fuel pump relay failure

[mtdr]

Had an incident where my engine (coyote) shut down after about a 3 hour drive. I turned the key off then on and noticed I did not hear the fuel pump. I removed the relay from the fuse panel and it was pretty hot. I replace it with a spare I had. Fuel pump worked again and I proceeded home. After arriving I put my fingers on the relay installed. I was also hot. Not so much you could not touch it but non the less, hot. I know this relay has to be operating for continued use of the fuel pump, but should it be hot.

I'd appreciate any thoughts from the forum.

Tim
Mount Dora, FL

[mtdr]

The relay that failed was a TYCO that came with the Ron Francis wiring. I am more worried about the heat in the relay itself. I hope there isn't a problem in the wiring circuit.

[rich grsc]

You should be using an electronic relay, not a mechanical one.

[boat737]

You should be using an electronic relay, not a mechanical one.

Please elaborate.

[rich grsc]

I'm sorry, solid-state, not electronic. This is a returnless fuel system?

https://www.delcity.net/store/Hella-Solid-State-Relay/p_809798.h_809799

[BEAR-AvHistory]

Should be a return system. Where on the board it the pump relay?

[Railroad]

It may be a pump issue.

[2bking]

........ After arriving I put my fingers on the relay installed. I was also hot. Not so much you could not touch it but non the less, hot. I know this relay has to be operating for continued use of the fuel pump, but should it be hot.

Short answer is it should feel warm to hot. Just because the relay feels hot doesn't necessary indicate a bad relay. An energized relay generates heat.

There are two sources of heat inside the relay. The first is the heat generated in the coil when the relay is latched. It is between 1.4 to 2 watts depending on the coil resistance (higher quality relays have a higher resistive coil and consume lower power to operate). The second sourced is the voltage drop across the contacts where the switched current flows. A .1V drop at the contacts (typical of quality relays, TYCO relay specifies .2V @15 amp load) with a 20 amp load will generate 2 watts of heat (TYCO will generate 3 watts). This and the coil generated watts inside the cube relay will cause the outer shell to feel hot but may be a normal condition. The TYCO relay spec says it will work in a 125C environment. A case temperature of 54C will feel hot to the touch. Should you be in a 25C environment, that's about a 30C rise in case temperature so operation in a 125C environment would make about a 160C case temperature. It seems to be capable of working under the dash as well as under the hood.

There are also external sources of heat such as the wiring to the relay and type of connections. Whether push on terminals or the socket is used, contact resistance can generate heat here same as internally. But contact resistance seldom gets better with time and usually becomes apparent when the insulation on the wires starts to melt and smoke appears.

[DaveS53]

FWIW, GM uses mechanical relays for the fuel pump and fan in the fuse/relay boxes that come with LS engines. You should have a 30/40 amp rated relay. The linked solid state relay is only rated 20 amps.

[mtdr]

I'd like to thank everyone for their input. I have replaced the tyco with one from O'Reillys auto parts. (2ER13). I also will keep a spare in the glove box at all times.

More information: I noticed corrosion on pin 30 of the TYCO at time of failure. My chassis was at the paint shop and perhaps they rolled it outside and exposed it to rain(?). With the position of the fuse/relay panel you could see how the contact could get wet. On further inspection, opened the relay and found a burnt area between the case and relay. Can only imagine that there was water inside.

King, thanks for the explanation of the relay especially related to the heat. I can't see as I have any wiring issues. Hope that is the end of this glitch.
I remember talking with you a couple years back about your design of the drivers side foot box. That worked out perfectly for me. Myself and many others enjoyed watching your build. Great job! Thanks again.