Installing HFS-5 in 1998 VW Jetta. ECU switches ground?

[tsa1982]

Hello,

I have continuously had a problem with my HFS-5 install. The install was performed by a qualified shop in Connecticut USA, Sleepers Performance.

The correction of this install has been left for me to figure out though...

From my research it appears my car has a NEGATIVE switching ECU. The Aquamist DDS3 is wired to the ground side of the #1 fuel injector at the ECU. The positive side of the fuel injector lead on the DDS3 is wired to the positive circuit that runs the injectors, but this was done at the fuse box because it was the least intrusive way to connect to the positive lead without splicing another wire at the ECU plug. This is possible because the + circuit that runs the injectors is the same circuit that runs the fuel pump relay. It is a constant power source if the ignition is switched on.

The HFS-5 system is injecting mixture when the car is set to accessory and engine not running. This is a problem.

What is the wiring configuration needed in order to control the DDS3 with a ground switching ECU?

Thank you for being here to help!

Ted Anderson
CT USA

[Richard L]

If you can disconnect the red wire from the DDS3 and wire it to a +12V that "only" come alive on key position 2 (pre-crank). Once this i sdone, you will not have any more problem. If all fail to cure, there is always plan B - "to the fuel injector +".

Do ypui have a ECU pin out diagram, I mauy be able to help you finding a correct wire.

[tsa1982]

I have a Bentley manual I can scan on Monday if need be. My deduction of the engine and ecu wiring is that there is always 12v at the fuel injectors, switched to ground through the ecu.

I do not know why the ECU or DDS3 thinks the fuel injectors are operating at full duty cycle when the engine is in key position 1.

The red 12v DDS3 wire is wired as the installation manual shows but the source is always active in key postion 1. As far as I know there are no 12v sources that are only active in key position 2, because switching is done with the ground.

[Richard L]

In the absence of an +12V on the fuel injectior(-) the DDS3 will think the fuel injector is fully switched to ground. In key position1, the fuel injector may not have 12+ on the injectot(+)


Which version of DDS3 do you have? v8, v9 or v10.

[tsa1982]

You have been very helpful.

I must admit that the problem has boiled down to installation error. The + side was wired to the wrong source, causing it to come on in key position 1. I have moved the wire and the system now fully functions correctly after 2 years.

I love the Aquamist system, I wish I would have done the install myself to have avoided this headache.

Thank you again for helping me figure this out!!!!!!

[Richard L]

Better late than never. Enjoy your extra power.

[tsa1982]

FWIW the system was functioning properly when the engine was running. I just risked pouring a whole bottle of juice into the intake if someone tried to leave the car in key 1.