only 9 volts at fuel pump
Discussion
well i did have the car running and all was going well! went to start her today and she fired up all for about 2 seconds and then cut out. after a little scratching my head and testing, i've found that i'm only getting 9v to the fuel pump, i also noticed that one of the relays is getting a little warm not sure if the two could be related.
Firstly, are you getting a good earth connection with your multimeter (-) lead? If not, that'll give you a false reading. If you have to, extend it back to the batery (-) post with a length of wire.
Certainly if the pump was taking loads of current it would drag the supply down - but not if the pump's disconnected, obviously. Could be that the relay contacts are arced to hell... DC motors are an inductive load which is the worst thing you can switch with a moving contact, as in a relay; when you break the current you get a nice spark that vapourises the contacts, eventually leading to carbon deposits and a resistive connection.
The relay is a standard 4-pin, single pole, 12v coil, 30A type. It will have terminals numbered 30/51, 85, 86 and 87. 30/51 is the feed from the battery, 87 goes out to the pump, 85 and 86 are the coil terminations. If you can find a 40A-rated device, so much the better, but it shouldn't need it. You could temporarily swap with MOST of the other relays already on the car, my preference would be something little-used like the boot release or washer pump. Just don't use the injection system 'Main' relay as it's different (has two '87' terminals instead of one).
Certainly if the pump was taking loads of current it would drag the supply down - but not if the pump's disconnected, obviously. Could be that the relay contacts are arced to hell... DC motors are an inductive load which is the worst thing you can switch with a moving contact, as in a relay; when you break the current you get a nice spark that vapourises the contacts, eventually leading to carbon deposits and a resistive connection.
The relay is a standard 4-pin, single pole, 12v coil, 30A type. It will have terminals numbered 30/51, 85, 86 and 87. 30/51 is the feed from the battery, 87 goes out to the pump, 85 and 86 are the coil terminations. If you can find a 40A-rated device, so much the better, but it shouldn't need it. You could temporarily swap with MOST of the other relays already on the car, my preference would be something little-used like the boot release or washer pump. Just don't use the injection system 'Main' relay as it's different (has two '87' terminals instead of one).
On the generic SD1 Efi system there is a 1.2 ohm ballast resistor to reduce the fuel pump voltage to about 9 volts,
The original purpose was to reduce pump noise. Even with 9 volts the pump is perfectly capable of sustaining the fuel pressure in excess of 36 psi.
Some folks dish the ballast resistor, the fuel pressure maximises at about 55 psi - much more than is required, the pump life is reduced and noise increases.
Dunno about TVR's tho'. The more noise the better - usually!
I would not worry about the pump relay getting a little warm, the pump is pulling 2-3 amps or therebouts.
Your fault is probably elsewhere, the engine is starting on the rush of fuel from the CSI, and then dying after that is consumed, suggesting the main injectors are not firing to sustain combustion, so you have to look for reasons therin.
Good Luck
The original purpose was to reduce pump noise. Even with 9 volts the pump is perfectly capable of sustaining the fuel pressure in excess of 36 psi.
Some folks dish the ballast resistor, the fuel pressure maximises at about 55 psi - much more than is required, the pump life is reduced and noise increases.
Dunno about TVR's tho'. The more noise the better - usually!
I would not worry about the pump relay getting a little warm, the pump is pulling 2-3 amps or therebouts.
Your fault is probably elsewhere, the engine is starting on the rush of fuel from the CSI, and then dying after that is consumed, suggesting the main injectors are not firing to sustain combustion, so you have to look for reasons therin.
- Running signal from coil neg to pin 1 of the ECU.
- Power supply to injector power resistors missing.
- ECU toast.
- Wiring/connector problems on any of the above 3 items.
Good Luck
Edited by honestjohntoo on Monday 20th September 10:41
i just assumed that the pump would need 12v to run! if it only needs 9v then i'm going to assume the pump is blocked or knackered as i'm not getting any supply at the engine, i've been only running small amounts of fuel in the tank due to the car not being road worth for the last year so guessing i've dragged some crap through. i've read some where that its possible to reverse the pump to clear blockages, is this true and if so how?
Yes, peeps do that to eject crud. Find the connector from loom to pump and disconnect.
Take a 12 volt battery and connect it to the pump terminals, I'm pretty sure the loom earth wire will be Black so you can work the polarity out easily enough.
You wont knacker the pump by doing this as it is capable of taking 12 volts anyway.
So that you have some idea WTF you are doing its always a good idea to read-up about the component first. The PDF available from this clicky will enlighten.
Take a 12 volt battery and connect it to the pump terminals, I'm pretty sure the loom earth wire will be Black so you can work the polarity out easily enough.
You wont knacker the pump by doing this as it is capable of taking 12 volts anyway.
So that you have some idea WTF you are doing its always a good idea to read-up about the component first. The PDF available from this clicky will enlighten.
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