SOLVED!!!! update. Just as I suspected. Bought the vtec online, not the cheapest but mid range price. It was faulty. *Lots of problems with online parts) Anyway, went to junkyard, pulled one year newer car (mines an 03, found an 04) pulled the OEM vtec spool solenoid unit, and dropped her in with my new screen. eAnd viola, NO MORE Stuttering!! She's fixed. 

recap and moral to this saga...do not let leaking fluid go! The power steering fluid dripped and destroyed quite a few things down the passenger side engine. Especially the electrical plugs and grounds. 

Thanks for the help here. Now going to clean the IACV, chk throttle position sensor, and analyse entire AIR flow from filter to mass air flow sensor to throttle. All is well. 😋 

The voltage which needs to be at 12 or higher to engage....on the back probe to switch.....

.....not enough to engage the vtec

 The vtec oil pressure switch is used by the computer to monitor the vtec solenoid operation, it isn't used to energize the vtec solenoid valve. 

The computer sends a reference voltage to the vtec oil pressure switch signal wire which gets pulled down to near 0 volts (maybe 0.5 volts or so) when the switch is closed (the switch is normally closed). When the vtec solenoid is energized by the computer the oil pressure opens the switch and then the reference voltage will be on this signal wire (on the old hondas it's typically a Blue/Black wire). The other wire is Ground.

This is like a thermistor circuit where there's an internal resistor in the PCM. The voltage is measured between that internal resistor and the oil pressure switch.

The voltage gets pulled down by the Closed oil pressure switch grounding the circuit. When the PCM energizes the vtec solenoid the oil pressure switch should Open and the voltage on the signal wire should be close to the reference voltage. But that's not happening on yours. The oil pressure isn't opening the switch so ..... (P2646 Rocker Arm Oil Pressure Switch Circuit Low Voltage).

Have you tried cleaning the strainer?

Here's the question I'm asking myself.

If @gotitfixxed manually energizes the VTEC solenoid with engine running, what's the voltage reading on that Blue/Black wire from the VTEC oil pressure switch?

Grab an extra Tpin to backprobe the VTEC solenoid Power wire and (engine running) jump battery voltage to it. 

That will take the PCM's duty cycle voltage control of the VTEC solenoid out of the equation and make the "multimeter voltage reading" of the oil pressure signal wire consistent (not averaged) and accurate.

Dear Dear Jack,

I am well aware of the screens, both, as well as the pencil solenoid under the tensioner. Cleaned them but may need to re chk the screens again. THey were not very clogged the first time. 

Again- these are the things I have done: *

               *replaced with aftermarket vtec ( may try OEM)

               *cleaned and replaced with new screens (all related, including the one behind power steering) replaced all three oring with screen. 

There is much more to this list but unrelated to what I am still experiencing. studder(limp mode) at 2500rpm, once warmed up and the ONLY code p2646, over and over after clearing code but only once I reach temp and rpms.

It was suggested to back probe the blueblk wire on the harness for the switch on the vtec. It was at 10volts (not 12)  Holding it I noticed the volts drop. Would that be a normal drain? Actually I am thinking this as I write...but Why only ten volts? Battery is 13.3 volts (good)

Thanks for your input. Seems I need to look at wiring and probe through harness. Maybe all the way back to ECU. 

arg,

Rene'

UPDATE but not final

Ok, I will share (sorry if I m repeating myself) but I think I may have solved the low voltage/not enough (12v) going to ecm to engage. Recal above, i back probed the switch blueblk wire and it was only receiving 10volts = not enough to turn vtec on.

Battery is good but alternator seems to 'charge' but drain the battery when engine off. Battery drop in voltage is more than .5amps (forgive the miss use of volts/amps...battery when engine running 14.5, add load, drops to 13.5-12.7 (normal) but when I turn engine off, battery continues to drop to 13. ish. its a subtle drop but I have noticed cranking has become more noticbly difficult, like a dead battery. 

The very first issue began when I noticed the high pressure hose/ power steering LEAK. Knew there was a leak, but could not determine where. The leak has drenched the passenger side of engine, under chassy (pside only, common) Replaced hose. All down the vtec spool solenoid. Now going over every part, pully, ground wire, and crevus this power sterring fluid dripped on, including my new belt splashing it everywhere.

The one thing it did drench heavy on one side, is the alternator. The alternator certainly affects current or in this case drain as well on battery. So, if I clean or better yet replace with new (PIA to do the rebuild brushes/bushings) this should give me full charge and hold in current, which talks to computer which talks to vtec. 

Forums all say alternator can be sneaky culprit if weak. simple test does not really address if ground is off.

I have done the 'remove positive battery cable, test light back to battery and viola...I have somekind of ground occuring. Checked all fuses...could point to aftermarket backup camera/radio previous owner rigged. Still have not addressed this, but going to look first to this drenched alternator.

will chk back by end of week. {black}:laughingoutloud:  

Posted by: @gotitfixxed

Just as I suspected. Bought the vtec online, not the cheapest but mid range price. It was faulty.

Thanks for letting us know! Unfortunately these days the quality of new parts is frequently abysmal.

https://www.youtube.com/watch?v=qkOk7uKDMBQ