Exhaust VTEC Cam not opening - Honda Prelude Forum

ExtrudeLude · 08-27-2009, 04:34 PM

so my NA build was tuned a few weeks ago. Making a dissapointing 175. Considering we were looking for something closer to 230 whp, something is definitely wrong. Im pretty sure the VTEC on the exhaust cam isnt opening up. The problem first occurred before the engine was ever in the car. When we were trying to time the cams with it out of the engine, we had the same problem. The mechanic said it was probably because of air leaks and should be good once everything was hooked up. Well, he was mistakingly wrong. Does anyone know what could cause vtec on the exhaust cam not to open up? Ive just been driving it around with the 175 whp because i need the car for school. I want see if there is anything I can try before we have to go take the head off.

My build thread
My new prelude Project

madcatz · 08-27-2009, 06:23 PM

no VTEC solenoid?

ExtrudeLude · 08-27-2009, 06:31 PM

it has the vtec solenoid, but could it possibly go bad to were it only opens up the vtec on the intake cam?

madcatz · 08-27-2009, 06:34 PM

could the cam actually be stuck?
IIRC the cam actually shifts to allow the secondary valves

ExtrudeLude · 08-27-2009, 06:43 PM

i have no clue if it is stuck, if nothing else works im just going to have to take the head off and give it a look. I have a stock head in my garage for me to reference too and see if it is missing a part or something.

G_Loc · 08-27-2009, 08:32 PM

Just out of curiosity... What exactly leads you to believe that "the exhaust cam isnt opening up"? And how did you verify this with the engine off (no oil pressure) and out of the car?

This may help you: VTEC video - Car Videos on StreetFire

As you can see from the video, the cams don't do anything, they just spin along. At the right RPM range and oil pressure, the VTEC solenoid opens up allowing oil into the appropriate orifices. The pin inside one of the rockers moves to engage the center rocker, then the middle cam lob (high profile) is the one that's doing all the work.

Do you feel a sudden rush of power and more engine noise at 5200 RPM? That's when VTEC is supposed to kick in and its pretty noticeable. Any check engine lights?

prepreludesh · 08-28-2009, 01:30 AM

What are you using to tune the car with? If you're using a Hondata, you could have VTEC turned off. It has happened to me before and led to lots of frustration because checking the program on the laptop to make sure it was "turned on" was the last thing we tried checking.

ExtrudeLude · 08-28-2009, 06:05 AM

My car was tuned at Balanced Performance, in georgia, by Ed on a dyno. The result was a weak 175 whp. We were looking for something more like 230. The cams in the car are crower stage 2 with the bigger lobes. (They might be called stage 2.5 because of the bigger lobes idk). It was being tuned on a p72 hondata s300 ecu.

We think the problem is that the VTEC on the exhaust cam is not engaging. The VTEC on the Intake cam is engaging though. We know that some sort of VTEC is engaging because it does give about a 10 hp boost and gets louder when vtec should hit.

When the ENGINE was out of the car and on a stand, we were timing the cams with a tool from honda that simulates oil pressure by using air pressure. The engine was not on a dyno out of the car. Only the vtec on the intake came was engaging when the engine out of the car. The mechanic said that it was most likely due to a leak and would be fine once the engine is in the car and everything is hooked up.

The dyno chart in my sig is not the actual dyno. It is just some picture of a dyno. The horsepower does start dropping off around 6.5-6.8k. With the crower cams, horsepower should be able keep increasing over 7.5K at least.

left me know if you need any other information.

G_Loc · 08-28-2009, 06:15 AM

Could have a blocked oil orifice on the exhaust side. Did you remove and clean the VTEC solenoid already?

ExtrudeLude · 08-28-2009, 07:29 AM

Quote:

Originally Posted by G_Loc

Could have a blocked oil orifice on the exhaust side. Did you remove and clean the VTEC solenoid already?

no, im going to try that tonight. Any other options in the meantime?

prepreludesh · 08-28-2009, 08:22 AM

What kind of A/F ratios are you seeing at the top of your RPM band? (5k and up)

ExtrudeLude · 08-28-2009, 04:39 PM

just cleaned out the vtec solenoid, made no difference.
my a/f ratio was perfect all the way through the pull.

after looking at the dynosheet again, the power actually started dropping off at about 7200 rpms, but should probably top off at around 8000