Fuel pump relay

Roughly a year ago my truck lost connection to the fuel pump relay due to a pin melting. I moved the pins to a vacant slot in the fuse box and put in a new relay. The relay is a skinny version of the stock square one and napa said it was all the same.

It lasted about a year untill last week it wouldn’t start due to no fuel pump. I bypassed the relay with a piece of wire and got fuel pressure. I replaced the relay and it started right up.

This lasted about a week I drove it about 20 miles from work went to run an errand in town before I went home and when I came back out it wouldn’t start again. And again no fuel pump….

I bypassed it again and had fuel pump. So this time to get a mile home I left the wire in the pins and drove it home.

I inspected the pins on the fuse box and they do not appear to be getting hot but pin 87 is melted at the base of the pin.

I know it must mean something is drawing more amps than it can handle or has a bad ground but I’m not sure how or where to start figuring this out any ideas?

Even something as simple as a loose connection can cause arcing and thus melting around the connection point.

Oh I forgot to mention it is a 96 k1500 rcsb.

And It has had the updated harnness. I know of the connection on the frame rail near the tank. It has been cleaned and tight before but it’s been a while since I was there

I would test amp draw on the pump. Sounds likely the pump is pulling to much ampage.

Any idea how old pump is?

Most multimeters will test a 10A load. Some will test 20A for "short periods", but really they're meant for 10A loads.

MY meter has fuses made out of Kryptonite, or gold, or unobtanium. It's one of those that is supposedly good for 20A "short-term". One friggin' fuse inside the meter is $10+. So it pays to not overload the amperage testing part of the meter.

That said...I don't know what sort of ammeter you have access to. The fuel pump draw should be something like 6--7 amps. So a typical multimeter would be adequate unless the pump has excess current draw.

The BEST way to check fuel pumps is with a low-amperage probe, connected to an oscilloscope. That way you can check the amperage draw of each individual bar of the fuel pump armature. You could also calculate the fuel pump RPM as well.

You'd want to test the voltage supply to the pump, as close to the pump as practical--typically at the rearmost harness connector before the harness goes up 'n' over the fuel tank. And verify that there's no voltage on the ground for the fuel pump, too. Both voltage tests have to be made with the fuel pump RUNNING.

If the engine won't start even after cranking long enough to build oil pressure, there's something wrong with the oil pressure bypass--the oil pressure switch or the wire harness that powers the fuel pump when the engine has oil pressure.

A plugged fuel filter will make the pump work harder; increases the current draw. Be sure your filter is still good.

I put the fuel pump in roughly 30000 miles ago and maybe 5 years? The filter has been replaced since then.

I do have a multi meter though I’m pretty certain it’s 10 amp max. I don’t have any other kind of ammeter.

The first time the relay died last week I turned it over enough to build oil pressure and it didn’t make any difference.

I am going to “the big city” tomorrow is there a budget friendly ammeter or tool that I could pick up?

I do have a fuel pressure gauge though I’m not sure if that would tell me a lot.

I finally got some time to do some investigating.

The receiver pins in the fuse box look fine and seem to be tight. I did do an amp draw test and had 6.75 amps. My battery is low so it’s on the charger right now and I’ll try it again with a charged battery. I’m wondering if the pin that melted just isn’t connecting snug with the female side making it hot?

I got some factory relays while I was at the salvage yard the other day both square and rectangular 5 pins so I’ll try a factory one too and see if it works

I did the amp test again and got about the same. I did notice however that the oem relays I got at the salvage yard and the after market relay I got at napa are slightly different. The pins on the oem on are ever so slightly thicker and fit tighter than the aftermarket relay. I believe this could have caused my issues.

I slapped an oem relay in it and I’m gonna let it ride for now I’ll keep an eye on it though. I did stash more of the relays in my glove box if I need them. Hopefully I wont

dirtautoguy said:

The pins on the oem on are ever so slightly thicker and fit tighter than the aftermarket relay. I believe this could have caused my issues.

Click to expand...

Giving the pins a few degrees twist tightens them up.

So just an update on this issue. Last week I drove about 2 blocks to my dads house and the truck wouldn’t run due to no fuel pump.

I tried bypassing the relay like last time and it did not work. After about a week of messing with it in my spare time which wasn’t much I found that I had no power on pin 30. The relay would click to prime but no power was available to turn it on. The lights were on but no one was home so to speak.


Today I took the fuse box apart and his is what I found. Pin 30 was burnt to a crisp. I did a continuity test on the end of the pin and I probed the wire where the black stops and had no continuity.

So today I took all the wires to the fuel pump relay and wired them up to an external relay with 1/4” terminals and I put an inline fuse on pin 30. It runs now and seems to be working. I am hoping that IF I have any issues with it from now on it will be external so I can get to it easily.