Looking for VCT Information

[OGJET]

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

Hi Mike, yes but I can’t upload hpl files to this forum.

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[engineermike]

I looked a bit and I don’t think there’s anything useful in those logs anyway. You need to cut down to about 10-15 parameters all on the fastest polling rate to get better resolution. It’s possible that whatever it is isn’t going to show in the log anyway. I’m wondering if it isn’t something like a bad ground or shorted wire.

 

[K4fxd]

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

Looks like I'm wrong. I used to be able to convert but I forgot what I did.

 

[raptor17GT]

had another look at the files i took in forscan and from my limited knowledge it looks like my exhaust cam in bank 2 isn't moving that much? VCT solenoids were apparently swapped over in Bank 2 so original exh now in the inlet cam but same p0024 as before the swap (if they actually did it and that's an open debate) Out file is going to shops and in file is coming back home, funnily enough.

 

[ihasnostang]

i added all items from forscan regarding VCT, recorded a datalog, exported a csv, imported into excel, added graph of desired exhaust angle vs actual exhaust angle.

 

[raptor17GT]

i added all items from forscan regarding VCT, recorded a datalog, exported a csv, imported into excel, added graph of desired exhaust angle vs actual exhaust angle.

many thanks for your pictures, i tried something similar today and got this
hot idle looks like yours

hot engine rev blip

cold engine

this is EXT_ACT2 versus EXH_DSD which um doesn't look great

 

[robbo810]

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.

That is a great overview of how it all works.
I have 2020 gt with comp cams and have had multiple bank 1 intake phaser failures, comp replaced them under warranty and now my cams go to 0 under wot and over 6k rpm and then return to normal once the rpm comes back down.

I have replaced cam sensors and checked all wiring which seems ok.

I have some hpl logs if you would be able to look at them?

Any help would be much appreciated!

 

[engineermike]

I have some hpl logs if you would be able to look at them?

Any help would be much appreciated!

if you post logs I’ll look at them. Log Vct schedule and see if it’s going “disabled” (I suspect it is). It can go disabled for a number of reasons. You should also log the cam angles and cam solenoid duty cycles.

 

[TrackGT]

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.

Thank you for the detailed write up. I’m monitoring VCT Intake Duty cycle on the pass and drivers

Should I be concerned about the % difference between the two?

Consistently between 5%-8%.

 

[engineermike]

I wouldn’t worry about that unless it sets a code or can’t control cam timing.

 

[TrackGT]

I wouldn’t worry about that unless it sets a code or can’t control cam timing.

Thanks. A little background... I was getting Code P0340 and P0344. I replaced the Pass side intake cam phaser and the codes went away. The thing I can not understand is before I replaced the phaser, the Pass side intake cam always showed a duty cycle reading of 5%- 8% above the drivers side intake cam. After replacement, they seem to have switched and the drivers side is now consistently 5%-8% higher.

Car is a 2015 but only has 8K miles on the engine and 20K on the chassis.

It feels like it is running fine, but your comment "Total area under the error curve over time will eventually accumulate and it will throw a DTC, but this could take a while." is scaring me thinking that it is only a matter of time before I start seeing codes again.

 

[psbee]

I have the same issue as above. Mine can happen at WOT or part throttle. It falls flat on its face, VCT goes disabled, Lean condition and Fuel trims through the roof. My tuner is asking about grounding issues but I have double checked all. I'd be interested to see what eveyone finds out. Thanks! PSB

 

[TrackGT]

I have the same issue as above. Mine can happen at WOT or part throttle. It falls flat on its face, VCT goes disabled, Lean condition and Fuel trims through the roof. My tuner is asking about grounding issues but I have double checked all. I'd be interested to see what eveyone finds out. Thanks! PSB

Are you getting any codes?

When you lean off the throttle, do the duty cycles resume? Or do they park at zero until you shut off the car and restart?

 

[psbee]

Are you getting any codes?

When you lean off the throttle, do the duty cycles resume? Or do they park at zero until you shut off the car and restart?

No codes and they recover right away, if I don’t let off it goes into a cycle of stumbles. Most of mine are between 4-5k.

 

[TrackGT]

No codes and they recover right away, if I don’t let off it goes into a cycle of stumbles. Most of mine are between 4-5k.

I don't know what the Duty Cycles % supposed to be at, but when I'm WOT they jump to either 0% or 80% but there's no difference in power. As soon as I lean off they go back to around 55%-65%. Everything feels normal.

Before I changed the Phaser, they would lock out at 0% (regardless of RMP) and I would lose almost all of the power and the engine would stutter and tick until I restarted the car.

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