[sloboy89]

I've had two wiring harnesses for my electronic VVT go bad on me, so rather than look for another used replacement, I embarked on a journey to find another way to activate the VVT solenoid. Essentially, the printed circuit board that is located within the white plastic connector acts to put 12 volts across the two prongs of the solenoid when a trigger signal is sent from the throttle position sensor (TPS). Therefore, I figured that if I could find a suitable relay that is triggered by the TPS signal, I could activate the solenoid by grounding one prong of the solenoid and connecting the other solenoid to the relay output (with the relay input connected to 12VDC).

I tried the standard Bosch-style coil-driven relays, but the signal from the TPS was insufficient to trigger the relays, so I went looking for another solution. After some research, I decided to try a solid-state DC relay. I ordered the 10A relay below on eBay ($9.00), waited a few weeks for it to arrive from China, and then tested it out.

A little bit to my surprise, it actually worked, and the VVT is back in business. I mounted the relay on the side wall of the engine compartment near the intake plenum. It's only been a couple of days, so I will keep checking on it. For those interested, also below is a wiring diagram of my set-up.

 

[Stevew]

McGiver would be proud!

Rich,

Nice work at an attractive price! How did you draw the schematic?

10A for the relay is no doubt overkill, but who cares? And the input trigger range is impressive!

As you know, solid state electronics do not thrive in a high temp environment, but your mounting location on the sidewall should provide a satisfactory heat sink. And of course, it will only get hot when energized by the TPS at WOT. How long do you keep your pedal to the metal? Try to keep it floored for less than 20min at a time and you should be OK .

Only suggestion would be a fuse in the 12V power line (yellow?).

You didn't mention how the other two harnesses failed. I trust they did not combust.

All the best.

 

[sloboy89]

Rich,

Nice work at an attractive price! How did you draw the schematic?

10A for the relay is no doubt overkill, but who cares? And the input trigger range is impressive!

As you know, solid state electronics do not thrive in a high temp environment, but your mounting location on the sidewall should provide a satisfactory heat sink. And of course, it will only get hot when energized by the TPS at WOT. How long do you keep your pedal to the metal? Try to keep it floored for less than 20min at a time and you should be OK .

Only suggestion would be a fuse in the 12V power line (yellow?).

You didn't mention how the other two harnesses failed. I trust they did not combust.

All the best.

I just did the drawing in PowerPoint.

The green/black wire is the 12V power; the yellow is the signal from the TPS. There is an in-line fuse (8A) on the green/black wire before the block connector. I modified the diagram to show that fuse.

There is a big heat sink on the back of the relay that is flush against the steel compartment wall.

Nothing too exciting on the failed harnesses. First one was a broken solder connection on the inaccessible back side of the circuit board. Second one just stopped working. I think it was one of the transistors that failed.

 

[SteveB2175]

Rich,

Thanks for posting this !!

I had a VVT harness fail last year, and as far as I can tell there is no new source for these. I purchased a use one, and so far it is working, but it's nice to know there is an alternative solution.

I'm saving your post in my list of reference material.

-Steve

 

[Stevew]

Add to sticky list?

 

[sloboy89]

I updated the wiring diagram to annotate the existing wires.

 

[Alfonso75]

only 2 volts on yellow when throttle fully open (no vvt operational) any idea where 8 volts comes from

 

[sloboy89]

only 2 volts on yellow when throttle fully open (no vvt operational) any idea where 8 volts comes from

The yellow wire comes directly from the throttle position switch (TPS). Maybe there's something wrong with your TPS? You can check whether it is functioning using the procedure on pages 33-35 of the L-Jet diagnostics:

https://www.hpsimotorsports.com/l-jetronic--spider-

 

[Alfonso75]

switch checks ok voltage on yellow won't go above 2 volts

 

[sloboy89]

switch checks ok voltage on yellow won't go above 2 volts

Does the car start and run?

 

[Alfonso75]

yes

 

[sloboy89]

Other than the yellow wire to the VVT, the wires to the TPS all go to the Fuel ECU. It is beyond my knowledge as to what voltages/signals should be on the ECU pins.

 

[Alfonso75]

thanks for info I was leaning towards ECU Fuel pump runs all the time and below 1500 RPM car will miss from time to time