Factory Speed Limiter

[nikp]

I had what i thought was a fuelling issue at high speed on my FD - I think i've figured out what the issue is: I think it's the mazda factory speed limiter! It makes sense cos i hit it in only fifth gear whether i'm on full boost or partial throttle, etc. (Obviously this is all done in the confines of a private test track! :3gears-rh ).

So, my question is, how do i remove this 'feature'? I used to have a speed converter to convert from kph to mph which i understand removes this. But i now have a speedo in mph, so no longer use the speedo converter.

[Adriansturgess]

As I understand it jap imports are speed limited to approx 112mph (law in Japan). Fuel supply is momentarily cut at this speed and it has nothing to do with what gear you are in or how much boost.

[nikp]

Yeah - that's how i understand it too (It's pretty much exactly whats happening)

My question is how do i disable it!? I know it's disabled when an after market speed converter is fitted. I think there's some sort of feed to the ECU isn't there?

[Adriansturgess]

I had same problem and got Rotechniks to remove it while the car was in for service. Don't know what they did or how easy it would be to do yourself. Forget what they charged me but I think it was around the £100 mark. :)

[WeasleRx7]

When my speedo convertor wasn't working, one of the guys at RX Motors offered to remove the limiter for me.

I was told it was just a single wire that goes to the ECU and it just needs snipping. 2 minute job including removing and replacing the trim. They had even located the wire and were just ready to snip it! I opted just to remove my converter and get it replaced.

Unfortunately I didn't look as to the colours of the wire, but I did see that it was just a single wire going to my ECU. Maybe one of the tuners here can tell you which one it is. I can only tell you it's possible (sorry).

[WeasleRx7]

Just had a look at my ECU, and the cable is still separated from the loom.

It's on the 2nd multiplug from the bottom and is green with a black stripe.
(EDIT)** Not the right cable, please see later posts **(EDIT)

If no one else can confirm this is the correct cable, maybe just remove that one cable from the muliplug and give it a try?!

Small print: Due to the fact that I am no expert, or in anyway qualified to offer advice, any changes made will be at your own risk!! :)

But what's the worst that could happen??

[nikp]

Cheers - i'll check it out. Although, I'm going to work from behind the dash i think. I've had that apart numerous times now, so i am familiar with the cables back there. I also know which ones have been snipped for the speed converter, so i shall just look for a green wire with black stripe. Might not tie up completely, but it'll be worth a look. Cheers for the input: i knew it was a single wire.

[WeasleRx7]

If you want to try snipping that cable, trust me, it's much easier to do it at the ECU.

Just remove the one trim panel on the left of the passengers footwell (the one that holds your emergency flare if you have one), and hey presto ECU is there and cables are all in full view!

I've also had my dash off a number of times, and this is much much quicker. Also if it doesn't work for some reason, you dont need to strip the dash to re-connect it. I'll take a pic.....

[WeasleRx7]

I seem to recall this cable does come from the speedo loom behind the dash, but here's a pic of the location of the ECU anyway.

[nikp]

Cheers - nice one! Is the ecu in the passenger footwell?

[WeasleRx7]

Yes mate, as per photo ^^^^

But as I said before, this cable wasn't singled out by myself so I can't confirm either way it's the right one. Having said that though I've not had the trim covering the ECU off since I had the problem, so I'm sure it's the same cable!

Just be ready to reconnect it if the limiter isn't disabled.

[nikp]

Righto! Cheers - i'll check it out.

[TonyBlair]

I'm confused...

when my car arrived from the land of the rising sun it had a HKS Speed Limit Defencer. It's a little device that was wired into back the ECU. I looked about on the net and it seems the sole purpose of this "Speed Limite Defencer" was simply to cancel out the speed limiter.

I can't see why HKS would bother making such a device if all you really need to do is cut a wire? Anyhow, not too bothered about it since I have a Apexi ECU now - which boviously doesn't have a speed limiter built-in ;)

Cheers
Jon

[WeasleRx7]

I don't know the answer to that one Jon, but hopefully Nikp will report back to us with his findings...?

[nikp]

I haven't done it yet, but as far as i understood, it was a single wire going to the ecu was all that there was that controls the speed limiter. My question was which one was it, and what do i need to do.


As found on the ebay auction for the speedo converter:
"There is also a special wire on the unit which goes to the E.C.U which will remove the 112MPH Restriction"
(http://cgi.ebay.co.uk/MAZDA-RX7-SPEEDO-CONVERTER-DELIMITER-CHIP_W0QQitemZ4566697961QQcategoryZ52640QQssPageNa meZWDVWQQrdZ1QQcmdZViewItem)

[craig]

what speed are you doing when this kicks in mine does the same thing but only some times it gets to 180 kph and just backs its self off ,i have a little black box that has been banging around so i m thinking its that that has gone funny

[Adriansturgess]

I'm confused...

when my car arrived from the land of the rising sun it had a HKS Speed Limit Defencer. It's a little device that was wired into back the ECU. I looked about on the net and it seems the sole purpose of this "Speed Limite Defencer" was simply to cancel out the speed limiter.

I can't see why HKS would bother making such a device if all you really need to do is cut a wire? Anyhow, not too bothered about it since I have a Apexi ECU now - which boviously doesn't have a speed limiter built-in ;)

Cheers
Jon

I think this must be the device that Rotechniks fitted to my car. I certainly had a bill for parts and labour. Does seem odd if it actually only needs a wire disconnecting. :confused:

[nikp]

hmmm....maybe it's not that simple then. I dunno...i too am confused!

[TonyBlair]

Well, since I don't use the HKS de-limiter (as said in previous post I have an Apexi now) I would be willing to sell it on to whoever wants it.

I *think* I managed to download the wiring instructions for it some time ago - will have a look this evening.

Cheers
Jon

[Adriansturgess]

what speed are you doing when this kicks in mine does the same thing but only some times it gets to 180 kph and just backs its self off ,i have a little black box that has been banging around so i m thinking its that that has gone funny

180kph equates to 112mph. This is the speed at which the limiter cuts the fuel supply momentarily.

[WeasleRx7]

Well I would try cutting the wire myself, but since I have a converter fitted behind the dash I'd need to exceed 180mph in order to know if it works!!!

Even if I found a private road long enough, I don't think my Rex is capable of any where near that speed!!! :(

[Adriansturgess]

Anyway you wouldn't know if the cut in power at 180mph was the limiter cutting in or your rotors beginning to melt. :rollin

[TonyBlair]

Not that my Rex could achieve 180mph, but I'd hate to think what "fuel cut" would do to the engine at that speed. :eek

[Pointman]

SO, ...... the big question is, does anyone wish to try cutting this wire and finding out if the restrictor is removed, OR, do we all buy one of those Ebay kmh to mph convertors with the limiter removal ?

I personally don`t fancy cutting a wire, so my next question is, has anyone bought one of those ebay chips, and do they work ?

Thanks

[WeasleRx7]

My speed convertor does not remove the limiter, but it does fool the speedo and ecu into thinking that my MPH is actually only KMH. This corrects my speedo gauge to read as MPH and effectively raises the limit to 180MPH. So why would I need a speedo converter that also removed the limit completely?

The only reason I can see that a car with a standard ECU would need a limit removal, would be in the case of Nikp where he has actually changed the speedo guage to a MPH one, but the japanese ECU is still thinking the signal it's getting is KMH and so cuts the fuel at 180KMH (112MPH).

[WeasleRx7]

I'm sure the EBAY chips with the limit removal will work, but why would you need it removed? A car with a standard ECU will never exceed 180MPH!!! :)

[nikp]

do we all buy one of those Ebay kmh to mph convertors with the limiter removal ?


That's the problem: I can't! I have a speedo that already reads in mph! So, my only options are these:

1. Cut said wire.
2. Upgrade to Apexi PFC & commander!

Damn! These choices are hard! ;)

[WeasleRx7]

My point about the speedo converters that also remove the limiter with a wire to the ECU is that they are completely pointless! As if you're running a standard ECU then you'll never hit the 180MPH limit you get with a lesser converter, and if you have an aftermarket ECU to cope with the mods to get you to 180 then it's not got a limiter anyway!... If you follow me?

Back to the point of this thread.... How to remove the limit imposed by a japanese ECU when using a UK speedo?

Cut the wire?!!! (hee hee)

Buying an Apexi is an expensive option just to remove the limiter.

Just had a thought... To remove the speed limiter on a Eunos Roadster all you do is remove a screw from the back of the speedo which breaks the connection from the speedo to the ECU. This is effectively the same as cutting the cable. So it could be just as simple as that on the REX.

[nikp]

hmm, i don't agree that just because you've converted from kph to mph with a special converter that the speed limiter will be converted to 180mph - it depends upon where that feed is coming from. The feed going to the ECU may be the feed that comes from the gearbox directly - which is not specifically a speed (At least not in kph or mph). Therefore converting the speedo will make absolutely no difference to the speed at which the limiter cuts in.

I don't think i've explained myself too well!

[WeasleRx7]

I've got the answer.... Don't cut the green/black wire! :)

I've just spoken to Tim and Ian at RX Motors. The wire you want is the Green with a RED stripe. It's on the lowest multiplug which is 11 pins wide. and if you count 5 pins in from the edge you will find a Green/red cable. Cut that one!! :) :) :)

Turns out the cable I thought it was is for the injectors, so not a good idea to cut that one at all!!!!

[WeasleRx7]

OK so with my speed converter, why doesn't my car cut out at 112MPH (180KMH)??

I don't have a special cable that goes to the ECU, so it must be getting it's signal from the speedo.

[Adriansturgess]

My speed convertor does not remove the limiter, but it does fool the speedo and ecu into thinking that my MPH is actually only KMH. This corrects my speedo gauge to read as MPH and effectively raises the limit to 180MPH.

As a matter of interest have you successfully taken your car over 112mph or is this all theory?

[WeasleRx7]

The car has been well over 112mph on a private track. Same with my wifes MX5 which hit the limiter at 112MPH also, but was unrestricted when I removed the screw/connection on the back of the speedo.