Honda / Acura K20a K24a Engine Forum banner
1 - 20 of 42 Posts

Formerly unix4linux
Joined
305 Posts
Discussion Starter · #1 · (Edited)
I'm having an issue where VTEC on my K24A is not engaging at all. I swapped this engine into a 2003 Honda Accord EX. This is indeed the 3-lobe VTEC engine. I am using a factory ECU with KTuner. VTEC engagement is set at 4800 RPMs. I have sufficient oil in the engine as I've triple checked this. I have been working with a tuner via an e-tune but I have not been able to pinpoint this at all.

On the fuel graph below, I see a slight demand for fuel right at engagement but it doesn't seem like enough of a request, which makes me think VTEC isn't actually engaging:

Rectangle Slope Font Parallel Pattern


I also added the VTS and VTP lights to indicate when VTEC engages. This is probably not the best test as it only indicates the ECU actually sending the signal. However, it at least tells me the ECU does send the signal.

The engine is using the K24A4 Honda Accord intake manifold and throttle body as well as the Accord's Exhaust manifold and exhaust. I am not getting any CEL's either so that's a plus. I would have expected to get a code for low oil pressure for VTEC solenoid if there wasn't any sufficient pressure or oil. As you can see in the screenshot above, the VTS light is engaging, though again, I think all that means is that the ECU is sending signal for engagement but not that it's actually engaging.

I've also swapped out the solenoid for another working one but still the same issue. I've use the solenoid from the K24A4 and the one from a K20Z3. The original one from the K24A broke, which is why I am not using that one. Also, I noticed that the solenoid from the K24A (the broken one) is missing the pressure switch. It has a bolt instead of the sensor. See image below for comparison:

White Glove Font Gas Personal protective equipment


That is why I am using the K24A4 Solenoid and/or the K20Z3 instead because the K24A Solenoid is broken. Regardless, neither of the two engage VTEC.

My rev limits are as follows:

Rectangle Font Parallel Screenshot Number


And my VTEC settings as well as VTC are as follows:

Rectangle Font Parallel Circle Number
Rectangle Font Parallel Circle Paper product


I'm not sure what else to try here except buying a gauge to check for true oil pressure to ensure I have the correct oil pressure delivery at 50-60 PSI for engagement. However, I would have expected a CEL to come on if that were the case. The issue here is that I can't even hear it engage at all.

Any thoughts? Next steps for me would be as follows if there isn't anything else to try here:
  • Purchase oil pressure gauge and test to ensure I have sufficient oil pressure at idle and engagement
  • If the above passes, purchase VTEC air pressure test kit and test if the rocker arms are engaging in lock mode at TDC with pins when 45 PSI of air pressure is passed through the assembly of each rocker set

Thanks in advance!
 

Formerly unix4linux
Joined
305 Posts
Discussion Starter · #4 · (Edited)
Does Ktuner not have a simple on/off display for vtec ? That鈥檚 a shame. Have you had any problems with your speed sensor ? When I got my k24a going I had no vtec as well and that was my issue. The kpro I have wasn鈥檛 set up to read the speed sensor and wouldn鈥檛 let vtec engage at 鈥0 鈥 mph.
I'm not sure if they have anything other then the VTS light to show when VTEC engaged. I think the speed sensor is fine. Looking at the first image, it reports my speed just fine from the sensor readings I've selected and it matches my speedometer as well. I have to keep digging to see if the KTuner has an option where it has a toggle to read the speed sensor to ensure it's enabled.
 

Formerly unix4linux
Joined
305 Posts
Discussion Starter · #5 ·
I think All the Jdm motors come without the pressure sensor in the vtec solenoid. B series , K series , H etc.
That is indeed interesting. I'm curious how it works without one. Learn something new everyday and to think I've been doing this for a while, now 馃お
 

Registered
Joined
289 Posts
Why do you think vtec isn't engaging? What's your test to verify that it isn't already working as designed?
 

Formerly unix4linux
Joined
305 Posts
Discussion Starter · #7 · (Edited)
Why do you think vtec isn't engaging? What's your test to verify that it isn't already working as designed?
No sound at all when all valves are suppose to open, fuel graph doesn't show indication. I would expect at least crossover engagement sound. I suppose the next test would be to disconnect the exhaust from the catalytic (after the O2 sensor) to see if I can get a more pronounce pitch at crossover

Tuner also says he's not seeing evidence of VTEC engagement
 

Registered
96 civic HX K24a
Joined
2,001 Posts
No sound at all when all valves are suppose to open, fuel graph doesn't show indication. I would expect at least crossover engagement sound. I suppose the next test would be to disconnect the exhaust from the catalytic (after the O2 sensor) to see if I can get a more pronounce pitch at crossover

Tuner also says he's not seeing evidence of VTEC engagement
i will say my k24a after tuning doesn鈥檛 have much of a crossover sound with vtec window beginning at 3900. I would expect to hear it @4800 + at least a bit.
 

Formerly unix4linux
Joined
305 Posts
Discussion Starter · #10 ·
Is there an option

i will say my k24a after tuning doesn鈥檛 have much of a crossover sound with vtec window beginning at 3900. I would expect to hear it @4800 + at least a bit.
I agree! I think opening up the exhaust would be a good and easy test. I'll put it up on the lift tomorrow and disconnect it to see where I get. But definitely still open to suggestions. The fact that fuel demand doesn't change at crossover just makes me wonder if something is wrong.
 

Registered
96 civic HX K24a
Joined
2,001 Posts
I agree! I think opening up the exhaust would be a good and easy test. I'll put it up on the lift tomorrow and disconnect it to see where I get. But definitely still open to suggestions. The fact that fuel demand doesn't change at crossover just makes me wonder if something is wrong.
you should definitely hear it open header no matter what rpm 馃槅
 

Registered
Joined
289 Posts
I agree! I think opening up the exhaust would be a good and easy test. I'll put it up on the lift tomorrow and disconnect it to see where I get. But definitely still open to suggestions. The fact that fuel demand doesn't change at crossover just makes me wonder if something is wrong.
If the cross over is well tuned then the torque increase at change over should be nearly zero, if the torque increase is zero then the fuel demand change will also be zero.
 

Formerly unix4linux
Joined
305 Posts
Discussion Starter · #13 ·
If the cross over is well tuned then the torque increase at change over should be nearly zero, if the torque increase is zero then the fuel demand change will also be zero.
I would have expected that at the level of all valves now activated simultaneously, you'd at least see some additional but very minor fuel delivery request considering there is more air being supplied demanding more fuel for the total combustion mixture. The torque part I understand. This isn't like hitting nitrous or boost, which somehow some people think this is what VTEC is 馃槈. It should be very smooth for sure.

However, I don't even hear a pitch change at engagement. There should be an audible but subtle change at the very least even with stock components.
 

Formerly unix4linux
Joined
305 Posts
Discussion Starter · #16 ·
I'm now wondering if I disconnect the downpipe from the exhaust manifold, that'll be before both O2 sensors, essentially eliminating both sensors temporarily for this test. Will this be OK or will I get thrown into safe mode, which won't even allow the car to rev past 3k RPM's? What if I separate the cat from the downpipe, which effectively only removes the second O2 sensor but still gets reading from the primary?

Again, I just want to test if I can at least hear VTEC engage
 

Formerly unix4linux
Joined
305 Posts
Discussion Starter · #17 ·
Well, the only option I do have is to disconnect from the exhaust manifold because the bolts from the catalytic are rusted and seized. So this will prevent an accurate reading since both O2 sensors, though connected, won't sense proper exhaust
 

Formerly unix4linux
Joined
305 Posts
Discussion Starter · #18 ·
Ran the car with disconnected downpipe. No VTEC engagement at all at 4800 rpm (you don't ever hear the engagement/crossover of the additional valves opening up) but my logs show the ECU is at least commanding it. I've tried three solenoids so far so I'm suspecting something electrical at this point. I even went up to about 6k rpm just in case something in the settings is off but the settings in the ECU look good

Before I order an oil pressure gauge to ensure I'm getting proper oil pressure, any way I can test the solenoid and pressure switch?
 

Formerly unix4linux
Joined
305 Posts
Discussion Starter · #19 · (Edited)
Reviewing the logs, I can see that at the 4800 RPM mark and higher on this first small and gradual pull, the VTP light is still on but no VTS light, which tells me that because of no O2 readings, it's not engaging it or commanding the ECU like I thought it was from my previous last post. You can also see in the column/rows diagram, my ECT look good so the car was up to temperature at that point.

Rectangle Slope Font Parallel Screenshot


However, on the second gradual pull, I do see the ECU commanding and engaging:

Rectangle Slope Line Font Parallel


On this third one, I get something again:

Rectangle Slope Font Parallel Screenshot


Again, on this fourth one, nothing:

Rectangle Slope Line Font Parallel


Something is definitely up. I can't consistently reproduce. Sometimes it sends signal and sometimes it doesn't but even when it sends signal, I get no real engagement. With open headers/manifold, this should be significantly obvious. To be fair, I just don't know if the CEL complaining about the O2 sensor is causing this.

This was the WOT 3rd gear pull, though with exhaust and O2 sensors fully bolted on:

Rectangle Slope Line Font Parallel


It's consistent each time sending signal to VTS at 4800 RPM's with everything bolted up so I'm going to say that with open headers, the signal for VTEC engagement is unreliable for sure due to no readings from O2 but like I said, it doesn't engage even when signal is sent.
 

Registered
Joined
681 Posts
don鈥榯 know for the Ktuner, but on KPro or Doctronic ECUs for the older K20a2, you need a minimum speed for VTEC to engage. VTP also needs to be active for the switch to be triggered. No VSS speed signal, no VTEC. This is until you disable the use of the VSS sensor.
On my K20a2 build, VTP is active from as litte as 3000 rpm. You can log it and it being shown on a graph.
 
1 - 20 of 42 Posts
Top