Fuel Pump Rewire Alternative?

[skyrunner]

Hey guys, I have been reading about the fuel pump rewire that is needed for these cars and I was just thinking about an alternative. Since you run a new relay controlled off of an existing relay, couldn't you just replace the wire on the old relay instead of introducing a new part into the system (one more thing to break)?? I imagine running the wire from the MFI or Fuel pump relay back to the pump wouldn't be too difficult, since you basically have to run that much wire for the "rewire" anyway. And I can't imagine it would be too hard to run a new line direct from the battery to the relay.

Just curious what you guys think about this. I have a non turbo so I probably won't ever need to do this, otherwise I would test it out to see how difficult it would be.

 

[assault187]

Its better to just do the whole rewire. It will pull strong voltage right off the battery when the ignition is turned on to "flip" the relay. If you look at the OE wire you will notice it IS a small gauge wire, and considering DC voltage flows ON the wire strands rather the threw it, A larger wire gauge with a higher strand count will work best so there will be little to no voltage drop to the pump. The fuel pump turn on is controlled from the ECU and its output isnt that great, so running a replacment wire will not sufice and its best just to do the whole rewire.

 

[Splitpi]

Hey guys, I have been reading about the fuel pump rewire that is needed for these cars and I was just thinking about an alternative. Since you run a new relay controlled off of an existing relay, couldn't you just replace the wire on the old relay instead of introducing a new part into the system (one more thing to break)?? I imagine running the wire from the MFI or Fuel pump relay back to the pump wouldn't be too difficult, since you basically have to run that much wire for the "rewire" anyway. And I can't imagine it would be too hard to run a new line direct from the battery to the relay.

Just curious what you guys think about this. I have a non turbo so I probably won't ever need to do this, otherwise I would test it out to see how difficult it would be.

Your running a larger "thicker" power line to the Pump. You could cut open all your wiring harnesses, pullout the stock pump power line and put in a new power line then retape the harness and use the old relay (which I believe has enough amperage to handle the fuel pump by the way). .. but that is about 100x more work than running a new line and having the existing line switch another relay at the pump.

The issue isn't the relay, its the line. The rewire puts a thicker cable which in turn decreases voltage drop under load on the pump side. More voltage = more pump flow. Here is a website to help you calculate loss due to cable thickness.

I.e. 14 Gauge wire pulling 8 amps @ 12v over 8 feet will drop 3.3% or register 11.6v
a 12 Gauge line would only drop 2.1% or register 11.8 V.

 

[skyrunner]

I think you guys are missing my point. I'm not talking about cutting open the old harness, simply using the relay that is in place. I assume that the wiring to the coil is fine and does not need to be changed. So can't you simply run a new line from the battery to the *old* relay, and then another new line from the relay to the pump? It seems like a much simpler solution to me?? I know, then you will have cut one line from who-knows-where to the power side of the old relay, but I doubt that would hurt anything to leave that line unconnected. Also, the other side of the relay, the switched side, goes directly to the pump, so if you cut the line on both sides, it wont be connected to anything. Why isn't this just as good as the rewire (and simpler: fewer parts!!)?? Just curious. Maybe I will try this just to see if it works

 

[Locke]

I don't see any problem with doing it your way. Don't forget to add a fuse or circuit breaker.

 

[Splitpi]

I think you guys are missing my point. I'm not talking about cutting open the old harness, simply using the relay that is in place. I assume that the wiring to the coil is fine and does not need to be changed. So can't you simply run a new line from the battery to the *old* relay, and then another new line from the relay to the pump? It seems like a much simpler solution to me?? I know, then you will have cut one line from who-knows-where to the power side of the old relay, but I doubt that would hurt anything to leave that line unconnected. Also, the other side of the relay, the switched side, goes directly to the pump, so if you cut the line on both sides, it wont be connected to anything. Why isn't this just as good as the rewire (and simpler: fewer parts!!)?? Just curious. Maybe I will try this just to see if it works

I'm not following...

Either way you must run a new thicker line. Then its a very simple matter of connecting the existing line to the new line with the relay. I don't really see how you can simplify it further really without cutting out the old line and running a new line between it.

 

[Supa Dexta]

Pick up an amp wiring kit and be done with it. You can find decent kits for 10-20$ That come with 8 or 10g, inline fuse holder, etc.. I just picked up one locally at a "low cost, has it all" type of store..

 

[skyrunner]

I'm not following...
...without cutting out the old line and running a new line between it.

That is exactly what I am proposing. But no need to unravel the wire harness, just run a new line and snip and tape up the old one.

 

[Splitpi]

That is exactly what I am proposing. But no need to unravel the wire harness, just run a new line and snip and tape up the old one.

Ahh... that would work. As I believe the stock relay will handle the amperage. Shouldn't see much over 12A.

I would though for a safety's sake wire a 20 amp fuse in line and in an accessible area (incase you do blow it), just in case.