Tell me about the LZ9's VVT cam

[Jonpro03]

My interest is pretty good and peaked. I'd like to know how the stock ecm activates the VVT and VI. I want to learn how it works, what are the physical characteristics? What kind of signal is sent and under what conditions. Is it as simple as sending a 5v signal at a certain time? My thought is that I can run one of these motors with a Megasquirt, but I need to know what kind of inputs the motor expects from the ECM. Reason being, I found a damn near new motor at a junkyard:

2006
Engine
Chevy Impala 3.9L,EFI,ATOD,FWD,AC,NOTES 2,010miles A e3060 149667 $675

Ya, 2k miles. I know that a Megasquirt3 is capable of doing it, but I have a MS2 and I think I might be able to pull it off. Please tell me anything and everything you guys know about this motor!

Thanks!

[Fieroghini]

I've been down this road but am not an expert so take my advise with a grain of salt. The engine won't start with the cam fully retarded. It will fall on it's face at 5,000rpm with the cam fully advanced. If you did figure out how to use the phaser you would need to read the cam sensor signal to see where it's at for reference. If you don't you may as well degree the cam in for best overall performance manually. My solution was to install a 3400 cam from the 60degree store and 3400 timing set. If you want to use vvt, use the stock computer. If you use an older computer you'll need a 1999 grand prix alternator with the 3100.

[Joseph Upson]

Without the OE PCM for the VVT control it's best to fix the cam in place and add performance enhancements as has already been suggested. You should have several alternator options from front wheel drive cars with the same housing style. What you have to be careful of is not getting an alternator that is computer controled and those are usually two terminal late model alternators. I'm running a high output from a 2000 Tahoe that required some clearancing and a bracket adaptor for the lower mount that I made however the bracket can be purchased because upgrading to the AD244 series alternator is very common for people running high output stereos.

Installing the VVT module one gear sprocket tooth retarded should get you close but if you are set on some VVT use you can install it normally and tap and die the center hub to install a screw stop internally to limit it to the proper centerline degree when retarded. I did successfully install a screw with a jam nut this past weekend but the LS1 pistons do not have the proper valve reliefs limiting any cam phasing and since my compression ratio is pretty high the efficiency should have improved enough to reduce the effectiveness of VVT. For example, you increase compression with long duration camshafts to regain some of the bottom end power lost.

[Jonpro03]

Do you know what kind of signal is sent from the ecm to the engine to adjust the cam though? Is it like, just a 0-5v signal to for adjustment, or is it way more complicated than I think it is?

[bszopi]

It may be a 0-5v signal, but I am pretty sure it is a PWM signal which is programmed to look at various engine parameters and adjust the cam accordingly. So yeah, probably way more complicated that you are thinking.

[Fieroghini]

You do need to be careful about which alternator to pick. For example a 2002 3400 alternator doesn't fit. It looks the same but the bolt spacing is about 1/4'' different. Play it safe and get a 1999 grand prix, unless you use a stock 3900 pcm. For what it's worth I powered the vvt with 12v quite a bit and it never failed, it just wasn't worth it. You will still need to reference the cam signal. with changing rpm's, oil pressure and chain stretch I doubt the phaser will stay constant. I'm fairly convinced that the phaser is for emissions and not a power adder. I'm not going to beat up the subject so last time I'll say it, I've been down this road and it was too much effort for poor performance. There are 3 reasonable options, stock pcm, degree in the stock cam or install a 3400 cam. If I were to do it over I'ld use the stock pcm.

Here is pefore and after stock cam and 3400 performance grind cam.

[SappySE107]

The engine is locked in the full advance position, and retards itself based on what the engine is doing. At cruise it retards the cam a lot for better mileage. The variable upper is junk. I hope the non variable is better but have yet to test it. The upper is 12v and not variable, just power on to open I believe. Not home to verify right now on its default position. Cam is oil pressure and its PWM. I have a DVD that explains it but no way to convert the good bits to avi.

[robertisaar]

BUMP.

any other useful information here may be beneficial to my nAst1 project as well.

The engine is locked in the full advance position, and retards itself based on what the engine is doing.

this may be one of the VERY useful bits i'm looking for... is this implying that when no power is applied to the VVT actuator, the cam is at the +25* or whatever it is that GM advertised it as being capable of? if so, then a really simple equation of converting a +12V duty cycle should give the basis of control for it(if 0% is +25*, and 100% is -15*, anywhere in between should be linear).

[SappySE107]

Its about 9 degrees advance max. The majority of travel is on the retard side.

[robertisaar]

well, that answers one very good question...

ALLDATA supplies very little information about it...

http://60degreev6.com/forum/showthread.php/34223-3900-Info/page6?highlight=cam+phaser

post 60:

"Basically it uses oil pressure to actually move the cam back and forth, but the oil pressure is turned off and on by an electrical valve controlled by a stream of off and on pulses that vary in their ratio of OFF times to ON times."

normal PWM operation scheme

"The cam timing can be varied by a total of 27 camshaft degrees in relation to the crank."

so, 9* of advance and 18* of retard

http://60degreev6.com/forum/showthread.php/34223-3900-Info/page9?highlight=cam+phaser

and post 89, Marc confirms the 27* total movement.



so, it would seem that when the circuit that is controlling the VVT is at a 0% duty cycle(no power applied), the cam will be advanced 9*. when 100% duty cycle is commanded, the cam will go 18* retarded, and it should act with a linear change in between...

seems fairly easy to impliment to me, of course, it would be very wise to use the cam position sensor as a closed loop control and modify duty cycle based upon it... then pre-emptively adjust for oil pressure and temperature changes after those have been worked out... but otherwise, this MAY be enough info for me to go off of to plan on the code changes i'll need to make... ideally, it would be good to get some baseline tables from GM calibrations though.

[SappySE107]

20psi min for it to work is 1 thing you might wanna know:P I have all the values HPTuners allows me to see.

[Joseph Upson]

well, that answers one very good question...

ALLDATA supplies very little information about it...

http://60degreev6.com/forum/showthread.php/34223-3900-Info/page6?highlight=cam+phaser

post 60:

"Basically it uses oil pressure to actually move the cam back and forth, but the oil pressure is turned off and on by an electrical valve controlled by a stream of off and on pulses that vary in their ratio of OFF times to ON times."

normal PWM operation scheme

"The cam timing can be varied by a total of 27 camshaft degrees in relation to the crank."

so, 9* of advance and 18* of retard

http://60degreev6.com/forum/showthread.php/34223-3900-Info/page9?highlight=cam+phaser

and post 89, Marc confirms the 27* total movement.



so, it would seem that when the circuit that is controlling the VVT is at a 0% duty cycle(no power applied), the cam will be advanced 9*. when 100% duty cycle is commanded, the cam will go 18* retarded, and it should act with a linear change in between...

seems fairly easy to impliment to me, of course, it would be very wise to use the cam position sensor as a closed loop control and modify duty cycle based upon it... then pre-emptively adjust for oil pressure and temperature changes after those have been worked out... but otherwise, this MAY be enough info for me to go off of to plan on the code changes i'll need to make... ideally, it would be good to get some baseline tables from GM calibrations though.

Fully advanced appears to provide very good fuel economy, fully retarded is too much and must be for the purpose of EGR function as hp and tq dropped considerably relative to running the cam in the fully advanced position. With the cam at max retard I could almost see the fuel gauge needle move toward empty, with the cam at full advance it took noticeably longer for the fuel level to change. Wish I had the piston to valve clearance necessary to allow full advance on the new motor so I could use the logic circuit in the Zeitronix controller to allow me to set a point at which to retard the cam to a limited angle for higher rpm efficiency.

[robertisaar]

20PSI minimum...... hmm, Joseph mentioned in an email that it's normal for the gen4 oil pump to have it's relief setup for ~45PSI? so GM didn't want too much of a swing in operating range, did they? is there some type of valve that will prevent operation below that, or is that just a GM recomendation?

these values may be of use for setting up a baseline tune, should you want to share them.... otherwise, i can think of at least one person who had a VVT 3500 impala they played with for a while, maybe get a couple of different options going on?

[trotterlg]

Finally something that I know a little about. Likely the full advance is not at zero pulses or voltage, things don't like to work down to zero, so it probably starts retarding at something more than zero. PWM is how modern regulated power supplies regulate their voltage, your computer power supply (the one you are typing on) uses PWM to regulate the voltages. The cam actuator likely only sees the average of the voltage so a 50% duty cycle pulse will make 6 volts if you are using 12 volt pulses, so putting a variable DC voltage to the actuator will cause it to go to position related to the constant DC voltage applied. If I were to try to fake out the cam I would pick off some pulse that is related to engine speed, something as simple at an ignition pulse, or the crank sensor pulses. Using those pulses you fire a retriggerable multivibrator, this is a device that, when it receives a pulse it outputs a pulse of fixed width that is not dependent on the width of the input pulse. If an input pulse were to occur before the output dropped low the output would remain high, this would be the maximum retard point of the cam. You would just do the calculation for the engine RPM and pulse rate you want to have when the cam is in full retard and set up the electronics to make it happen. This is not a very complicated thing to do. This would only adjust the cam related to engine RPM, but would probably be a good place to start. Larry

[bob442]

wonder if one could use d-tec to controll it