A few weeks ago, I noticed a strange dip in power at around 7000 rpm when I had my accelerator mashed to the floor in 4th gear. It was significant enough that I felt my head fall forward a bit for a brief second, then jerk back slightly when the motor moved out of the "power dip". (Similar to the feeling when you have your cruise control on, and you reduce the speed by one or two clicks, then increase by a couple clicks.) It also was happening pretty consistently that I know isn't related to road irregularities.

The car behaves as it always has when I'm not in VTEC.

I don't really feel it in 1st thru 3rd gears, I believe because the motor moves through the power dip too quickly for me to notice. I haven't tried having my accelerator pressed to the floor at 7000 RPM in 5th and 6th gears because I really can't afford that kind of ticket. ("Uhmm, officer I was noticing a dip in my powerband at 7000 RPM... and needed to confirm it in 5th and 6th gears." Officer: "I see. With your vehicle travelling in excess of 100mph, you're busy staring at the tach??!! Get out of the vehicle please..." )

Well, yesterday I was cruising on Hwy 280 and decided to accelerate into VTEC in 4th, then hold it in VTEC for a while. Even on a smooth, level surface while trying to keep my accelerator steady, I was feeling the motor having rapid dips and recoveries in power-- almost like a cylinder was occasionally misfiring. I'm not sure exactly RPM this was-- I was in 4th going approx 70 or 75mph with OEM gears.

My theory on what may be causing this-- and try not to laugh too hard (but this is the ONLY close time correlation with this sudden change in motor behavior)-- is that several weeks back I added some Mr. Moly oil treatment as a 30,000 mile gift to my engine. My suspicion is that since the engine tends to consume more oil when in VTEC-- and by "consume" I understand that to mean that more oil gets into the cylinder during a combustion cycle-- that the Mr. Moly oil treatment somehow vaporizes a bit in the cylinder and makes for less efficient combustion? I could be off-base, but this is the only change I've made recently to my car other than having the wheels aligned to OEM specs.

Any ideas?

p.s.-- I sure wish xviper hadn't left. That man knew his stuff and I would've been curious to see what he had to say.

 

Any mods to your car, checked oil level, spark plugs? A friend of mine had a similar problem but it was through just about any gear. We checked his oil and noticed that it was low which kinda makes sense since I believe VTEC operates with oil pressure pushing the pin to engage the higher profile lobe on the cam. I'm far from being knowledgable like XViper but thought I'd throw this in. Other than that, I really have no clue. Maybe something with the VTEC solenoid? IDK. Hope you get this figured out.

-Spanky

 

Sounds like the MAP sensor.

 

no mods that would affect engine behavior or vehicle acceleration/decelleration.

I am meticulous about checking my oil. as of late, it's only down 1 x and I usually would top it off, but because of this latest strange behavior I'm not sure if I want to top it off with the Mr. Moly.

 

hrmm. maybe I'll try the MAP whack. can't hurt-- thanks for the suggestion.

 

(in the Aflac duck voice) Map Whack!

 

tritium_pie Posted on Oct 28 2006, 05:04 PM
Be gentle with it.. don't wack it to bits
Also, maybe, clean the contacts and make the xviper-zip-ty-thingy to secure it better?

 

well guys, I did the MAP whack... and it's really hard to gauge whether you're tapping too light or too heavy... but I figured if I balled up a paper napkin and tapped on it pretty strongly with the end of a small Mag flashlight (2 x AAA battery kind), would do the trick without risking too much impact on a small area.

I drove it up to SF on Hwy 101, put it in 4th and brought my S into VTEC and... everything is back to normal. thanks everyone for the MAP whack suggestion.

I'm so curious as to what the heck would cause the MAP to go out of whack?

 

There seems to be a rash of them each fall so I have suspected it is a change in temperature and humidity that affects the quality of the electrical connections.

 

I seem to remember someone (maybe X himself) throwing out the idea that it was the unplugging of the sensor, and the resulting scrubbing of the contacts, that may be the real solution. Following this logic, I do a unplug/plug when I check the oil level. No problems yet.