I have a k-jet b-21F with Chrysler whitecap. After about five minutes of operation the GREEN fuel pump relay gets too hot to touch. I have since replaced it about two times because the old ones end up molten where the square connector plugs in. I keep about 7 or 8 spare relays in my map pocket just in case! Why is it over heating?? The fuel pump is brand new Bosch from IPD as is the in-tank uint. I also installed new filers at both the firewall and inside the tank. I The electrical connections to the main pump are kosher. The fuse for the main pump; albeit new, will become thin as a hair and red hot. The insides of the dead relays are a molten mess of soldering and green plastic. The wires leading to the square plug are always hot to the touch. I mean third degree burn kind of hot! What's going on?

Those K-jet relays are a known problem area, but there's something amiss in your car, going through them that fast.

If you have an Ammeter capable of handling up to 15Amps, remove Fuse No. 7, and jumper across the fuse terminals with the ammeter. (Red lead to the left terminal, Black to the right). Start the engine - you should see about 9 Amps. This is the current draw of both main and tank pumps - and a little for the control pressure regulator and the O2 sensor system - and is what the relay has to handle.

If your relays are persistently overheating with this current, have a look at the wire connectors at the harness plug. A bad connector will get very hot and conduct the heat into the wires, and via the terminal(s) into the relay circuit board.

Thanks Volvodad. The plug isn't exactly square anymore and the blades where the contacts are made are porbably 75 percent covered in melted stuff.I'm going to replace the the plug somehow and see what happens.

The reason it started getting all melty was from running a fuel pump way past what the relay could handle. It got to a point where for about the the past Year I have been running on a switch made with a green pnp fog lamp switch (acc position above the headlamp switch) using a connection jumpered from fuse 5 (or7?).

Yeah, kinda dumb, but once I made that jumpered connection and recovered from a no start situation in the middle of nowhere I kinda rested on my laurels and forgot about it. I thought "cool I'm using a real volvo switch as a kind of theft device and pump acuator in one!" Hah till one day I went into work leaving the switch and the pump running until the relay imploded which - I'm sure compromised the wiring even further. 14 bucks later a new relay but still have the super hot wires.

Pre-85 cars are scarce and k-jet car are extreeeemly rare here in Miami. Can I use an LH plug for the relay from a non-k-jet car, say from a post 1985?

The later LH relay harness plugs look to have the same 6-terminal configuration, if so the plastic housing would work. Wire colours and thicknesses will probably be wrong. You can remove the LH spade connectors and place your K-jet ones in there.

Some people rewire the K-jet fuel pump circuit such that the original relay terminal 87, which carried fuel pump power on its Yellow-Red wires, is just used to trigger another relay - a simple 20/30Amp Bosch type. This second relay gets battery power from a new wire (with 15-amp fuse), and its output is connected to the Yellow-Red fuel pump wires. This removes about 80% of the current load from the stock fuel pump relay, while retaining its safety feature of making terminal 87 live only when ignition signals are coming from the coil.

That's pretty darn clever. I may have to print your response and implement the change in my '84 T wagon. I redid the plug going into the relay with another boneyard plug out of a 740, as all the wires were cooked in a previous life. Definitely a kind of under-engineered piece on these cars, and 26 years of vibration, heat, and oxidation don't help much either.

Hi, Ben - I surely can't take credit for this idea, I first saw it on the "stealthfti" website, which has a lot of useful Volvo modification info.

http://www.pbase.com/stealthfti

Scroll down to the thumbnail "Fuel Pump Power" for the how-to details. Personally I think the guy went a little too far, but it's also unlikely he'll EVER have a power-to-the-pumps problem again!

The added relay mod plus Art's usual thoughtful solution of re-terminalling to eliminate corroded copper should get you another 30 years out of your K-Jet.

My understanding of this problem (which necessarily only comes from my experience) is the relay is up to the task. The under-engineered part is the spade connector itself and its ability to retain the crimp force on the harness wire over 20 years. It is a tail-chasing problem, because the heat takes the spring force out of the connector and its crimp, increasing the contact resistance, increasing the heat.

So replacing the items that suffer damage from proximity, like the relay or the connector shell, won't help much, if done alone. Offloading the relay with a second relay will be effective if that relay's spade terminals are new and properly crimped. A second benefit is, the auxiliary relay is cheap and plentiful at your local auto parts store, so if for some reason the rewiring isn't up to snuff, you're not out looking for another k-jet relay.

Another effective fix is to use a new terminal and a short length of new wire, spliced into the overheated one a few inches up the loom, cutting out the oxidized copper. Most of us do not own the correct crimping tools to install the barbed, snap-in female spade terminals, so we solder them, a whole lot easier to do with fresh material.

There are two places in a 240 with this same problem repeatedly reported - the k-jet fuel relay socket, and the 86+ headlight relay socket. Here's an example of the headlight relay.





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Art Benstein near Baltimore