Wont start when cranking since going electric f/pump

[mini1380cc]

Hi All,
I'm hoping someone can help out here. I have recently swapped the mechanical fuel pump for a solid state fast road pump. The feed and earth for this comes from the fuse box on the bulk head, using ignition live. Since making this change the car will not spark whilst cranking and it only fires up when letting go of the key.

I think this is something to do with too much load when the starter motor and pump are running together and its only when the starter disengages that the coil then gets enough current to spark.

As you can imagine it takes a few attempts to disengage right at the point when one of the cylinders is at the point of firing. The battery is fairly new and can crank for literally minutes, so i don't think that is the issue.

Any ideas?

[tr7v8]

Use a meter or bulb to check there is power on the pump & oil when cranking, I'd bet there isn't any. If it is conventional points then run a wire via a fuse from the battery 12V straight to the coil ign or + connection. If it runs then you have a wiring fault from the ignition switch to the coil.

[mini1380cc]

I'm a little confused by your reply. The oil pump is mechanical and shouldn't come into the equation whatsoever. The fuel pump is getting power as you can here it ticking with ignition and the fact that the car runs fine once started therefore the pump is pumping.

All that has changed is taking an ignition feed from the fuse box for the new pump. I thought an ignition feed would be appropriate so that the bowls can prime before cranking.

Should be be taking the feed from somewhere else? Somewhere that wouldn't affect a current drop on the coil?

[tr7v8]

mini1380cc said:

I'm a little confused by your reply. The oil pump is mechanical and shouldn't come into the equation whatsoever. The fuel pump is getting power as you can here it ticking with ignition and the fact that the car runs fine once started therefore the pump is pumping.

All that has changed is taking an ignition feed from the fuse box for the new pump. I thought an ignition feed would be appropriate so that the bowls can prime before cranking.

Should be be taking the feed from somewhere else? Somewhere that wouldn't affect a current drop on the coil?

Bugger! Typo it is meant to read COIL!

[mini1380cc]

Yeah its defo an issue with the coil and current. Before adding the electric fuel pump the car ran fine so we should be able to assume that the wiring at the coil is fine, also as the car runs it would prove that the coil is doing its job once the starter disengages.


I suppose the question is this...


Is there a recommended place to take the fuel pump feed that would allow sufficient current to the coil pack in order to get a decent spark whilst cranking?

[miniman]

Why not try this:

Switch on the ignition and let the fuel pump prime the system, then disconnect the pump and try starting the car (i.e. so the pump is no longer drawing load that the starter motor might want).

Might be worth putting a relay into the circuit so the connection you're currently using only has to close the relay rather than supply the pump.

[mini1380cc]

That could be easy enough, I'd just let it prime then pull the plug at the fuse box end.


If it fires up doing this it would confirm that there is too much draw with the pump added. Where do I go from there?


This is the second pump by the way as I thought the pump was the issue.

[stevensdrs]

You need a fuel pump relay so that the ignition circuit only provides low current to the relay which activates high current direct from the battery via an inline fused connection to the pump.

[mini1380cc]

Well that's it fixed. The rev counter was faulty and drawing too much current. Disconnecting it from the coil instantly fixed it.