MSefi.com read only forum (Jan.15,2018)

I got a MSD fuel pump (nice pump for $77) which came with no instructions (I called MSD, they recommend a 30 amp fuse). Is a 10 amp fuse enough? I think the '93 Bonneville I'm using parts from had a 20 amp FP fuse.

If I use a bigger FP fuse, I'd need a bigger main fuse. Should I run a seperate fuse for the fuel pump/O2? What size would be good for the injectors/MS/FI side of the schematic?

Thanks

Take a look at the relay board schematics to get an idea of fuse ratings for the circuits you mention. If the rating is inapropriate for two compnents on the same line, I would seperate them.

As far as the Fuel pump... 10 amps may not be enough. I've seen older (less efficient) pumps draw about 10 amps when cold... I can't imagine that would be the case with a new pump, but you never know.

If MSD says "30 amps" then I would use a 30 amp fuse. (If for nothing more than warranty retention.

If your "main fuse" has a rating lower than 30 amps it may safely be increased if everything upstream (wiring, maybe a relay) is rated higher. Remember, these fuses are put in place for short protection only, so it's likely the wiring could handle more than 30 amps.

Good luck!

-Brian

Hi Tug,
Approximate flow is 43 gph (282 lb/hr) gasoline (specific gravity 0.788) @40 psi and 12 volts/5.4 amps, this is right from MSD's website (http://www.msdignition.com/fuel_7.htm)
I've been running this pump (as the primary on a twin pump setup) for sometime now, and have never blown my 10 amp fuse, even with FP as high as 60psi.

Brad J.

Thanks, Brad!

The pump says 125 PSI max on it but I hope I never get close to that, and was hoping a smaller fuse would work.

I'll start with 10A, but if If I do have to bump the fuse to, say, 20A, would it be OK to bump the main fuse to 30A, or might that lead to other trouble? The wiring will be heavy enough.

I'm not using the relay board, BTW.

Thanks again

I didn't use the relay board either, but the fuel pump,injectors and MS all have their own fuses.My injectors (8-2.4 ohm) have 2-10amp fuses, the MS has a 3amp,the MSD pump uses a 10amp and the big FP (SX EFI pump) is running a 20 amp.Every component gets it power from a common power terminal that is powered through a 40 amp relay controlled by the ignition switch.I don't run a "main" fuse, didn't feel it was necessary.

Brad J.

Actually, I'm not set up for a main fuse yet either. I was planning on putting it inline. (It might be a handy disconnect too.) I rearranged the fuse/relay box from the rt. kick panel of a '93 Bonneville, it worked nicely. Not sure where I'm going to mount things yet though.

I'm glad you mentioned all your fuse sizes. I hadn't thought much about it, was planning on using 5A injector fuses like the drawing shows. For four injectors. Doh! Guess I better bump them to 10s.

Thanks!!