Double_J

iTrader: (28)

More like questions I suppose but here goes.


My battery is relocated to the trunk and my fuel pump is wired to the battery.

In an effort to figure out why my fuel pressure dropped towards the end of last year, I hooked up a voltmeter to the car. The voltage on both the powerFC, and the voltmeter seem to range a little bit. I assume that is normal but how much is normal?

The PowerFC reads around 13.5-14 volts. Usually it is in the 13.8 range.....

The voltmeter is reading 13.09-13.7 range.....

Now I guess you could have a bit of a drop since the current has to get to the back of the car. I also assume that the two readings might not be accurate, and that is why they do not line up.

Before I go further I want to also mention I put an electronic thermometer by my air filter. ( This was done for another reason ).

I have noticed that as the temperature rises under the hood, the voltage seems to go down. It also seems that my car back fires much more when it is hot ( under the hood ).

I have not monitored the PowerFC readings to closely in the past so I have no comparison for the knock but it seems like climbs as the temperature increases too.

Is it safe to assume I might need an alternator or new wiring at the very least? That as it gets hotter, the current drops, and the chance of knock increases?

thewird

iTrader: (8)

Try testing before and after the relay and see if there is a difference. Have your alternator rebuilt and see if there is a difference. Keep in mind at idle you don't have full voltage.

thewird

rd_turbo

iTrader: (4)

The resistance of any conductor (new or old) will increase with temperature. Here's a quick formula for your reference: http://www.allaboutcircuits.com/vol_1/chpt_12/6.html

Also Google "resistance of XX awg wire" for whatever wire gauge you're using, that will give you a starting point for comparing resistance. Larger gauge wires are not immune, but less sensitive to temperature swings and less likely to heat up so a bit of a vicious circle.

There are way too many variables here and if you're doing this theoretically, you'll also need reliable temperature readings.

You didn't indicate if your voltage reading was at the battery or right at the pump. If not at the pump, that's where you need to start. Not sure how your pump was rewired, but basically the relay should send full battery voltage once triggered and, at that point, there should be a negligible voltage drop between the battery and the feed at the pump. If there is a substantial difference, change the wiring and/or relay.

Double_J

iTrader: (28)

I put the volt meter on the battery because it was easiest and I figured the current would be the same since the battery and the pump are close.

The readings were taken on the highway. All cruising speeds on the 401. Water temps were always the same but as the intake temps rise the volts go down. I assume things must be heat soaking, and thats why the temps continue to rise.

I am talking a bout a 30-40 minute drive.

I will try to see how it was wired, and go from there.

Double_J

iTrader: (28)

I got another question. Assuming it is a wire that is causing a problem ( and not the alternator ), would getting an upgraded alternator make the issue worse or would it be a bandaid fix? Another words, would it cause a faulty wire to heat up more quickly or would it have enough power to over come a potential shortcoming?

thewird

iTrader: (8)

It would do neither. If the wire was overheating, it would continue to overheat. The pump only draws the amount of current it needs regardless of how many amps are being produced by the alternator.

It's wired directly from the battery to the relay and then to the pump. So the only thing in between would be the relay. I would look at that. You could try hooking it up direct (skipping the relay) and see if its the same.

thewird

Double_J

iTrader: (28)

I don't see a relay.....

I see a blue and red wire.....

Blue goes to the -terminal. Red goes to +

Unless it is under the plastic along the side. The wires tuck under there but I did tear it apart.

thewird

iTrader: (8)

There has to be a relay somewhere or your fuel pump would be on all the time. I'm sure its in there somewhere :P

thewird

Double_J

iTrader: (28)

Yes I get that

The red wire goes to the switch on the battery box. The one that was installed when the battery was relocated. I am pretty sure I've measured power from that point while the car was off but it wasn't 12v. I can't remember to be honest.

Is it suppose to get power all the time? Would that kill the power when the car is off? I vaguely remember us looking for the switch at the dyno shop. The tall guy who did the mod came over and flicked the switch on the battery box.

I will also try removing the plastic panel to see if its tucked under there too.

ScrappyDoo

iTrader: (7)

I don't think you are looking for the relay in the correct spot. The relay is between the fuel pump and the battery. Trace the wires from the pump backwards and you'll find your relay.

Double_J

iTrader: (28)

Just found it! It was under the plastic panel. Those panels are stupid. In order to get the one off, I had to undo almost all of the others.