Honda Prelude Forum - PreludeDriver.com

recently bought a 1993 prelude with a v tech in it dont know much about these engines . i was wondering if it was normal to have a fair bit of air blowing out the oil filler hole , when i remove the oil cap while the engine is running. also how do i tell if the v tech is working i have an automatic
tranny i'm not shure how to tell if i kicks in at the right r.p.m. what shoul i be expecting .

new to preludes any help appreciated

Not sure about the air in the oil fill hole. But VTEC usually kicks in around 5200rpm. You should hear a difference in the overall motor and exhaust sound.

It's normal for air to blow out of your valve cover, but usually it should go through the PCV valve, and not out your oil filler cap. This is called 'blow-by' and it's something that happens to almost all engines. Doesn't mean anything is wrong. I would get an oil filler cap that seals properly if I were you, and it likely wouldn't hurt to get a new PCV valve (they're inexpensive).

If you remove the oil cap when the engine is running, you will get some air coming out of the valve cover. If you leave it off and drive the car, you're going to end up with a huge mess in your engine compartment. So don't ever do that.

Yes, it's normal to feel some air coming from the oil fill hole, especially in an older car. A lot of air is not a good sign though. If it is excessive, you're possibly looking at worn out piston rings, which means low compression. Does the engine run rough? If it does, remove the oil fill cap and/or the dipstick and see if it runs rougher. This allows un-metered air to enter the engine, and since the air flow meter doesn't know about it, you end up with a leaner fuel mixture and rougher running. This is a good way to check to see if a car has low compression without actually doing a compression test. It's not definitive, but it can be a good cue that something is wrong.

So if it's already running rough; there is a lot of air coming out of the valve cover hole; and you can make it run even rougher by removing the cap, you might want to consider having it looked at or move on.

Vtec needs a few things lined up before it will engage:

Engine coolant has to be 140 degrees or higher,

Vehicle speed has to be 19 mph or faster

Engine speed 4900 rpm or higher

You should be able to tell when vetec engages because, as has been stated already, the engine sound (intake) will change and you should feel a decent torguey kick in the seat of the pants. Vtec is not noticeable in the SOHC F series engines like the Accord, etc. But is more noticeable in DOHC Prelude 22's.