Main fuel pump relay keeps overheating. Wondering if the pump is drawing too many amps. Main pump isn't that old and in tank pre pump is new. Checked the fuse and relay socket wiring. Applied Dielectric grease. Any ideals????? Anyone know the ohms resistance of the main pump.

I read through your posts, and I'm thinking that you should pull the relay and fuse tray. I had a photo once upon a time of me taking a brass brush to the exposed contacts for all fuses. You can pull each set of fuse contacts out and inspect, clean, and "tighten" them. I think that either the fuse or relay socket is loose. Could also be the other end of the wiring, but the heat being that local is weird.

The original relays can be easily repaired/improved if you remove the solder and replace it with tin-silver solder. At the very least, it melts about 40F higher than lead-tin solder. It's really critical to clean the contacts inside the relay, but if this is multiple relays... I'm not sure.

How did you determine the fuel relay is overheating?
Are you blowing fuses 1 or 11?

Bill

Bill, the relay has a browning spot where the power feeds it on the spade. Opened the relay cover and found melted solder on the related circuit board. Somethings draw excessive ampre. Happened to three relays so far. All were fixsd with some rewiring. Checking the main fuel pump wiring this weekend. Two year old main pump and one month old in tank pump. Running a modify relay to which I wired it so the 12volt by-passes the contacts in the relay.

Poor contact in that socket on the relay tray is a known problem area for 700s and 900s. Presumably a previously overheated relay due to a worn pump, an inferior relay or improper seating can soften the plastic and allow poor contact. From there the problem escalates, even to a new relay, with the now poor contact overheating relay pins and socket contacts witnessed by darkened areas on the relay board and further melting of the socket to the point of crispy black edges and relay failure. Flip over the relay tray to verify this and if you can’t get it cleaned up with tight reliable contact then consider replacing the relay tray or even just the socket with a good used one. Others may have more ideas in the way of bandaid fixes.
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now

Yes ! I did pull the fuse / relay tray out and went over everything. Cleaned and applied dielectric grease to every fuse and relay connection. The new relay just melted it's solder at the power in stop. Thinking about clipping in a separate fuse holder but, need to order a heavy gauge one. Runs find with by-passed relay but, something is pulling power. Could just be cheaply make relays. Lots of draw between two little contact.

Yes, smells like an insufficient relay. Think Genuine Volvo, Stribel or KAE that order, or Hella if it was the smaller cubed one used with some later NA B230 engines
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now

Does your relay have a part nr. ?

My recently replaced funky FI relay was a Stribel 12V 898151.
Got a new #3523608 on ebay for $20, and that fixed it.
Beware junk yard or used fuel relays.

What are the values of the fuses you have for F1 and F11 now?

Were you blowing either of those fuses before?

Would not bother with a use relay. Changed my 25/amp.fuse to a 30/amp. Fuse. The wiring to the relay is large enough gauge and stays cool now. It would seem to be narrowed down to insufficient quality of manufacturing. It all gets down to the relay contacts being able to flow transference of power. My emergency by-passed relay eliminate going through the contacts. Seeing 9 volts stamped on the relays metal parts make me think its under rated. Checking the main pumps electrical connections this weekend.

Were you blowing fuses F1 or F11?

Never blew the fuse. 25amp fuse just heated and deformed. Circuit has large enough gauge wire to use a 30 amp fuse. No problem occurred when switching out the fuse. It all leads/traces back to the relay. Runs fine when using my by-pass relay. So the contacts inside the new relays are not holding on the pump side to the power transference. Relay did have a 9 volt stamp in the metal. Weak point in a cheap brand of relay. Three.relays have suffered the overheating. All failed at the soldered circuit. Repaired each one with new solder. Could the in tank primary pump be the problem of the power draw? I did replace with a supposedly more powerful pump. The blessing of this whole dilemma is the fuse box / relay tray come out when servicing. Thank You Volvo 740 designer's.👍

Ignition switch contacts were pitted. 243000 miles of starting showed it life span of electrical demise. The other problem was the relays needed a heavier wire from the power to the contacts. Manufacturer use the thin circuit board to transfer the power.I just stripped some twisted cooper wire and soldered it from the power input to the contact side of the relay. Manufacturers use a thin strip of solder instead of a wire which inturn acted like a fuse and blew. I chased a whole lot of electrical gremils to figure this one out. Replacing the high mileage ignition switch is something I would higly address in everyones High mileage volvo. Now since replacing my ignition switch, everything gets the 12 volts it needs. My 745t has never preformed this well. I did open up the old switch and found pitfed contacts and blackened areas where they were arcing.

Hi Paul,

Were you blowing fuses? F1 or F11?
I'd urge you to go back to the standard Volvo circuit since you have probably
bypassed safety fuel shutoff circuitry.

I'm using the 1989 740 LH 2.2 B230FT here.
#235 The fuel relay is actually two relays in one box fed by F1 25 Amp fuse to
FI relay pin 30

The first sent of contacts is closed by ECU pin 21 providing the ground
to FI relay pin 86/1
This sends:
+12V to #284 AMM pin 5 (AMM gnd = pin 1) to Ground "H"
+12V to #464 RSR coil pin 2 (RSR gnd = pin 1) to Ground "N"
+12 to 2nd relay coil FI pin 85 (Gnd via item #76 Charge Air pressure switch
to ECU pin 17)

The second set of contacts sends:
+12V to RSR contacts that provide:
1. +12V to #376 Ballast resistor (for injectors)
2. +12V to #196 IAC
Both of these items get their ground from the ECU

+12V from FI pin 87/2 To F11 15A fuse for fuel pumps
1. +12V to #210 tank pump (Gnd at "J")
2. +12V to #211 fuel pump (Gnd at "M")

You can see you have more than the two pumps drawing current.

Bill

I already have a relay I by-passed internally so the power by-passes the contacts. The thing is I brought two spare relays that had Sweden Parts on the box. I opened both relays up and found a 9 volts.stamped onto the metal frame of the coil tower. Running the by-passed relay now. Just doesn't have the safety feature now.

The question I would have - is the excessive heat caused by a high amperage draw, an arcing internal solder joint, a poor connection between the spade and the socket, or a poor wire-to-socket connection within the relay panel. Just some more food for thought….