How to tell if VTEC has not engaged for some cylinders?

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9 September 2006
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Orange County, CA, USA
What if the pin does not join the mid rocker with the two end ones for just some cylinders when oil pressure goes up?

One way to tell is if you get an O2 sensor for each cylinder, then the mixture will be richer for the non-working cylinder.

But is there any other way to tell? How does the VTEC engagement warning light work? What is it looking for? Is there an oil passage that passes through all those VTEC mechanisms in series so that all must be in position otherwise the warning light will go on?
 
Would an O2 sensor downstream of each cylinder really tell you anything? The VTEC cam profile improves valve timing for better power strokes at higher RPMs, but the fuel-air mixture wouldn't change, and combustion should be complete prior to the exhaust valves opening regardless of which lobes are being used.

The VTEC feedback loop does not have any knowledge of the physical cam configuration and whether the slide pins are engaging properly. It's merely a pressure sensor downstream of the VTEC solenoid that confirms that the solenoid is completing the hydraulic circuit when the ECU tells it to.

Good question, I've wondered about it myself.
 
Can you run engine without valve cover on, at idle, then switch on VTEC solenoid via electrical bypass, and shine flash light at the rockers to see? I don't think there'll be any oil spray since oil pressure is contained inside the camshaft bearings. But I don't know how the valve sleeves, springs, and rocker / camshaft interface are lubricated.

The cylinder not on high cams will flow less air, but gets more fuel injected since ECU thinks all cylinders are on high cams, so it'll run rich.
 
Pressurize the oil system, activate the vtec solenoid, then rotate the crank with a ratchet, look at the rocker arms and see if they are following the VTEC rocker.

And yes, the a/f will change if a certain cylinder isn't engaging as the a/f mixture is richer on VTEC and if there isn't sufficient air, the A/F will show richer on that particular cylinder than the others.
 
The cylinder not on high cams will flow less air, but gets more fuel injected since ECU thinks all cylinders are on high cams, so it'll run rich.

Good point, as long as you're in WOT mode (not sure if VTEC only happens in WOT mode). But the O2 sensors would likely have to be widebands, as stock sensors aren't good for distinguishing between somewhat rich, rich, and very rich.

I know a guy who adjusts his valves at the track with the engine running. I was surprised when I heard this, but he says at idle there's almost no oil splatter at least on his car. How do you pan-fry chicken and pork chops at home? With a splatter shield of course.

This is a non-issue, it just does not happen. When you hear the sound of hooves think horses not zebra’s

I'll take your word for it, but I look at the diagrams and wonder how the return spring gets each dowel back into exacty the right place each and every time, for decades and hundreds of thousands of miles, without ever "sagging" or having the pins gall or bind. I don't get the hooves and zebras reference. :confused:
 
i was also not familiar with the hooves & zebras thing, but i like it

I don't get the hooves and zebras reference. :confused:
I think Brian just means when you're trying to get to the bottom of a mystery (what's making that sound?), start with common (horses) rather than exotic (zebras) explanations. ;)
 
I know a guy who adjusts his valves at the track with the engine running. I was surprised when I heard this, but he says at idle there's almost no oil splatter at least on his car.
What car and what engine was that? How do you get the lock nut socket to stay on the nut when the rocker is moving? I suppose the reason for this is to get the tightest clearance possible, in order to maximize valve lift, so he has to adjust it by feel while the engine is hot? Do they do that with F1 engines too, back in the old days?

I suppose you can still check that each VTEC pin engages by turning engine by hand, supply oil pressure externally, engage VTEC solenoid by electrical bypass, then watch those pins lock the arms together for every cylinder. But that still doesn't prove every one of the pins will engage at 8000 rpm. There is very tight clearance for those pins, otherwise if they're loose the two outside rocker arms will chatter when the middle arm is in charge. And because of that tight clearance, they may not engage if worn or just out of alignment.

Follow-on question: how does a DOHC VTEC head lubricate the valve guides, cam lobes, and rocker arm bearings? If it's done via the same oil passages that lube the camshaft bearings, then there may not be any oil spray if you run engine at idle with no valve cover.
 
It's probably a domestic v8
 
Follow-on question: how does a DOHC VTEC head lubricate the valve guides, cam lobes, and rocker arm bearings? If it's done via the same oil passages that lube the camshaft bearings, then there may not be any oil spray if you run engine at idle with no valve cover.

Oil WILL spray everywhere if the valve cover is off, even at idle! Hell, oil sprays out of the oil filler cap if you don't have it on.

The valvetrain is oiled via the cam plates. There are tiny holes that run along the length of it that "drip" oil down onto the cams and rocker arm assembly.

Also, I want to know how in the H3LL someone can possibly adjust valve lash WHILE the engine is running... :confused:

A) is serves no purpose (if it's because you want the engine hot - rather than cold - then warm the engine up first)
B) its dangerous - I dare you to stick you're hand in there with a 3"-5" long feeler gauge while the engine is running
C) it would make a mess

Doesn't make sense.

PS: The pins in the rocker arms only move about 1/8" to engine the VTEC rocker arm.
 
There is very tight clearance for those pins, otherwise if they're loose the two outside rocker arms will chatter when the middle arm is in charge. And because of that tight clearance, they may not engage if worn or just out of alignment.

There's no reason for any 'excessive wear' on the VTEC engagement pins nor for them to 'go out of alignment'.

All the rockers share a common pivot point - the rocker arm shaft. For each set of 3 rocker arms on the intake (or exhaust) side of each cylinder, all 3 VTEC pins are at the same radial distance from the center of the rocker arm shaft.

For any cam, let's say for example that a particular cam has a valve closed duration of 60 degrees (when both the VTEC and non-VTEC cam lobes are closed), then that means that for 60 degrees of duration, all 3 VTEC pins will be in perfect alignment, thus if there is oil pressure supplied (VTEC), then the pins will slide to one side or the other freely.

It sounds like you're thinking that the pins only have one specific moment where they can function and move, but that simply isn't the case. In my simplified example, 60deg of shared valve closed time is ~17% out of one rotation where the pins are in exactly alignment. Plenty of time to engage/disengage VTEC.

If for whatever reason there WAS wear in the rocker arm, rocker arm shaft, to cause the pins to go out of alignment, you would hear some pretty nasty noises and hitting VTEC would be the last thing on your mind :P
 
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