High gas pressure on fuel rail [Lovato]

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Hakosuka
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High gas pressure on fuel rail [Lovato]

#1 Post by Hakosuka » Wed Jan 30, 2019 8:26 am

Hello guys, I have problems with my Lovato LPG system, basically it works, but not as it should.
I was at a service, they said the pressure sensor on the fuel rail is reading 1.5 Bar instead of 1.3 Bar. They suspect the problem is in bad injectors, which can't flow enough, that's why the pressure rises.
The car has normal power to about 2500-3000rpm, then no real power. Probably running lean.
Car is a Volvo 740 Turbo (2.0 155HP).
I could eventually replace the injectors with new https://www.lpg.auto.pl/en/index.php?s=info&id=1982, because the shop wants to charge me 200€.

What I would like to know, if anyone has experience with this kind of problem. Really don't want to start throwing money at wrong parts...

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Re: High gas pressure on fuel rail [Lovato]

#2 Post by LPGC » Wed Jan 30, 2019 1:41 pm

Bad injectors wouldn't affect the pressure reading. Injectors that won't flow enough wouldn't increase the pressure reading but might see the engine run lean at high engine loads.

Changing pressure from 1.5 bar to 1.3 bar is usually as easy as adjusting the pressure adjustment screw on the reducer. If you have a complete Lovato system (with Lovato reducer) I'd be interested to know which Lovato reducer you have because most Lovato reducers are not adjustable up to 1.5 bar.

An installer might advise changing injectors (or just changing injector nozzles) if the flow rate of injectors isn't a good match for the engine and gas pressure combination (especially if the reducer has a very limited range of pressure adjustment). Injectors that can't flow enough gas (for the engine at the given pressure) are not necessarily bad/broken, they might just be a bad choice by the installer for the application. The easiest way to get injectors to flow more gas is to increase nozzle size and/or increase pressure. Changing nozzle size doesn't necessarily mean changing injectors, just changing the nozzles on the injectors.

If you do change injectors or nozzles you will need to fully recalibrate your LPG system. Injectors and injector nozzle size must be a good match for your engine/pressure combination, if you have a reducer that isn't very pressure adjustable and don't want to change the reducer then getting the injectors/nozzle size correct is more critical because the injectors/nozzle size must be a good match for the engine at the given pressure. I've seen lots of Lovato installs where nozzle size was too small for the engine / reducer pressure... but lots of Lovato reducers seem to be adjustable only up to around 1 bar pressure. I've fixed such problems on Lovato installs by drilling nozzles and recalibrating the system.

Would hope there's been some misunderstanding(s) between you and the installer you visited. Or someone's been spouting bs. If I knew which installer you visited it might give me more insights but it would probably be best to tell me in a PM.
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Hakosuka
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Re: High gas pressure on fuel rail [Lovato]

#3 Post by Hakosuka » Wed Jan 30, 2019 2:01 pm

I am from Slovenia, so...
He said that the pressure should be 1.3 Bar, and that he turned the reducer down as much as it would go and that it is still too much (1.5Bar).
Like the injectors are faulty (he mentioned springs inside them getting weak?) and are raising pressure before them.
I will probably take my car to another installer, didn't seem like they are experts, really.

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Re: High gas pressure on fuel rail [Lovato]

#4 Post by LPGC » Wed Jan 30, 2019 2:07 pm

As said above, faulty injectors wouldn't effect the pressure.
I wouldn't know of your local installer in Slovenia but if that's exactly what he told (weak springs in injectors causing pressure to be too high) he's wrong.
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Re: High gas pressure on fuel rail [Lovato]

#5 Post by Hakosuka » Wed Jan 30, 2019 2:11 pm

Yeah, basically that is what he said. He couldn't guarantee that changing them would make the car work fine.
He also opened the reducer and said it looks like new. Filter was changed some 6h of LPG operation before.

Any ideas, what could be wrong?

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Re: High gas pressure on fuel rail [Lovato]

#6 Post by LPGC » Wed Jan 30, 2019 3:17 pm

Difficult to say what's wrong without checking it over myself or at least seeing some readings etc, a wide range of very different issues could cause the symptoms you mentioned in the opening post.

This is a long shot but is a potential issue which would explain both the higher than expected 1.5 bar pressure reading and the lack of power when you put your foot down (provided the original install was all good and provided the 1.5 bar reading falls when you put your foot down)... If the manifold pressure pipe to the reducer had become disconnected from the reducer.
With that pipe disconnected from the reducer the reducer will output gas relative to atmospheric pressure instead of relative to manifold pressure as it should - so if the reducer is actually set at closer to 0.9 bar output pressure (which is closer to what I'd expect with a Lovato reducer) and the engine runs 0.4 bar absolute manifold pressure at idle the system will read 0.9 + (1 - 0.4) = 1.5 bar at idle, but then if you put your foot down and manifold pressure due to turbo boost raises to 1.3 bar absolute pressure the reducer pressure relative to manifold pressure will fall to 0.9 + (1 - 1.3) = 0.6 bar. If the LPG system is set up to expect 0.9 bar relative to manifold pressure 0.6 bar might not be low enough to cause the system to switch back to petrol due to low pressure. That's just one theory but neatly fits the limited info and symptoms you've been able to provide. The following is really just an aside.. A default setting in most Lovato ECUs sees the system automatically add some petrol injection (petrol injectors taking up a portion of the fuelling which the LPG system cannot provide) when it detects gas injectors having to open for a duration which comes close to the injectors not having time to close and re-open in time for the next pulse and/or pressure falling much below what is expected, but it's unlikely this function could compensate fully for a reducer that outputs gas relative to atmospheric pressure especially on a turbo'd engine.

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Hakosuka
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Re: High gas pressure on fuel rail [Lovato]

#7 Post by Hakosuka » Thu Jan 31, 2019 7:30 am

I somewhat understand what you are saying, but on the last service, they replaced the vacuum hose going to the reducer. So, I doubt this is it.
Maybe one other thing that would be of importance. I recently replaced my turbo manifold-the original one cracked, so I made one myself. Along with that, the boost was raised to OEM setting of 0.5Bar, because the car only had 0.2-0.3 Bar boost before the fixing. It is only a minor change, but this might be the problem?
I have the car for about 1 year now, I asked around, and I found a mechanic who serviced the car before I was the owner. He said the car was always down on power, but not sure since when.
The LPG system was installed in 2009, it is possible the LPG was fitted to a lower boost than it should be and this is now the actual problem. We are not sure about this, only speculating. I don't understand why wouldn't they just set it up properly. Probably still something is wrong with the system.

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Re: High gas pressure on fuel rail [Lovato]

#8 Post by Hakosuka » Thu Jan 31, 2019 8:40 am

However, this doesn't explain why it works OK on boost in lower rpm(1500-3000rpm). :/

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Re: High gas pressure on fuel rail [Lovato]

#9 Post by Brian_H » Thu Jan 31, 2019 4:51 pm

Where is your vacuum line being taken off the manifold that goes to the reducer? A photo might help there?

Hakosuka
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Re: High gas pressure on fuel rail [Lovato]

#10 Post by Hakosuka » Fri Feb 01, 2019 7:48 am

Yeah, directly from the inlet manifold.
I will try to get some more info on the system and take some pictures on Saturday

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Re: High gas pressure on fuel rail [Lovato]

#11 Post by LPGC » Fri Feb 01, 2019 9:47 am

Hakosuka wrote:
Thu Jan 31, 2019 8:40 am
However, this doesn't explain why it works OK on boost in lower rpm(1500-3000rpm). :/
It could explain that. The window available for gas injection pulse length decreases as rpm rises.
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