel pump relay but only 4-5volts out.
So I took the relay apart and had a look, no obvious signs of a problem and when putting 12v across the coil sure enough it closes. So I plugged it back in with the top of and manually closed it, bugger-me 12v out and the pump works!
Cleaned the relay contacts and put it back together and the dam thing fires up.
Looks like it was probably the relay after all so I’m going to pick up a new one and replace it. We’ll see how it goes from there but it’s looking like another passenger foot well gremlin
probably the relay base, they corode badly. if its the loose one on a "flying lead" the joints can be iffy...re-make, replace the base.
VW part i believe.
change the relay every year anyway...£6- from bosch. they're special and have surge suppressors inside so don't put non-std part in, risks the cpu output drivers.
another possiblity is the lamba sensors. no seriously! they take their 12v from the same point and can load the circuit. they usually blow the fuse big time tho.
loverly colour yours BTW...don't see enough red ones...sound like the Mrs now...i'll get me coat...
>> Edited by Guillotine on Sunday 2nd January 16:26
VW part i believe.
change the relay every year anyway...£6- from bosch. they're special and have surge suppressors inside so don't put non-std part in, risks the cpu output drivers.
another possiblity is the lamba sensors. no seriously! they take their 12v from the same point and can load the circuit. they usually blow the fuse big time tho.
loverly colour yours BTW...don't see enough red ones...sound like the Mrs now...i'll get me coat...
>> Edited by Guillotine on Sunday 2nd January 16:26
Guillotine said:
probably the relay base, they corode badly. if its the loose one on a "flying lead" the joints can be iffy...re-make, replace the base.
That's the one. Not very happy about them just being stuffed loose behind the carpet. I was thinking of making a plate with a small second fuse/relay box.
Guillotine said:
another possiblity is the lamba sensors. no seriously! they take their 12v from the same point and can load the circuit. they usually blow the fuse big time tho.
I couldn't determine where the purple/white feed from the relay went. At some point it chnages to a yellow/black feed to the intertia switch. So is there some junction/joint which feeds the sensors too?
Guillotine said:
loverly colour yours BTW...
Thanks
RAW-SEWedge said:
I couldn't determine where the purple/white feed from the relay went. At some point it chnages to a yellow/black feed to the intertia switch. So is there some junction/joint which feeds the sensors too?
On mine the fuel pump relay has two outputs, one drives the fuel pump (via inertia cutout etc) the other powers the lambda sensor heaters. Incidentally, this is the main reason you can't use an ordinary changeover relay for the fuel pump, because that would leave the lambda sensors heaters off while the engine was running and on while you were parked, this flattens the battery over a few hours.
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