Switch limp mode on and off

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sugarisbadforyou
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Switch limp mode on and off

Post by sugarisbadforyou »

Hi

I have a Xantia HDI 110 and as the title suggests I want to be able to switch limp mode on and off. The reason: my car has no speed limiter and limp mode does that job very nicely.

A circuit would need to be switched. Can anyone think of a circuit which triggers limp, could be switched off without doing any harm and when switched back on would allow limp to cancel without 3 starts or a code clearance?

Many thanks for any constructive replies.
wellad
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Re: Switch limp mode on and off

Post by wellad »

Usually something triggers limp mode because there's a problem, and limp mode prevents you from causing further damage. It stands to reason then that anything you do to engage limp mode, will damage the engine if you leave it disconnected. If you want to be able to lower the power with a switch, either the turbo solenoid or the MAF would be a good place to start without causing damage. You could also look into switching a pot to +5v off the fuel rail sender, which would do the opposite of a tuning box, i.e., lower rail pressure and less power, and be a lot more controllable than the above two without throwing an EML and "antipollution fault".

I can't think of anything you can disconnect that will limit revs but still allow full power. It's possible by building a frequency to voltage circuit to measure road speed, and switch a relay with the above pot solution when a comparator detects you've exceeded a set voltage (speed), but that might be a bit involved? :-D I don't think there are any (cheaply) available off the shelf solutions for this.
2003 Citroen C5 2.0 HDI 110
Northern_Mike

Re: Switch limp mode on and off

Post by Northern_Mike »

A small block of wood glued to the back of the accelerator..

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Hell Razor5543
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Re: Switch limp mode on and off

Post by Hell Razor5543 »

According to Paul (citroenxm) it is possible to add cruise control to a 110HDi Xantia, as the ECU already has the function. IIRC what is needed is the stalk, some wiring, and (possibly) a couple of switches (for the clutch and brake pedals). Other than that I cannot say.
James
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RichardW
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Re: Switch limp mode on and off

Post by RichardW »

It needs to be a relatively late car for the ECU to have cruise - mine does (built dec 2000) but Paul's doesn't (maybe a year earlier). However, looks like my ECU might be making its way to N Wales to enable Paul's CC!!
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sugarisbadforyou
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Re: Switch limp mode on and off

Post by sugarisbadforyou »

Thanks. My car is around April 99 so probably does not have cruise - how can I check?
Hell Razor5543
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Re: Switch limp mode on and off

Post by Hell Razor5543 »

It is not that it DOESN'T have cruise control, it's that it may not need much to add cruise control to it.
James
ex BX 1.9
ex Xantia 2.0HDi SX
ex Xantia 2.0HDi LX
Ex C5 2.0HDi VTR
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RichardW
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Re: Switch limp mode on and off

Post by RichardW »

Not really - no HDi Xantias have cruise, but only late cars have the cruise software built into the ECU. Paul cannot enable it on his car, as it is not there in the ECU, whereas on mine there is an option in the ECU to enable it (but still no control stalk etc - although mine does have a clutch switch fitted). The only way to check is to get it onto a Lexia and have a look what it says in the injection ECU section. Note that it is cruise only (ie constant speed) and not a limiter as later cars have built in.
Richard W
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Re: Switch limp mode on and off

Post by wheeler »

I don't think deliberately using limp mode as a speed limiter sounds like a good idea, apart from anything else you will probably find that it guzzles fuel when doing this. Could be dangerous also if you need to accelerate quickly away from danger, just flicking the switch back on may not switch off limp mode till the ignition has been switched off & on or even the fault codes cleared.
Northern_Mike

Re: Switch limp mode on and off

Post by Northern_Mike »

sugarisbadforyou wrote:Hi

I have a Xantia HDI 110 and as the title suggests I want to be able to switch limp mode on and off. The reason: my car has no speed limiter
Might I ask what is wrong with your eyes and right foot?
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