CVT swap? (Into 2005 Civic, replacing 4-spd auto)

[EcoCivic]

Originally Posted by cRiPpLe_rOoStEr

Even though nowadays a dealership makes a large profit from service, trying to push customers into something newer for which they may be able to charge a higher fare due to the increased complexity seems advantageous. No wonder they often perform services with fewer care once the vehicle is older, plus it leads to fewer need to keep spare parts for them on inventory.

Yeah I don't go to the dealer unless I need a service that no one else can do like flashing the ECU or if I quickly need an OEM part. Other than that I do everything myself and usually buy my parts online.

Last time I went to the dealer to get an ECU flashed, they told me they couldn't get it to flash and that there must be some type of electrical problem with the car that's keeping it from working and they said for them to diagnose it, I would need to get a new ECU from them for ~$1K and if it still didn't work I would need to pay them by the hour to diagnose it.

They offered to try again for free with another ECU, so I went back to the junkyard and bought a second ECU and took it back for them to try again, which unsurprisingly supposedly still didn't work. I don't think they even tried to flash it though at least the second time because I paid attention to how I set the replacement ECU on the passenger seat and it was still in the exact same position as far as I could tell and the car was parked in the same place I left it in when I gave them the keys.

I asked on a Honda forum what could cause an ECU to not flash other than being defective and everyone pretty much said unless there's a problem with the OBD port they probably didn't even try. That's why I would prefer to have the job done by a locksmith because then I could see them do it and they wouldn't have any incentive to try to sell me a new ECU or diagnostics.

[EcoCivic]

Well I "solved" the problem of the high/loping idle by pulling the ECU's speed signal pin out of the plug. That way my EPS system stays happy and my speedometer/odometer work, the ECU just doesn't know the car is moving. Initially the only thing I noticed is that my Scangauge no longer showed my MPG, but then I noticed that I no longer get good engine braking when coasting in gear. I looked at the fuel trim and it doesn't look like the ECU is going into decel fuel cut anymore. I guess it won't if it doesn't see that the car is moving. It seems like trying to get the auto ECU to work properly with this swap is a losing battle.

After reading a bit, it looks like a high idle while coasting is normal for some manual transmission cars. Hopefully that isn't the case with these Civics, I really don't like it when the engine revs way up for no reason and lopes when I'm rolling in neutral.

[Ecky]

"High" idle while rolling is typically something like 1000-1200rpm, from my experience.

[EcoCivic]

Originally Posted by Ecky

"High" idle while rolling is typically something like 1000-1200rpm, from my experience.

Thanks, that wouldn't be so bad. Do you know why this is done? I have heard that it is to help splash oil around the transmission or to make re engagement smoother for people who don't rev match, but I'm not sure.

[Ecky]

I've never heard an official explanation. My guess was that it's easier on the syncros when you put it back in gear, because most people don't rev match. Just a guess though.

[EcoCivic]

Finally had the proper 5 speed ECU programmed by Honda. I have been driving around with the 5 speed ECU for a couple weeks now and I have good news and bad news.

Good news: Overall the driving experience seems smoother than with the auto ECU. The 5 speed ECU seems to try to help with upshift rev matching. When I press the clutch to shift, the RPM now slowly drops to about where it needs to be in the next gear so it's easy to time shifting and releasing the clutch for smooth shifts. It's not stalling on takeoff anymore either. The one time it stalled with the new ECU was my fault because I forgot to downshift to 1st gear before taking off. Oops.

Bad news: The engine still surges somewhat at low speeds in low gears, but not as bad. Not sure why. The idle is still high when coasting too, but it doesn't lope anymore. It seems to idle at around 1500-1800 RPM when in motion, which still seems too high to me. For some reason, it seems to idle a little higher with the AC on. I'm not sure if something else is wrong or if that's just how these cars are. Since it idles fine when stationary, I assume that's just how these cars are and there's nothing I can do about it.

[Ecky]

I wonder if there isn't some mechanical difference, such as the IACV, or perhaps the idle screw should be adjusted differently for a manual car?

[EcoCivic]

Originally Posted by Ecky

I wonder if there isn't some mechanical difference, such as the IACV, or perhaps the idle screw should be adjusted differently for a manual car?

I think you may be onto something there. I have an Acura RSX-S throttle body, I wonder if that could have something to do with the high idle. As a test I tried taking the idle screw all the way out so the throttle closed completely, which made no difference other than causing the throttle to stick closed. I also swapped the electronic IACV actuator to the D17 one and cleaned the IACV, which again made no difference.

I'm thinking I will see if I can retrofit the D17 IACV onto the K20 throttle body to completely eliminate it as a possible issue, but I have a hard time believing that's the problem because the ECU seems to be in control of the idle speed. If it wasn't, I would think turning the AC on would force the idle RPM down instead of slightly increasing it. And while stationary, the idle is perfect.

However, one interesting possible explanation I read last night is that the ECU's ignition timing curves are different (more advanced) while in motion compared to while stationary, so if excess air is entering the engine through a vacuum leak, the ECU may not be able to drop the idle down to normal by closing the IACV completely. I checked for vacuum leaks and found none, but still interesting and potentially useful information if it's correct.

[Ecky]

You're absolutely right about that assumption - if the ECU doesn't see an idle state, it doesn't enter idle ignition tables.

[EcoCivic]

Originally Posted by Ecky

You're absolutely right about that assumption - if the ECU doesn't see an idle state, it doesn't enter idle ignition tables.

Good to know, thanks for the information! Now that I think about it, I wonder if the ELD being unplugged could be affecting the idle RPM while coasting. I'll have to try plugging it back in and see if that makes any difference.

Something else interesting is that the ECU has not set a code for any IACV or idle speed issues, which would seem to suggest that it is getting it's way with the idle speed. I know from experience that these cars will set codes if the idle is high and the ECU can not bring it back down to normal for whatever reason. Maybe the high idle while coasting is just how these cars are.