Mixer Ring Orientation

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308RRC
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Mixer Ring Orientation

#1 Post by 308RRC » Mon Sep 14, 2020 2:05 am

I am installing a closed loop Gastec FP32 LPG system on my 1988 Range Rover. I have the mixer ring to go between the air flow meter and inlet manifold. Problem I have is that I don't know which way it goes. There is a flat side and the other side is angled with holes for the LPG to come out from. So does the flat side of the mixer ring go toward the air flow meter or toward the engine?

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Re: Mixer Ring Orientation

#2 Post by Gilbertd » Mon Sep 14, 2020 8:20 am

This is the type I use on the Rover V8 https://tinleytech.co.uk/shop/lpg-parts ... -wire-afm/, the fatter side fits onto the throttle body in place of the hose which then fits on the thinner side. How that compares with what you have I've no idea, a picture might help.
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Re: Mixer Ring Orientation

#3 Post by 308RRC » Mon Sep 14, 2020 8:53 am

Here is a picture of the mixer.
gas ring.jpg
gas ring.jpg (35.79 KiB) Viewed 132 times

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Re: Mixer Ring Orientation

#4 Post by LPGC » Mon Sep 14, 2020 9:36 am

You've got a fairly standard mixer, Gilbert has explained how it should be orientated.

The little grub screws are there to clamp the unit onto the throttle body.
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Re: Mixer Ring Orientation

#5 Post by Gilbertd » Mon Sep 14, 2020 9:54 am

Also worthwhile putting a thin smear of RTV on the throttle body where the mixer fits on so there's no air leaks.
96 Saab 900XS, AEB Leo, sold
93 Range Rover 4.2LSE, Lovato LovEco, sold
97 Range Rover 4.0SE, multipoint, sold
98 Ex-Police Range Rover 4.0, AEB Leo, daily motor
96 Range Rover 4.6HSE Ascot, AEB Leo, my spare


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Re: Mixer Ring Orientation

#6 Post by Fox vehicles » Wed Sep 16, 2020 8:51 am

Is the Range Rover a 3.5 or 3.9?
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Re: Mixer Ring Orientation

#7 Post by 308RRC » Wed Sep 16, 2020 12:03 pm

Its a 3.5 litre with the 14CU EFI.

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Re: Mixer Ring Orientation

#8 Post by 308RRC » Thu Sep 17, 2020 8:23 am

I have the mixer in but have now ran into another problem. I can just get the car to (just) idle only if the high speed valve in the LPG line from the converter to mixer is completely closed all the way. The air/fuel gauge in the car shows even with this all the way in its extremely rich. With the setting in this position the car will only rev to around 2000rpm then it runs out of LPG. I have tried 2 mixers an OMVL and a BRC both do the same. Am I missing something?

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Re: Mixer Ring Orientation

#9 Post by LPGC » Thu Sep 17, 2020 11:18 am

There will be 2 adjustment screws on the reducer/vaporiser, 1 screw for sensitivity, 1 screw for idle bypass.
Sensitivity controls how much gas comes out of the reducer for a given amount of signal (suction created by the mixer).
Bypass allows a set amount of gas to come out of the reducer to the mixer (and engine) regardless of signal.

To start with when setting the system up you should leave the idle bypass turned completely off so no gas comes out of the reducer unless it is sucked out by signal - especially since your results so far point to mixture being too rich (you have to screw in the in-pipe adjuster or the engine idles too rich). You'll probably need to reduce sensitivity too. Try to set sensitivity so it idles nicely with the in-pipe adjuster open about half way.

What reducer are you using.. [You mentioned you've tried BRC / OMVL mixers, did you mean BRC / OMVL reducers]? I find that BRC reducers are usually preset with fairly average settings that tend to work OK-ish straight out of the box on most installs (but may have a small amount of bypass preset), OMVL reducers usually come out of the box needing sensitivity to be increased for most installs (but usually don't have any bypass preset).

Most of the above assumes petrol injectors do turn off when it's switched to run on gas! If petrol injectors are still working it will get petrol and LPG at the same time so will obviously run too rich even with a small amount of gas entering the engine. How have you set the system up to turn off petrol injectors when it's switched to run on gas?

What happens when 'it runs out of LPG'? If the engine misfires due to a very rich mixture an AFR gauge may show a lean mixture, AFR gauges read excess air in the exhaust and there's a lot of excess air if cylinder(s) are misfiring.
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Re: Mixer Ring Orientation

#10 Post by Fox vehicles » Thu Sep 17, 2020 11:47 am

I think the problem you have is it's the 3.5 engine, these have the flap type air flow meter which means at idle the flap will be closed reducing the amount of air going through the mixer. On this engine there are two ways of sorting this problem.
One way is to fit a plate mixer onto the air filter side of the air flow meter, but it is important to fit a blow back device on the engine side of the afm to protect it against backfires. (The air hose will be filled with a nice explosive mixture of gas and air) The other option is to use the mixer you have, BUT you will need a balance pipe fitted to the rear (diaphragm side) of the reducer and connected to the air intake pipe of the engine. This will hold the gas back at idle and allow you to set the mixture correctly. It will depend on which reducer you have as to whether or not you can do this though,,,, I would still recommend using the blow back arrester on the afm, The problem with the 3.5 is if you bend the flap it won’t run on either fuel as it can restrict the air (you can remove it from the hose as a emergency fix, but it will only run on lpg like this)
This is the pale mixer,
https://tinleytech.co.uk/shop/lpg-parts ... -flow-mtr/
This is the blow back flap
https://tinleytech.co.uk/shop/lpg-parts ... -type-afm/
Get it right and they run lovely on LPG :)
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Re: Mixer Ring Orientation

#11 Post by Pinger » Thu Sep 17, 2020 4:52 pm

Fox vehicles wrote:
Thu Sep 17, 2020 11:47 am
The other option is to use the mixer you have, BUT you will need a balance pipe fitted to the rear (diaphragm side) of the reducer and connected to the air intake pipe of the engine.
This is of interest to me.
More info on it would be appreciated, eg, where in the 'intake pipe' it is connected (downstream from the throttle valve presumably) and how to connect to the back of the reducer. (I'm also in the 'rich at idle' trap).

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Re: Mixer Ring Orientation

#12 Post by Fox vehicles » Thu Sep 17, 2020 7:46 pm

Hi the balance pipe needs to be fitted between the afm and the mixer, and connected to the back of the reducer. Some reducers are designed for this and the hole in the back plate is threaded to take a fitting, most are not, but if you just have one hole to atmosphere then it is usually quite straight forward to make a fitting up for the pipe. The rest of the back plate must be sealed for the balance pipe to work.
How it works. The reducer low pressure diaphragm normal reacts to the suction of the engine relative to atmosphere, the flap type afm courses the engine to create a large amount of suction on the mixer. Hence rich mixture at idle By fitting the balance pipe the low pressure diaphragm is now relative to the pipe the mixer is fitted in so again reacts to the suction of the engine. No more rich at idle 😉
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Re: Mixer Ring Orientation

#13 Post by 308RRC » Fri Sep 18, 2020 7:04 am

Yes I did mean reducers not mixers. By running out of gas I mean that if I try to rev It past 2000rpm it doesn't get enough gas to keep running. Today I installed a balance pipe between the BRC reducer and to a point between the air flow meter and mixer and made sure there were no vacuum leaks. This pipe has not resolved the problem at all. I don't now what else to try.

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Re: Mixer Ring Orientation

#14 Post by 308RRC » Fri Sep 18, 2020 7:08 am

Also I tried running the car with the hose at the back of the air flow meter off so the mixer had no restriction. I can get it to idle quite well like this but when you touch the throttle the engine dies.

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Re: Mixer Ring Orientation

#15 Post by Pinger » Fri Sep 18, 2020 9:39 am

Fox vehicles wrote:
Thu Sep 17, 2020 7:46 pm
Hi the balance pipe needs to be fitted between the afm and the mixer, and connected to the back of the reducer. Some reducers are designed for this and the hole in the back plate is threaded to take a fitting, most are not, but if you just have one hole to atmosphere then it is usually quite straight forward to make a fitting up for the pipe. The rest of the back plate must be sealed for the balance pipe to work.
How it works. The reducer low pressure diaphragm normal reacts to the suction of the engine relative to atmosphere, the flap type afm courses the engine to create a large amount of suction on the mixer. Hence rich mixture at idle By fitting the balance pipe the low pressure diaphragm is now relative to the pipe the mixer is fitted in so again reacts to the suction of the engine. No more rich at idle 😉
Thanks.
When I asked, I forgot you were writing in the context of the flap meter. Connecting the back of the reducer to inlet manifold vacuum occurred to me as a potential work around to cure the richness at idle (relative to out of idle) that I currently have (no flap meter).
Your post at least confirms the reducer is responsive to this type of manipulation.

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Re: Mixer Ring Orientation

#16 Post by Fox vehicles » Fri Sep 18, 2020 9:41 am

The balance pipe will only help with the rich idle, once the flap opens in the afm there is no longer a problem. With the hose off the afm it should run normally, no different to setting up a 3.9 or anything else with a mixer. Did you adjust the vaporiser when you had the pipe disconnected? Are you sure the petrol is turning off, how have you done this? On the 3.5 there is a thick-ish orange and brown wire which is the power to the injectors, On the range rover you can find this coming from one of the relays under the driver’s seat where the ecu is located, I normally cut this wire with a relay to stop the injectors firing. Make sure you have no air leaks, especially where the mixer fits to the plenum, as already motioned by Gilbert. The BRC vaporiser has two adjusters on the side, one is usually a knurled nut, this is the idle bleed, and I would start with this 1/2 - 1 turn out. There are two Allen key fittings, the smaller of these is the sensitivity adjuster, the larger is a blank and to be left alone. Both adjusters are out for more in for less. If you end up with the sensitivity screw out a long way, more than 3 turns ish, open the bleed a little more then re-adjust the sensitivity screw. Do you have a power valve fitted in the pipe between the vaporiser and the mixer?
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Re: Mixer Ring Orientation

#17 Post by Fox vehicles » Fri Sep 18, 2020 9:48 am

Don't connect the balance pipe to the inlet manifold, this would cause massive suction on the diaphragm at idle and not be helpful. The balance pipe only goes to the hose between the afm and the mixer. To start with you can just wedge the door open in the afm, this way you can leave the air filter and pipe work connected, this will help setup the gas mixture correctly. Keep in mind it won’t run on petrol like this. :?
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Re: Mixer Ring Orientation

#18 Post by Pinger » Fri Sep 18, 2020 11:00 am

Fox vehicles wrote:
Fri Sep 18, 2020 9:48 am
Don't connect the balance pipe to the inlet manifold, this would cause massive suction on the diaphragm at idle and not be helpful. The balance pipe only goes to the hose between the afm and the mixer. To start with you can just wedge the door open in the afm, this way you can leave the air filter and pipe work connected, this will help setup the gas mixture correctly. Keep in mind it won’t run on petrol like this. :?
Mine has a hot wire meter so the MAF isn't at the root of the problem.
Sounds though that manifold vacuum would be too severe. I think, I'm going to get on top of my calibration without resort to anything so drastic but I keep my eyes open for other potential solutions nonetheless. Cheers!

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Re: Mixer Ring Orientation

#19 Post by Fox vehicles » Fri Sep 18, 2020 11:40 am

No Problem, hope some of it helps, let us all know how you get on, If the vap is good it should be relatively straight forward to sort it, do you know what size choke the mixer has? Also has this setup run correctly in the past or is this a fresh install?
I’m sure between the clever minds here on the forum someone will be able to point you in the right direction :D
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Re: Mixer Ring Orientation

#20 Post by Pinger » Fri Sep 18, 2020 12:01 pm

Fox vehicles wrote:
Fri Sep 18, 2020 11:40 am
No Problem, hope some of it helps, let us all know how you get on, If the vap is good it should be relatively straight forward to sort it, do you know what size choke the mixer has? Also has this setup run correctly in the past or is this a fresh install?
It's an ongoing thing following a lack of top end performance (an existing system with new parts). New reducer (yesterday, hooked up both outlets to improve gas supply) and new mixer which is adjustable in that it has air holes which can be blocked or unblocked. Currently experimenting with how many holes can be unblocked as a compromise between top end performance and correct calibration. If that doesn't work out, next on the list is to reinstate the old reducer in parallel to up the gas flow.
Fox vehicles wrote:
Fri Sep 18, 2020 11:40 am
I’m sure between the clever minds here on the forum someone will be able to point you in the right direction :D
Indeed! I have a separate 14 page thread (Advice Please) and without the help from this forum I wouldn't have a clue what to do. Tapping the best minds on LPG systems is an asset beyond price.

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