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2001 nsx na1 automatic to manual swap ecu question.

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Hi, I recently acquired a 2001 acura nsx automatic na1 and have some questions about which ecu to use for the auto to manual swap. The main question I have is which manual ecu do I use if my car is a 2001 nsx na1? To my research, na1 was produced between 1991-96 for manuals and all auto nsx's (regardless of the years) are na1 with the depowered engine. Since 97-05 nsx's manuals came with the 3.2 liter, my guess is that I can't use the ecu's from 97+. Another thought that I have was to use a ecu from a manual 95-96 nsx. Correct me if I am wrong but the 95-96 ecu's are obd2 and still had the 3.0 engine in manual, thus I think might work for my 2001 nsx since it is also an obd2 with the 3.0 engine(besides the cams and springs). Another question that I have is, do the 95-96 obd2 ecu's share the same female plugs as the 2000+ nsx's ecu plugs? For example, the integra came in obd2a 96-99 and obd2b from 2000+. the plugs are different but a simple jumper harness can be used to use an obd2a ecu on an obd2b chassis. I do not know if the nsx's is also like this and would like to know. I am in California so being able to pass smog will be a plus, but if converting my 2001 nsx to a manual will not pass smog then that's also isn't a issue. Sorry for the loads of questions but being able to finally own my dream car has me really hyped for the future. I am new to the nsx platform but I am ready to learn. Thanks for reading my long post.
 
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First off, all I know about this is divined from the service manual and other member's posts, not hands on experience so take it for what it may or may not be worth.

My initial reaction is assuming that the car still has its original ECU, do you really need to change it? Transmission control is offloaded to a separate module and the service manual suggests that the external pin connections are the same on the auto and manual ECUs. There is a data line between the ECU and the TCM and some other shared connections; but, that data may all be one way (ECU to TCM) Those terminal pins on the manual ECU may still be present, its just that the external harness may not be populated to use those pins. If you disconnect the TCM you may generate diagnostic error code so you might need to leave the TCM connected to the ECU (even if there is no auto gear box) if you want to avoid the CEL indication. You definitely will need to reconfigure clutch and neutral switch connections to the ECU; but, those connection configuration changes all appear to be external to the ECU.

The primary requirement in picking an ECU will be the ability to support drive by wire. I can't remember whether DBW came in 1995 or 1996 which may reduce your range of options. The DBW system did undergo some changes from the early years. I don't know whether this involved hardware or was just firmware tuning. That may or may not present a problem trying to use an earlier ECU with your 2001.

The other things that changed during production is the controls of the evap system and the secondary air system. There was an evolution of the evap system with a final version (I think) in 1999 or 2000. An early ECU is probably not going to play well with a later evap system which will be an issue if you want to try and maintain emissions compliance and not have your car smell like a refinery when it is parked on a hot day. My 2000 Na2 has secondary air injection on start up to fire up the catalytic converters quickly. If your 2001 auto also utilizes secondary air injection an early ECU will lack the controls for that. That may or may not be a problem. There may be some other production changes during production that make mixing an early ECU with a later car a bad idea.

I seem to recall that although the auto and manual ECUs had different part numbers, they were essentially identical. There was an internal resistor or shunt inside the ECU that could be snipped to convert from an auto to a manual ECU . This caused the fuel maps to be switched and perhaps caused the ECU to ignore the data line to the TCM. You don't want to do this because you don't want to switch the fuel maps. However, it suggests that the ECU changeout may not be necessary. Of course, all that is anecdotal because I haven't done it.

There are a number of members who have done the auto to manual conversion on early cars. I believe @drew has done this and McLargeHuge has a project thread


Their experience with converting early Na1 cars may help you suss out the need to change the ECU. As a first step, I would get the service manual for 2001 and the electrical trouble shooting manual and carry out a detailed analysis of the ECU pinouts and the related connections to try and confirm what the differences are. Personally, I would try everything possible to try and retain the original ECU.
 
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Thank you for the well detailed input on the ecu's. I was under the impression that keeping the auto ecu in my 2001 nsx will throw a code because it will be looking for the auto trans which won't be there. But if I don't need to change out my ecu for a manual ecu then that would be the best bet. I also wasn't sure if there were major changes from the earlier ecu's so your input really helped. If everything else is external of the ecu then that won't be a problem when converting to manual. You mentioned that the auto ecu's has a resister that can be cut to switch maps from auto to manual, but I only seen people do that on the 91-94 ecu's. I wonder if that will also work on the new ecu's like my 01. I won't be switching cams and springs anytime soon so keeping the auto map will be fine. After posting my question on prime, I also ran into McLargeHuge thread and currently reading it from start to finish. He has a lot of info and I will be taking my time reading it to fully understand the auto to manual conversion. Anyways thank you for taking your time to share your input on the ecu's and helping me understand the nsx's platform. I do not know when I will be converting my car as I still need to do more research. In the mean time, I will keep an eye out for a 5 speed transmission. Thank you
 
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You could be correct that the 'cut the resistor' provision only applies to the pre OBDII ECUs. As I noted, I am going purely by anecdote on this one. Even if that provision exists in the OBDII ECUs, you probably don't want to do it because you end up with the wrong fuel maps. I think the salient point is that the early auto / manual ECUs are essentially identical and there is a good chance that because of the exceedingly low production numbers for the later NSX with an automatic that Honda would make a single ECU that was useable for both applications (even if it had different part numbers).

A further perusal of the service manual suggests that transmission problems are flagged by a blinking D indicator on the shift display. There is no mention in the service manual that transmission problems will trigger the CEL. The DTCs for the transmission can definitely be read with an OBDII scanner so the sole purpose of the data line between the ECU and the TCM may be to allow the OBDII scanner connected to the ECU to read DTCs stored in the TCM. You might be able to completely disconnect the TCM without generating a CEL.

Of course, all of this is informed by trying to parse what is and isn't said in the service manual. A more direct answer might be obtained from member @Kaz-kzukNA1. He is not always active on this forum; but, he is active on the NSX Club Britain forum.
If you pose a question on the NSXCB forum about doing the conversion by just disconnecting the TCM you will probably get a definitive answer rather than informed speculation - although providing informed speculation fueled by too much coffee in the morning can be entertaining.
 
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Cutting the resistor only applies to 91-94 since the resistor in question selects which half of the EPROM address space is used. The manual programming resides in 0x0000-0x3FFF and the auto programming resides in 0x4000-0x7FFF, with the resistor being connected to address bit 14.

95+ ECUs have all of the programming contained within the microcontroller itself, so are still something of a black box. As far as I know, no one outside of Japan has bothered to try to reverse engineer these ECUs since they can't be rewritten without replacing the entire microcontroller with another single use chip, and frankly there's just no point since the chips are very expensive (if you can even find them).

I know some guys on the old Honda forums would just leave the AT controller in the car and come up with creative ways to trick it into thinking the AT and shifter were still there so that might be an option. But really a DBW-capable standalone and competent tuner are probably your best bet unless you need the car to be OBD2 compliant for emissions reasons.
 
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Thank you for the well detailed input on the ecu's. I was under the impression that keeping the auto ecu in my 2001 nsx will throw a code because it will be looking for the auto trans which won't be there. But if I don't need to change out my ecu for a manual ecu then that would be the best bet. I also wasn't sure if there were major changes from the earlier ecu's so your input really helped. If everything else is external of the ecu then that won't be a problem when converting to manual. You mentioned that the auto ecu's has a resister that can be cut to switch maps from auto to manual, but I only seen people do that on the 91-94 ecu's. I wonder if that will also work on the new ecu's like my 01. I won't be switching cams and springs anytime soon so keeping the auto map will be fine. After posting my question on prime, I also ran into McLargeHuge thread and currently reading it from start to finish. He has a lot of info and I will be taking my time reading it to fully understand the auto to manual conversion. Anyways thank you for taking your time to share your input on the ecu's and helping me understand the nsx's platform. I do not know when I will be converting my car as I still need to do more research. In the mean time, I will keep an eye out for a 5 speed transmission. Thank you
One other thing to consider is that it is very possible to use your AT ECU with the MT. The FancyCraft wiring diagrams that Tyler linked in his build describe this process. You will need the 2001 factory electrical troubleshooting manual because it will tell you where the AT-related inputs are for the 2001 ECU. Basically, you "fool" the AT ECU by swapping the inputs for the MT components. For example, the AT neutral "N" position on the gear shift lever becomes the MT neutral switch inside the transmission. The ECU doesn't know or care that it is coming from the MT, it just needs to see "neutral".

Of course, you'll still have the 7,500 rpm rev limit if you stick with the AT ECU, but otherwise it should run fine if you wire up all of the inputs correctly.
 
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But really a DBW-capable standalone and competent tuner are probably your best bet unless you need the car to be OBD2 compliant for emissions reasons.

'Competent tuner' could be the rub. Depending on where you are, not so easy to find. In addition, the OP is working on a C30A with the cams for an automatic and there may not be a significant base of experience for that particular configuration. The aftermarket ECU is a viable option; but, it would not be the path of least resistance and it would not be cheap.

Even if OBDII is not a requirement, for me having a functional evap system is a requirement. If it is not a race car, stepping into the garage on a hot day to be greeted by l'eau d'refinery from a non functional / missing evap system is a non starter for me. I am no longer in to old car smells and I am old enough to have seen the effects of intentional gas sniffing from the pre fentanyl days. The post 2000 evap is heavily integrated into the ECU and if you want to retain the evap you are going to have to figure out how the ECU controls it.
 
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If the method @Honcho suggested can be made to work I think that's 100% the way to go.

As far as the AT cams go, the AT engines run identical ignition timing tables to the MT engines and marginally different fuel tables to account for differences in VE so it shouldn't be anything strange as far as tuning goes, I compared the tunes a while back out of curiosity.
 
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One other thing to consider is that it is very possible to use your AT ECU with the MT. The FancyCraft wiring diagrams that Tyler linked in his build describe this process. You will need the 2001 factory electrical troubleshooting manual because it will tell you where the AT-related inputs are for the 2001 ECU. Basically, you "fool" the AT ECU by swapping the inputs for the MT components. For example, the AT neutral "N" position on the gear shift lever becomes the MT neutral switch inside the transmission. The ECU doesn't know or care that it is coming from the MT, it just needs to see "neutral".

Of course, you'll still have the 7,500 rpm rev limit if you stick with the AT ECU, but otherwise it should run fine if you wire up all of the inputs correctly.
Thanks for the reply. Sorry for not getting back to everyone's reply as I am busy with work lately. Okay that makes more sense by tricking the auto ecu so it thinks its in the neutral position. The nsx's ecu is just the main part of the auto to manual swap that I'm not confident in. I did a auto to manual swap in my integra years ago and it went smooth as there are plentiful of manual ecu's out there for the integra. Most of the wiring was just making connections where the auto shift lever use to be. Besides that it was a breeze. I still have lots to learn as the nsx's platform is very new to me. I plan on keeping the car as oem as possible as I still want to pass california emissions. Making power and tuning isn't on the list atm. If keeping the auto ecu and converting to manual won't throw a code then thats way I'll take for my nsx. Another question I have is, lets say in the future I want to be able to rev higher and I changed the cams to manual cams and valve springs. Would I have to change out my ecu for a manual ecu? There wasn't a 3.0 liter manual ecu that was made after 97 so what would I have to do to be able to achieve the higher red line and power of the manual 3.0 nsx's. I don't think the auto ecu will work in this situation as the red limit will still be at 7,500 rpm. Thanks for explaining to a newbie.
 
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If you install manual transmission cams into your 3.0 l engine, you will always have a mismatch. The ECU for the 3.0 l auto engine will not have fuel maps that match up with the manual transmission cams and the ECU for the 3.2 l manual will not have fuel maps that match up with the 3.0 l engine. It will be close enough that it should run in both cases; but, will be suboptimal in both cases. The 3.0 l with cams & 3.0l auto ECU combination could be borderline risky as it will likely run lean at wide open throttle when the ECU is in open loop. The 3.0l with cams & manual 3.2 l ECU will likely run rich at wide open throttle when the ECU is in open loop. Depending on the Ve discrepancy between the engine and the ECU fuel map, closed loop fuel trim may be able to correct the AFR to the closed loop target. If not, you may find yourself with a perpetual check engine light because of excessive fuel trim and a guarantee that you won't pass an emission test. Too many unknowns to provide a definitive answer. Its not a place I would go if you want any certainty.
 
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Thanks for linking my thread. Like was said already my car is pre-'94 so there are no issues at all dropping in a manual trans and keeping all the A/T ECUs and control units. Wiring in the M/T reverse and neutral switches is pretty easy on those and even uses the old A/T shift solenoid connectors.

The biggest thing to me would be passing CA smog. I can't even register my JDM car in CA without paying several grand and waiting 3-4 months to have all sorts of tests done. I have no idea how an aftermarket ECU would play with CA smog but I have to assume it's a major roadblock, so I would be inclined to keep an OEM ECU at all costs.

I think what you said last about keeping your A/T ECU after the swap and wiring up the manual switches is the safest path, and in my case (again pre-OBD II) did not throw any codes. There should be no difference in emissions quality doing that and I would assume no real way for a smog station to know the difference unless they pull up your registration info and are checking for a different transmission than came from factory for some reason. I assume for CA smog that OBDII tests and all emissions monitors must come back clean to pass.

Swapping in M/T cams to your 3.0L engine is another story since there is no OEM ECU with that setup (post-'97, 3.0L with M/T). If you were in any other state but CA I would say you have room to experiment (like here in GA I have no emissions test whatsoever), but in that case I think you'd have to go with a smog-certified aftermarket option w/tune or find a way to tune an NA2 ECU to your setup.
 
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If you install manual transmission cams into your 3.0 l engine, you will always have a mismatch. The ECU for the 3.0 l auto engine will not have fuel maps that match up with the manual transmission cams and the ECU for the 3.2 l manual will not have fuel maps that match up with the 3.0 l engine. It will be close enough that it should run in both cases; but, will be suboptimal in both cases. The 3.0 l with cams & 3.0l auto ECU combination could be borderline risky as it will likely run lean at wide open throttle when the ECU is in open loop. The 3.0l with cams & manual 3.2 l ECU will likely run rich at wide open throttle when the ECU is in open loop. Depending on the Ve discrepancy between the engine and the ECU fuel map, closed loop fuel trim may be able to correct the AFR to the closed loop target. If not, you may find yourself with a perpetual check engine light because of excessive fuel trim and a guarantee that you won't pass an emission test. Too many unknowns to provide a definitive answer. Its not a place I would go if you want any certainty.
Okay that makes sense. Keeping the auto cams and the auto ecu will be the only choice since I want to pass smog in California. Like you mentioned there is too many "what if's" in this situation since my car is a 2001 and with a 3.0 engine. Maybe running the 3.2 manual ecu will probably work but the fuel tables won't match what the 3.0 engine requires. That's too much of a expense to just test to see if it will work and pass smog. In California the cars made in 2000+ is only required to have the catalytic converter and o2 sensors "ready" when they do the smog check. The car doesn't need to be put on the roller and have the sniffer in the exhaust pipe. They will plug their scanner in the obd2 port and check if those are "ready". If they get a incomplete from either the cat or the o2 sensors then it will fail the smog test. Essential it is easier to pass smog with a car that is 2000+.
Thanks for linking my thread. Like was said already my car is pre-'94 so there are no issues at all dropping in a manual trans and keeping all the A/T ECUs and control units. Wiring in the M/T reverse and neutral switches is pretty easy on those and even uses the old A/T shift solenoid connectors.

The biggest thing to me would be passing CA smog. I can't even register my JDM car in CA without paying several grand and waiting 3-4 months to have all sorts of tests done. I have no idea how an aftermarket ECU would play with CA smog but I have to assume it's a major roadblock, so I would be inclined to keep an OEM ECU at all costs.

I think what you said last about keeping your A/T ECU after the swap and wiring up the manual switches is the safest path, and in my case (again pre-OBD II) did not throw any codes. There should be no difference in emissions quality doing that and I would assume no real way for a smog station to know the difference unless they pull up your registration info and are checking for a different transmission than came from factory for some reason. I assume for CA smog that OBDII tests and all emissions monitors must come back clean to pass.

Swapping in M/T cams to your 3.0L engine is another story since there is no OEM ECU with that setup (post-'97, 3.0L with M/T). If you were in any other state but CA I would say you have room to experiment (like here in GA I have no emissions test whatsoever), but in that case I think you'd have to go with a smog-certified aftermarket option w/tune or find a way to tune an NA2 ECU to your setup.
You are right about the aftermarket ecu's in California. It's a no go if you want to pass smog with a aftermarket ecu. Since your car is obd1, you would just need to pass visual and the sniffer in the exhaust pipe. Running a oem ecu will pass smog with no issues. For the cars that were produced in 2000+ the smog stations plug their scanners up to the obd2 port in 2000+ cars, a aftermarket ecu will 100% fail since it doesn't have emissions programmed into the ecu. So keeping the oem ecu is a must in my situation. But like you said with a jdm car I wouldn't even know where to begin to get it smog legal in California. I did once pass a 2000 acura integra with a jdm engine running the usdm ecu. The car didn't have to be on the roller and the usdm ecu gave the technician the okay so it passed smog with no issues. Maybe it was just by luck because I some how passed visual.

If keeping my auto ecu after doing the manual swap won't throw a code then I think I will be fine passing smog after the manual swap. I just wasn't sure if the nsx has more requirements compared to the fwd chassis when swapping to manual. If for some reason the car has a check engine light or throws a code on their scanner then it will 100% fail the smog test. In California the smog stations don't care about the drivetrains as long as the engine passes the emissions test and have no codes then it will pass.

After reading everyone's comment I don't think swapping to manual cams will be an option anymore if I still want to pass smog in California. As of right now the goal is to manual swap and still be able to pass smog. I still need to find sometime to completely ready your thread about your nsx's journey @Big McLargeHuge . Thanks for sharing your knowledge on the topic.
 
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