98 vt on gas backfiring through airbox

[jjrrww]

hi all,my v6 vt on gas is back firing through the air box and has destroyed the box now.i recently went on a long drive (2000klms) and it seemed each time i had to climb a hill it would backfire but it was fine while sitting on 100 on the highway.then i tried by turn on the power button which makes the car kick down a gear sooner and rev longer and when i did this it did not backfire at all .i will have to fix the problem first before getting a new box as this was happening before the airbox became damaged.

[mwb235]

jjrrww it sounds like your gas setup badly needs a service/tune-up. I'd check the spark plugs (must be the correct type and gap for LPG) and spark plug leads - if these are faulty you'll have no end of trouble.

Also get someone who is experienced with servicing LPG systems (not just a standard grease monkey) to adjust the mixtures with computerised equipment - your system may just be running too lean or too rich.

LPG systems go out of tune easily and quickly (or at least the older-style mixer setups do - i dunno about gas injection haven't driven one yet). Make sure you have the gas mixtures checked/adjusted every 3 months, and the system serviced every 6 months minimum.

If you still have issues after that then you might have a bad installation - but still any gas specialist worth a pinch of salt should be able to work this out for you.

Btw what setup are you running? Is it Impco or SprintGas by any chance? My VL had, and my current VT has, SprintGas and it's never backfired whereas the Impco setup on my VR backfired a lot. IMO Impco is not suited to Commodores (better for Fords) but that's just my experience. Obviously any system should work fine if installed and adjusted properly.

Good luck.

[deserthead]

As said above.

I'd also be checking your ignition system.
Plugs, leads, coils, those will be ur main trouble makers.

If ur ignition system is up the shite then u'll get backfire probs no end!!!

[hovo]

mate
Mine just did exactly the same thing. $55 for a second hand air box. $72 for a set of gas compliant leads, checked the plugs they're ok. Good as new. Gas is soooo fussy about spark. It wouldn't even run once the box was destroyed. But it was perfect on petrol which isn't as fussy.
Jim
Ps for what it's worth, mine is an impco. While ever the ignition (read spark) is good there is no trouble but if there's the slightest doubt about that spark, look out. The reason the power button helps is because it lessens the chance of the motor being under serious load and this lessens the chance of a lead and/ or plug misfiring.

[jjrrww]

mate
Mine just did exactly the same thing. $55 for a second hand air box. $72 for a set of gas compliant leads, checked the plugs they're ok. Good as new. Gas is soooo fussy about spark. It wouldn't even run once the box was destroyed. But it was perfect on petrol which isn't as fussy.
Jim
Ps for what it's worth, mine is an impco. While ever the ignition (read spark) is good there is no trouble but if there's the slightest doubt about that spark, look out. The reason the power button helps is because it lessens the chance of the motor being under serious load and this lessens the chance of a lead and/ or plug misfiring.

thanks everyone, and jim sounds pretty close as it is an impco system and i asked a back yard mechanic guy and his first suggestion was the leads .i dont know if the leads or plugs were changed when the gas was fitted . so are you saying the car will back fire even if it was 1 lead or does the whole ignition system have to break down for it to backfire.would a proper mechanic be able to determine the problem as leads or plugs with a diagnostic.
also after i got the install done when i start the car the engine fires up and revs a little but the revs drop and the engine almost stalls and theres a couple of clicks from the gas system and the revs come back up to idle again ,this all happens in a few seconds and has sometimes has caused a small backfire like a pop or puff in the system .

[hovo]

mate
Mine had one crook lead. You could see where t had been arking out. Didn't worry the petrol system one bit, but literally blew the arse out of the gas system, well the airbox anyway.
Jim

[azzaVT]

If you've got a crook lead it will arc over to another lead, this can result in the plug firing when the inlet valve is open... not a big problem when running on petrol but... when running on LPG your whole intake system downwind of the LPG ring/carb is full of combustable gas. BOOM! then futt futt fut!

Get a blow-out preventer fitted. It's an inline pipe, with a couple of holes in the wall, that has a sleeve of neoprene over it. It will save your intake box and pipes etc in the case of a backfire. Earlier options had a flap-valve on the filter box, easy enough to DIY if you're handy with tools and stuff. like this bloke says...

[bricat]

Get a set of top gun MAX leads for your car Low resistance and will more than likely eliminate the problem. If it still carries on change plugs

[White Tiger]

Get a blow-out preventer fitted. It's an inline pipe, with a couple of holes in the wall, that has a sleeve of neoprene over it. It will save your intake box and pipes etc in the case of a backfire. Earlier options had a flap-valve on the filter box, easy enough to DIY if you're handy with tools and stuff. like this bloke says...

its easier to cut a hole in the top half of the air box and silicon a bath plug in cheaper to makesure the bath plugs on a string though

[bpefi]

Lpg is very hard to ionize as it is a gas - it also burns with a lot of heat as it comes in as a gas - there is no cooling of liquid turning to vapor as there is in petrol. Your spark plugs must run one heat range colder - better still get the new Bosch plugs that are designed for LPG. Otherwise get some Pulstar plugs - they are awesome yet pricey - just search at google. Get a new set of leads preferably Bosch that are also designed for LPG. Make sure the gaps are around .7-.8 mm no further. 1.5 is way too much for the ignition system. They work well while they are ok - one parts breaks & you have to replace the lot coils & DFI module. They last much longer & are more reliable by dropping the gaps & you need to do this for the Lpg anyway. Put dialectric grease (Supercheap) good for sealing water etc out of connections - stops connections & plug leads from sticking on - always easy to remove & refit. You can use it anywhere there is a connection as it will make a better connection & stop arcing. Do not forget to put it on the coil part of the lead as well. If you have a coil driver then you can loadtest the ignition coils - if not & the problem is still there just buy Bosh or genuine only. The rest is too hard for me - but let me know as I have all the information you require - I have access to some good databases!
good luck

[jjrrww]

hi again,i have fixed the backfiring problem it seems.i noticed that when i was on petrol and in top gear and i slowly pressed the pedal down to just before kickdown into 3rd ,the engine seemed to miss a beat randomly or almost drop a cylinder but it was hard to tell as it only did it at that point or going up a hill while in top gear.so i opted to try plugs first as they were less than the leads and the leads on the car were top gun 8mm leads that someone must have put on the car in its earlier days.the plugs were a little worn but not bad although the gap on the old plugs was way to wide compared to the new bosch platinum plugs.also and maybe most importantly one of the coil packs was very slightly loose from one bolt not quite tight enough.the coil pack moved only half a mill or so at one end but that also could have caused the problem.hard to say as the car is running perfect now.

[slavetothegrind]

g'day all, ive heard about cutting a hole in the air box and installing a flap to stop the air box from being damaged due to backfire. can anyone please tell me exactly where to cut the hole in the new unit. the engine does not backfire anymore due to upgrading the leads and correct plug gaps but i would like to install the flap just incase. any help would be appreciated.

[strgas]

anywhere in the airbox above the filter

[dah_man_ben]

mate, as they all said, check spark plugs, leads etc etc

but a trick that i used on my old VS was to put an ocky strap over the airbox to hold it down, but leave it undone. then if it ever does backfire (which it really shouldn't if it is tuned well and you are using good plugs, clean air filter etc), then the lid pops off, lets the air out and pops back down again without any need to replace the airbox.

worked for me

[dvs18u]

mate
Mine had one crook lead. You could see where t had been arking out. Didn't worry the petrol system one bit, but literally blew the arse out of the gas system, well the airbox anyway.
Jim

just a quick idea for u get in ur car start it put it in drive pull up ur hand break and push both ur brake and accel pedals and see if ur engine is missing this will tell u if u got a an issue quick any easy if yes change spark and leads then test ur coils with a multi meter to see if they are ok