ECU not getting vehicle speed good or bad

Two40sPlease · Post by **Two40sPlease** » Thu Jul 23, 2009 7:34 am

The previous owner of my 240sx disconneted the speed signal wire to the ecu. Will this cause problems with my tuning. Does this effect closed loop operation??

Matt · Post by **Matt** » Thu Jul 23, 2009 2:16 pm

if may affect usage of some of the tables in the ECU

for example fuel cut/recover are dependent on ECU > 20km/h

It could affect O2 sensor operation (check logs to see if O2 sensor is bouncing when in closed loop operation)

Highly advised to reconnect speed signal. Some people disconnect to get around speed limiter ...

Two40sPlease · Post by **Two40sPlease** » Thu Jul 23, 2009 3:13 pm

I can verify that the O2 sensor was definitely working today (causing problems actually it thinks stoich is 13.3). And I disabled fuel decel cut off successfully as well which is really strange being that my consult never displays speed and the wire is indeed disconnected.

PL · Post by PL » Wed Aug 19, 2009 1:51 pm

Some Nissan ECU's will get very upset if the speed signal isn't present. I don't think it affects the tuning so much as the actual running of the engine. They will simply injector cut at a certain point. S13 SR20DE is a classic for this. I do wiring looms for engine conversions, so I've now seen this a few times.

The S13 DE will run fine until it's held wide open (6000rpm+) at high load (3rd gear+) continuously. So most road cars won't even see the problem. But race cars can and do. Once they've run for about 5 seconds under these conditions they will injector cut. Hard.

Others I've seen do this during bench testing are GTiR SR's and I recently tested a Z32 ECU and they do it too. S14 SR20DE's will do the same, but take longer - about 10 seconds. Most will recover once RPM drops below a certain point.

Most SR20DET's don't seem to care.

PL

Two40sPlease · Post by **Two40sPlease** » Thu Nov 19, 2009 10:14 am

ooooh Wow, I mudt not have read your last post Pete. I never knew why my redtop wouldn't let me reve up past mid 6K rpms depite setting the rev limiter higher. Maybe this is why.

STATUS · Post by **STATUS** » Mon Nov 23, 2009 11:11 pm

PL wrote:Some Nissan ECU's will get very upset if the speed signal isn't present. I don't think it affects the tuning so much as the actual running of the engine. They will simply injector cut at a certain point. S13 SR20DE is a classic for this. I do wiring looms for engine conversions, so I've now seen this a few times.

The S13 DE will run fine until it's held wide open (6000rpm+) at high load (3rd gear+) continuously. So most road cars won't even see the problem. But race cars can and do. Once they've run for about 5 seconds under these conditions they will injector cut. Hard.

Others I've seen do this during bench testing are GTiR SR's and I recently tested a Z32 ECU and they do it too. S14 SR20DE's will do the same, but take longer - about 10 seconds. Most will recover once RPM drops below a certain point.

Most SR20DET's don't seem to care.

PL

agreed and becomes more of an issue once the more power you make, if you get wheelspin the ecu freaks and cuts the injectors.

i wired a 26 to a s13 and the car was sweet 365rwkw on the dyno but once it span the wheels it would cut randomly, the customer had no speedo so i did not wire it initially (this was years back) hooked up the vss and bang issue went away.

PL · Post by PL » Tue Nov 24, 2009 9:00 am

I've now made up some little oscillator boards that I fit inside the ECU. Very simple - you just gotta find 5V, GND and the speed signal inside the ECU and solder the wires to these points. Then the ECU sees a constant speed signal. Not ideal but it stops the cut. I mainly use these on track cars.

PL

robots · Post by **robots** » Sat Jan 16, 2010 5:27 am

r33 rb25 ecus are speed signal junkies.
They will not make the same power, sound different, no rev cut. Only violent inj. cuts. Scary shit. Also I think VCT won't run. Wire speedsignal in.

R32 RB20DET doesn't seem to care about speed signal.

PL · Post by PL » Sat Jan 16, 2010 8:48 am

RB20DET's are not quite as bad as what you said about the 25 but they do need the signal or they'll hard cut similar to S13 SR20DE - everything is fine until you hold them wide open at full load for more than a certain time. This time seems to vary between ECU's but usually 5 to 10 seconds.

So some drivers never even notice it. But those that really give their engines a hammering will hit it. That's why it tends to be track cars that have the problems.

PL