LPG blowing up air boxes theory!.

[Robo]

Keep coming across threads with stories of filter boxes blown up by lpg back fire etc.
I recently noticed my ign leads were shorting out on front radiator bracket and between themselves
So I moved em a bit and used some cable loom on said bracket to insulate it.
Now the funny thing is, for the next couple of days I had carby back fire, which wasn't apparent before.
So it appears power is passing between leads and incorrect ignition is happening.
Just wondering If anyone else thinks power jumping between leads could be the major factor in causing this back fire issue I keep reading about.
:blowup:

[Bigrig]

I like the theory mate, however most is when starting cold as the lpg dissipates from the cylinders overnight and without a petrol squirt start, it pumps it in to the point of flooding it (as such) and the resulting first ignition basically explodes without firing - causing a backfire .. blew my box apart this way about 3 weeks after having the truck on my first "cold start on gas" ... subsequently, I got rid of gas, but that's my very rudimentary understanding of why it occurs to most ...

That said, you've possibly demonstrated another potential cause though ... and who knows, it could be more probable than the 'perceived' cause I've stated above!! One for Mythbusters!!!! lol

[taslucas]

Jumping power could do that but it would probably do it fairly consistently while the engine is running. As bigrig said, the lpg problem happens only on a cold start. I split a seal in the carby with a backfire not long ago but luckily got away with just tightening the screws up.




Tap, crackle, pop

[Winnie]

I got a pretty good backfire once when switching from petrol to LPG, engine was warm.

Tappa tappa

[gec]

My son has now had two cars on gas, and when he got the first one he was told not to pump the accelerator when starting the car, consequently he has never had a backfire and never blown his airbox, the previous owner was told this by his gasfitter after he blew his airbox. So the theory is, keep your feet away from the go pedal when starting your gas powered vehicle, hot or cold.

[The BigFella]

most backfires with lpg are caused when you get a small air leak and the fuel mixture burns lean, causing a pre-ignition of sorts.
Have experienced this at full throttle pulling up a hill fully loaded, kaboom! Resulted in the mixer being blown to bits. I have fitted a pipe out of exhaust pipe and drilled 4x 1/2inch holes and covered these with an old stubby cooler. Worked a treat!

[Robo]

Not to sure if our problem is exactly the same.
Got sick of std points and plugs and not handling lpg heat and tune and wanted a setup with less maintance.
So I embarked on a retune, and managed to tuned starting problem out about 2yr back.

I put it down to resistance in cap/rotor and std type spark plugs.
Took about 4 attempts at setting iridium plugs to get it just right for LPG.
And backing lpg mix off, very very slightly.

I found that with a extended rotor I lost a great deal of usable power from coil.
so went back to std rotor.
Notice a great deal of power lose with the extended rotor and this backed my theory of electrical power lose available for burn, as torque was not there straight up with the ext rotor, car felt like it dropped a cyl worth of power, so I have a new bute ext rotor for a emergency spare.
The smaller extended rotor gap requires less energy needed to bridge the gap and as a result less energy is expended across gap.
and the same goes for the plugs.
I found that using a std rotor and the smaller "iridium plugs" plug gap gave me a setup that worked for both fuels better, without backfire issues.
The increased energy available for plugs to burn fuel, either fuel, seemed to be working a treat.
I have no flooding issue as iridium plugs exposed finer electrodes and concentrated spark nicely.
plugs are 1 range cooler for LPG and the increased performance from plugs and extended life have paid off nicely from using the iridium plugs.
Iridium handles heat alot better than std plugs, ( 10 fold "so to speak" ).

The only problem I have is the perceived problem of elec power jumping between leads and causing a the odd miss fire whilst driving.
I noticed the burn marks on leads and that's why I recon this is the problem at hand and was seeking to find if anyone else noticed something similar.
cheers

Using Bosch LPG leads.
Epoxy GT30RT coil.
Pertronic cam sensing.
NGK iridium.

[patch697]

Not to sure if our problem is exactly the same.
Got sick of std points and plugs and not handling lpg heat and tune and wanted a setup with less maintance.
So I embarked on a retune, and managed to tuned starting problem out about 2yr back.

I put it down to resistance in cap/rotor and std type spark plugs.
Took about 4 attempts at setting iridium plugs to get it just right for LPG.
And backing lpg mix off, very very slightly.

I found that with a extended rotor I lost a great deal of usable power from coil.
so went back to std rotor.
Notice a great deal of power lose with the extended rotor and this backed my theory of electrical power lose available for burn, as torque was not there straight up with the ext rotor, car felt like it dropped a cyl worth of power, so I have a new bute ext rotor for a emergency spare.
The smaller extended rotor gap requires less energy needed to bridge the gap and as a result less energy is expended across gap.
and the same goes for the plugs.
I found that using a std rotor and the smaller "iridium plugs" plug gap gave me a setup that worked for both fuels better, without backfire issues.
The increased energy available for plugs to burn fuel, either fuel, seemed to be working a treat.
I have no flooding issue as iridium plugs exposed finer electrodes and concentrated spark nicely.
plugs are 1 range cooler for LPG and the increased performance from plugs and extended life have paid off nicely from using the iridium plugs.
Iridium handles heat alot better than std plugs, ( 10 fold "so to speak" ).

The only problem I have is the perceived problem of elec power jumping between leads and causing a the odd miss fire whilst driving.
I noticed the burn marks on leads and that's why I recon this is the problem at hand and was seeking to find if anyone else noticed something similar.
cheers

Using Bosch LPG leads.
Epoxy GT30RT coil.
Pertronic cam sensing.
NGK iridium.

Interesting read.... Im not sure I fully support your findings but it has intrigued me enough to do some research of my own on the subject.

I have however had a similar problem with ignition leads which I corrected by installing high performance low resistance leads (1000 ohm from memory).

Installing low resistance leads in your setup would not go towards supporting your theory of resistance causing the release of unused energy however so it may not be a path you'd choose to take.

Best of luck with your research & keep us posted on what you find.

[patch697]

My son has now had two cars on gas, and when he got the first one he was told not to pump the accelerator when starting the car, consequently he has never had a backfire and never blown his airbox, the previous owner was told this by his gasfitter after he blew his airbox. So the theory is, keep your feet away from the go pedal when starting your gas powered vehicle, hot or cold.

Good sound advice given here. If an LPG system is tuned correctly, putting your foot on the throttle at start up would cause the air fuel ratio to lean out thus causing a lean out back fire.

[MudRunnerTD]

My friend Patch!!!! Very very good to see you mate. Mind your step though fella they gave me Mod rights ;)

[zmaster]

My experience with LPG is the same, blew the airbox to pieces after dodgy leads crossfired. Have since replaced with eagle 9.5mm leads and fresh plugs. According to LPG pros, the ignition system needs to be tip top on LPG. My system starts automatically on fuel I thinkl, 'cause I can hear the full pump running when switched to LPG and have never had backfire on start up, but then I don't touch the gas peddle. A mates blew to pieces in the middle of the state forest after his son went to move the truck, not happy. Thankfully I've not had a backfire since upgrading ignition. Bottom line is the LPG must go in favour of a 150l fuel tank.

[Robo]

Interesting read.... Im not sure I fully support your findings but it has intrigued me enough to do some research of my own on the subject.

I have however had a similar problem with ignition leads which I corrected by installing high performance low resistance leads (1000 ohm from memory).

Installing low resistance leads in your setup would not go towards supporting your theory of resistance causing the release of unused energy however so it may not be a path you'd choose to take.

Best of luck with your research & keep us posted on what you find.

Thanks for your input.
I guess I miss-led a little, quote myself.
"I put it down to resistance in cap/rotor and std type spark plugs".
I meant this part of thread/post with the notion of it not working together properly, if ya follow.

I cant remember what the Bosch leads were resistance wise,only they were LPG suitable, it was 2 yrs ago now.

I was originally trying to hi light the idea of wayward spark causing ign problems, but thought I'd throw my tune in for consideration also.
All good, anything on the table to improve power and reliabilty.
cheers