mikevernon
Active Member
- Joined
- Jan 3, 2008
- Messages
- 61
- Location
- Kenilworth, Warwickshire
- Car
- SLK320, BMW Z3, 530d, Caterham 7, Frogeye Sprite
I have a 2002 SLK 320 which has been standing for some months and now will crank but won't start. I replaced the crank sensor but stupidly didn't bother to check for fuel pressure first, and I now realise that the car won't start because the fuel pump doesn't run, not because the CPS was faulty. (I was fooled into thinking that the fuel system was ok because engine started the first time I tried it and ran for a short time, presumably because there was some residual fuel pressure in the system). I always tell other people to take a logical approach to problem solving rather than replacing parts until the problem is cured, so I'm ashamed that I didn't follow my own advice!
Before I take off the fuel pump I need to find out if is receiving power. I haven't yet taken the plastic cover off the pump to test it because that looks an arkward job. I have uncovered the K40 relay thanks to Bazzle's post, but I'm not sure which of the 5 coils supplies power to the pump. When I turn the key to the first position (ignition on) the contacts on coils 3 and 4 close (counting from the left, ie. the side with the 40amp fuse). Turning the key to the second (start) position has no further effect, so the contacts on coils 1,2 and 5 remain open. Manually closing the contacts on number 1 operates what sounds like a fan motor, and doing the same on number 5 operates the horn. I'm guessing that the fuel pump should be operated by the closing of one of these sets of contacts, but which one? I believe that the pump only runs for the first 2 seconds after switching on, or when the starter motor is running, shouldn't I be able to observe the relevant contacts closing under those conditions?
The soldering on the K40 circuit board looks absolutely fine by the way. Can anybody point me in the right direction to test the fuel pump without getting under the car and removing the cover? If I knew which wire supplies the pump from the K40 unit I could simply jump a 12v feed to see if the pump operates.
Before I take off the fuel pump I need to find out if is receiving power. I haven't yet taken the plastic cover off the pump to test it because that looks an arkward job. I have uncovered the K40 relay thanks to Bazzle's post, but I'm not sure which of the 5 coils supplies power to the pump. When I turn the key to the first position (ignition on) the contacts on coils 3 and 4 close (counting from the left, ie. the side with the 40amp fuse). Turning the key to the second (start) position has no further effect, so the contacts on coils 1,2 and 5 remain open. Manually closing the contacts on number 1 operates what sounds like a fan motor, and doing the same on number 5 operates the horn. I'm guessing that the fuel pump should be operated by the closing of one of these sets of contacts, but which one? I believe that the pump only runs for the first 2 seconds after switching on, or when the starter motor is running, shouldn't I be able to observe the relevant contacts closing under those conditions?
The soldering on the K40 circuit board looks absolutely fine by the way. Can anybody point me in the right direction to test the fuel pump without getting under the car and removing the cover? If I knew which wire supplies the pump from the K40 unit I could simply jump a 12v feed to see if the pump operates.
