looking for vct technical info

[pstrbrc]

Strictly looking for some technical info on my VCT. ('98 Zetec) Looking at the VCT hardware, I'm making some assumptions about how it works and what's inside based partly on YouTube - car engine ford Ti-VCT 3d.
So here's some questions:
Does the default position (no signal to the solenoid) advance or retard the exhaust camshaft?
Does the factory ecu use pulse width modulation to adjust the camshaft advance/retard in an infinitely variable fashion, or is it simply full advance/full retard?
How many degrees of advance/retard does the VCT system offer?

All of these questions have to do with an installation into a gen2 Escort with MegaSquirt ecu, and I'm exploring the options re: the VCT. That is, whether to eliminate the VCT or build a freestanding controller just for the VCT.

 

[2000ZxT]

The VCT on these cars only retards the timing. When no pressure is applied it is at normal timing. A solenoid opens up and allows oil pressure to actuate the cam sprocket. Now that leaves me to wonder if it is on a jet and the more the solenoid opens allowing more pressure further retarding the cam, meaning if it is like that then it should simply be controlled by a set of voltage parameters. I am not positive it is like that but it is my best guess, I do have two sets of gears and solenoids maybe I should take one apart so we really know how it works.

I have a Focus SVT head I have always wanted to make a stand alone box for to control the VCT. Obviously it's vct-I but I can tell it's the same exact system just backwards.

But anyways VCT-E doesn't do anything for performance it is a cleaner version of a regular EGR system basically. Your best bet is a VCT delete, ZXTuner.com sells them (warning he sometimes takes forever to ship), or if you are handy you can make one on a lathe (I have a drawing somewhere) too and then you just need a longer bolt to make it fit. Otherwise you can just leave it unplugged and you will be fine. If you want VCT get a focus svt head the cams are way better.

 

[pstrbrc]

Now that leaves me to wonder if it is on a jet and the more the solenoid opens allowing more pressure further retarding the cam, meaning if it is like that then it should simply be controlled by a set of voltage parameters. I am not positive it is like that but it is my best guess, I do have two sets of gears and solenoids maybe I should take one apart so we really know how it works.

It wouldn't be variable voltage, since the ecu is digital. It would be pulse width modulation. That is, digital control only has on and off. But if you send a pulse of "on" followed by a time segment of no signal, and you do this over and over very rapidly, the solenoid acts as if you supplied a constant partial voltage. If your ecu varies the width of the pulse, the solenoid can mimic a solenoid being controlled by continuous variable voltage. But that doesn't mean that you can control a solenoid with variable voltage if it was designed to be controled by pwm.

But anyways VCT-E doesn't do anything for performance it is a cleaner version of a regular EGR system basically. Your best bet is a VCT delete, ZXTuner.com sells them (warning he sometimes takes forever to ship), or if you are handy you can make one on a lathe (I have a drawing somewhere) too and then you just need a longer bolt to make it fit. Otherwise you can just leave it unplugged and you will be fine. If you want VCT get a focus svt head the cams are way better.

Actually, I want to use the VCT so that I can buy some stage 2 cams and still have a car that will be docile, emissions-legal, and highway-economical when I don't want to terrorize canyons.
So, I'm going to test the solenoid with variable voltage and see if the pindle acts accordingly. But I still need to know the range of the VCT pulley. Anybody!?

 

[amc49]

Up to 22 degrees I believe, all only retard from default location which is advanced to internal stop in cylinder. It increases overlap by delaying exhaust closing point to allow for exhaust to intake dilution to replace EGR's same function. Some amount of oil pressure MUST be applied to keep it in the default forward location, otherwise cam would fall back retarded from friction of valvetrain. Even with zero oil pressure, there is an internal spring that assists with pulling back advanced, to help oil overcome the train friction again. If you start up motor with zero pressure and no oil in passages, you will hear a rapid snapping noise as the cam winds backward from friction with the tappets, spring snaps it back forward trying to hit stop and repeat. Oil pressure coming up stops the noise after a few seconds. Spring is there to aid coming back forward against the load since harder to go that way than the other.

When setting cam timing set as normal but make sure the exhaust cam is rotated clockwise to internal cylinder stop as looking at front of sprocket. There is a hex on cam to wrench it, pull toward front of car. With cam against stop, ordinary zetec camtool must fit in other end like always.

 

[pstrbrc]

Up to 22 degrees I believe, all only retard from default location which is advanced to internal stop in cylinder.

AHA!!! I knew you would know something!!! 22 degrees is a bunch. If that's 22 degrees camshaft, that makes it 44 degrees crankshaft.

It increases overlap by delaying exhaust closing point to allow for exhaust to intake dilution to replace EGR's same function.

OK, I'm not arguing with you, but this doesn't make sense to me. I would think that closing the exhaust early, therefore not letting all of the exhaust gasses out, would dilute the intake charge. My brain says that more overlap would allow some of the intake charge to sneak out the exhaust unburned, therefore causing higher hydrocarbon count in the exhaust, which is a big no-no. Explain?

Some amount of oil pressure MUST be applied to keep it in the default forward location, otherwise cam would fall back retarded from friction of valvetrain. Even with zero oil pressure, there is an internal spring that assists with pulling back advanced, to help oil overcome the train friction again. If you start up motor with zero pressure and no oil in passages, you will hear a rapid snapping noise as the cam winds backward from friction with the tappets, spring snaps it back forward trying to hit stop and repeat. Oil pressure coming up stops the noise after a few seconds. Spring is there to aid coming back forward against the load since harder to go that way than the other.

OK, one reference (about a later gen Ford vct system) said there was a pin that locked it in place when no oil pressure, so I was unwilling to take a wrench to my system. It's all apart on the bench, and the pulley isn't attached to the camshaft, so I didn't really have any leverage to put a torque on it. I've got a busted camshaft around here somewhere (guess how that happened!! ) so I'll bolt it up to the stub, put it in the vice, and check it out. Fact, when I do it I'll put a degree wheel on it and see how much advance/retard it has.

When setting cam timing set as normal but make sure the exhaust cam is rotated clockwise to internal cylinder stop as looking at front of sprocket. There is a hex on cam to wrench it, pull toward front of car.

OK, that would imply that I'm setting it at full advance. I want to think that the EPA would insist on a default with egr functioning, even at the loss of performance, rather than default in performance mode at the loss of egr functioning. Does this make sense????

 

[amc49]

'My brain says that more overlap would allow some of the intake charge to sneak out the exhaust unburned, therefore causing higher hydrocarbon count in the exhaust, which is a big no-no.'

That part is somewhat correct. The exchange occurs both ways. Remember, exhaust gases even at that point are under pressure. Intake valve just opening allows for backflow (reversion) since intake manifold port behind it under vacuum from other cylinders. This with a common log type exhaust manifold. Once you go to tuned header your statement becomes more correct. The loping irregular idle you hear when an engine is cammed big comes specifically from the patchy burn created by extra exhaust mixing with intake due to much increased race cam overlap. Stock motors idle smoother because that overlap cut way back.

'I was unwilling to take a wrench to my system.'

You can safely do it, just don't force it, you'll feel hitting the limit pin. Could be more difficult with cylinder filled with oil though, mine was empty, I could move with ease even though could feel the spring forcing back to default location. There is a hex cast into exhaust cam just for the purpose, procedure is called out in Ford service manual.

Put a degree wheel on it like you say, the 22 degrees came from paperwork I copied from the service manual, that could easily be crank not cam. One place mentioned 2 instead, I think they made printer error there, 2 is a useless number. Not enough to do anything.

'I want to think that the EPA would insist on a default with egr functioning, even at the loss of performance, rather than default in performance mode at the loss of egr functioning. Does this make sense????'

Nay, my good man, try turning on an EGR valve all the time and see what happens. You'll freakin' hate it............

Feel free to correct me with anything you find out. I can be just as full of crap as the next guy.

 

[pstrbrc]

My brain says that more overlap would allow some of the intake charge to sneak out the exhaust unburned, therefore causing higher hydrocarbon count in the exhaust, which is a big no-no. I'm sticking with that. Here goes.

#1. Yep, yer right. The VCT pulley allows 22 degrees of camshaft adjustment. however....


#2. I'm sticking with this: I want to think that the EPA would insist on a default with egr functioning, even at the loss of performance, rather than default in performance mode at the loss of egr functioning. Does this make sense????'

Now, you said...

Nay, my good man, try turning on an EGR valve all the time and see what happens. You'll freakin' hate it............

Yeah, but...
A traditional egr system pipes exhaust into the intake system. Under idle you then have MAJOR vacuum in the intake because of a closed throttle plate. Then open a ~3/8" pipe from the exhaust to the intake! My senior project for my mech eng degree (back in '80) had to do with radical use of egr for max fuel efficiency, and, of course, we never could get a car to run well at idle and full egr. We did some rough dilution calculations and came to the conclusion that we were trying to get an internal combustion engine to run on an intake charge that was ~80 percent diluted. But...
Rough calculations on this engine says that @ .050 lift exhaust closes at ~ 3 degrees btdc, so 44 degree advance would mean exhaust closing at 47 degrees btdc, and if I do my calculations on thermodynamics and moles and everything else, I get ~40 percent dilution. Incidentally, that's just about what we found to be at the ragged edge of workable 29 years ago, and we were using Holley 4bbl carburetors and mechanical advance piont-fired ignitions. Imagine the possibilities with modern engine controls...

Further, when I checked the degree range, I found that the default spring holds it at full advance, with all adjustment towards retard. I would guess that the reason the book tells you to put a wrench on the exhaust cam and pull clockwise (advance) is to make sure it is pulled all the way up against the default bumper, making sure there is no residual trapped oil giving a false "full advance".

So now I have to figure out how to put the system together and pressurize it, then energize the solenoid. Then we'll see what happens. Then the next thing to do is put an oscilloscope on my wife's car and see when the solenoid is activated and when it isn't. By George, this is getting exciting!

 

[amc49]

'so 44 degree advance would mean exhaust closing at 47 degrees btdc'

Don't you mean retard? The default against the pin location will be the closest to TDC, as system activates, cam will drop back to retard more, thus increasing overlap. One thing I'm not clear on myself is whether or not oil pressure can be used to BOTH advance and retard. I do know positively that if you start up with VCT cylinder dry, the snapping noise occurs until pressure forces some sort of stabilization in cylinder/cam phasing thus overriding the spring windup fighting the valvetrain. Noise sounds exactly like when you fast rachet a gas cap on fuel tank. Maybe pressure drops off to allow retard then pumped back up to aid spring advancing cam again.

Bear in mind that just because mechanical conditions allow for 22 degrees movement, it may not move that much, as controlled by the software.

'Under idle you then have MAJOR vacuum in the intake because of a closed throttle plate.'

Yep, but the exhaust dilution does add to it. I refer you back to the cam lope issue, no big vacuum leak there per se, but effect of uneven running nevertheless turns most people off.

'I would guess that the reason the book tells you to put a wrench on the exhaust cam and pull clockwise (advance) is to make sure it is pulled all the way up against the default bumper, making sure there is no residual trapped oil giving a false "full advance".'

Yep..........I'm thinking just a quick way to get back to cam timing point with tool in ends. Engine rolled around with no oil in VCT could have exhaust cam anywhere, last thing to do is relocate (wrench it) it to right spot, then insert cam tool. These motors non-interference so no harm there, but if one loosens cam sprocket, between VCT variable and loose sprocket one could get lost. I think you should not loosen sprocket on at least exhaust cam when re-belting. Saves confusion about where one is, then just wrench the cam to pin and time that sucker. That way sprocket to cam phasing still preserved, guarantees zero VCT code issues on startup.