Can someone with a 1.5D engine with the Lucas type fuel pump do me a favour please?
There's a microswitch on top of the fuel pump that is activated by a plastic cam on the accelerator arm (it's for the EGR). The switch is pushed in when the accelerator is pressed. It plugs into the loom down the front of the engine.
What I want to know is if the switch is normally open or closed (with no accelerator). This can be done by unplugging the switch from the loom and checking its resistance. If it's 0 then it's normally closed and if it's very high then it's normally open.
Thanks in advance
Anyone with a 1.5D engine
Moderator: RichardW
It probably isn't as simple as that especially if the 'switch' has three wires coming from it.
The 'switch' is in fact a potentiometer or variable resistor and when fully wired has a connection each end of a carbon track and a middle connection to a 'wiper' which sweeps across the track. You need to follow the wiring to the other end and find out what the connections are there. If it has only two connections it will be simpler to work out. When turned fully anti-clockwise, the resistance between the wiper and the left terminal on the track is lowest and highest on right terminal. When turned fully clockwise the situation is reversed. If your 'pot' has only two connections coming from it then it depends entirely on which end of the track is wired and the further the wiper is turned away from it the higher the resistance. There are other issues like logarithmic pots and linear (yours is likely linear) but it is not important in this situation. Sorry to make things appear complicated but you should be able to work it out. My Renault sytem has a pot shaft as the fulcrum for the throttle lever and has three wires which go to the ECU which does all the calculation so I can not help you as far as connections are concerned. Rotodiesel might be able to help there.
The 'switch' is in fact a potentiometer or variable resistor and when fully wired has a connection each end of a carbon track and a middle connection to a 'wiper' which sweeps across the track. You need to follow the wiring to the other end and find out what the connections are there. If it has only two connections it will be simpler to work out. When turned fully anti-clockwise, the resistance between the wiper and the left terminal on the track is lowest and highest on right terminal. When turned fully clockwise the situation is reversed. If your 'pot' has only two connections coming from it then it depends entirely on which end of the track is wired and the further the wiper is turned away from it the higher the resistance. There are other issues like logarithmic pots and linear (yours is likely linear) but it is not important in this situation. Sorry to make things appear complicated but you should be able to work it out. My Renault sytem has a pot shaft as the fulcrum for the throttle lever and has three wires which go to the ECU which does all the calculation so I can not help you as far as connections are concerned. Rotodiesel might be able to help there.
No, no, this is definately a basic sealed-unit microswitch. It has 2 wires coming out of it and a plunger thats pressed by the cam (Cam has a 'step' profile on it so it's either on or off). I dissected the one off my car as it was knackered(ie permanently open ciruit). The contacts inside were so badly corroded that they just fell out making it impossible to tell if it's meant to be normally open or normally closed when the plunger is not pressed.
The switch operates a solenoid, which in turn activates a vacuum powered EGR valve.
The switch operates a solenoid, which in turn activates a vacuum powered EGR valve.
Oops, my mistake. Really, I do know, just wan't thinking when I wrote it! No, haven't checked out the price for a new switch. As the car goes fine without it. I patched in a toggle switch on some long leads and fed it thru to the cabin. Took it for a spin and tried flicking the switch. The only noticable result was above 3500rpm when it would reduce the power slightly whith the switch in one position.
Was the switch on or off when the power was reduced? The EGR valve is there primarily to reduce nitrous oxide levels but the engine apparently runs cooler and knocks less with it in place. I would be thinking to replace the switch either with the original part or some rigged up equivalent that switches at the same point.
Have been doing some probing over the weekend....
Power appears to be increased with the EGR disabled.
When the switch (on the fuel pump)is open, 12V appears at the relay that opens the vacuum line from the brake master cylinder to the EGR valve!?! With it closed the voltage drops to about 1V.
By listening to the exhaust note the EGR appears to recirculate when the pump mounted switch is closed. The exhaust at the tailpipe has a slightly more muted sound and there is an increase in sound around the EGR vave on the manifold, which I suspect means EGR valve open.
Beezer, you can't be too far away? I'm in central Aberdeen.
Power appears to be increased with the EGR disabled.
When the switch (on the fuel pump)is open, 12V appears at the relay that opens the vacuum line from the brake master cylinder to the EGR valve!?! With it closed the voltage drops to about 1V.
By listening to the exhaust note the EGR appears to recirculate when the pump mounted switch is closed. The exhaust at the tailpipe has a slightly more muted sound and there is an increase in sound around the EGR vave on the manifold, which I suspect means EGR valve open.
Beezer, you can't be too far away? I'm in central Aberdeen.