Since installing megasquirt my fuel pump no longer turns on so instead of trying to figure out whats wrong I was just going to rewire my stock fuel pump and get rid of the almost 25 year old wiring. Actually this might just give me and excuse to put in my new MSD pump. My question is what should I wire it into that turns on when the key is on start? Or should I just wire it to a switch?

This is a dumb question, but with an aftermarket pump seperately wired in like that how would the pump know when to shut off or slow down or whatever the heck it does if your only idling or something? Im not quite sure how all that works?

thanks
Rob

 

stock the pump is only on when cranking or when there is oil pressure, and I think there was some kind of timer built in so if there was a lag between the engine starting and when oil pressure built up the pump would stay on. close analysis of the stock wiring and the diagram will tell you what you need to know. if you successfully built and installed MS, this should be no problem. a relay that will turn the fuel pump on when the ignition is on might be OK by itself, but for safety's sake and the sake of your battery I would use a stock style setup so you wont run your fuel pump unnecessarily.

 

alright thanks. I guess Ill try to make it work with the stock setup. I have checked all the basics but cant figure out why I have no power to the pump maybe it has something to do with the fuel pump control module?

 

Have you traced the power wires w/ a multimeter? I toasted my fuel pump control module... so I know it can be done.

 

Nismo, I just put in my MSD pump and well doing so I used my dvm to see if the power wire to the pump had power which it didnt, makes sense. I was searching and found a post were you had mentioned something about the FPCM and how it was located above the ECU. So for the hell of it looked in that area but im not sure which one is the contol module?

Is this it?

 

Indeed that is it.

 

well that explains a lot. It was not hooked up. Im going to go out on a limb and say that would cause my pump to not have power?

 

Prolly an excelent chance... how was your old fuel pump getting power?

 

If you want to re-wire it not using the stock setup, I used a 10ga wire with a relay and 30amp fuse. The heavier gauge wire will give you little or no voltage drop at the fuel pump. Voltage drop = fuel volume drop

 

Nismo, It worked fine before I installed Megasquirt but when the harness was made I must of left it out. So that means I have to find that plug if I even have it and try wiring it into my new harness.

I will most likely end up going with your idea Veyenyl. How fast will it drain my battery with the pump constantly going? Will it cause the pump to overheat or anything like that?

thanks

 

Also where is the fuse for the fuel pump located?

 

The pump only turns on when you turn the ignition switch on so it shouldn't drain your battery. I have the fuse wired in-line with the power wire going to the relay.

 

unless i'm mistaken, (which happens more than i care to admit) your fuel damper (regulator) controls the pressure. I had a bad (my whole wireing harness needs to be replaced) wire to my fuel pump. I ran a hot lead from the top fight fuse to a switch and then to the pump. (the top right fuse on my 75, 280 only has power with thge key on!) the switch is for safety. I can kill the fuel any time. MAKE SURE YOU INSTALL A FUSEABLE LINK IN THE WIREING!!! Good luck.

 

Fuel damper & fuel pressure regulator are two different things... Fuel damper controls surges from the pump, fuel pressure regulator controls... you got it... the fuel pressure.

 

correct as always Nismo.

 

also since he ditched the stock wiring/ecu/afm there was a switch (micro switch i think) built in the afm to allow the stock relay to turn on the fuel pump, with that removed, wont it not have that signal anymore? i'd say do veyenel's idea and save some head ache.

 

Id be interested to see if this is true?

 

the fuel pump turns on for 5 seconds when the key is in the on position, and is also on when cranking.

 

Where exactly should I tap into? All the obvious places have really thin wires and im guessing I should wiring it into something atleast as the thick as my 10ga fuel pump power wire?

thanks

 

The only thing you'd need to tap into would be an ignition wire to kick on the relay. Any power wire that is hot when you turn on the ignition can be used. Then just run a 12v wire to the relay, hook up ground, and switch, then run the output wire to the fuel pump.

 

alright thanks Nismo

 

Personally if I were in your situation I would get a relay, a 12v rocker or toggle switch, an inline fuse and some good quality wire and wire the pump to the rocker/toggle switch and relay. Seems like a good idea to me...isn't the fuel pump on all the time when the engine is running anyway? I would think it would have to be or you would get no fuel to run the car.

 

last thing you wanna have to do is remember to flick a switch. currently the fuel pump uses a relay under the hood triggered by something (ignition) you could use that trigger to make a new relay turn of and hench turn on the pump. no need to really tap into anything else when the system is alreay in place. after all a realy uses less that 3amps to turn on.

 

I apreciate the help. I haven't worked on any cars for alteast 6-7 months now and have forgetton most everything. What size/type relay do I need? Is it something I could just get at Radioshack?

So if I use a new relay and a 30amp fuse then i can just wire it into say the ignition switch?

 

Just get a heavy duty relay at AutoZone / your parts store. They look pretty much like the stock relays:



And here's how to wire it (replace "spotlights" with fuel pump):