Fuel Pump Relay - how warm is this supposed to get?

[ArchStanton]

I know this is the up-teenth fuel pump relay discussion.

1988 240. I was experiencing intermittent stalling at speed, especially on hot days. The problem temporarily alleviates if you let everything cool down. So I replaced the fuel pump relay. The old one only looked to be about 10 years old. The problem did not go away. Popping the cover off the fuel pump relay, Coil 1 clicks on and then gets hot with the ignition on, even though fuel pumps are off. Hot enough to can't keep your finger on the coil after a minute or two. This is with the engine and fuel pumps off. The relay is drawing 0.9A on pin 30, about half of which gets output to the ECU and half to the MAF. The female connector block and all the spades look good and seem to make good connection. Wiring looks good. Cleaned up the grounds. I replaced the 25A fuse and holder behind the battery because it was in a bad way. No change. New and old $20 cheapo fuel pump relays have the same behavior. If I disconnect the wires that go to the MAF and ECU the input current on pin 30 goes down to about 0.2A, but coil1 in the relay is still heats up. I don't see any broken or melty solder joints in either relay.

The heat is definitely coming from the relay coil. Is that normal? At this point I've ordered a nicer $50 relay. Not sure what else to do? I replaced the in tank fuel pump a few years ago when it failed, and I replaced the main fuel pump last year because it was getting noisy. They work fine and draw the proper amperage. But they're not even in the circuit when this thing is cooking. My stop-gap solution is to position the relay under the floor blower and crank it to 4.

Thanks!

 

[Mr. V]

I suspect it's a resistance issue; not sure what to do other than look for lousy connections or a crimped wire somewhere.

 

[dl242gt]

Did you clean the grounds on the intake maifold? The fuel rail hold down bolt grounds are very important.

 

[945T]

It's normal for these fuel pump relays to get fairly hot to the touch when the fuel pumps have been running. If yours has become unusually hot then I'd normally say it's a badly worn main fuel pump that's now drawing excessive current, but you've pretty much eliminated that thought with relatively new pumps plus you say the fuel pumps aren't running when you check it. My second thought would be an under-rated fuel pump relay. My preference has always been the heavier duty Stribel white relays that are rated for 30 amps. To the best of my knowledge the Volvo OE relays are rated for 25 amps, while some say the OE Volvo ones were made by Stribel so are also 30 amps. Kaehler (KAE) are also rated for 30 amps and generally highly regarded. Cheap aftermarket relays are often only rated for 20 amps. In your case with both new pumps and a new relay, I'd also be suspicious of the relay connector. With repeated heated and cooling cycles over a number of years the copper female terminals can oxidize and the copper metal start to harden and loose it's grip on the relay terminals. I'd now want to try doing some maintenance on that relay connector using contact cleaner and tweaking the sides of the female terminals in for a better grip. Failing that I'd start thinking about a heavier duty relay and a new relay connector.

 

[bobxyz]

"Hot enough to can't keep your finger on the coil after a minute or two."
If you mean it's too hot to touch a minute or two after turning on the key, then that's not normal. If you mean that with key on you can only hold your finger on the coil for a minute or two, then that's normal.

 

[ArchStanton]

Ugh, I forgot to check the fuel rail grounds, thanks. But they are good.

I disconnected pin 86/1, the ground signal from the ECU, and replaced it with a wire straight from the battery post ground. Coil 1 still heats up. So I don't think it's a ground or connector issue. And there's nothing else in the circuit. I think these two relays are both junk. A more expensive one should be on its way in the mail. Fingers crossed.

I appreciate all the help. Definitely learning a lot here!

 

[ArchStanton]

Well, I got the expensive Meyle relay and that one is not getting hot. So that's one success. Here's a pic of the Meyle next to the other two hot relays. Significantly different construction.


However, I'm still getting fuel cut outs at high throttle. In the rear now I see that I have 13.1V going to the sender pump. But zero amps. I just replaced that thing a few years ago. I guess I get to do it again? Maybe I did a number to the whole circuit somehow when I replaced the main pump. Not sure how that would have happened.

 

[945T]

Glad you're making progress. Double check that the in-tank pre-pump is correctly wired +/-. Some have a black wire that would normally be used as ground, but should in fact by wired for +12V from the relay. Way back (over 20 years ago) I mis-wired one for a relative's 240 that then had excessive fuel starvation symptoms at 2,000+ rpm. Embarrassingly, before telling me it still wasn't working right, they took it to a shop who soon figured out what I'd done wrong.

For fuel starvation issues, there's always the question of when you last replaced the fuel filter?

BTW, just because the Meyle relay uses plastic sealed PCB relays doesn't mean they're superior to open-frame relay coil construction. Plastic enclosures keeps out moisture, but open-frame cools better. It's the quality of the contacts, coils and construction that really matters. Made in Germany Meyle is generally considered high quality, but the made in Hungary white Stribel and Volvo OE relays are generally considered superior. I'll take the Meyle and KAE 30A relays any day over other unknown brands.