I have 2005 Accord 5speed manual 4cyl. I have problem with acceleration. When i accelerate fast and car is in higher rpm(4000 and up) car makes this jumping acceleration. I think maybe there is not enought cold air going to the engine(but i use K&n high flow filter). Or maybe there is something wrong with one of the spark plugs. Any ideas guys? Thank you
Better explenetion: Car doesn't accelerate smoothly. it goes like this
up up up up then normal no acceleration and up up up again -this is in duration of 4 seconds. Maybe one of the piston doesn't delivery enought power.
And i have manual transmission so this little jump in acceleraton isn't automatic transmission shifting. can u help???

Not enough explanation, if you just feel a burst of acceleration consistently through to redline that's the VTEC kicking in, some feel it some don't. If it's more jerky on and off then that's another issue, maybe someone else will chime in once you give a better description.

Around 4000 your overhead cams switch from the economy lobes to the performance lobes with increased open time and overlap between the intake and exhaust valves.

Around 4000 your overhead cams switch from the economy lobes to the performance lobes with increased open time and overlap between the intake and exhaust valves.
I'm pretty sure that switch is supposed to occur at ~2000RPM...

the K24A4 does not have "performance lobes". the VTEC switchover is at ~2300 where it goes from 3-valve "swirl" mode to full 4 valve operation.

Long time ago I read both happens. At 2000 3-4 valve switch and around 4000 the larger lobes come in and increased overlap between intake and exhaust occurs. Search for explanation of iVTEC here on the site and you'll find a video from Hondas international website explaining iVTEC.

EDIT: Here's the video

http://world.honda.com/HDTV/news/2005-4050705a/index.html

P.S. the video is explaining the 1.8L i-vtec in the civic, there are some differences, some other videos on the site explain the 2.4L i-vtec (same explanation but are longer videos and also explain the 2.4 i-VTEC with IMA).

Here...

http://world.honda.com/HDTV/news/2005-4050705b/index.html

Well I haven't watched the video (it's giving me problems...) but whatever happens at 4000RPM shouldn't be too obvious. I notice it in my car but it's not super jerky, not like in a 3-stage S2K or Lude

Long time ago I read both happens. At 2000 3-4 valve switch and around 4000 the larger lobes come in and increased overlap between intake and exhaust occurs. Search for explanation of iVTEC here on the site and you'll find a video from Hondas international website explaining iVTEC.

EDIT: Here's the video

http://world.honda.com/HDTV/news/2005-4050705a/index.html

if you've seen k24a4 head teardowns, you'll see there are only two intake lobes per cylinder. There is no third switchover.

Well I haven't watched the video (it's giving me problems...) but whatever happens at 4000RPM shouldn't be too obvious. I notice it in my car but it's not super jerky, not like in a 3-stage S2K or Lude


Totally agree it shouldn't be that noticable.

I might be wrong about performance lobes, maybe it's just an adjusted angle on the intake lobes for increased overlap (VTC?), but that's what I understood. from reading about the engine.

To my knowledge the 4000RPM switchover is a fuel map....if your fuel filter is partially blocked it could cause jumpy acceleration...maybe bad fuel too :dunno:

from acuranews.com for the RSX/RSX-S. the accord's system is idential to the base RSX.
The RSX employs a version of VTEC to boost performance and reduce emissions that applies variable timing and lift to the intake valves only. Additionally, the RSX system is further simplified by utilizing only two rocker arms per pair of intake valves (instead of the usual three). During low rpm operation, intake air is drawn almost exclusively through the primary intake valve, thereby creating a very strong swirl effect to maximize combustion. At 2,200 rpm, the secondary rocker arm engages the primary rocker causing both intake valves to open for the same lift and duration, substantially increasing airflow into the cylinder and boosting performance.

The RSX Type-S uses the same high-performance three rocker arm VTEC design as the NSX, to vary the lift and duration of both the intake and exhaust valves for maximum power output. At lower rpm, the valves follow low lift, short duration camshaft profiles to help boost low-end torque. Above 5,800 rpm, the intake and exhaust valves are operated by high-lift, long-duration cam profiles, for maximum high rpm horsepower.

I'm not sure about the Accord having different cam profiles (it may) but I do know that the 2.4L iVTEC varies intake/exhaust valve overlap depending on engine *load* not engine RPM. It uses different sensors to detect how much power you need.

At idle, there is no overlap in the cylinder for smoother idling.

When cruising, there is a little overlap which allows some exhaust gasses to be burned with the main charge for better fuel economy.

Under acceleration, there is a lot of overlap for better breathing and more horsepower.

The engine can speed up or pull back the overlapping from 2000RPM and higher. Unlike older VTEC systems that had a single engagement point, in theory, the K24 has infinite engagement points and infinite overlapping scenarios. The only thing that I don't think is variable is the profile which would vary *how much* (or how deep) each valve opens.

If you floor it at 2000RPM, everything will go WOT. If you're just cruising along at 80mph in th gear at 3000RPM, you're in cruise mode with little overlap. :yes:

edit: Hello! I knew I saw this somewhere recently :D

http://automobiles.honda.com/models/engineering_featuredemos.asp?NUM=0&ModelName=Accord+Sedan

True that it's based on load and not RPM but...

There should be a lower ceiling. If I floor it off idle, VTEC should not engage until at least 2000RPM.

Just because I'm cruising at xxxxRPM doesn't mean VTEC shouldn't engage. At some point, it should still come on to help overcome drag.

The video also says that under acceleration, the system will vary valve overlap depending on RPM...whatever that means :dunno:

Does anyone know the actual engagement points for the 3.0L SOHC V6 in some of our Accords? I know it is just a VTEC engine and not an i-VTEC, so in theory it should only have a few engagement points along the RPM band?

I think I remember hearing somewhere before that the "performance" timing comes into play at around 4,000rpm, and that it has an "economy" mode below around 2200rpm. I'm not sure of any of this so if someone knows the actual numbers it would be great (I have a long commute to/from work each day and want to know what rpm levels I should be keeping it at during cruise).

Thanks in advance.

True that it's based on load and not RPM but...

There should be a lower ceiling. If I floor it off idle, VTEC should not engage until at least 2000RPM.

Just because I'm cruising at xxxxRPM doesn't mean VTEC shouldn't engage. At some point, it should still come on to help overcome drag.

The video also says that under acceleration, the system will vary valve overlap depending on RPM...whatever that means :dunno:

From what I understand, yes, yes, & yes. :D

I believe if you floor it, VTEC won't do it's thing until it's at least 2000RPM.

Aerodynamic drag on the car would increase load on the engine to maintain a set speed and then the engine would adjust timing for extra power as needed.

I think from 4000RPM up, the engine automatically overlaps but the more urgent the need for power is (i.e. flooring it) the greater the overlap thru redline.

At any rate, it works and works well. :yes: The system is pretty intelligent and seems to be able to interpret all shades of gray and make power as needed. I'm not sure if on occasion I'm feeling it kick in or it's just the slight DBW lag and then the engine processes the request and BAM. :dunno: But it is definitely more noticable on Preludes, RSXs, and the Civic Si.

I'm not sure about the Accord having different cam profiles (it may) but I do know that the 2.4L iVTEC varies intake/exhaust valve overlap depending on engine *load* not engine RPM. It uses different sensors to detect how much power you need.

At idle, there is no overlap in the cylinder for smoother idling.

When cruising, there is a little overlap which allows some exhaust gasses to be burned with the main charge for better fuel economy.

Under acceleration, there is a lot of overlap for better breathing and more horsepower.

The engine can speed up or pull back the overlapping from 2000RPM and higher. Unlike older VTEC systems that had a single engagement point, in theory, the K24 has infinite engagement points and infinite overlapping scenarios. The only thing that I don't think is variable is the profile which would vary *how much* (or how deep) each valve opens.

If you floor it at 2000RPM, everything will go WOT. If you're just cruising along at 80mph in th gear at 3000RPM, you're in cruise mode with little overlap. :yes:

edit: Hello! I knew I saw this somewhere recently :D

http://automobiles.honda.com/models/engineering_featuredemos.asp?NUM=0&ModelName=Accord+Sedan

that's something else, all k series motors also have a cam phase sprocket on the intake camshaft. It's controlled by oil pressure and adjusts the phase of the camshaft relative to the crank. This effectively changes the overlap of the intake valves relative to the exhaust valves.


these are k20a3 cams, which are interchangeable with the k24a4. Note two lobes per cylinder on the intake cam and the sprocket.

http://www.csupomona.edu/~jcwang3/cams.jpg

yes, the overlap definitely varies, but that's the VTC (the "i") of i-VTEC. we were originally talking about the separate cam lobes, the "VTEC" part.

When my VTEC activates, I get torque steer.

Conundrum, if you try it out you should be able to feel each step. Try putting it in 2 and maybe 1/2-3/4 throttle off idle with the AC compressor ON. Those are the times when I feel it most. I also heard that even the normal VTEC systems have variable engagement on the low end. In general if you keep it under 80 (seems to be the golden speed for Honda, VCM on Ody's disengages at ~82MPH) you're not VTECing (under cruise of course).

Conundrum, if you try it out you should be able to feel each step. Try putting it in 2 and maybe 1/2-3/4 throttle off idle with the AC compressor ON. Those are the times when I feel it most. I also heard that even the normal VTEC systems have variable engagement on the low end. In general if you keep it under 80 (seems to be the golden speed for Honda, VCM on Ody's disengages at ~82MPH) you're not VTECing (under cruise of course).

Cool, I tought it was just my imagination, I do feel it more pronounced with A/C on too. I just put it up to the A/C disengaging at load to allow more power delivery to the road. :dunno: I know my old civic felt kind of the same with the A/C on and that wasn't a VTEC engine.

Well the weird thing is that I've never felt the AC disengage (judging by the air coming out) at 1/2-3/4 throttle so I don't think it is. The other day the AC compressor was cycling on and I floored it to pass a couple idiots...and then I felt hot air...THEN I knew it turned off