No power to fuel pump fuse

[Ian Bowers]

Hey guys, had to AAA the car home last night. It's been fine for the past 7,000 miles, I washed it yesterday and then it wouldn't start. I replaced the fuel pump fuse, it started right up, drove it, got gas, no problems. Went to pick the GF up and it wouldn't start. Test light does nothing on the fuse, jumping the relay does nothing.

1987 325 w/95 S50, red label ecu, fusable link is fine. I'm at a loss--any ideas that I'm overlooking?


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[dirtbag30]

check the main relay?

or try this? ive had similar issues before and i remember there being issues with the main relay too, found out they got wet and it ruined the relays.

OK, so I am gonna try and shed a little light for you here, you seem really stuck.

First, make damn sure you have a testlight. I mean a $5 cheapie is fine, they sell one at WalMart for $5.37 or whatever, that is just fine. I hear of you NOT having an actual LIGHT BULB I will quit offering any help...seriously, have a test light in your hand.

Even if you solder wires on a light bulb, I don't care...test light ONLY.

The reason is simple: a meter will read voltage even if it can't pass enough current, so you need some kind of actual "load". Light bulb = load, make sense?

Now, start with the first relay, the one furthest forward. That is your main relay. The main relay provides power to the fuel pump relay AND the DME. If it does not work properly, you get no fuel pump.

Remove the bracket that holds all 3 relays and flip it over. Grab your test light and probe the biggest of the 3 wires that make a row in the center of that relay. The test light should light up. Now, have someone else turn the key on while you are holding the relay block: that main relay should "click". As soon as it clicks, the other 2 wires (the medium red and red/white) should go live. If they don't, again, you have no power to the fuel pump...so you have to fix that first.

Now, assuming you have power to the input of the fuel pump relay (from that test you just did) it is time to test the fuel pump relay.

Remove the relay, look at the contact map on the side. You will see that "30" connects to "87" when the relay is switched. 30 is the wire from that main relay, 87 is the wire that feeds the fuel pump.

So, now that we have power going into the fuel pump relay (key on, main relay working) look at the bottom ("pin" side) of the fuel relay (oh yeah, that is the one in the middle, the rear one is the O2 sensor heater relay) look carefully at the terminals: they have tiny little numbers.

Here is the actual answer to your question: you jump from "30" to "87" to power your fuel pump.

You can shove a paperclip in the sockets if you must: I use a short hunk of wire with 1/4" male non-insulated "spade lugs" crimped on either end. Hell, a pair of needlenose will do just fine, but get the right pair jumpered: 30 to 87. Do not fuck that part up, read your shit carefully.

IF it does not spin up (early cars run BOTH pumps off the same relay) you need to test voltage at the pump. Go back to your transfer pump (main pump on late cars) that is under the hatch, under your back seat: use your test light to make sure you have power at the pump itself: no power means bad wiring (assuming the relay is still jumpered) but the reality is that mot likely, you have a bad main relay.

Figure it like this: that one little relay runs everything in your car, basically: fuel and DME. 20+ years is a LONG time.

Let me shed a tiny bit of light on that, too: every time a relay "opens" or "closes", there is a tiny spark. The tiny spark does 2 things: first, it eats a tiny bit of the contact (itself smaller than a pencil lead) and it makes a little carbon soot. Both the hunk of metal missing and the soot mean a crappier connection...multiply that by 20 years of starting and stopping the motor, you can understand WHY they fail.

Hope that helps: do a I say and you will have a working fuel pump in no time.

Oh yeah...the crush in the vise thing is true: if you crush it, it is likely bad.

Good luck!

Luke

[Ian Bowers]

Gave that a try, I have no power to any relays with the test light.

I have 12v at all eyelets on the firewall, 12v at the starter, 12v at the fuse box, 12v at the green wire going through the c101, but no voltage to any of the relays, dubya tee eff.

[dirtbag30]

check the crank sensor too.

[Ian Bowers]

AFAIK, crank sensor would prevent the fuel pump from firing during crank, but it should still prime, and it wouldn't have an affect on the lack of 12v to my relays. :\

[mpowerful]

On the m50 harness there is a separate power wire that runs the main relay and the others. Track that one down and check voltage going in there.

[Ian Bowers]

Update:

fusable link was blown. I replaced it with a standard audio fuse/holder during the swap, and the fuse itself looked fine, had no appearance of being blown, but I replaced it for shits and grins, all is well in 24v land again.