1st gear rev limiter
Joined: Sep 2002
Posts: 25
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From: Swindon, Wiltshire, England
Re: 1st gear rev limiter (Deckedlude)
What you are getting is classic JDM VTEC fitted with KPH to MPH converter / delimiter problems.
Basicly the pulse signals from the VSS (vehicle speed sensor) are divided by the convertor to a slower speed to show MPH rather than KPH on your speedo (this also in effect delimits the car by changing the 180KPH limiter to a 180<U>MPH</U> limiter).
The problem arises with first gear because Honda build a safety circuit into the VTEC and engine revs ECU control. Basicly what they did was to make it impossible for you to over rev the engine or engage vtec while stationary or going in reverse.
The speed that they set this safety margin at was 20<U>KPH</U> - easily reached before the natural VTEC entry point. Now then, because you have slowed down the signal to the ECU by a factor of 1.6 (to read MPH) the ECU is no longer "seeing" the signal it needs to release the engine from it's safety limit.
You basicly now have to be doing 32<U>MPH</U> (20KPH x 1.6) before the ECU "sees" the signal pulses it needs to and as 32MPH in 1st gear is way up in the rev range you are hitting the safety limiter before reaching 32MPH.
Your options to get around this problem are....
1) Find and remove the KPH to MPH convertor - This will restore everything back to how it should be BUT you will have a 180KPH speed limiter (112MPH)
2) Find the convertor (probably tapped right into the VSS wiring at the gearbox) and split the output signal (should be an orange wire). Wire it so that the original VSS output wire goes to the ECU (ECU then "sees" KPH) but take off a feed from that wire and run to the Convertor, the signal output from the convertor should then be wired direct to the speedo (speedo then reads MPH) - This will restore 1st gear back to normal, will show MPH on speedo BUT will still have 180kph(112mph) speed limiter.
3) Run the system as you are doing now but wire in a microswitch into the circuit and attach it to the gearchange linkage so that when 1st gear is selected it reverts back to sending KPH signals to the ECU.
Hope that helps
Basicly the pulse signals from the VSS (vehicle speed sensor) are divided by the convertor to a slower speed to show MPH rather than KPH on your speedo (this also in effect delimits the car by changing the 180KPH limiter to a 180<U>MPH</U> limiter).
The problem arises with first gear because Honda build a safety circuit into the VTEC and engine revs ECU control. Basicly what they did was to make it impossible for you to over rev the engine or engage vtec while stationary or going in reverse.
The speed that they set this safety margin at was 20<U>KPH</U> - easily reached before the natural VTEC entry point. Now then, because you have slowed down the signal to the ECU by a factor of 1.6 (to read MPH) the ECU is no longer "seeing" the signal it needs to release the engine from it's safety limit.
You basicly now have to be doing 32<U>MPH</U> (20KPH x 1.6) before the ECU "sees" the signal pulses it needs to and as 32MPH in 1st gear is way up in the rev range you are hitting the safety limiter before reaching 32MPH.
Your options to get around this problem are....
1) Find and remove the KPH to MPH convertor - This will restore everything back to how it should be BUT you will have a 180KPH speed limiter (112MPH)
2) Find the convertor (probably tapped right into the VSS wiring at the gearbox) and split the output signal (should be an orange wire). Wire it so that the original VSS output wire goes to the ECU (ECU then "sees" KPH) but take off a feed from that wire and run to the Convertor, the signal output from the convertor should then be wired direct to the speedo (speedo then reads MPH) - This will restore 1st gear back to normal, will show MPH on speedo BUT will still have 180kph(112mph) speed limiter.
3) Run the system as you are doing now but wire in a microswitch into the circuit and attach it to the gearchange linkage so that when 1st gear is selected it reverts back to sending KPH signals to the ECU.
Hope that helps
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lmike6453
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Sep 14, 2008 07:59 PM
