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tricking the ECU into thinking the steering wheel is turning 

 

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 Post subject: tricking the ECU into thinking the steering wheel is turning
Posted: Sat May 10, 2014 4:26 pm 
Getting Side Ways
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Hi all,

My car has had JTG liquid gas injection and for the most part I love it. great power, fantastic economy.

What I don't love is that the JTG piggyback computer is as dumb as a box of hammers and has no diagnostic or calibration ability that I can see (the installer said as much himself. It is a piggyback of the normal PCM so in many ways it doesn't need one)

The problem I have currently is that the idle on gas is about 50-80 rpm lower than on petrol.. this is a problem as I'm usually idling back out of the driveway in the morning when it switches to LPG and the car nearly stalls (occasionally it actually does)

I spoke to the installer who said there was no provision for idle adjustment on the gas system.. and changing it in the PCM would make the engine idle too high on petrol.

Then he said something really cool that I smacked myself for not thinking of myself.

He said that the early vapor systems had a very similar problem and they used to work around it by hooking a relay up so that it was triggered by the gas system being on.. and that relay was hooked into the power steering sensor such that when the car was on GAS the PCM was tricked into thinking someone was turning the steering wheel hard. The PCM would then compensate by adding roughly 50 rpm to the idle speed and that solved the problem of the bad idle on gas.

That is very clever.. I was annoyed that with all the idle problems I had before the tune... it didn't occur to me as a solution.

Does anyone know by what mechanism the steering sensor tells the ECU that it's turning? I'm guessing it's simply a pressure sensor that detects high oil pressure in the box as it would when it's turning wheels and the closer it is to a solid earth the higher the oil pressure would be..

If I'm right all I have to do is find that sense wire and run it though the relay to earth.. possibly though a resister as I doubt it would have no resistance at all, even when at full turn.

The end result should be that when I'm on gas the engine will idle 50 rpm or so higher than on petrol.. which should be perfect or close thereto.

any thoughts or suggestions folks?


regards

Frank
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 Post subject: Re: tricking the ECU into thinking the steering wheel is turning
Posted: Sun May 11, 2014 12:46 am 
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In the E series that's all it is, a switch, I think normally closed. The P/S pump doesn't work very hard on straight ahead, so once steering is turning, pressure then increases to a max at full lock.
Your relay contacts should be able to go in parallel across the P/S switch wires, power the relay coil off Gas lock off supply (or whatever opens/closes LPG supply).

 

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96 XH Longreach 'S': LPG, Alarm, 3.23:1 LSD, Cruise, Trip Comp, ABS, Power Windows, Mid Series Dome Lt, Climate Ctrl
97 EL Futura S/W: LPG, Alarm, LED int Lts, Trip Comp, F/Lane Dome Lt, Climate Ctrl, T5 Conversion

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 Post subject: Re: tricking the ECU into thinking the steering wheel is turning
Posted: Sun May 11, 2014 2:09 am 
Getting Side Ways
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snap0964 wrote:
In the E series that's all it is, a switch, I think normally closed. The P/S pump doesn't work very hard on straight ahead, so once steering is turning, pressure then increases to a max at full lock.
Your relay contacts should be able to go in parallel across the P/S switch wires, power the relay coil off Gas lock off supply (or whatever opens/closes LPG supply).


Its a little more complex than that.. the priming system comes on regardless if the car is set to gas or not. (so it can switch to it smoothly if needed.) So I can't use the gas lockoff power as the relay would be triggered all the time.

There looks to be some relays on the factory loom that have been added, presumably to switch between gas and petrol injectors.. those ones would only have power if the car is switched to gas so that would work as a feed to this new relay.

I'll get under the car tomorrow and see if the steering box has one of those little pressure senders on it.. if it does seems a quick test would be to test the impedance between earth and the sensor wire normally and when someone is swinging the wheel around.
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 Post subject: Re: tricking the ECU into thinking the steering wheel is turning
Posted: Sun May 11, 2014 9:38 am 
Getting Side Ways
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the switch is on the pipe just behind the p/s pump mate
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 Post subject: Re: tricking the ECU into thinking the steering wheel is turning
Posted: Sun May 11, 2014 1:29 pm 
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^^^^ Yep, nicely above the alternator.
frankieh wrote:
Its a little more complex than that.. the priming system comes on regardless if the car is set to gas or not. (so it can switch to it smoothly if needed.) So I can't use the gas lockoff power as the relay would be triggered all the time.There looks to be some relays on the factory loom that have been added, presumably to switch between gas and petrol injectors.. those ones would only have power if the car is switched to gas so that would work as a feed to this new relay.
Yes, I figured it may not be straightforward.
As with SVI systems, you may find the petrol injector inputs go via the LPG ECU, so it shuts them down, and provides data to the LPG injectors. Don't know much about Liquid setups unfortunately.

There would be power on LPG used to activate gas tank contents display, or a changeover to show this on the dash gauge. Probably your best bet.

 

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96 XH Longreach 'S': LPG, Alarm, 3.23:1 LSD, Cruise, Trip Comp, ABS, Power Windows, Mid Series Dome Lt, Climate Ctrl
97 EL Futura S/W: LPG, Alarm, LED int Lts, Trip Comp, F/Lane Dome Lt, Climate Ctrl, T5 Conversion

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 Post subject: Re: tricking the ECU into thinking the steering wheel is turning
Posted: Sun May 11, 2014 6:35 pm 
Getting Side Ways
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WA, Australia

snap0964 wrote:
^^^^ Yep, nicely above the alternator.
frankieh wrote:
Its a little more complex than that.. the priming system comes on regardless if the car is set to gas or not. (so it can switch to it smoothly if needed.) So I can't use the gas lockoff power as the relay would be triggered all the time.There looks to be some relays on the factory loom that have been added, presumably to switch between gas and petrol injectors.. those ones would only have power if the car is switched to gas so that would work as a feed to this new relay.
Yes, I figured it may not be straightforward.
As with SVI systems, you may find the petrol injector inputs go via the LPG ECU, so it shuts them down, and provides data to the LPG injectors. Don't know much about Liquid setups unfortunately.

There would be power on LPG used to activate gas tank contents display, or a changeover to show this on the dash gauge. Probably your best bet.


yup.. I'll get my multimetre on the main lpg loom and test which of those only has power when the gas is on..

I have news on the power steering sender though.. If you have a BA/BF and you want an extra 50 or so RPM at idle.. unplug the power steering pressure sender and the idle will increase...

So the sender is an open circuit when the wheel is turned hard.. and a lower impedance when it isn't'... I unplugged it and the idle picked up nicely.

considering how many topics there are on here talking about bad or low idling BA falcons that little tidbit should come in handy.
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