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[Tezray]

Some of you may be aware that i've recently replaced my LPG injector rails due to mine being very tired and only returning around 15mpg 

I was hoping that all would be well after this and it mostly is but it's still not 100%. The economy is now reasonable (about 23mpg on my last tank) but the power seems to be approx. 20% down on petrol. With this in mind I decided to replace my ignition leads hoping that this would help and it's made a marginal improvement but it hasn't been the fix I was hoping for 

I'm now starting to get really fed up with it. I've replaced injector rails, hoses, filters, spark plugs and ignition leads. I've also spent a long time getting the LPG map perfectly aligned to my petrol map...

Does anyone have any suggestions? The only thing I can think left to do is remove the plenum and inspect the pipes running to the injector nozzles and the nozzles themselves incase I have a blockage. It runs superbly on petrol and it runs well on LPG, it's just the power isn't there.

Any help is much appreciated as i'm running out of ideas 

[TheBoy]

You've done most things I can think of....  ....I'm out of ideas beyond the system not being able to provide enough gas - but you'd probably see it going lean on Gas Synchro


I was chasing down a VXR8 earlier, and being low on gas, it flicked back to petrol at WOT at very high speed and at full bore. Apart from the bleeping, I didn't notice any power gains when it flicked to petrol. So I'm left undecided if you should be able to tell between gas and petrol, beyond placebo  :-/

[albitz]

If you had a blocked/twisted/kinked pipe unfer the plenum you would have a very noticeable misfire imo. I certainly did when I had a kinked pipe. It wouldnt run on that cylinder at all.

[Omegatoy]

have you ever changed the gas filter? i did around 200,000 miles on lpg in various straight six,s(senators and carltons) , once set up they needed nothing
apart from changing sparkplugs slightly more often,except lpg filters every 10kg

[Tezray]

Thanks for your suggestions guys, yes the vapour filter has been replaced. TheBoy, I wish I could put it down to the placebo effect but unfortunately it really is down on power on gas 

Albs, I think that really has to be my next step as I can't think of anything else! Even though the LPG map is good and matches the petrol map I still get the error message "injectors fully open" when I open her up. So i'm thinking that despite the injectors best attempts the gas just isn't getting through at WOT? Maybe I have 1, 2 or several twisted, blocked or leaking pipes from the injectors to the nozzles?

Who knows  All I do know is i'm sick of it not performing on gas. Even getting up to motorway speed is an effort on gas so I flick back to petrol and then once cruising go back to gas!! It drives perfectly well on gas and is fine when cruising/light acceleration, but anything demanding it just can't cope with.

[TheBoy]

Thanks for your suggestions guys, yes the vapour filter has been replaced. TheBoy, I wish I could put it down to the placebo effect but unfortunately it really is down on power on gas 

Albs, I think that really has to be my next step as I can't think of anything else! Even though the LPG map is good and matches the petrol map I still get the error message "injectors fully open" when I open her up. So i'm thinking that despite the injectors best attempts the gas just isn't getting through at WOT? Maybe I have 1, 2 or several twisted, blocked or leaking pipes from the injectors to the nozzles?

Who knows  All I do know is i'm sick of it not performing on gas. Even getting up to motorway speed is an effort on gas so I flick back to petrol and then once cruising go back to gas!! It drives perfectly well on gas and is fine when cruising/light acceleration, but anything demanding it just can't cope with.

Is it going lean at WOT? It should stay rich.

[Tezray]

According to the map it's not going lean but my lambda reading only ever reaches 0.7 - 0.75v.

I whipped cylinder 1 spark plug out yesterday when I changed the leads and it looked a nice colour, neither rich or lean. If lpg runs rich will it leave sooty deposits on the plugs/exhaust etc?

[TheBoy]

According to the map it's not going lean but my lambda reading only ever reaches 0.7 - 0.75v.

I whipped cylinder 1 spark plug out yesterday when I changed the leads and it looked a nice colour, neither rich or lean. If lpg runs rich will it leave sooty deposits on the plugs/exhaust etc?

The voltage is irrelevent, they are not wideband

On the graph at the bottom, just have both lamdas showing, then give it some large from a standing start, up to high speed. Both lamdas should be rich (high - above around 0.5v) for the duration of WOT


Not sure I've explained that very well, so let us know if thats unclear

[TheBoy]

plugs are not very useful at this stage, as I suspect most of the time, mixture is right. Its when at full load it suffers.


Option B, is switch to petrol above, for eg, 90% engine load.

[Tezray]

I would like to switch to petrol at anything over say 90% load but as I only have the basic Stag 300 controller I don't think that's an option 

I'll try to watch the lambda values when I hoof it, if it was lean though where would I go from there? I don't understand how the map can be aligned to the petrol map but it just doesn't perform  :-?

Do you know if I could upgrade my controller? Would I have to swap out the whole loom?

One other thought (and it is a long shot)... could the quality of the gas be my problem? I always get mine from asda  :question

[Lazydocker]

I would like to switch to petrol at anything over say 90% load but as I only have the basic Stag 300 controller I don't think that's an option 

I'll try to watch the lambda values when I hoof it, if it was lean though where would I go from there? I don't understand how the map can be aligned to the petrol map but it just doesn't perform  :-?

Do you know if I could upgrade my controller? Would I have to swap out the whole loom?

One other thought (and it is a long shot)... could the quality of the gas be my problem? I always get mine from asda  :question

Right... I was "Otherwise Occupied" yesterday and didn't really spend much time online. I'm having a think now.

Firstly, even your basic Stag 300 has the option to switch back to petrol at high RPM (but not at high demand like the plus can), there is a difference But it would be adequate

Do you know what vaporiser you have fitted? There are a few possibilities... Have you changed the liquid phase filter? Also might need to drain the "Heavy Ends" if it's been fitted a while, especially if using cheaper fuel all the time I'm not saying this will solve the issue, just a possibility

Other checks to make, which aren't as easy, are on the solenoids... It is possible (although less likely) that they aren't opening fully and that you're getting a restriction in flow.

If you wanted to update the ECU it should be a straight swap, although I'd say that has to be a last resort as my saloon ran perfectly (gearchange lag excepted) on the normal Stag ECU, for 55+k miles, with no noticeable power loss right up to the red line That was running 3.0mm injectors (Red Valteks) and 1.0 BAR Vaporiser pressure.

As I have said before, I'm more than happy to have a look over it if we can meet up at some point, just to see if you've missed something obvious

Just as an aside, how long has the LPG fitted and how many miles has it done on LPG?

[Kevin Wood]

We know that an Omega runs fine on a Stag 300 and those injectors (when drilled to 3mm).

The unknown is the vapouriser, tank, valve, etc. so my first check would be that the vapour pressure is holding up under full load. This will implicitly check the filters, since the effect of a clogged filter will be to drop the vapour pressure.

So, check that the vapour pressure is at least 1 bar at idle and that it doesn't drop significantly under full load.

Kevin

[Tezray]

Thanks for your responses guys 

LD, I haven't replaced the liquid phase filter however I have had a look at it and there is no dirt/debris/nastiness at all. What do you mean by draining the heavy ends? I know I could set it to switch over to petrol at high rpm's but it's high loads as well as high rpm's that it's not happy with. How would I go about testing the solenoids? I guess a drop in vapour pressure may also be an indicator of this?

Kevin, I haven't looked at the vapour pressure when under load so I will have a look at this. I know that at idle it does sit at about 1.2 - 1.25  bar though. The LPG kit was fitted in 2008 I'm not sure how many miles it's covered though I'd have to look through old paperwork/MOT's.

I don't have my laptop with me today so I will update tomorrow with any vapour pressure findings. I'm also going to check over all the hoses to make sure there are no kinks.

[Kevin Wood]

Kevin, I haven't looked at the vapour pressure when under load so I will have a look at this. I know that at idle it does sit at about 1.2 - 1.25  bar though. The LPG kit was fitted in 2008 I'm not sure how many miles it's covered though I'd have to look through old paperwork/MOT's.

Exactly what I'm running on my 3.2. Should be fine if that pressure holds up under load (it may drop to 1.1 or so, but if it's dropping significantly that might be a worry).

[Tezray]

Well I spent my journey into work monitoring the map and making some adjustments. Looking at the vapour pressure it is running generally at 1.25 bar; at WOT from standstill/lower speeds I saw this drop to 0.79 bar (worst case) and at higher motorway speeds I didn't see it go much below 1.0 bar. I don't know if this difference may just be because the engine was warmer once on the motorway?

I think I may have overstated the lack of power to be honest it didn't feel too bad this morning but still doesn't pack the punch that petrol does. I checked out my lpg hoses last night and couldn't find anything suspicious although cylinder 2 fuel line from injector to nozzle was under a bit of strain but not kinked. I sorted this by turning the bracket slightly that holds the rail.

I was wondering this morning if my lack of performance is just a mapping issue. I'm struggling to keep the fuelling from going rich at anything over roughly 70% throttle. When I first installed the injector rails I really had to turn the multiplier up to bring it in line with my petrol map, but now they've settled in I'm really struggling to bring them down! I've circled two areas of concern - The first one is at about 70% throttle. The crosshair always hovers around 95-100KPa and if I turn the multiplier down it doesn't bring the crosshair down, it does however start running quite rough at that point. The second area is at WOT and it seems turning the multiplier down isn't bringing the fuelling down either.



The error message is the usual "injectors fully open" by the way. Maybe drilling my nozzles to 3.0mm was too much? I'm starting to think it's just an old basic LPG system and I will never get it performing to a level I'm happy with