Greetings, so i have a bit of an odd issue with my 93 Del Sol SI. Ever since i bought the car anytime i get up into the upper 4000 rpm range (when vtec should kick on) I get a nice bright F-U of an engine light which I've found to be code 21, indicating a vtec solenoid issue

Ive read just about every thread i can find on the topic and cant seem to identify the problem
Ive checked for continuity in the valve which is present, there doesntd seem to be a short in the wiring anywhere as im getting voltage from it and ran a different wire from the ECU to the solenoid just to make sure with no change.
I've checked the solenoid by connecting it to the battery where it clicks perfectly every time, i've also opened up the ECU (which looks to have been replaced at some point as there's an auto sales place sharpied on the side) and it looks absolutely flawless, no signs of corrosion or anything looking burnt or disconnected. Oil level looks good, even topped it up just to make sure it was at the full mark. Temp gauge goes up to nearly halfway as it always has

Apart from just starting to replace things (aka the ECU and solenoid) I'm really at a loss, I'm not quite sure what else it could be and would of course rather come up with the least costly solution possible

Any thoughts or wisdom would be very appreciated, thanks in advance <3

 

Visual inspection is generally a useless exercise to determine whether an ECU is good.

 

Oh? I had gotten the impression from others that typically if there was an issue there would be a clear connection failure or burn marks or something of that sort.

 

continuity in the valve?

 

Yes it was reading about 14 ohms and the honda spec is 14-30 i believe

 

NOPE

Life is never this simple.

 

Would your best guess just be a bad ECU in that case?

 

Yes, if you followed the service manual troubleshooting and did the tests correctly.

 

Of course has to be the most expensive of the issues, any recommendations on where to get the best deal on an ecu? ebay seems to be ~$120ish, would i be better off hitting up a junkyard?

 

If you shop carefully, eBay is a safe place to buy an ECU, given that the buyer has all the power. You may struggle to find the ECU at a junkyard, but it's worth a try.

 

That's so true. Every time I go looking for parts at a yard, EVERY Honda I come across has already had the ECU pulled.