Electric Fuel Pump

[VWRacer]

I've been reading in another thread about fuel filter issues and was wondering why the TD's don't use the external electric pump like the one sees on Mk1 gasers? Is the problem supplying the IP with too high pressure, something else or just that it simply doesn't need the help?

Thanks!

[vwmike]

You really don't want to run a CIS pump on your diesel. The Rabbit ones move 128 l/h and are capable of supporting 100 psi.

[malone]

PD TDIs first got the external electric fuel pump, they definitely needed it anyway.

Bosch approves the use of an electric fuel pump for rotary pump TDIs as well. The idea is to help the injection pump work better, and it probably does.

The low pressure side of the fuel injection pump may last longer due to less long-term stress from drawing the fuel.

I used an electric fuel pump for my 1.6TD... no problems. It's useful for priming so the engine fires up on the first few cranks if the pump is dry. Dry pumps are rare to have so this benefit is probably negligible.

A TDI chip tuner from the East Coast claimed to have 8HP gain in the upper RPM from an electric pump, in a modded 240 HP TDI (they supposedly dynoed before/after pump).

Because I haven't seen any negative effects of using an electric fuel pump, I'll continue using it.

[QuickTD]

A low pressure electric or mechanical lift pump is often used on other diesels with VE pumps. A lift pump makes priming a snap and might marginally improve high rpm power. Injection timing is controlled by injection pump housing pressure, so you don't want high pressure. If you choose to go with a lift pump, it would be best to use a low pressure unit. 5psi would be plenty. The small cylindrical solenoid type pumps that look like an inline fuel filter work quite well.

[2383 GTD]

When you really start increasing fuel delivery, it is easily possible to pull a vacuum at the intake port of the IP.  I've done a lot of measurements with this, and was successful with several solutions, using various fuel pumps.  A CIS pump will work fine, as will most FI pumps.  Be advised, the gas fuel pump will draw more current when used on our cars.

As far as the 8 whp increase with the fuel pump on, I would suspect with the fuel pump off, it may simply be from a slight or strong vacuum being created in the fuel line, which decreases power.  The process qualitatively behaves as follows: a noticeable, fairly linear decrease in power, injection timing starts to become retarded, then onto a massive, non-linear loss in power etc.  The power loss will be most prevalent wherever maximum fuel delivery occurs, and often well before it if you are pumping a large quantity of fuel.

A good test would be to dyno the car a few times without the fuel pump producing full pressure, but with no vacuum, say at 1psi fuel pressure.  A PWM power supply allows this, or a simple bypass.  Then, dyno the car under the same starting conditions (engine temp, IC temp, hopefully same atm conditions, etc) again a few times with the fuel pump producing full pressure.

[VWRacer]

Good stuff here, guys. Thanks!

Yeah, the CIS pump is rated at 65-75 psi, so that's probably overkill. However, I have some of those small solenoid types for carbed engines that put out well under 10 psi, so that might be a solution.

I was thinking of applying this to my diesel racer project. It seems that the fuel filter is a potential bottleneck in the fuel system, what with its need to filter down to near-micron size. A few psi of positive pressure might be just the ticket for maintaining good flow through the filter at sustained high rpms.

[andy2]

At my work we run 5psi supply to vw/ve pumps on the test bench as per bosch test procedure.without a supply pump the stock setup its probably fine up to a point where we make the pump deliver 100%+ fuel than stock,this probably causes a higher than desireable inlet restriction.I was going to put a supply pump on mine I just never got around to it.