14 CUX Hotwire gear input. Pin 34

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GDCobra
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14 CUX Hotwire gear input. Pin 34

Post by GDCobra »

On the 14 CUX there is a gear input at pin 34 (Orange/Black wire normally I think). On a vehicle equipped with auto trans' this goes to a switch to earth and my understanding is that this adds RPM presumably when the 'box is in gear (including reverse), the setting for this on my map is 100RPM, probably standard.

Problem is my car is manual transmission so this pin is wired to ground via a 510 ohm resistor. The problem is I don't know if this represents on or off.
Anybody know?

The reason I'm looking at this is I sometimes find reversing a bit troublesome and quite often stall (I blame the lightened flywheel but problem may be the nut that holds the steering wheel) so what I'd like to do is wire this up to the reverse light switch so that when I engage reverse the RPM will be lifted and I should suffer less embarressment.

I can find this out by experimentation but not in a position to run the engine at the moment so would appreciate it if anybody knows.



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Re: 14 CUX Hotwire gear input. Pin 34

Post by ChrisJC »

I have had a look at RAVE, and it isn't that helpful!
All it says is that it is a Neutral Switch (automatic gearbox) (load input). It doesn't say what effect it has.

If you were wanting to lift the tickover, other options might be the Heated Front Screen Sense, or the Air Con Load Input.
Of course they need some experimentation which you can't do at the moment.

FWIW, on my Thor engine, the tickover is poor, so I have permanently enabled the air-con input to lift it a little.

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Re: 14 CUX Hotwire gear input. Pin 34

Post by GDCobra »

Hi Chris, thanks for your feedback.

I have since done some testing (not with engine running) with RoverGauge and found the following (worth having here for others to reference):

ECU.34 state --- Reading in RoverGauge
Disconnected ------ Drive/Reverse
Grounded ------ Park/Neutral
510 resistor ---- Manual

I'm assuming that the additional RPM is added when "Drive/Reverse" is active (would seem strange to lower the RPM when put into gear) which is a slight problem. On the manual gearbox the only signal I can get is when I select reverse, this would be a closed connection, If I link this to ground on one side and ECU.34 on the other this would imply the "Park/Neutral" state so I'd actually get the oposite of what I (believe) is required. I think the idle would drop when I put it in reverse.
This is not insurmountable, I could run the reverse switch signal to a relay and use the normally closed contacts to feed ECU.34 effectively reversing the action of the switch, or there may be other ways to do this, need to investigate.

You are correct there are other possibilities with ECU.8 (Heated screen) & ECU.21 (A/C). I thought I'd use ECU.34 as this seems logical as its purpose is a gearbox input (although that's not really important) but also because IIRC this has the highest RPM increase setting (100RPM going from memory) so I'd get the highest RPM increase straight away without having to re-burn a chip.
I think these RPM increases are additive so I could actually ground more than one and get a greater RPM increase without re-programming, although I think I may have removed these other from the loom (if they were ever there to start with).

I than hit a second problem. I put my meter over the reverse switch output terminals (these are currently un-terminated as I don't have a reverse light) and found that when I engage reverse the switch is not made, oh how I wish I'd tested this when I installed the gearbox as it's a complete b**tid to get at now, so until I fix this I'm scuppered anyhow.

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Re: 14 CUX Hotwire gear input. Pin 34

Post by GDCobra »

Just checked the settings on my chip.
Idle = 800 (which I knew)
Neutral idle adjustment is 100
AC compressor idle adjustment is 50
Screen heater idle adjustment is 0

So without rewriting the chip I can achieve an increase of 100, 50 or 150 RPM via a switch/relay.

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Re: 14 CUX Hotwire gear input. Pin 34

Post by GDCobra »

OK, just closing the loop on this for anyone else who comes across it.

My logic on previous post was completely wrong, Chen ECU pin 34 is grounded RoverGage indicates Park/Neutral in the "Selected Gear" area and the target idle RPM increases by the setting for the Neutral Gear Idle Adjustment, 100RPM in my case.

Seems strange to me that the idle would increase in Park/Neutral and decrease in Drive/Reverse but I'm not that familiar with auto boxes, it is always possible that Rovergage has got the indicators transposed.

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Re: 14 CUX Hotwire gear input. Pin 34

Post by DaveEFI »

I have the factory issued anti-stall mod on my SD1 auto. It uses the starter inhibit switch and controls an extra air valve similar to the one used for the AC. That gives the same 750 rpm idle speed in drive as in neutral.
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Re: 14 CUX Hotwire gear input. Pin 34

Post by ChrisJC »

The idle speed is dropped when in gear to reduce transmission 'creep'. So everything is in order.

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Re: 14 CUX Hotwire gear input. Pin 34

Post by GDCobra »

ChrisJC wrote:
Fri Mar 26, 2021 6:17 pm
The idle speed is dropped when in gear to reduce transmission 'creep'. So everything is in order.

Chris.
Ah! I guess that makes sense now I think about it. I'm only really familier with 'modern' auto boxes. The DSG in my daily driver (effectively a manual gearbox with auto operation) disengages both clutches when the brakes are on so no creep.

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Re: 14 CUX Hotwire gear input. Pin 34

Post by DaveEFI »

ChrisJC wrote:
Fri Mar 26, 2021 6:17 pm
The idle speed is dropped when in gear to reduce transmission 'creep'. So everything is in order.

Chris.
That doesn't make sense to me. Why would you want a higher speed in neutral and park?
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Re: 14 CUX Hotwire gear input. Pin 34

Post by GDCobra »

DaveEFI wrote:
Fri Mar 26, 2021 6:52 pm
ChrisJC wrote:
Fri Mar 26, 2021 6:17 pm
The idle speed is dropped when in gear to reduce transmission 'creep'. So everything is in order.

Chris.
That doesn't make sense to me. Why would you want a higher speed in neutral and park?
That was my initial thinking Dave but as Chris has mentioned it is more about reducing the speed when in gear to reduce creep, although if a lower idle is acceptable when in gear why not use all the time?

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Re: 14 CUX Hotwire gear input. Pin 34

Post by ChrisJC »

It's probably not acceptable all the time - alternator charging at night time with lights and heater on. Maybe even coolant circulation and cooling fan speeds are a shade low.

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Re: 14 CUX Hotwire gear input. Pin 34

Post by GDCobra »

I've just been looking at the notes on 14CUX tuning and associated modifications and the subject of the Idle modificaiton based on gear selection seeming to be a bit backward came up.
One theory which was postulated is that this is to meet expectations users may have of previous auto vehicles.
On carburettored vehicles or injection systems without automatic idle control when the car is put in gear the engine RPM drops due to the additional drag of the transmission. With this 'in-gear' setting dropping the RPM the veihicle would have a simlar 'feel'.
All seems a little pointless to me but it's not the most unusuall thing to happen with this system.

All I need to do now is get my reverse switch working and I'll be good to go. Only problem with that is access is severly limited but fingers crossed I'll get it done.

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Re: 14 CUX Hotwire gear input. Pin 34

Post by DaveEFI »

Doesn't ring true to me. Most surely want the slowest idle possible without stalling. Emission control often raised this.

The reason for a switch - even with closed loop idle speed - is that the idle valve without would react only when the engine slows, and may cause it to stall. A switch can tell it to open up before the gearbox actually engages gear and applies the load.

All in IMHO. :D
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Re: 14 CUX Hotwire gear input. Pin 34

Post by GDCobra »

DaveEFI wrote:
Tue Mar 30, 2021 2:42 pm
Doesn't ring true to me. Most surely want the slowest idle possible without stalling. Emission control often raised this.

The reason for a switch - even with closed loop idle speed - is that the idle valve without would react only when the engine slows, and may cause it to stall. A switch can tell it to open up before the gearbox actually engages gear and applies the load.

All in IMHO. :D
Totally agree with that Dave but the reality is that the idle is dropped when in gear and and that’s the biggest thing which doesn’t make sense to me.
Obviously I’m trying to do the opposite, get the lowest idle when the engine is just, er, idling (not in gear or with any additional load) (particularly to keep underbonnet temperatures down) and then lift it when we’re getting under way, particularly when reversing where clutch control can be a bit of a chore.

I currently have 800RPM as the standard setting with an additional (in my case 100 RPM if I ground the Gear Position with the reverse switch. If I want to I could also use one of the other idle modifiers via a pressure switch on the clutch that give me a higher idle when ever I’m in gear clutch in

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