Mechanics

FUEL PUMP VOLTAGE

1986 Honda Prelude

Electrical problem
1986 Honda Prelude 4 cyl Front Wheel Drive Manual 250K+ miles

I have a 1986 Honda Prelude 1.8L Carbureted Manual Trans. I'm only getting 2.7 volts to the fuel pump through the wire harness with the cut off relay in. When I try to by-pass the relay to test the fuel pump I get 0 volts with the ignition switch in the on
position. What could it be?
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Fgb56
October 25, 2010.




Power the fuel pump direct from the battery and see if it'll come on. If it does best test the main relay thoroughly-could be the injectors shorted out dragging down the voltage they tied in together to include all the solenoids-
AD

Rasmataz
Oct 25, 2010.
The fuel pump powers on with 12 volts applied directly to it. This is a carbureted engine 2 carb 1.8L. No main relay just a fuel cut-off relay that tested good. What else do you think it could be? The ignition module is new and I have a good spark also, pump is just not turning on when it's plugged into the harness. Can't even hear it turn on. Really low voltage like 2.7 all the grounds are good. I have 12 volts at the fuse block. The pump doesn't have a fuse just the relay between it and the fuse block.

Tiny
Fgb56
Oct 25, 2010.
Sounds like a problem with the ignition switch-check the ignition coil if you have battery voltage on the pos. term.

See diagram


http://www.2carpros.com/forum/automotive_pictures/12900_fp_68.jpg


Rasmataz
Oct 26, 2010.
Thanks I'll do that. Also when I measured the coil primary it was 1.9 ohms. The values should be 1.07 to 1.6 ohms so it's out of range slightly. The secondary is 9,300 ohms, the range should be 7,000 to 11,000 ohms. Could a bad ignition coil primary cause the pump not to turn on too by dragging the voltage down? I'm trying to understand this from an electronic perspective.

Tiny
Fgb56
Oct 26, 2010.
I checked the voltage on the + side of the ignition coil and it's 12 volts (battery voltage). Do you have a wiring diagram of the ignition coil, where ALL the wires go. There is a blue wire, a black/yellow wire and a black wire from the distributor harness. Could this possibly be the problem, the wiring of the coil? Right now the blue wire is on the - negative terminal, the black/yellow is on the + terminal, There is a brown wire from the switch harness going to the - terminal on the coil also. There is a larger black /yellow wire going to the switch harness that is on the - terminal. A gray ground to the body from the switch harness and two blue wires that go to a harness on the - terminal. The black wire from distributor harness is a bullet connector that plugs into a black/red wire on the harness. I'm going to check all the grounds and see if I have continuity.

Tiny
Fgb56
Oct 26, 2010.

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