s1ngle

iTrader: (1)

Question for you guys:

recently i dynoed my turbo D and I dont think its hitting vtec. I hooked up a little led to test the ecu signal for vtec, and indeed its coming on.

My question however, is this:

I know that VTEC is oil pressure activated... so can i be assure that just because my ecu sends that signal that VTEC is actually being engaged? I was thinking the ECU sends the signal after a certain amount of RPM, but the actual oil pressure activates it.

I'm thinking my oil pressure is causing the problem, not actually engaging vtec even though the light comes on...


how does VTEC really work?
help!

s1ngle

iTrader: (1)

well after doing some more research, i found this:

When driving the vehicle with the rpm high enough for VTEC operation, the engine control module (ECM) operates the variable valve timing solenoid to open the solenoid and allow oil pressure to be applied to the pistons in the intake rocker arms. This action causes the outer rocker arms to be pinned to the middle rocker arm and now the three rocker arms operate as a unit, using the high-lift camshaft lobe for improved high-end power. When the engine rpm drops below VTEC operation, the VTEC solenoid is not energized and hydraulic oil pressure is turned off. This allows the return spring to return the pistons to their rest position and lets the rocker arms operate independently again. The VTEC transition between low and high rpm is smooth and normally not felt by the driver.

The ECM also looks at other inputs for VTEC operation - engine temp, engine oil pressure and vehicle speed (VTEC does not turn on unless the vehicle is moving). A separate oil pressure switch monitors the VTEC system. If a problem occurs, the ECM can turn off VTEC operation and will set a code, turning on the "check engine" light. In some cases, it can also cause a driveability problem.

The VTEC oil pressure switch is a normally closed switch. The ECM sends a voltage to the switch and expects the voltage to go through the switch to ground. If the ECM reads a voltage on that circuit when the VTEC system should not be operating, it will turn on the "check engine" light and set a code. This code will be a P1259 on a vehicle with OBD-II.

When the ECM energizes the VTEC solenoid valve to turn on the VTEC system, the ECM expects the VTEC oil pressure switch to open and see the voltage on the circuit. If there is a delay with oil pressure opening the switch, the ECM will set a trouble code and may limit fuel delivery, causing a driveability problem.

Reasons for no VTEC operation include low engine oil level, VTEC solenoid not opening or the screen behind it is restricted, an engine that has low oil pressure, or an oil pressure leak to the rocker arm assembly. In some cases, when engine work is performed, a missing or damaged O-ring can cause incorrect oil pressure to the VTEC system.

When diagnosing a trouble code P1259, always look at freeze-frame data. This data will tell you if the code is set at high or low engine rpm. If the code is set below 4,000 to 6,000 rpm (depending on the engine), check the oil pressure switch circuit for a faulty switch/connection or poor ground. When the code sets during VTEC operation, check for an oil pressure or mechanical problem with the VTEC system.

----------------
it kinda answers my question... so for future reference for everyone else.

jdmitr

Look at your oil pan. I have fixed several issues for customers that did not have vtec but also had no cel. We checked the bottom of the pan first, an indeed they had dented pans, which caused low oil pressure due to the pan smothering the pick up from getting oil. This may help you out unless yu have an aluminum pan of course (which won't dent like steel).

If your pan is dented you can just take it off , pound it out, clean it, and put it on with a new OEM gasket, and Honda bond (where needed).

s1ngle

iTrader: (1)

thanks jdmitr, a good suggestion... Cause in fact I am not getting a check engine light.

however, i have a Y8 with the alum. oil pan, and its not dented. So I guess I dont think that could be the problem. I do have an oil pressure gauge that i'm gonna hook up asap... to even figure out if this IS a low oil pressure situation or not.

Edit: Is there any way that I can have low enough oil pressure to not engage vtec but still not throw a code for low oil pressure? hrmmm

Frozen E

Your oil pressure idiot light won't come on until the oil pressure is at some ungodly low level. In the low single digita I believe. My B16 was burning oil before I blew it up and it actually got down to the point where I was damn near 2 quarts low one time. I checked the oil when I realized that I was getting a very weak VTEC to none at all even after that car had been warmed up properly. I was surprised as hell when I saw how low on oil I was. So yeah, it's VERY possible that you just don't have enough pressure to lock those extra rockers in. Hook up that oil pressure gauge and see what you get.

Audi RS4

VTEC (which stands for Variable Valve Timing and Lift Electronic Control) is an electronic and mechanical system in some Honda engines that allows the engine to effectively have multiple camshafts. As the engine moves into different rpm ranges, the engine's computer can activate alternate lobes on the camshaft and change the cam's timing. In this way, the engine gets the best features of low-speed and high-speed camshafts in the same engine.

NO VTEC


CROSS OVER



During low RPM operations, the two outer cam lobes directly actuates the two valve rockers. These low PRM lobes are optimized for smooth operation and low fuel consumption. The high RPM lobe actuates the follower. But since the follower isn't connected to anything, it doesn't cause anything to happen.

At high RPMs, oil pressure pushes a metal pin through the valve rockers and the follower, effectively binding the three pieces into one. And since the high RPM lobe pushes out further than the low RPM lobes, the two valve rockers now follow the the profile of the high RPM lobe. The high RPM lobe's profile is designed to open the valves open wider, and for a longer duration of time, thus allowing more fuel/air mixture to enter the cylinder. The improved breathing allows the engine to sustain its torque output as RPM rises, thus resulting in higher power output