Closed loop LPG

[Quagmire]

Right so the situation is this- i know I am in the Rangie forum, but figured there were more v8/LPG gurus in here:

-B-Reg ragtop 90

-3.5 v8 rebuilt last November - is a 9.35:1 SD1 recon block, running 10 bolt heads and standard 3.5efi cam.

-Using a 2 pin module Lucas electronic dizzy.

-P6 style round airbox

-Running on SU's, LPG is an open loop kit from Tinley, running a Bigas M84 vapouriser feeding via y-piece to the tinley mixer plates on each carb.

Plans for the future are to:

-Fit EFI and megasquirt, i have all the parts necessary on the LR side of things (have a lot of old flapper stuff around). Need to get EDIS and the squirt when funds allow. This would then allow me to run much more efficiently when on petrol and avoid drying out carb syndrome, and am hoping to be able to use a different ignition map when on LPG.

So, the question is this. Are the closed loop stepper-motor type power valves worth using? I was looking at the one on Tinley, as this comes with a lambda sensor and boss, which will be needed for the EFI later. I could then let this control the mixture when on LPG, with the megasquirt providing the ignition side of things.

Closed loop thingy, second down on the page here:

Tinley

Thanks

[FridgeFreezer]

Wonder what the stepper is acting on to adjust it? Seems to me you could very easily DIY that setup although I suppose £120 isn't too extortionate for a working setup.

[Bowie69]

Had one, got about 10-15% improvement in economy and MUCH smoother acceleration through the rev range, it was uncanny, really..... setting it up was a piece of cake, just adjust the vapouriser screw at idle until the lights *just* stay on red (bit rich, better idle though) then bring the revs up to 3000 and adjust the power valve manual setting until it flashes red-green-red-green. Take it for a drive and test the above under hard acceleration and tweak if necessary. When I installed mine it was freakily in exactly the right place from factory.

It now lives on a friends LPG-only 4x4 (Mazda 626 2.0 16V engined) and he's had a 30% improvement in MPG and smoother running -though his open loop was more than likely not setup quite right anyways....

Big improvement over the open loop, I would do it again if I was running it as a daily driver for sure.

The lambda probe should be ideal for the proposed MS install as well (it's a 4-wire heated version).

*edit* meant to say, the destructions are in pigeon-Italian and almost useless, just follow the wiring diagram on the back.

HTH,

Bowie.

[Highway_Star]

The stepper sits in the vac/supply pipe betwen the mixer and the vaporiser. So depending on your point of view it either controls gas supply to the mixer by a; regulating the flow of gas to the mixer or b; regulating the vacumn pulling the gas from the vaporiser.

Good ones will have the capabality to program and learn maximum, minimum and median stepper positions. As well as stepper position under throttel closed/ over run conditions, temporary stepper position under full throttle conditions. Really needs to be connected to a TPS or throttle closed/full open microswitches for that though. It's often best if the system goes open loop at idle, as the constant nudging the mixture up and down will make the engine hunt otherwise.

I guess the simple add on ones I've seen will simply try to maintain stoic at all times.

You also need to set the vaporiser up properly. Basically close the idle circuit completely, screw the main (power) circuit in until the engine starts to falter at idle and just about stalls, then open up the idle circuit until it runs smoothly and the idle mixture is right. Helps if you can see the lambda probe output on a laptop (although I see this Tinley box has LED indicators, better than nothign) or have a gas analyser handy. Heck Colourtune does a good job of this

[geoffbeaumont]

Can't comment on the difference between open and closed loop, as I've only run closed, but you don't need separate lambda sensor(s) for the two fuelling system - the LPG kit I had was patched into one of the hotwire systems sensors, which worked fine. So you can factor that into your calculations when deciding if it's worth doing.

[tel]

ive fitted the tinley closed loop system its defently worth it as longterm use on lpg you could end up melting a piston if running too lean for a long time on gas, closed loop lets you control the mixture to get it spot on so hence prolonging engine life aswell as more power and more mpg

[Quagmire]

Well, i've ordered one, i took the line that the lambda was needed anyway for EFI at some point so that knocks off some of the cost. We'll see how it goes.

I have my fuel figures recorded for the last 4000 miles so we'll see what the real-world increase there is (if any) post-install...

My figures had dropped recently due to a couple of problems i had, so my overall is currently 15mpg. Peak over this period was 22.1 mpg, and the lowest has been around 11...

I had been attaining around 16mpg overall before i had the issues (self induced) with kinked hoses and dirty gas and air filters. Last two tanks were 16.44 and 15.86mpg respectively so we'll see!

Thanks for all the replies

[Bowie69]

Good luck with it

[Quagmire]

Well so far with the closed loop i have got to here, the instructions are next to useless so as Bowie said, you have to go on the wiring diagram alone:

(For anyone interested in pointers as to colours, I was using the kit from Tinley )

Lambda bung welded into Y-piece, and lambda fitted.

The lambda wires were extended into the battery box by soldering on some nice lengths of the appropriate colour.

LPG controller loom slightly rearranged so that the lambda signal connection (green) and box earth (black) remained in the battery box, rest of wiring routed forward to engine bay. Controller box to stay in battery box.

Blue and red wires connected to LPG stop solenoid as stipulated in wiring diagram

Purple and white wires from LPG control box left unconnected (no TPS or injection emulation stuff)

The wiring for the stepper valve comes with a nice connector on the end already, so nothing to do there- just route to the correct location.

I then connected the lambda heater wiring up using a relay- i wasnt sure how much current it might draw and when a relay is only £2 from Maplin whats the point in putting strain on any wiring?

Using a single pole, normally open 12V 40A relay I connected an ignition switched live to the trigger side and then connected the lambda heater wiring to the switched side, with a 5A fuse inline. This means that the lambda probe is heated (and therefore should resist fouling) whenever the engine is running, and not just when running on LPG. The heater wires are not polarity conscious and so just connect one side to power (from relay) and one to ground.

From Googling around, and also with thanks to Fridge Freezer I found that the wiring on my VW/Audi probe was a failry common setup and was like this:

White: Heater

White: Heater

Black: Signal out

Grey: Signal ground

So the green from the box connected to the black of the probe, and the grey was connected to a good earth (direct to battery terminal).

I have not yet put the valve in, but have plugged it in and could see it operating as the system tries to adjust the mixture. I seem to be getting rich on idle, flicking to lean every so often so it must be pretty close already. Couldn't really rev it up and see what i got as i didnt want to pee the neighbours off.

Will see what happens tomorrow when i get the valve in, perhaps i will try to get some pictures too when i have tidied the wiring B)

[tel]

glad its working out for you i have the same kit as you i was playing with the settings on mine earlier too trying to get it spot on think its preety much there now

[FridgeFreezer]

For reference, the easy way to test lambda sensors and find out what's what is to heat the tip up with a blowlamp until it just glows. Ignoring the heater wires, you should get somewhere between ~0.1 and ~0.9v (100 - 900mV) DC on the other two wires, depending how rich your blowlamp runs . If you get minus volts, the wires go the other way round