car wont start by key but will bump start
Moderator: martauto
hi there my sport will not start by ignition but will bump start, it will go for a few minutes and then cut out, i have replaced the fuel pump relay, and tested the pump, the car isnt getting petrol, when running its going great no missfires, any help please
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jamie325isport
- E30 Zone Regular
- Posts: 689
- Joined: Sun Jan 16, 2005 11:00 pm
- Location: W.Sussex
Has the alarm played up at all recently? If it has one? Ive had it before where a car will turn over but the imobilliser wouldnt allow power to the pump. Have you got power to the pump? Although it runs fine for about 10 mins and dies? Mmmm. Would think likely cause is a duff pump.....
Wanted:- One Genuine 7J Alpina. PM me
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Brianmoooore
- E30 Zone Team Member
- Posts: 49358
- Joined: Mon Jan 10, 2005 11:00 pm
How did you measure this 7 volts? With the pump plug disconnected?
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Brianmoooore
- E30 Zone Team Member
- Posts: 49358
- Joined: Mon Jan 10, 2005 11:00 pm
Your fuel pump draws a current of around 2A. Your meter draws a current of about 0.000001A.
To record 7 volts, you have 'lost' around 5.5 volts somewhere, which, at that current, is a resistance of about 5,500,000 ohms.
Now reconnect the fuel pump, and through 5,500,000 ohms it will receive about 0.0000136 volts.
In other words, as I've posted before, leave the meter in the cupboard - it is useless for testing unloaded circuits, and test with a small 12 volt bulb on a couple of pieces of wire. I do most of my electrical fault finding with an old E30 indicator repeater bulb, holder and wire with the plug cut off.
There should only be power at the fuel pump plug when the engine is actually turning, or you have linked 30 and 87 of the pump relay socket.
There should be no power there with the ignition on or off.
To record 7 volts, you have 'lost' around 5.5 volts somewhere, which, at that current, is a resistance of about 5,500,000 ohms.
Now reconnect the fuel pump, and through 5,500,000 ohms it will receive about 0.0000136 volts.
In other words, as I've posted before, leave the meter in the cupboard - it is useless for testing unloaded circuits, and test with a small 12 volt bulb on a couple of pieces of wire. I do most of my electrical fault finding with an old E30 indicator repeater bulb, holder and wire with the plug cut off.
There should only be power at the fuel pump plug when the engine is actually turning, or you have linked 30 and 87 of the pump relay socket.
There should be no power there with the ignition on or off.