[20v_lover]

Great news

The ktuner would have thrown an error if there was anything wrong. You could have set vtec very low as well to get a low
oil pressure cell as an additional check but i was fairly confident that it was activating.

 

[Teedohs]

Great news

The ktuner would have thrown an error if there was anything wrong. You could have set vtec very low as well to get a low
oil pressure cell as an additional check but i was fairly confident that it was activating.

Yep, that's what I figured too but I needed more evidence so I went a bit overboard to ensure it was indeed working. Thanks for the feedback!!

 

[K_Tegra]

at least for drive by cable throttle cars, TPS % needs to go to 100%.
for the K20a2, VTP needs to be on (triggered by sufficient oil pressure) for the cam switch to happen. If VTP drops the moment VTEC engages, it will disengage again instantly as indicated by the VTS status. VTP is positive at higher rpm at all times as this just indicates sufficient oil pressure for the VTEC mechanism to work.
In KPro you can disable the VTP switch and it will ignore the VTP signal and engage VTEC at any oil pressure.

Hey this post may be old as of current day 1-2-24 but K-Tuning lives on and I’m here because I’m also suspicious about my k24A2 not kicking in its Vtec because after 4k rpm the power starts to flatline. I see Lotus is pretty well known and educated in this field so I am humbled by people like yourself and am grateful for Teedhos for creating this post. I’m hoping to find what the fix will be, as I’m learning all of this real time.

 

[K_Tegra]

On the ktuner it's normal behavior for the VTP light to go off when the VTS/vtec gets activated. I also think that your
vtec is engaging. You running the stock intake,cams ect ?

Tune WOT finish set the higher cam angle to 0 degrees and see if the AFR's has changed also check your cam angles that its then using.You could also try and set vtec lower at 4000 to see if theres a change in the AFR graph before the initial 4800 engagement.

With vtec set so high on stock cams which iam assuming it is you might not be able to hear it engage. With the stock oem cams i usually engage vtec at about 3600 to 4000 rpm depending on the setup.

View attachment 105527
View attachment 105528

I also think it's kinda impossible to get the fueling right on the car using etuning if the car was not going into vtec.

The tuner will be adjusting the high cam fuel tables from the logs you sent surely he would have picked up if something is wrong. Maybe i am wrong but from what you posted that is my take on it.

I’m still kinda new to k-manger and all that but, those two graphs look almost identical minus a few minute details.. can you elaborate on that just a little bit so I know what I’m looking at? I also feel that my Vtec is not kicking in because it feels the power and flatlines after 4k rpm. It’s a new build I bought and are finishing. K24A2 / k-proV4 on obd1 stock long block with the added K-tune essentials. Runs GREAT but common sense tells me there’s still work to be done.

 

[K_Tegra]

Whewww...this mystery is solved! Here is what I tried:

• Tested continuity on VTEC pressure switch (both sensor connector and wiring)
• Tested continuity on VTEC solenoid (both solenoid connector and wiring)
• Checked oil level
• Checked oil pressure
• Checked VSS
• Checked TPS calibration
• Tested primary and secondary rockers at 42 PSI (per service manual) for each TDC cylinder
• Bypassed VTEC pressure sensor

Those tests above all checked out good. Here is what didn't work and/or added to the confusion:

• Testing with open headers
  • This was a bad test for several reasons. It's before both primary and secondary O2 sensors, which throws a MIL and possibly prevents VTEC from engaging since there are no AFR values being reported to the ECU. I could never get VTEC to engage here but I suspect it was due to the MIL I created when both O2 sensors were bypassed when I disconnected the downpipe from the exhaust manifold
• VTP and VTS indicators in KTuner
  • The fact that the VTP indicator was shutting off when VTS was turning on made it seem like the pressure switch was either sending a bad signal to the ECU or that the pressure switch was bad. I learned that this is how KTuner works for those indicators (thanks @20v_lover for pointing this out and I was also able to confirm after your suggestion)
• 80% TPS at WOT
  • This was confusing because some were saying this should be 100% at WOT. I thought the reading was normal at 80% for this ECU and was able to confirm with KTuner that 80% is the factory reading and this is normal.
• Changed VTEC to 4k RPM engagement with corrective lower/upper limits
  • This didn't make a difference. I still couldn't hear anything

Solution

Since the exhaust and catalytic were rusted shut, I took a leap of faith and just cut the exhaust bolts RIGHT AFTER the catalytic and ran it open this way. Took it for a test drive and I could finally hear a very, very faint/subtle but repeatable sound at VTEC engagement point. Now I know it definitely works. The issue here is that the catalytic seems clogged.

Next steps

• Replace catalytic completely with just a straight runner (now)
• Replace 2" stock exhaust (later in the future)

Thank you all for the assistance on this one

So what was the mechanical malfunction? There must be or had been a reading for air flow in/out the engine. Having a clogged catalytic is restriction but has no threshold on the vtec other than flow and AFR but a tune can accommodate for that so I imagine it would be hard to notice the driving performance from the flow restriction. You must have been getting blow by for a while like a leaky oil pan and valve cover gasket leak? How much more information have you gathered since solving the problem and making some improvements? It’s been a while so I want to ask if you might have any updates or added info? I’m asking because I’m still new to k series and k-pro/manager and I’m ago also questioning my vtec but no cat, just resonator and muffler 2.5” piping obd1 kpro v4 on pump and an e85 tune if needed but no flex sensor yet. There is a cel.. the day I bought the car the seller said it was for the o2 because on day of purchase the car only had headers with the o2 at the end so he said it’ll go away with exhaust. Well I have a good flow exhaust and also cut the length of the cai pipe to make it fit and added a filter too! The car has a ktune harness so there’s not that many things that could be going wrong, plus the guy was doing a pretty good job of everything based on what you will find when shopping for someone else’s project that you want to buy and finish because they threw in the flag or what ever. Sorry for a long question on an old post but this was a good post and it’s better to build to this post than to have too many of the same posts with the same questions you know.

 

[K_Tegra]

Great news

The ktuner would have thrown an error if there was anything wrong. You could have set vtec very low as well to get a low
oil pressure cell as an additional check but i was fairly confident that it was activating.

Hey that’s a really intuitive idea for deducing

 

[Lotus]

first log into your ECU and check the error that causes the CEL.