The only thing I could imagine it being caused by, is low oil. I had topped off my oil a while ago and the Vtec was engaging fine. Last night though, it stopped engaging and I was getting a rev limit at 5000 rpm again. I checked the oil level when I got home and it was half way between the full mark and the low mark. I guess this is what causes it to limit my rev at 5000 rpm.

Can anyone confirm if this is true or at least possible?

 

Oil level is directly related to VTEC engagement. I don't know what's up with this rev limit though. Is it possible that your TPS could be going bad? Andy would be able to answer that one better than I.

 

I tried it again tonight. Oil was full, 1st gear: Vtec engages, 2nd gear: Vtec engages, 3rd gear: Vtec engages, 4th gear: Vtec doesnt engage and I get a rev limit at 5000rpm. After that 1st, 2nd, 3rd gear didnt engage either. What the hell is going on!!!

Oil level is fine. And if Im on the highway in 5th and I downshift to 4th and the rpm happens to go past 5000rpm, I will get no response from the gas pedal whatsoever until I get back down to 5000rpm....where it just bogs at 5000.

Im fed up of this. What the hell is wrong with my engine. Sorry, Im just venting, any help would be greatly appreciated though. Im really losing my patience here.

 

Are you getting some sort of check engine light? Is it possible the ECU is in limp mode? What ECU are you using and what speed are you going when the VTEC wouldn't engage in 4th gear?

 

I'm getting a code 22 (Vtec pressure switch). I also have a code 91 (FTP low voltage), that's because my 96 dx doesn't have a FTP sensor and the 98 P72 ECU is looking for a signal from it. Those are the only two codes that I'm getting. I don't think they would cause me to be in limp mode. I don't remember what speed I was going when it didn't engage. But I know for sure the I get a rev limit at 5000 rpm. Really strange.

Would a dirty oil screen cause this kind of intermittent problem?

Maybe I should just change the entire Vtec unit.

 

Fixed it! It was a bad knock sensor connection at the ecu. Vtec engages no problem now and I don't get a rev limit at 5000rpm.

 

did You reall solved the problem permanenly with fixing knock sensor?