WOT shifting modification...DIY!

[KATwo40]

As most already know, the 5spd 240sx (USDM) has a 5th gear only rev limiter, that's set to about 5200rpm. Well, I've found a way to modify this system so that it's now a very useful tool in racing the vehicle, especially for drag racing.

Following the directions below will make it so that you can use this factory installed rev limiter for either launch control (if you're brave enough to launch at 5,000rpm) or WOT shifting (meaning you don't lift your accelerator between gears). The WOT shifting is VERY useful on turbocharged KA's that need that continuous spool. It's basically a crude form of anti-lag.

Have fun with it!

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What you need:

About 6 ft. of 14-18ga. wire (preferably joined jackets...like a trailer harness wire set that has the wires all attached, and split at the ends).

One generic momentary switch with the ability to be wired one of two ways. It MUST be capable of interrupting the circuit when the switch is CLOSED (button pushed in) and then completing the circuit when the switch is OPEN (button out). Here's a photo of the switch I used. Make sure your switch has 3 prongs.



Drill (cordless is handy)5/16" metal bit1/8" metal bit

Wire connectors (2butt style or solder, 2 female spade type)Electrical tape or heat shrink

Piece of metal approx. 1/2" x 1/8" about 4-6" long.

Locate the 5th gear sensor on the passenger side of the transmission. It will be toward the rear of the trans, near the tailshaft housing. It's the sensor immediately forward of the speed input sensor. It looks like this, especially if it's leaking like mine!

(click thumbnail)



Snip the wires between the sensor and the wire terminal (plastic connector coupling). Then, separate the coupler and pigtail that you've just created. Leave the sensor plugged into the transmission.

Attach the pigtail/terminal assembly to the ends of the two wires (crimp connections work, but soldering is best). Snake the other end of the wire pair (this is where the joined jacket wire pair comes in nice...) up along the bottom of the car, up the firewall and through the grommet for the A/C drain. It's a little tricky, but it makes for a great wire pass-through and it's well hidden. Once the wire(s) is/are pulled through the firewall, snake them back around the heater panel and all the normal crap you'd do to hide wires behind the dash area. I did not take photos of this part. If you can't figure out how to run some wires through your firewall and behind the heater control, you don't need to do this project.

I made this bracket for a switch mounting surface. I used a piece of aluminum 1/2"x1/8". It can be bought at the local hardware store in 6ft. lengths for about $4.00 per stick. It also cuts very easily with a hacksaw. Make the piece long enough so that the switch button arm will be in contact with the clutch pedal arm. Drill a 5/16" hole in one end of the bracket. Mount it to the brake pedal bracket near the steering shaft, using the existing stud/nut combination. There's plenty of room. Use an 1/8" drill bit and some small craft screws (hardware item) to fasten the switch to the other end of the bracket. Once mounted up, it should look something like this.



Set the switch so that when the clutch pedal is all the way up (foot off the pedal) the switch button is depressed.



You want the switch button to release when the clutch pedal is depressed toward the floor about 5-10mm.



Attach the female connectors to the wire ends and plug onto the appropriate spades. The spade labeled "COM" should ALWAYS be connected. The other two spades will determine what switch position opens/closes the circuit.

Again, be certain that the circuit is wired so that when the clutch pedal is in the full upward position, the engine will rev to the moon (switch button pushed in, circuit broken). This way, when the pedal is depressed (between gears, WOT) the engine won't rev over 5200rpm.

After test driving and comparing the standard and WOT shift methods, I found that the WOT method was much smoother between gears, with less forward pitching, and the turbo lag decreased quite significantly.

Thumbs up for a free mod (unless you don't have the scrap lying around to do this, then it might cost you about $10.00...at most.)!

[Chezedik]

This should be in the KA-T sticky. Why did you put it in NA?

[S14tat]

i have a JWT ecu that elimates the 5th gear rev limiter. would that still work if i do that trick?

[KATwo40]

i have a JWT ecu that elimates the 5th gear rev limiter. would that still work if i do that trick?

Nope. Yer boned.

And this applies to KA or KAT. (for the comment about the forum location...)

[deviousKA]

The algorithm for the 5th gear settings such as the fuel map and the rev/speed limiters is more complex than just the 5th gear transmission switch input. It uses the transmission switches, speed sensor, and a few other inputs in different places in the code for different operating conditions. The ecu is doing some changes when you manipulate the 5th gear switch, but not all, it depends on your current speed and a few other things (I would have to look up the assembly).

I am working on a fully definable launch limiter feature on these ecus, primarily the ka24e stanza board. It requires some reworking of the code to reduce the complexity of the 5th gear algorithm.

[KATwo40]

Are you saying this mod is harmful to the engine or the ECU?

[deviousKA]

I am building an ecu simulator to try figure all of this out, I havent looked at this part of the code in a couple months and havent disassembled it all so I am not 100% certain of all of the functions, but there are a few issues.

What ecu/car are you running? The single cam 5th functions are a bit more clear, they are more complex, but the way the ecu is designed (8bit), easier to figure out. The single cam uses 4 seperate fuel maps in comparison to the dual cams 3, both ecus uses at least one of these in the 5th gear high load low rpm conditions.

The ecu is switching to these maps when you close your 5th gear switch, but, they are also determined by speed and rpm. So you dont really know what fuel map you are on in different conditions when using the 5th switch directly. The problem is the amount of variables here. There are a few that I didnt mention, I would have to refresh my memory looking over the code.

This ecu simulator that I have finished (waiting on some parts to come in) will allow me to monitor everything while trying to rewrite the code for launch or shift limiter. What I am planning to do is rewrite this 5th gear routine and simplify it, removing the map switching portion.

Something like Rev limt XXXX until XX speed, or if 5th switch XX then rev limit XXXX.

More than likely what is happening in your situation is the highly rich 5th fuel maps are diving in and out dependent on speed. If you have your ecu chipped you can copy a main fuel map an place it in the 5th gear map location and see if it solves your problem. You can also change that 5200 rpm limit with ease.

At a minimum you need a chipped ecu to do some changes while testing this, this will allow you to set your limiters low and change the fuel/timing maps so you can do more controlled tests.

edit: I meant speed not rpm above, fixed.
Modified by deviousKA at 9:16 PM 3/12/2006

[KATwo40]

Hmmmm....

I'm running the S13 (1993) KA24DE -T with stock ECU (5spd).

I see what you mean by the ECU switching maps momentarily when the 5th gear switch circuit is closed. This would be very bad if I'm trying to drive with the circuit closed, but I really don't see how it would matter much when the circuit is closed only between shifts, at which point the throttle is on the floor and the upper rev limit (5,000ish rpm) is reached. While the maps might be wrong for any load, it really seems like it wouldn't matter much at all, since there's almost no load at all on the engine during this momentary event. Then, as the clutch pedal is brought up and the circuit is open again, the ECU should default to the other map, yes?

As of now, the only immediate problem I keep getting is that the ECU intermittently fails to recover from the rev limit function and won't run unless I click the switch on the 5th gear circuit again, at which point everything returns to normal. I'm not really sure what happens here, but I must find out before I blow something up.

Only place I could see a problem with this is when the car actually is in 5th gear. Then, the ECU isn't into the correct 5th gear maps. That might be an issue, I'll have to do some interstate driving with datalogging to see what impact it has.

I'm learning more about chipping the ECU and what's involved, but at this point I'm quite the novice. I just received a book that's supposed to be pretty in-depth from a beginner level to advanced. Until I understand it more, I can't really discuss a lot of this stuff with you, because you'll have to "dumb it down," if you will, so that I can understand. I wouldn't want to insult you by wasting your time when I should be studying more on the subject before approaching you with questions like this.

Thanks again for all your input. I'm very curious as to how your emulator works out. I'll be watching on the ECCS boards, also. I registered there today and posted the question about the intermittent engine kill problem.

[deviousKA]

Well Id like to mention that I hope I didnt sound rude in my posts here, Im all for getting things like this working and the effort and testing you have done so far is good.

Im not sure why the ecu isnt kicking back out of "5th mode" instantly, the ecus procedure may need some conditions met a certain amount of times (loops) before it does, im more familiar with the single cam ecu personally.

Not switching to 5th gear condition when you actually are in 5th gear isnt a huge problem really, although considering you are boosted it is a bit more critical. I have run disabled 5th maps NA without a problem, just keep an eye on your a/f's.

You could run 2 switches, leave the 5th transmission switch intact and hooked up, and then just tap your other switch into the same wires. This way it would still go to 5th condition when in 5th gear, and also go into 5th condition any time you close your other switch on the pedal. While in 5th gear the primary switch will be closed and your secondary will have no effect. Try that.

[KATwo40]

That's a pretty good idea. Just for kicks, I ran out and did a few low to medium load pulls in 5th gear and watched the AFR's. They seemed to be in fair order, but quite honestly, it's really tough to watch all the data and drive at the same time. Next week I'll be ordering the RPM converter for my LM-1 so I can do AFR datalogging. At that time, I plan on downloading the latest consult and installing the link and all that crap. I'll do some more in-depth datalogging at that point. If you want to see the logs, I'll be happy to pass them along in order to assist you in the emulator setup.

Thanks again for the tip. I'll try to get that switch re-wired to include the 5th gear switch and see how it goes.

[deviousKA]

Sounds good.

Within the next week I will have that simulator up and running as well, I would be glad to converse any information I find.

[tryiian]

Bump! what`s happening with the results of this thread?

[KATwo40]

I've been playing around with it a bit more, but I have no emulator for the setup, so I'm not exactly sure what the ECU is doing.

I have not had any more incidents where the ECU failed to recover from the shutoff portion of the limit. I'm really not sure what happened there.

Devious is very very busy with lots of other things going on. He'll be getting this information together when his time permits. I make certain as to not rush him on this stuff, since his wealth of knowledge doesn't have to be free, but he choses to make it free.

We'll be sure to post up our findings as soon as we know something solid.