saiko_cl_duck

Credit to Palayah8ta for digging it up

*CELs and LIMP MODE
Any number of things can throw you into limp mode and you definately won't have vtec. Most likely if you have a CEL fix that first then worry about VTEC. CEL can be a great indicator as to whats going on, and that light is lit for a reason. even when people say, "I have a CEL but thats a different issue" ,fix that FIRST, then worry about vtec. many codes that are set have alot to do with why vtec isn't working. If your car is not acting right take apart the dash and check that your CEL light is not burnt out. it should light up when you first turn the key on.

*VSS/ SPEEDO
If your car loses its speed reference vtec will not engauge. the ecu will see it just as if you were sitting still reving the engine, no vtec

*OIL
If you don't have the correct oil presure no vtec:
possible causes; dented or damaged oil pan , not enough oil, or oil is so old and crappy it is thin as water

*VTEC OIL PRESURE switch
The VTEC oil presure switch is what feeds back information the the computer to tell it wether or not the opening of the solinoid has alowed high presure oil into the vtec oil gallerys. Once the solinoid opens oil shoud presurize the vtec oil ways pushing the locker pins into place while the oil presure sensor right next to the vtec solinoid feeds back info to the ecu.

*TEMP
The cars coolant temp needs to be at a certian temp for vtec to engage, if any of your temperature sensors are screwed up that is another possibility to look into

*VTEC SOLINOID Gasket/Screen
A cloged or dirty screen that is part of the vtec soliniod gasket causes vtec to not engage or be intermintent.

*THROTTLE POSITION
If your throwing a code for the TPS being bad or wacky this can also cause intermitant or no engagement, from my expermiments, whether vtec engauges or not is throttle position dependent.


Testing the mechanics of VTEC

*You want to check are that you have the appropriate oil presure at head when approching the rpm vtec engauges. I have seen motors where their just wasn't enough oil press and it doesn't throw any CEL but vtec just doesn't work and you hit the 6500 rev limit. The way to check is take the 10mm bolt out of the head that is on the front left if you are facing the motor. This bolt gives you access to the oil way of vtec, this is the same bolt that you remove to do the air presure test listed below. But anway you need to get a gauge that screws into the oil port. Now from here you have two choices. once you have the gauge installed you can either raise the car up and run the car in gear in order to simulate the speed so the vtec solinoid will open and then measure the presure OR you can disconnect the 1 pin connector from the vtec solinoid and aply batery voltage tot he solinoid in order to open it so oil can/should flow into the vtec oil gallerys. The test has to have the motor reving at least up to if not beyond 5000rpm in order to get an accurate oil reading. now what ever way you shose to get the solinoid to open with the car runing is up to you but at 5000rpm you should read a minimum of 60 psi of press at that port. if you do end up having enough oil press i would investigate a bad vtec oil presure sensor. Also not having enough oil presure can also account for "Late" engaugement, where you reach the apropriate press after the preset engaugement point and then the ecu alows vtec to engauge because the required oil presure has been met.

*Secondly you want to make sure that your solinoid is opperational, take it off and using a 12 volt source and a ground make sure that the solinoid operates quickly and smoothly when 12v is applied. this is the valve and if it isn't working vtec won't either

*Third if all else fails you can check that vtec mechanics work by using air presure(this test should then be followed up by the oil presure test) Take off the valve cover, take the plug out of the front of the head next to the header, either find a fitting that you can adapt your air hose to screw in the head or get a blow gun with a rubber tip. with another person you have to block the bleed hole on the 5th cam cap and while applying 40-60 spi of air presure , slowly crank over the motor using the main crank pully and watch to see that all 3 rockers lock togther and start to follow the middle lob, the VTEC lob. you may even hear a tiny click as the pins in the rockers lock the 3 togther. also you will be able to tell that the vtec lobe is being followed as the lift or how far the valves are pushed down is much greater. with the appropriate air presure and if everything is workign corectly every valve should be following the vtec lob. make sure that you have a good air compresor that can keep up with keeping a presure of 40-60 psi. if you don't have luck try raising the presure a littlbe bit, but i wouldn't go much hiogher than 80 psi.

Once you have verified that all the mechanics are working : vtec solinoid, oil press, and valve assembly then you can move from there and see where the problem lies in wiring.


Other Info

Things i haven't seen but are possible are, a faulty vtec solnoid, vtec oil presure sensor, and if your ecu is not detecting the RPM signal.

More vtec presure switch info

The vtec presure switch is just that , a switch , its on or off depending on the oil presure. the ecu sends out about a 10v signal from 1 pin and runs it thru the presure switch back tot he ecu. if the presure is to low the switch stays closed and the ecu "sees" this by the 10v returning, after the vtec solinoid opens the ecu is expecting to see that the switch is opend by the oil presure and for its 10v feed back to disapear.


THE JUMPER WIRE THEORY

If you just jumper the wire your simulating a switch that never opens, on the flip side however if you just disconnect it i think the ecu is smart enough to know that before the engaugement point it wasn't "seeing" its 10v feedback so it throws a vtec malfunction. doing some testing you can get a multimeater: remove the 2p connector from the vtec presure switch , measure voltage with the ignition on between the two pins on the plug you should measure about 10v, this will indicate the wires to the ecu for the vtec presure switch are good, then turn the key off and measure for continuity between the two terminals on the vtec presure switch. seeing as this is a switch its natural state is closed you should measure close to no resistance thru the switch. now this info just means the switch is good if you read continuity thru it but that doesn't mean that the switch is opening when it is supposed to. i would investigate the presure switch further if the oil presure tests are done and found that the correct oil presure is indeed there.

Also where you car is hitting its rev limiter can give away even more information, if you can only rev to 6500 and then hit a fuel cut then your not in limp mode but one of the requirements for vtec to engauge has not been met.. such as temp, oil press speed, etc..

IAB solenoid activates on a P13 (91-96) at 4600, and 4900 on a P5M (97-01)
VTEC solenoid activates on a P13 (91-96) at 4900, and 5200 on a P5M (97-01)

But if you car is only reving to (i think limp mode if 5000 rpm) then you have something seriously prohibiting the car, and most likely almost definatly your CEL should be on, and like i said fix and present codes befor eyou worry about VTEC.

(No, VTEC does not engauge if you sitting still in your car and reving it, the secondary runners will open up, but the VTEC soliniod will not open).

Which brings me to another point, part of what makes vtec work well is the fact that right before the secondary cam profiles engauge the secondary runners in the intake manafold open up to accomadate the engines greater demand for air flow when in VTEC. some times there maybe something wrong with the wiring that tells the IAB soliniod to remove vacume from the diaphram that holds them closed. If anything is wrong with the IAB system then that can cause vtec to feel like it is not engauging. The Iabs are rpm dependant only, and the do open if you reving the car in neutal. THe Iabs are held closed when the car is idling by vacume and continue to be held closed by vacume stored in the small canaster under the intake manifold so you will have vacume to the required rpm even at WOT. With key off and no vacume the IABs open due to a spring. so once vacume is removed they just go to their rest state which is open.

Wiring info
credit to jdmlude_dude ::check here for more info http://www..com/zerothread?id=833163

There are 2 wire tha come out of the vtec pressure switch, one is hot and goes to pin D6 and the other can just be grounded off on the motor or on the chassis

A4 = Vtec Solenoid
D6 = Vtec Oil Pressure Switch


if you take the ecu and look at the pins as if it were in the car, say you lay it on a table with the top facing up and you look as the pins, the "A" pin numbers will start on the very right, Example:
Top side w/ the sticker
----------------D6------------------------------------A4---
l --------------\/---- -------------- -------------------\/-- l
l l oo . . . . . . . . o ll . . . . . . . . ll oo . . . . . . . . ooo l l
l l oo . . . . . . . . o ll . . . . . . . . ll oo . . . . . . . . ooo l l
l -------------------- -------------- ----------------------- l
-------------------------------------------------------------



Alternator/Battery/Charging System Troubleshooting
Try these things first, before taking it to a shop. This link provides self diagnostic techniques.
[url]http://www3.telus.net/chemelec/Projects/Alternator/Alternator.htm[/url