i have a v8 chevy thats running ok on lpg, its a lpg sequential injection system .. but when i switch to petrol or switch off the engine , the lpg pressure in the injector manifolds rises to well over 2 bar .. ( i fitted a gauge in there to monitor it ) and on pulling the pipe off ..it seems nearer to 40 lbs or more to me when its released...
when its this high the engine is difficult to start. any ideas?
lpg pressure
Re: lpg pressure
Some systems normally run at well over 2 bar, no idea what system you have.munkymush wrote:.. but when i switch to petrol or switch off the engine , the lpg pressure in the injector manifolds rises to well over 2 bar ..
Static pressure after a switch off is normally higher than the idle running pressure, because on most systems it's referenced to manifold vacuum. When that rises after switch off, so will the gas pressure. Don't know if that's relevant here because we don't know what system you have or if it is referenced to manifold.
Most systems allow the engine to start on petrol and switch to gas later (though that may be within seconds), no idea what system you have or how it is set up. But it normally means the gas won't be implicated in a starting problem.munkymush wrote:when its this high the engine is difficult to start. any ideas?
cheers, Ross K
www.blazegas.com
gas pressure
thanks ross, i have an agis setup. it normally runs at 1 bar .. but its this excessive pressure that occurs when its turned off thats causing me a problem.. what exactly causes the gas to increase so much in pressure? one thing i have thats not standard is i made some brass manifolds that are fixed to the heads with brackets to do away with rubber pipes all over? would heat transfer form the engine through these cause a problem? cheers
gas pressure
i tried that ..i had a kme gold reducer.. then i bought a new bigas r121.. runs great ..but as i said its just building pressure after its turned to petrol or turned off...
Re: gas pressure
Firstly, I think we're not at all clear about what problem you think that this is causing you.munkymush wrote:.. runs great ..but as i said its just building pressure after its turned to petrol or turned off...
Secondly, some rise in the static pressure is quite normal after switch off. Not as much as 1 bar for sure! The most likely cause of that much rise is a seeping regulator. However, if the reg is undersized for the engine and/or not getting adequate hot water flow, it will be delivering unusually cold gas (at the correct pressure). Couple that with your metallic pipework, and a large pressure rise might be connected to heatsoak effects raising the trapped gas temperature through a big range after switch off. You could test for that by seeing what the pressure is when cold before start-up; if it's a temperature effect it will have dropped back at least some of the way overnight.
Thirdly, be careful about what you are measuring. "I fitted a gauge" - I'd guess you are getting an absolute pressure reading.
If the gauge said say, 1 bar, at engine idling ... it means the regulator is delivering gas at about 1.6 bar above manifold pressure (which is a vacuum at idle of around 0.35 bar absolute).
When you switch the engine off, manifold pressure rises to the atmospheric pressure (about 1 bar), and if the regulator is working correctly - your gauge would now read 1.6 bar absolute.
But if you switch from gas to petrol while the engine is idling, it should stay much the same gauge reading of course, with a little overshoot perhaps. If you can see the pressure slowly rising, you have a leaky reg and/or bad heatsoak effect.
However, if you now rev the engine hard - so that the throttle opens and raises the manifold pressure towards atmospheric - again, if the regulator is working properly the gas gauge will magically read something getting close to 1.6 bar (in this example). Once the pressure is 'trapped' in the rail, it can't drop again by itself - when the engine returns to idle it'll still say 1.6 bar. If it does drop, you have a leak.
cheers, Ross K
www.blazegas.com