Recently had alternator and charging issue which are all worked out now. Everything is working great except I had always noticed Fuel Pressure (Electric Aeromotive Pump) wasn't quite what I wanted. Was only putting out between 45-50lbs and under boost would start to drop off. Needs to be around 60 and with the boost referenced regularot should climb.

In checking the schematic for my engine management harness there is a relay that it wrapped into the harness for the fuel pump. This is trigged by the computer to come on for the first 5 seconds to load the injectors then of course once the engine is started. However, the main lead from the harness to the fuel pump, which therefore goes from the front to rear ofthe car, is only about a 20-22gauge wire. I also wanted to run it to the dash through a toggle switch in the asktray to kill the pump if I wanted to.

The switch gets hot and by the time power gets to the pump I'm only getting about 10.3 volts which is no where near enough.

So, would the best thing to do is run another relay from up front with a heavier gauge (14?) wire front-to-back and through the switch? I don't want to cut the one out of the harness if I can help it. I would also prefer not to run the main lead straight back without a switch.

Suggestions? Thanks!

 

great looking work!
if the switch is getting hot, excessive current is passing thru it, or the switch itself is defective. disconnect both ends of the wire going to the relay, and check for a short with an ohmmeter. if thats ok, check the relay for proper resistance, then the switch.

 

I would not trust them damn lit parts house switches for anyting over 2 amps, they are not good quality parts....so I would use it to control another relay, or inline with the computer control to break the existing relay coil power....and run a nice 14 ga wire to the fuel pump in rear, one shot, then make sure you solder all connections, no crimped push ons, modern crimp crap they sell at parts houses are all China, and they have thin metal in them, so the wire will slide out super easy due to no strength in the metal....you look at a for sure AMERICAN made crimp connector, and the modern junk we see on the shelf, and you will see what I mean....I have given up, and solder everything these daze.....

 

I swapped the switches around and even tested the voltage without the switch at the connections there and the other switches got hot when in line with the fuel system and without the switch I only have about 11.7-12v's with the Voltmeter showing 13.8 or so. Obviously between the engine management harness and how I wired it to the switches it's taking a hit and causing resistance.

As much as I hate to I agree with the striaght 14gauge shot to the rear. Maybe just put a cutoff switch on the ground side?

Thanks guys!

 

The longer the wire run, the larger the wire size you need to carry the same amount of current. You can continue to use the wire in the harness...just add another 14ga wire to run along with it and hook them together at each end. The switch may be getting warm because of the wire resistance; or it may be too puny, also. Check its current rating. Its rating should be at least twice the amount of current the switch will be seeing continuously.

 

if i understand you correctly, any switch that is used to control the fuel system gets hot? the switch contols the relay, and the relay controls the pump? if so, the relay may be shorted. disconnect the wire at the relay( the coil side) and measure the voltage at that point. with no load and an open circuit, the voltage should be tha same as the alternator output. you have a short somewhere, and it must be tracked down!
replacing the wire to the pump is not going to effect the switch, because the load from the pump has no bearing on the load on the switch. that's what the relay is for.

 

Not quite.

The relay is an integral part of the engine mangement harness. It is triggered by the computer. Out of the harness also comes this small gauge wire that is to go to the Fuel Pump which is in the rear of the car. This wire would of course have to come off the relay somewhere but it's upstream of the switch.

That line is as 7t1 stated probably just too small to carry the current that far and throw in the switch and more resistance and it's just getting overloaded.

I'm going to try running it straight back to see what I get at the pump then.

 

I like the idea of putting the switch in-line with the ECU control wire. That should be a very low current line and not cause the switch to overheat.

I got to thinking about electric fuel pumps and crashes from a recent thread so this weekend I'm adding a roll/crash switch that will turn off all of the relays connected to the ECU - same as turning off the key.



Rick B.

 

that's my point. if the wire to the pump is hot(assuming the pump is ok) a larger wire is needed. but if it's the switch that heats-up, there's a short in the switch circuit-not the pump circuit. and that could be a bad relay, switch, or just an old fashioned short.