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?

moconnor

iTrader: (14)

A small voltage from from the battery to the PFC is to be expected given the reasonably involved path involved.

Unless there is something seriously wrong with your ignition circuitry (or Twin Power), variations in alternator voltage will not cause ignition issues.

HawaiianRedMako

Are you measuring straight off the battery terminals? 13.5-14 volts is normal for a properly working alternator. The difference between the PFC and your VOM meter, could be the meter needs to be calibrated or it's tolerance level range is wider than a more expensive meter.

It's NOT a good idea to wire straight off the battery terminals w/o some fuse protection, if for some reason the fuel pump is defective and starts drawing too much current, the wires will burn and might burn your FD!

Try and measure off the fuel pump terminals, check the ground and fuel filter.

Temperature and voltage are inverse, high temperature = low voltage. Higher temperature means higher resistance in the wires, thus lower current and lower voltage "pressure"

Double_J

iTrader: (28)

I got another question. Assuming it is a wire that is causing a problem, 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?

moconnor

iTrader: (14)

The voltage drop is normal (all wires have resistance) as is the change with temperature.

Backfiring could be related to your tune, a worn dashpot or a whole host of other things.

HawaiianRedMako

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?

fuel pressure drop could be a number of problems, bad ground wire, clogged fuel filter, rubbish in gas tank, bad lead connection, or fuel pump going bad?

Adding an upgraded alternator is fine, only if you intend to add more electrical stuff like a boom box with amplifer that draws more current. Be sure to match the current draw (amps) of your fuel pump, too much will destroy it. That's why its advisable to use a fuse rating and not tap it directly from the battery without one.

However, you also need to use the proper wire size too. Too small wire, will cause it to heat up.