Quote:
Originally Posted by BoxsterGT
Anyone?
I too want a 40a "RELIABLE" relay for a Fuel Pump.
Len
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40A? Seems a tad, uh, overkill...
Fuel pump current draw is proportional to the regulated pressure; Bosch 044 motorsport pump typically draws ~11 Amps w/ CIS - and half that with EFI (~45PSI instead of 100PSI). Bosch cite absolute maximum current for that pump (which requires upgrading the electrical connectors from the factory M4/M5 to M5/M6) as 15.5 Amps - at which point it would be close to overloading "regular" 14 gauge wiring...
Even a 930 - which, stock, runs two fuel pumps, front and rear, through a single fuse position and a shared single relay (a common cause of unreliability readily addressed by a rewire to split each pump out to its own fuse and relay), wouldn't need 40A.
Fortunately, my (as far as I know) original relays in a 275,000 mile tub seem to working just fine - touch wood.
Nevertheless, I've thought about it a bit. Random thoughts.
Firstly, modern relays supplied as replacements are reported to be no better than the no-name garbage. Because they're likely the exact same garbage with a markup. Many have shared horrific pictures of the internals when their replacements died - and reverted to/still getting good service from used 40, 50 year old originals...
Secondly, part of the problem with the original relay bases is that the "round pin" configuration can cause overheating with too much current, especially when they get old/loose/dirty. Also, the relays seem to tend to work out over time as well, probably from expansion/contraction with heat cycles - which can't help. Cleaning/spreading the pins etc can help a lot - but it's like the old-design fuses; no substitute for clean, new contacts with as much contact area as possible. Hey-ho for ATO fuses.
Thirdly, apparently if you buy a new relay base these days, even if you specifically order the fuel pump one, you'll get the one with the thinner wires in the pigtail used everywhere else. Timmy2 builds these - and can supply replacements with the original thicker wire spec for the fuel pump(s).
There's more than one way to address these issues. I haven't done either of these - and flip-flop between the two approaches every time. Sigh.
PP member flightlead404 was printing relay bases (with 16 gauge milspec/tefzel wiring pigtails) that allowed you to use an ISO automotive relay instead. Which you can source at your favorite FLAPS... The industrial Panasonic ones have a good reputation, sealed, contacts rated for 10^6 operations, readily available/cheap as chips, and rated to 40A.
Alternatively, Restoration Design make a solid-state relay rated at 30A (suitable to replace the red fuel pump relay), part #RD-911.615.109.02. It plugs into the factory 5 pin relay base and accepts your original plastic relay cover. So no-one would ever know it's fitted unless they pull the relay and pop the cover - a plus for the concours types...
I don't know why our host doesn't offer it - maybe someone should ask them to?