240SX Nanny Speed Limiter

  • Thread starter Thread starter 240sxroadracer
  • Start date Start date
2

240sxroadracer

Guest
I have just completed an ITA 240sx and I am in need of a temporary fix for the Nissan Nanny speed limiter. I am not worried about the engine rev limiter at this time. The ECU is at JWT but it does not appear that it will be back to me in time for an event on March 14. I have been researching this for the past week and found the following methods so far. None seem to be definitive.

  • Cut pulse wire signal from speedometer to ECU.
  • Disconnect vehicle speed sensor from trans.
  • Disconnect 4th and 5th gear switches.
  • Replace manual trans ECU with auto trans ECU.
  • Install a potentiometer (reportable does not work because VSS sends an AC signal to speedo head that in turn digitizes it before sending to ECU).
  • Change the VSS gear to "lower" speed.
Car does not have a speedometer head. All outputs from trans are disconnected (VSS, 4th gear and 5th gear switches). It will still cutoff in high rev, WOT situations. The cutoff occurs well below the engine speed rev limiter, in the 4000 to 5000 range. I have also found that the ECU is suppose to be fool proof by going into cutoff if it does not see a speed signal for more than 4 sec at over 4000rpms (or some value near that). I have felt the cutoff a little in 3rd but mostly in 4th and 5th.

I am just trying to get some seat time and start sorting the car at a NASA event before going to SCCA drivers school. So I need it to just get around Road Atlanta without falling on it's front bumper. If anyone has any additional information or help, it would be greatly appreciated.
Thanks
 
Wish I could help. All the internet/forum fixes I found back then didn't work. Clip this wire, disconnect that, and as you found, she still shuts down. Other the the wolf ecu, I don't know of anything definitive. IIRC, there are different VSS gears available that will help, or at least raise the speed before you hit the limiter. If you have changed the rear diff to the 4/36, you are probably on ly getting about 98 mph.

If Joe Harlan or Darrin (sp) Jordan chime in, they are pretty sharp on these cars.

Sorry
 
Yep, there is no fix but the ECU. It is silly but true. Silly Nissan :blink:

Put the speedo head back in and you will get rid of the 4K cutout.
 
Speed sensor just reads number of teeth to tell speed on most cars. Cut off every other tooth to make it see half speed. Might work on the Nissan.
 
Cutting the wires or leaving unhooked didn't work at all.

You can do the switch to the Auto ecu. Make sure you check base timing, but set your dist, by total advance. The auto ecu will put in too much advance if you just set by base timing. You'll want to choose a safe degree of total advance (you might look some where around 30-35 degrees - check the manual) - at something like 4-5k rpm - choose an RPM just far enough to have the full advance.

The JWT is an easy way to go - but keep in mind they just opened up the ecu to other options as well.

Cheers,
Jason.
 
Fortunately JWT has come through (a big tip of the helmet to them, thanks). They reprogrammed the ECU in a week and I received a call yesterday that it is being shipped. It should arrive in plenty of time for the March 14 event. Thanks to everyone who provided information, it does not go unappreciated.
Thanks
Cesar
 
I just cut the wire on the ECU and mine works fine.
I am running a 93 240sx, speed sensor still in and working, both the 4th and 5th gear sensors are unpluged, and the green wire on the ECU is cut and I just ran Memphis this past weekend at 6100 RPM in 5th down the straight with no issues.
I can find the wire number and actual color code if needed.
But glad you got your new ECU.
Carver
 
CCARVER said:
I just cut the wire on the ECU and mine works fine.
I am running a 93 240sx, speed sensor still in and working, both the 4th and 5th gear sensors are unpluged, and the green wire on the ECU is cut and I just ran Memphis this past weekend at 6100 RPM in 5th down the straight with no issues.
I can find the wire number and actual color code if needed.
But glad you got your new ECU.
Carver
Click to expand...
I remember reading on one of the Nissan boards (240SX.org?) that the KA24E ECU is completely different from the KA24DE ECU, and that while you can fool the later you can't fool the former.

6100 in 5th? Damn, how long is that straight?
 
Long enought to take a nap and still get on the brakes in time to make the turn.
It was quite faster when I cought a draft off of one of the American Sedans.
RPM/ratio log shows it to be around 135 mph.
 
when you unplug 4th and 5th gear. the engine goes full rich WOT on the injectors. Easiest fix as listed is to use the auto ecu. i've tested it myself also using a resistor in the pulse signal so that I can use kph as a reference to mph readings. (i reached 142 according to the speedo).
 
Now I don’t know if this will work, but logically it should. The ECU should be reading slight voltage changes from you're speed sensor using that to calculate your speed. Once it reaches the predetermined threshold, the speed limiter kicks in and the car falls flat on its face. The trick here is to fool your ECU into thinking its still moving so you stay out of limp mode. There may be a way to wire in a resistor in that circuit to change the voltage the ECU reads thus keeping the signal but tricking the ECU. So in a nut shell, you're going 120mph but the ecu still thinks your going 35.
 
All is Well

I have to agree with erlrich that the sohc ecu must be different than the dohc. As I mentioned I had eliminated the speed input from the speedo head to the ecu as well as the 4th and 5th gear switch. I still had problems with the Nissan Nanny limiter. I installed the JWT tuned ecu for Road Atlanta this past weekend and ... much joy. The engine ran great with no Nissan engineered safety features to protect us from ourselves. Thanks again to all who helped with their advise.
 
i hope you have time to either wire up an s-afc or get some more dyno time. jwt ecu do run rich when pre-programmed. see if you can get some dyno time and trim back fuel and possibly gain a few more hp.
 
you can modify the stock ecu to accept an 8bit eprom so you can change timing maps, ignition maps, rev and speed limiter, +much more. this is legal in IT because the modification is within the ECU housing.

once you have the ecu modified, use rom editor to modify your values. if you need some advice regarding rom tuning, or the ka24e ecu, feel free to email me.
 
erlrich said:
Now it would be legal whether it were within or outside of the ECU housing.

I wonder if anyone has tried setting up a megasquirt on one of our cars yet?
Click to expand...
One of our local drift guys has his car set up with megasquirt. He has a turbo, but has proven that it is easy and reliable. I think that would be my route if we ever get to that point.
My stock ECU still runs the car great, I know there is more power in there, but no need to search for it untill I am out driving the car.
Carver
 
I have a megasquirt unit sitting in my garage. It came off a 16v that was MAP-based. However I currently have a 12v car/motor. I'm looking for a clean 16v car/chassis that I could put this on and see what a set of BC cams and Diamond pistons can do in nasa
 
You must log in or register to reply here.
Back
Top