Another possibility to drive a 'retro-fitted air box solenoid' could be from the kick-down switch under the accelerator pedal - as this is also activated under high rpm/load....

 

If I was going to test the solenoid, I would probably attach a small test light and drive the car.
This explanation is from the 2003 XK Training Guide.

 

Great, thank you for the attachment. it says the solenoid receives a constant 12 volts and is interrupted by ground as needed... Meaning the 12V holds it closed and the interruption opens it. Is that correct?

 

The constant positive supply on the solenoid means the EARTH side is controlled my the ECM.

As the document states "The ECM provides a PWM signal to control the operation of the solenoid."

When the ECM commands the 'flap-open' it sends a Pulse Width Modulated EARTH signal to the solenoid.

 

Thank you i appreciate your knowledge and patience. I measured 11.45 V with key on car not running. I pulled the air box out and the flap is closed by the spring by default. So the constant 12 volts does not activate the solenoid to do anything since it's naturally closed by the spring. I'm guessing then, on acceleration, the PMW signal makes the solenoid armature thrust outward to open the flap against the pressure of the spring. Then another PMW signal makes it retreat to default solenoid in, flap closed position. Is that correct? It seems so backwards, normally you apply voltage to make a solenoid armature move vs removing voltage right?
Then how do I know if my solenoid is acting on the ECM signal or may need to be replaced?
Thank you again. I certainly appreciate you.
Mark

 

l believe most electronic modules use ground switching to energise various functions.

 

Gone are the days when a POSITIVE circuit is applied. Modules usually GROUND (EARTH) signals to achieve actuator movement or relay control in modern cars.

If I was going to test the solenoid, I would probably attach a small test light and drive the car.

 

Thank you, very interesting. So the flap is closed and solenoid armature is in the in, position with no current (unplugged) and remains in the same position plugged in and 12 volt applied at start up. Then when current is removed, the armature shoots out to open the flap. But when the car is turned off, 12 volt is removed but somehow, the solenoid knows to stay in this time.
I'll try the test lamp. I've fixed and worked on devices using ac and dc for 50+ years and this makes no logical sense. I appreciate your trying to help me understand what must be very simple to you, but makes no sense to me.

 

With + voltage applied to both sides of solenoid you have no circuit, with no + voltage applied to either side you still have no circuit, with + voltage on one side and - on the other you now have a circuit.

 

Now, i technically understand that. Why someone would design it thst way vs simple off on +/- DC circuit is beyond me. But finally I understand. Thank you.

 

It saves on running multiple B+ power feeds, possibly high-current, for each circuit. For instance, most of the stuff at the rear of the car is served by one main feed to the trunk fusebox. Relays are then used to supply that power to its destination. They only need a small current to energise them.

 

So it looks like the 4.2l XKR ECM completely controls when and how much the flap opens, presumably with input from the AFM or engine load/rpm (or road speed, or ambient temp, or intake air temp, who knows). It is not a simple on/off.

It feels like you could still wire a simpler retrofit circuit with a permanent ground and a controlled 12V, like, off of the secondary fuel pump relay as a crude approximation.

The more complete solution emulating the ECM would be something like an ELM327 connected to the ISO-9141 (or CAN) bus. It would read load/rpm/AFM from the data bus, and then produce its own PWM signal with an appropriate duty cycle to achieve the same fully controlled percentage opening. Hard to believe someone would not have a ready-made programmable box for these kinds of projects already, but I have not researched it. Seems strangely overkill, but why not.

Best of luck, keep us posted.

 

I tested the solenoid with 12 volts. It activated but barley opened the flap a crack. Suppose i just leave the spring un-engaged? The flap will open itself with any suction. Anything wrong with that?

 

Just saw this. My solenoid only opens the flap a crack with 12, or 11V. Are you indicating higher voltage could push the solenoid out further to open the flap more? The armature will extend out further than it does with 12 volts. Maybe my solenoid is bad? Maybe I'll just take the spring off the flap and let it do its own thing under air suction. I've never seen a solenoid that was gradually moved the armature more or less. Is this pita little flap even worth all this? Lol

 

Yes, but is the solenoid grounded? I would assume applying 12V to a properly grounded solenoid would activate the full travel of the arm.

PS: I have an XK8 and no direct way to test this, I would encourage you to check if there is enough resistance to not blow things up.

That is what PWM does. It quickly cycles on/off and control what percentage of the time it is on vs off (duty cycle) to effectively control how much the solenoid extends.

 

The soleined is mounted in pure plastic. The only 2 connections are 2 yellow wires. No other

electrical paths.

 

If you want to retrofit a flap to the 4.0 airbox, you can easily control it with a (adjustable) boost switch.
Like this one:
https://prometh.com/collections/boos...itch-hard-line

 

I used these type back in the 70s for my Callaway VW Rabbit Turbo Kit. (still have it)

https://www.autoevolution.com/news/t...re-169891.html

 

One of those two yellow wires goes to a fused 12v supply that comes on with the ignition switch. The other wire goes to the Engine Control Module and provides the ground when the ECM decides to turn the solenoid on. To test that the solenoid is getting power and ground (as already suggested by motorcarman) connect a 12v test light to those two wires and see if it comes on when driving.

To see if the flap is the cause of your problems, why not jam it open or remove it and see if your hesitation goes away?

 

Perfect-thank you