Tune resistor for de-cat?

[jamienshelly]

Hi all,
I have removed my main cat and it seems to run ok, apart from smelling a little rich at tickover, it has an idle issue. It ticks over at 900-1000 rpm but after a while it falls to about 600 rpm and then recovers after about 5-10 seconds, I have set the base idle and it does the same, is it trying to trim itself but going to far because the cats are not there?, and do I need to change the tune resistor from cat one, to a non cat one,
It is a standard serp 400
Many thanks
Jamie

[QBee]

Have you left the lambdas in?

[SILICONEKID343HP]

Blitz will explain .

[QBee]

If you have left the lambda sensors in it should be fine with no change of tune resistor.
When I decatted mine it wouldn't hold any idle when warm. Turned out to be a heat sensitive stepper.

[Richard 858]

If you've fitted the Clive Ford decat Y piece he probably supplied it with a variable resistor, Whilst some motors seem to prefer the "green" setting mine is definitely happier on "white" which is effectively the standard, original setting. Lambdas still in & it runs sweeter than before decatting.

[QBee]

Richard 858 said:

If you've fitted the Clive Ford decat Y piece he probably supplied it with a variable resistor, Whilst some motors seem to prefer the "green" setting mine is definitely happier on "white" which is effectively the standard, original setting. Lambdas still in & it runs sweeter than before decatting.

Green if you have taken the lambdas out, white (= no resistor) if lambdas still in.
I think that decatting changes other parts of the balance, so alter things that change the idle.

[SILICONEKID343HP]

QBee said:

Green if you have taken the lambdas out, white (= no resistor) if lambdas still in.
I think that decatting changes other parts of the balance, so alter things that change the idle.

Why would you not want the lambdas on ? They trim for fuel economy .

[Richard 858]

Quite right Anthony, I did need to adjust potentiometer & idle slightly, but now idles at 1050-1100 cold & 850-900 warm.

[jamienshelly]

QBee said:

Green if you have taken the lambdas out, white (= no resistor) if lambdas still in.
I think that decatting changes other parts of the balance, so alter things that change the idle.

Thanks for the replies, I have left the lambda's in, so white it is. Im not sure what I have at the minute, but will check later.
Jamie

[blitzracing]

You should run white with the lambda probes, with or without the physical catalysts and running no resistors will put the ECU into a fault condition. The green tune will switch to the non catalyst map, but this is likely to be the original Range Rover tune, as it appears TVR only modify the map the car was sold with. The Range Rover map can be as much as 20 BHP down at peak power, and appears to runs leaner at full power, which you don't want. The white tune will still give peak power when the ECU goes open loop at 3400 rpm, or above 3/4 throttle. The only reason to ever run a green tune is it can reduce the shunting at low speed on some cars, and then it needs to be tuned for the TVR.

[jamienshelly]

One thing I have noticed is the lack of shunting, I used to get a little bit in 4th and 5th at low speed but now nothing, it seems to be a lot smoother in all gears.
Thanks Blitz, I hope that I have the white resistor but if I have the green then I can look forward to better things when I change it .

[blitzracing]

No- note the bit about the wrong map in green tune. You need a Tornado chip if you want to run green.

[jamienshelly]

I mean if I have the green, I look forward to the gains when I change it to white

[QBee]

Sorry, Jamie, I had assumed you had installed a Clive Ford Y piece. Now I am questioning that. What decatted Y piece have you installed?

All this discussion of resistor colours is based around the switchable resistor Clive supplies with his Y piece. The standard TVR catted and lambada'd setting is the same as the white position on Clive's resistor.

[jamienshelly]

Sorry I suppose I should have said, its a standard "Y" piece but with the cat removed.

[clive f]

QBee said:

Green if you have taken the lambdas out, white (= no resistor) if lambdas still in.
I think that decatting changes other parts of the balance, so alter things that change the idle.

Lambdas stay in regardless, I did pm you about this a while ago.