1. Home
  2. Automotive Technologies
  3. crossfiring with LPG but not petrol

crossfiring with LPG but not petrol

I had a car that was prone to going POP and blowing up air filters, when running on LPG. Eventually, found the cause was crossfiring, as 3 spark plug cables were bunched together in a narrow space. After rerouting the cables in a less intimate fashion, the problem is gone (for several months now....) I understand why this happens: if crossfiring occurs when some cylinder is on intake stroke, it takes less energy to fire the uncompressed gas. The intake valve is open, and the flame spreads to the manifold, with lots of fuel to go bang. But I wonder does this happen on a multi-point injected engine? The crossfiring could still occur. It would ignite a smaller amount of fuel, as the intake manifold only contains air. I expect it would still be enough to be heard.

Reply to
Orson Cart
Loading thread data ...

....

Maybe the intake manifold doesn't just contain air... maybe you have some leakage past valves that is occurring only with LPG.

--scott

Reply to
Scott Dorsey

absolutely - and the amount depends on the valve timing. most cars have some degree of timing overlap - it's used to charge intake manifold resonators.

Reply to
jim beam

The LPG may have a lower (spark) voltage requirement at the plug.

Reply to
Bob Flumere

"LPG has a much higher ignition temperature of 920-1020 degrees vs.

80-300 degrees for gasoline"

formatting link

Reply to
AMuzi

In message , AMuzi writes

Reply to
Clive

In message , Clive writes

Should not have been in the text I wrote, sorry.

Reply to
Clive

Thanks. Yeah, probably; first result of a search.

Here's a PE's report on that:

formatting link

Reply to
AMuzi

Perhaps I should clarify - LPG uses a mixer before the throttle, so manifold is full of fuel. Petrol uses sequential injection, so do not expect much fuel to be in the manifold. The crossfiring is an electrical phenomenon, so should happen for both fuels. Yet did not notice it with petrol. Petrol requires a lower spark voltage, so there would be less energy leaking between spark plug leads, but also lower voltage to fire the cylinder that should not fire, so I thought this factor would kind of cancel out.

Reply to
Orson Cart

Had never really considered this, but please cite your source.

Reply to
hls

fuel not being in the manifold is nothing to do with whether it's sequential but whether it's injected into the port or not. most sequential injection systems are also port injected, so that is why there's no fuel in the manifold. if you had an f1 manifold, the injectors would be above the throttle plates and the whole length of the manifold would be full of fuel despite it being sequential.

it's not electrical, it's because the valve timing means the intake is opening when there is still burning exhaust exiting the cylinder. with aggressively timed engines, this valve overlap becomes more pronounced, and with an easily flashed mix of lpg/air, any flame still in the cylinder from an open valve can burn back up through the manifold, particularly at lower rpms.

that's because the engine is built for and timed for gasoline, not lpg.

you're barking up the wrong tree with that thinking - see above.

Reply to
jim beam

MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.