Looking for VCT Information

[Torinate]

Hey all.

So I’m looking for VCT information. Not just the electrical part but also the mechanical part.

I’ve been chasing an off idle hesitation and idle miss fires for some time. Trying to get a plan for the spring when I get the car out to work methodically to get this solved.

So tell me about the VCT system. Not just the solenoids but the mechanical parts as well.

What happens with them when going from idle to throttle? Does the computer command them to change degrees? If the computer commands a change but they are slow for whatever reason, would this cause a hesitation?

What does the car do when going from idle to throttle? Say 40% pedal. From VCT, fueling, spark timing etc. I’m sure there is an order it does these things and to a certain set of parameters.

Is there a way to check if this is occurring? I’m sure logs may show what’s commanded, but will they show actual?

Thanks for the help!

Im determined to get this sorted in the spring so I can enjoy it more - even get back to the strip is the plan.

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[engineermike]

Whew, man that’s a lot.

The park position is 0 intake and 0 exhaust. The intake cams can advance 20 and retard 30 from there. The exhaust can only retard 50 and not advance. Negative is advance and positive is retard. There are 5 different cam schedules (disabled, emissions reduction, optimum stability, optimum fuel economy, optimum drivability, and optimum power). Various parameters determine what cam schedule is being used, but it’s mainly load and speed.

At idle they move to 20 intake, 0 exhaust which has very little overlap. At cruise they move to about 30, 50 (intake, exhaust), retarding both the maximum amount to extend the power stroke and reduce pumping losses. As load and speed increase the cams start moving towards the optimum power positions. At wot in optimum power, the intake starts fully advanced (-20) then retards to +10 as rpm rises. Exhaust stays in the 15 - 20 deg range.

There is a commanded and actual cam position for all 4 cams and it can be logged. You can also log error and phaser solenoid duty-cycle for all 4. Note that if any cam isn’t following commanded close enough then the pcm will use and report the more erroneous position of the two for BOTH, which makes no sense but that’s how it is. Also, if it gets bad enough it will disable vct. Total area under the error curve over time will eventually accumulate and it will throw a DTC, but this could take a while.

There are 4 phaser solenoids. These push on a shuttle valve in each cam. The shuttle valve directs oil to the advance or retard side of the phaser actuator. The Gen 2 phasers react very quickly as opposed to the slower ecoboost and Gen 3 exhaust phasers.

The pcm measures the cam position and compares to commanded. There is a feed-forward lookup then feedback PID portion of control to reduce the error down to less than the deadband. A resultant duty cycle is sent to the phaser solenoid.

In the pcm, ~13 different possible cam position combinations are defined and the engine is fully calibrated to run at any load and speed and any combination of cam timings. Each combination is called a mapped point. To further complicate things, each cam position combination is also fully calibrated to run with the imrc open or closed. So basically, something like 26 full engine calibrations exist in your pcm. The torque, speed density, borderline spark timing, and mbt are fully defined for each of the 26 mapped points. I’m sure you’re wondering by now why this is important to understand.….

The way it works is the pcm commands a position through a mapped point command, or between two mapped points. It doesn’t assume the cams are exactly where it commanded them to go. So at all times it is independently measuring the cam (and imrc) positions and using actual positions to determine which mapped point engine calibration data to use (how it interpolates is a whole other rabbit hole). Therefore, the (torque, sd, and timing) calibration data is for whatever the actual cam positions are, not what they are supposed to be. What this means is that the engine should “drive” almost completely normal even if the cams aren’t following commanded at all. In fact, I’ve electronically locked the cams in many different positions and drove around. The only time you could sense a difference was at idle and wot.

 

[KeyLime]

Engineermike...very nice write up. I learned a lot reading that.

 

[The Demon]

Whew, man that’s a lot.

The park position is 0 intake and 0 exhaust. The intake cams can advance 20 and retard 30 from there. The exhaust can only retard 50 and not advance. Negative is advance and positive is retard. There are 5 different cam schedules (disabled, emissions reduction, optimum stability, optimum fuel economy, optimum drivability, and optimum power). Various parameters determine what cam schedule is being used, but it’s mainly load and speed.

At idle they move to 20 intake, 0 exhaust which has very little overlap. At cruise they move to about 30, 50 (intake, exhaust), retarding both the maximum amount to extend the power stroke and reduce pumping losses. As load and speed increase the cams start moving towards the optimum power positions. At wot in optimum power, the intake starts fully advanced (-20) then retards to +10 as rpm rises. Exhaust stays in the 15 - 20 deg range.

There is a commanded and actual cam position for all 4 cams and it can be logged. You can also log error and phaser solenoid duty-cycle for all 4. Note that if any cam isn’t following commanded well enough then the pcm will use and report the more erroneous position of the two for BOTH, which makes no sense but that’s how it is. Also, if it gets bad enough it will disable vct. Total area under the error curve over time will eventually accumulate and it will throw a DTC, but this could take a while.

There are 4 phaser solenoids. These push on a shuttle valve in each cam. The shuttle valve directs oil to the advance or retard side of the phaser actuator. The Gen 2 phasers react very quickly as opposed to the slower ecoboost and Gen 3 exhaust phasers.

The pcm measures the cam position and compares to commanded. There is a feed-forward then feedback portion of control to reduce the error down to less than the deadband. A resultant duty cycle is sent to the phaser solenoid.

In the pcm, ~13 different possible cam position combinations are defined and the engine is fully calibrated to run at any load and speed and any combination of cam timings. Each combination is called a mapped point. To further complicate things, each cam position combination is also fully calibrated to run with the imrc open or closed. So basically, something like 26 full engine calibrations exist in your pcm. The torque, speed density, borderline spark timing, and mbt are fully defined for each of the 26 mapped points. I’m sure you’re wondering by now why this is important to understand.….

The way it works is the pcm commands a position through a mapped point command, or between two mapped points. It doesn’t assume the cams are exactly where it commanded them to go. So at all times it is independently measuring the cam (and imrc) positions and using actual positions to determine which mapped point engine calibration data to use. Therefore, the (torque, sd, and timing) calibration data is for whatever the actual cam positions are, not what they are supposed to be. What this means is that the engine should “seem” almost totally normal even if the cams aren’t following commanded at all. In fact, I’ve electronically locked the cams in many different positions and drove around. The only time you could sense a difference was at idle and wot.

Seriously…You know your shit my friend. I learned a lot.

 

[Torinate]

Whew, man that’s a lot.

The park position is 0 intake and 0 exhaust. The intake cams can advance 20 and retard 30 from there. The exhaust can only retard 50 and not advance. Negative is advance and positive is retard. There are 5 different cam schedules (disabled, emissions reduction, optimum stability, optimum fuel economy, optimum drivability, and optimum power). Various parameters determine what cam schedule is being used, but it’s mainly load and speed.

At idle they move to 20 intake, 0 exhaust which has very little overlap. At cruise they move to about 30, 50 (intake, exhaust), retarding both the maximum amount to extend the power stroke and reduce pumping losses. As load and speed increase the cams start moving towards the optimum power positions. At wot in optimum power, the intake starts fully advanced (-20) then retards to +10 as rpm rises. Exhaust stays in the 15 - 20 deg range.

There is a commanded and actual cam position for all 4 cams and it can be logged. You can also log error and phaser solenoid duty-cycle for all 4. Note that if any cam isn’t following commanded close enough then the pcm will use and report the more erroneous position of the two for BOTH, which makes no sense but that’s how it is. Also, if it gets bad enough it will disable vct. Total area under the error curve over time will eventually accumulate and it will throw a DTC, but this could take a while.

There are 4 phaser solenoids. These push on a shuttle valve in each cam. The shuttle valve directs oil to the advance or retard side of the phaser actuator. The Gen 2 phasers react very quickly as opposed to the slower ecoboost and Gen 3 exhaust phasers.

The pcm measures the cam position and compares to commanded. There is a feed-forward lookup then feedback PID portion of control to reduce the error down to less than the deadband. A resultant duty cycle is sent to the phaser solenoid.

In the pcm, ~13 different possible cam position combinations are defined and the engine is fully calibrated to run at any load and speed and any combination of cam timings. Each combination is called a mapped point. To further complicate things, each cam position combination is also fully calibrated to run with the imrc open or closed. So basically, something like 26 full engine calibrations exist in your pcm. The torque, speed density, borderline spark timing, and mbt are fully defined for each of the 26 mapped points. I’m sure you’re wondering by now why this is important to understand.….

The way it works is the pcm commands a position through a mapped point command, or between two mapped points. It doesn’t assume the cams are exactly where it commanded them to go. So at all times it is independently measuring the cam (and imrc) positions and using actual positions to determine which mapped point engine calibration data to use (how it interpolates is a whole other rabbit hole). Therefore, the (torque, sd, and timing) calibration data is for whatever the actual cam positions are, not what they are supposed to be. What this means is that the engine should “drive” almost completely normal even if the cams aren’t following commanded at all. In fact, I’ve electronically locked the cams in many different positions and drove around. The only time you could sense a difference was at idle and wot.

Wow! Thank you very much sir. Excellent information!!

That is a lot to take in!!! I've read it back a few more times and think I get it... As you know, I'm having these issues but never a check engine light, never flashing light, no stored codes. Nothing! So I know there's an issue, but the car doesn't think so. This to me is the most challenging part. I'm (obviously) trying to find things that would cause the car behaviours but NOT set a code. It doesn't appear this is it, as if the timing was delayed or off, it would set a code for it.

It's kind of like the misfires. I see them happening real time in mode 6 data, but they're not occurring enough to set a code. I feel the hesitation off idle when stepping on the throttle, but the car obviously doesn't report anything amiss. I was "hoping" that the electrical part was fine but a mechanical part was at issue and therefore no codes thrown but an obvious VCT issue. Does not appear to be the case.

Thank you again for your valuable information!

 

[OGJET]

Whew, man that’s a lot.

The park position is 0 intake and 0 exhaust. The intake cams can advance 20 and retard 30 from there. The exhaust can only retard 50 and not advance. Negative is advance and positive is retard. There are 5 different cam schedules (disabled, emissions reduction, optimum stability, optimum fuel economy, optimum drivability, and optimum power). Various parameters determine what cam schedule is being used, but it’s mainly load and speed.

At idle they move to 20 intake, 0 exhaust which has very little overlap. At cruise they move to about 30, 50 (intake, exhaust), retarding both the maximum amount to extend the power stroke and reduce pumping losses. As load and speed increase the cams start moving towards the optimum power positions. At wot in optimum power, the intake starts fully advanced (-20) then retards to +10 as rpm rises. Exhaust stays in the 15 - 20 deg range.

There is a commanded and actual cam position for all 4 cams and it can be logged. You can also log error and phaser solenoid duty-cycle for all 4. Note that if any cam isn’t following commanded close enough then the pcm will use and report the more erroneous position of the two for BOTH, which makes no sense but that’s how it is. Also, if it gets bad enough it will disable vct. Total area under the error curve over time will eventually accumulate and it will throw a DTC, but this could take a while.

There are 4 phaser solenoids. These push on a shuttle valve in each cam. The shuttle valve directs oil to the advance or retard side of the phaser actuator. The Gen 2 phasers react very quickly as opposed to the slower ecoboost and Gen 3 exhaust phasers.

The pcm measures the cam position and compares to commanded. There is a feed-forward lookup then feedback PID portion of control to reduce the error down to less than the deadband. A resultant duty cycle is sent to the phaser solenoid.

In the pcm, ~13 different possible cam position combinations are defined and the engine is fully calibrated to run at any load and speed and any combination of cam timings. Each combination is called a mapped point. To further complicate things, each cam position combination is also fully calibrated to run with the imrc open or closed. So basically, something like 26 full engine calibrations exist in your pcm. The torque, speed density, borderline spark timing, and mbt are fully defined for each of the 26 mapped points. I’m sure you’re wondering by now why this is important to understand.….

The way it works is the pcm commands a position through a mapped point command, or between two mapped points. It doesn’t assume the cams are exactly where it commanded them to go. So at all times it is independently measuring the cam (and imrc) positions and using actual positions to determine which mapped point engine calibration data to use (how it interpolates is a whole other rabbit hole). Therefore, the (torque, sd, and timing) calibration data is for whatever the actual cam positions are, not what they are supposed to be. What this means is that the engine should “drive” almost completely normal even if the cams aren’t following commanded at all. In fact, I’ve electronically locked the cams in many different positions and drove around. The only time you could sense a difference was at idle and wot.

Hi Mike,
I’m hoping you might be able to chime in on an issue I’m having, possibly with VCT.
2021 Mustang with stage 2 whipple. Car runs perfect except for one scenario.

Lets say I’m cruising on the highway in 9th gear, I go to overtake slowly so apply light accelerator pedal, the transmission shifts down to 8 and still in a low rpm high load situation, after a few seconds the VCT disables, AFR goes to 20, car has no power. I pull over, turn the car off, open and close a door to reset the PCM, start it up and it’s fine. Sometimes I need to wait a few minutes before it starts correctly again not with high AFR’s.

We are totally stumped on this. Do you have any ideas what it could be or how I can troubleshoot,
TIA

 

[engineermike]

Never heard of that one. Do you have a good datalogger? Any codes?

 

[OGJET]

Hi Mike,
Yes hptuners logger. No codes. It just disables VCT and AFR goes super lean.
When I reset the PCM it’s like it never happened.
Do you think the disabled VCT in itself explains the lean condition?

 

[engineermike]

I wouldn’t assume causality either direction just yet. What is the fuel source when this happens?

I’ve struggled to figure out causes for “vct disabled” because they don’t seem to be listed anywhere. I know low oil pressure, unplugged phaser, and high vct discrepancy will do it, but ford doesn’t seem to help much with diagnosing it. VCT also disables when other faults happen as well, so it could be a symptom not a cause.

 

[Gfswindle]

To further add information to this subject on VCT function. The phasers themselves are fed oil but oil pressure itself is not used to actuate the position directly. The shuttle valve directs oil between the advance and retard chambers and the pressure for that fluid change to happen is given by the torsional energy exerted on the camshaft by the valve springs themselves. Opening a valve requires force in the opposite direct of camshaft rotation while a closing valve exerts force in the same direction as the direction of rotation. The phaser uses these pulsing forces in combination with the spool valve to adjust how much oil is in each chamber changing the phasing of the camshaft. Here are some videos to show that in action.

 

[engineermike]

True for gen2 phasers and gen3 intake only.

 

[OGJET]

Hi guys. So, injector cut and VCT disabled at the same time. Logs attached .xlsx. Thanks. Your thoughts? I could relog different channels as this error is repeatable in that specific scenario.

 

[raptor17GT]

Whew, man that’s a lot.

The park position is 0 intake and 0 exhaust. The intake cams can advance 20 and retard 30 from there. The exhaust can only retard 50 and not advance. Negative is advance and positive is retard. There are 5 different cam schedules (disabled, emissions reduction, optimum stability, optimum fuel economy, optimum drivability, and optimum power). Various parameters determine what cam schedule is being used, but it’s mainly load and speed.

At idle they move to 20 intake, 0 exhaust which has very little overlap. At cruise they move to about 30, 50 (intake, exhaust), retarding both the maximum amount to extend the power stroke and reduce pumping losses. As load and speed increase the cams start moving towards the optimum power positions. At wot in optimum power, the intake starts fully advanced (-20) then retards to +10 as rpm rises. Exhaust stays in the 15 - 20 deg range.

There is a commanded and actual cam position for all 4 cams and it can be logged. You can also log error and phaser solenoid duty-cycle for all 4. Note that if any cam isn’t following commanded close enough then the pcm will use and report the more erroneous position of the two for BOTH, which makes no sense but that’s how it is. Also, if it gets bad enough it will disable vct. Total area under the error curve over time will eventually accumulate and it will throw a DTC, but this could take a while.

There are 4 phaser solenoids. These push on a shuttle valve in each cam. The shuttle valve directs oil to the advance or retard side of the phaser actuator. The Gen 2 phasers react very quickly as opposed to the slower ecoboost and Gen 3 exhaust phasers.

The pcm measures the cam position and compares to commanded. There is a feed-forward lookup then feedback PID portion of control to reduce the error down to less than the deadband. A resultant duty cycle is sent to the phaser solenoid.

In the pcm, ~13 different possible cam position combinations are defined and the engine is fully calibrated to run at any load and speed and any combination of cam timings. Each combination is called a mapped point. To further complicate things, each cam position combination is also fully calibrated to run with the imrc open or closed. So basically, something like 26 full engine calibrations exist in your pcm. The torque, speed density, borderline spark timing, and mbt are fully defined for each of the 26 mapped points. I’m sure you’re wondering by now why this is important to understand.….

The way it works is the pcm commands a position through a mapped point command, or between two mapped points. It doesn’t assume the cams are exactly where it commanded them to go. So at all times it is independently measuring the cam (and imrc) positions and using actual positions to determine which mapped point engine calibration data to use (how it interpolates is a whole other rabbit hole). Therefore, the (torque, sd, and timing) calibration data is for whatever the actual cam positions are, not what they are supposed to be. What this means is that the engine should “drive” almost completely normal even if the cams aren’t following commanded at all. In fact, I’ve electronically locked the cams in many different positions and drove around. The only time you could sense a difference was at idle and wot.

many thanks for this old post / thread but having a p0024 that wont go away (Ford swapped VCT solenoids but still same issue) I'll be reading your post a few times to get better understanding.

 

[engineermike]

Hi guys. So, injector cut and VCT disabled at the same time. Logs attached .xlsx. Thanks. Your thoughts? I could relog different channels as this error is repeatable in that specific scenario.

I started to look at these but it's very hard in Excel. Do you have hpl logs?

 

[K4fxd]

@engineermike.

if you have SCT it will open the excel file and make it usable. It's called live link.

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