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Boxster 986 '98 fuel pump relay - which pins are negative and positive
I need to check the relay with a multimeter, as the car won't start. Anyone know how should I connect the relay to the battery, which pins are positive and negative and which are the ones to connect with the multimeter? Thanks.
I need to check the relay with a multimeter, as the car won't start. Anyone know how should I connect the relay to the battery, which pins are positive and negative and which are the ones to connect with the multimeter? Thanks.
By not start I assume the engine cranks ok just doesn't fire?
Techs use a bypass relay to eliminate the relay. They connect "shop 12V" power to the fuel pump directly to ensure fuel pump has power and runs or doesn't as the case may be.
When my 2002 Boxster fuel pump quit that's what the tech did to verify it didn't run.
He knew the relay was ok because he loaned me his bypass relay which I used at home to confirm it wasn't the relay.
Messing around with the car's electrical systems is risky. A new relay isn't much so I'd be tempted to just buy a new one and try it. If it is not the relay box the thing and put it in the door storage bin for back up just in case.
From the Bentley manual: Operating fuel pump for tests (1997 - 2001 models).
To operate the fuel pump for testing purposes without having to run the engine bypass the fuel pump relay to power the pump directly.
Access relay panel 1 (above the fuel panel, left footwell) and remove the fuel pump relay. (Warning: fuse and relay locations may vary. See 97 Fuses, Relays, Component Locations.)
Using a fused jumper wire bridge terminals 30 and 87 (labeled 3 and 5 on the relay panel).
Make jumper wire from 1.5mm^2 (14 gauge) wire and include an inline fuse holder with a 15A fuse. To avoid relay panel damage from repeated connecting and disconnecting also include a toggle switch in the jumper harness. The fuel pump should run as soon as teh jumper wire is attached.
Yeah, I actually found that information eventually. For anyone who's interested the pins have numbers assigned to them on the relay:
- pin 85 is negative (smaller)
- pin 86 is positive (bigger)
- pins 30 and 87 let current through when connected to start the pump. These are the ones to connect the multimeter probes to.
This is how the relay looks from the bottom:
And this is how it's plugged, although I'm sure it only goes in one way:
Been working on this for weeks. Replaced relay. Tested and works as it should. Fuse tested and works as it should. Have applied direct power to the brand new fuel pump and it works and car starts and runs so it doesn't appear to be a DME problem. Have replaced ignition switch with new. Have plugged in small bypass cable to join 87 and 88.
Weird but maybe not or the key to the problem: Pulled out relay and put test light on each of the 4 relay pins (see the pic below which shows the pins). I would expect only ONE of them to have power to them being pin 86. Or one then two to have 12v after I turn on the ig key to on. But pin 86 and pin 30 BOTH have 12V power all the time key on or key off. Is that right? Also, I would expect one of the pins to go out when I switch off the ignition. It doesn't (and ig switch is new). Why would it have power on two pins all the time? Stupid question but is it because the one half of the relay is to energise the relay which then causes the other half of the relay to complete the circuit? If so why is my ignition switch not making any difference?
Next question is also weird. So if I jump pin 30 and 86 and test the connection to the fuel pump where it connects to the pump to test it, there is 12V power to the green and white at the plug (that also has the two fuel guage pins in between which work fine). But when I hard wired to test the fuel pump directly, it was the white wire side of the plug that made the pump function as it should. Is there a possibility that the wires inside the fuel pump are crossed? Is an aftermarket pump and when you replace the old pump you plug the new unit into the underside of the fuel sender unit then put the whole shebang into the tank. Maybe that is the problem? If the aftermarket pump was wired the other way around I could just swap the wires around and the pump should power up as it should with the motor running forward not backward.
But it still doesn't explain why the power is always on at the relay with the new ignition switch either on or off. Shouldn't one of the power in pins from the ig switch go on and off when I turn the key on and off surely?
What am I missing here? Pulling hair out as everything downstream of the fuel pump seems to check out. Also I can't figure out where the white and green and white wires that directly connect to the fuel pump come from. Like are they routed through the immobilisor or direct from the ig key? Thank you very much Jeremy in Brisbane Australia
04-23-2017, 03:48 PM
Boxster 986 '98 fuel pump relay - which pins are negative and positive
