Afternoon all;
My lovely green vectra wouldn't start this morning, cranked but no attempt to fire. Checked the codes using paperclip method, got usual crank & cam sensor plus P0201, P0202, P0203, P0204 - voltage high on each injector. Checked Haynes wiring diagram, realised injectors return current path is through the fuel pump relay. Removed relay, after hasty Google to locate, and replaced with paperclip. Car fires immediately.
Purchased lovely new purple relay from Vx dealer for relatively reasonable 17 quid, car works.
What did worry me is that the two relays which control the fuel pump and injector return were every warm to the touch, even after a 10 minute journey. Is this normal? In theory they should be dissipating very little power, just the current through the actuating coils, so i don't see why they should be warm.
Is this normal doctor?
P.S. Simtec 56.5 ECU
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It's the other way round; the fuel-pump relay also feeds "12 volts" to the injectors and the ECU provides a variable-length earth-pulse to open them.
The fuel pump takes a significant amount of current; so, if the relay is warm, that's not too surprising.
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Ah right Screwloose thanks for that, looking at the Haynes book of jokes properly it is indeed the live supply fed in parallel to the pump and the injectors, with the earth side of each injector having a connection to the ECU pins 40 -43 to provide the pulsed return.
Thinking about it these relays are sitting in a sealed black box with no ventialtion, so I suupose even a few watts of dissiaption will cause localised heating.
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The fuel pump current through the relay contacts should not cause the relay to heat up significantly. If it does, you have contact problems and the relay will not last long.
The heating is due to copper loss in the relay coil. Car manufacturers are not charities (especially GM) and don't give away any more material than they have to. Consequently cheap automotive relays have a mild steel magnetic circuit and minimal copper in their coils. Modern wire enamel makes it possible to run these pretty hot.
At the other end of the scale, old Post Office relays had machined cores and armatures made from magnetically soft Swedish iron and a low loss copper coil which was sufficiently long to equalise the iron and copper losses. These relays could be left fully energised with no perceptible coil temperature rise at all.
659.
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Yes, I'm tempted to drill some holes in the top of the plastic box the realys sit in, to lower the temperature a bit. On the other hand I suspect the relay I've replaced was the original, which has lasted 134481 miles, even at an elevated operating temperature. The guy on the parts counter did say the realys were a popular spares item mind you.
As a railway modeller; I find the old post office relays are still saught after for use as signal / point motors, for the reason you state :-).
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