Tii / E28 Fuel Pump Qs

[Einspritz]

Consider carrying and using a roll or two of the silicone stretchy tape. You can wrap the pump to the thickness you need.

 

Also great to have if you get a cut in your (silicone or otherwise) radiator hose as it will work over slippery coolant and then self seal. Impervious to fuel too.

[Swiss 2002Tii]

On ‎6‎/‎24‎/‎2018 at 1:23 AM, Einspritz said:

The OE wiring to the fuel pump is 1 mm wire. This produces a voltage drop of over 12%, so either pump cannot pump to the specification.

 

Comparing OE to the replacement, then the output will be even less.

 

Then considering that most harnesses are original, the resistance would be even more due to corrosion and oxidization.

 

The proper size wire should be ~2.59 mm / 10 Ga.. The ground wire doesn't need to be the same since it is very short, but would be good practice to do so.

Ted,

Are you referring to the wire gauge from battery to pump, or the wiring in the pump harness itself?  How to correct if the pump wiring itself?  I believe it's a sealed unit?

Tom

[Einspritz]

In short, from the fuse box to the pump connector in the trunk. That wire is in a sheath of its own and not a part of the general rear harness, so it is relatively easy to replace.

 

The background is that I have spent dozens of hours translating the wiring diagram into a spreadsheet of To-From, what gauge, color, terminal ends, in order to make new harnesses for my car.

 

In looking at that, I also looked at what the potential current draw is vs. the wire diameter and length. I ran a few "high draw" elements in my spreadsheets to determine the optimal wire size, and found that the fuel pump wire was insufficient for the current draw, and needed to be increased. The 12% represents the line loss to the pump, so 12 Volts at the fuse is not 12 Volts at the pump under draw. The specifications of the pump for pressure and volume are rated at a specific voltage and current. The larger wire will have zero line loss to the pump given the amperage draw. The brown ground wire that attaches in the trunk is too short to have an appreciable effect.

 

In general I see that too many owners don't realize or don't care that such old wiring has far reaching effects in the car. 40 year old wire may be cracked letting in moisture to corrode the conductors, general oxidization, loosening of connectors and a host of other vagaries. No wonder your dash lights are dim, the alternator doesn't charge, the tachometer flickers and your gas gauge is wrong.

 

The takeaway is that if you ant to replace the OE pump with the E28 pump, which has a lower performance than the OE, it might be best to have the wiring the best it can be for any pump.