Discussion and questions related to the course Practical Harness Construction - Club Level
I am not sure the correct place to ask some questions that I have, however I attended the Club level course so thought it would be appropriate to ask here.
My project scope changed part the way through the build and I changed from Non VVT heads to VVT heads on a Duratec V6 engine, basically the fords came rockers and Hydraulic tappets with non VVT, but the Jag had a different head with solid buckets and VVT.
This means that the Loom I had made from scratch for my Syvec S8 doesn't have provision for VVT, therefore I spent some time going through revising the documentation to what i have and what I believe I need and after following your course I am now in the process of making the changes.
One issue I have is that I don't have detailed information on the VVT, here is what I do know however:
1. The Valve is effectively an on/off switch, when activated it allows oil past, when inactive it shut oil off completely and this adjust the cam to two positions only (it doesn't continuously vary the timing).
2. The actuator has a two wire plug.
3. The Valve is controlled by a 300Hz PWM signal which sets it to either the fully open or fully closed position.
4. I am using an Ignition output that is PWM capable.
5. The Vlaves are controlled based on an RPM range, they are open at idle, closed in mid range, and opened again at high RPM.
6. There is every possibility that I wont be able to use these valves anyhow at the high rpm, what I am targeting is relatively unproven.
So my questions are:
a. Is it correct I control it with 12V?
b. Do I send the PWM signal through the Negative or Positive feed to the Valve?
c. Am I ok to control both valves from the same PWM signal from the Syvec?
That oil solenoid is fed a PWM signal which effectively gives in many intermediate postions not just on/off. The ECU handles this with the PID control, and will adjust the PWM so that the actual position meets the target. Normally you feed 12V to one side, and the PWM signal from the ECU grounds the other side.
You need to make sure the Syvecs ECU can handle the crank / cam pattern you will be providing, and can control the variable CAMs (are there 2 intake cams, one on each bank. Is the exhaust cam adjustable?). I would expect that it would, but you should work on configuring that so you can be sure all the pins required are available.
Thank you for your response.
Whilst the Valve has many potential positions, the Jag documentation I have found confirmed that the Valve only has two positions, Full open and Fully closed at set RPM targets. It is a 4 Cam engine but the VVT is only on the inlet cams.
I previously managed to get a megasquirt Map for the engine, they simply switched the valve and didn't PWM it which is not something I feel i want to copy. In fact they did not even use a cam position sensor and just used wasted spark.
The Syvec and supply a PWM signal, I have used 3 other inputs to control 2 fuel pumps and a water pump from pins of the same specs from the ECU. I do have a spare Full H bridge available if the amps are too high, but they are very small solenoids so Im expecting the Ignition output to supply enough amps to switch them both.
The Syvec spec notes on the ignition output is "can be used to drive up to 10A peak / 5 A continuous if driving a IGBT Coil, 40ma is TTL. Can also be used to drive PWM"
I am however a very long way from an expert in this field and i'm not sure how i can check?
You need to get better info about how it does actually work on your engine first because you obviously have some incorrect info as David pointed out. If it is just two state vvt on/off, then it is not PWM at all. Only fully variable cam phase systems require PWM so that also means you would also need cam position for both cams wired to the ecu aswell.
I dont know that engine at all, but the valve you show in the picture is typical of what a fully variable VVT solenoid would look like.
Google images of "Jaguar AJ30 camshaft" suggests that engine has fully variable intake cam phasing.
The info I have is from the Jag technical documentation and the contradiction you mention is contained within it hence my confusion. Ive attached the pages from this document but the final statement from it was:
"The oil control valve is controlled by a 300Hz PWM signal from the PCM which sets it to either the fully open or fully closed position".
I already had a single Can sensor and have re-organised my ECU to give me another input for a second, however after I obtained the Jag documentation it is not clear if I need two or just one so I managed to get a Map from the Megasquirt were someone was using the VVT, however their setup doesn't even have a cam sensor present and they just switch the valve so provided me no insight on how to do it properly.
However the documentation and the people I have found that have tuned with the valve present do all say that it is used either fully open or fully closed and it isn't variable in-between which seems odd that it is PWM.
Of cause what may have happened is that it was designed to be fully Variable, but they ended up simply using it as an on off switch but didn't do any redesign... all the castings for head, cams etc are all stamped ford even though it was Jag specific and not used in any fords so its possible they didnt have options for re-design.
From the advice on this thread it seems i have three choices now:
1. remove the VVT as per all the high power NA engines i have found.
2. Simply switch the pair of solenoid's using a single pin as per the Megasquirt example. Maybe do it in a more precise way using PWM.
3. Try and run the fully Variable and see how it goes, (means running another Insulated Cam sensor wire and another wire to the VVT solenoids (probably power and use existing two wires for the negative switching).
The Info I haven't provided is that all the examples of this engine i have found are all NA, however my engine is turbo-charged.
In the ford head we use very mild cams to make big power to 8000rpm (head work made big gains in efficency) so for my initial research engine i have simply flowed the heads and am going to try the stock cams with VVT.
I have a big spec engine in the wings, but i want to get the car running with a lower spec engine and gain some intel before the spec of the big engine is finalised.
It may be that the OEM Jag ECU isn't capable of running completely variable CAM, so they just use fullly advanced and fully retarded. From your description of the hardware however, I would expect to be able to do full VVT control with the proper ECU.
I took the decision to add an additional Cam sensor and move the solenoids to my spare pair of half bridges so they are fully separate, i can them PWM control each solenoid separately if i need and later remove it if it proves to add nothing or be pointless running it PWM.
Thanks for the help and advice.