VX II 3.8L Ecotec LPG Overhaul (Backfire/Air Box/Smell)

[DEiiTY]

Before I start, I will admit I am a complete noob and have next to no idea what I am doing. That being said, I do have an electrical engineering degree and I've toyed around with car electronics before, so I do have a capacity to learn, but there are so so many people talking trash and saying crap like "eagle leads gave me 20kw increase". I suppose I'm kind of like a disciple and in need of a prophet offering solid advice rather than "the wrong advices".

So I've had this issue going on a few years. Car would run fine, all of a sudden I'd get series of backfires, and every single time without fail it would shatter my airbox - this mostly happens when i punch it in the guts off the lights. I also sometimes get engine light come on for minutes at a time, recently it's been for full 1.5hour drives, but only on LPG, never happens on petrol. I've read a few threads which covered my issue so I know where my issues *should* lie.. I'm also getting horrible (from what I think) economy on both LPG and Petrol. LPG is around 320km of a usable 52L. A tank of Petrol is generally getting me around 420km.

So obviously I will need to get an LPG tune done (haven't had one in the last 5 years - yes I know, probably the source of my problems) but I have a very specific request, I want to know which parts to buy prior to getting a tune done to remedy my problem and hopefully prevent me from every having this issue again.

Background: VX Acclaim II MY02 Wagon bought in Feb 2005 (87,XXX km). Gas was installed June 2005 (90,XXX km). I currently have 243,XXX km on the clock, with about 90% of the 153,XXX km since owned done on LPG. Apart from the aftermarket LPG, car is completely stock.

• Spark Plugs:
  • I have: NGK BPR6EFS-15 - $5.45 ea.
  • I believe I should go for either:
    • NGK BPR7EFS (0.9mm spark gap) - cannot find supplier)
    • NGK BPR7EFS-15 (1.5mm spark gap) - $5.45 ea.
    • Bosch HR7DC+ (0.8mm spark gap) - $5.51 ea. - I think this is the right one for LPG
    • Bosch HR8DCV+ (1.3mm spark gap) - $5.51 ea.
    • Bosch HR8DPV (1.3mm spark gap) - $8.39 ea.
• Ignition Leads:
  • I have: Not sure what I have under the hood - it's dark AF at the moment... **will update in the morning**
  • I believe I should go for either:
    • Bosch Super Sports B6025I - $84.99 set of 6
    • Bosch Motorsports B6025HP - $126.98 set of 6
• Air Box:
  • I have 5th or 6th (2nd hand) stock from wreckers - completely fractured and shattered at points.
  • Looking for a cosmetic mod here (sound-wise) and more resistant to backfire splitting than the stock... If I could get some performance benefit without bleeding my bank that would be a bonus. I believe I want to move onto either:
    • Mace Engineering CAI - $270.00 - is this a waste of money?
      • Pod Filter to Suit - $30.00 - What neck size should i be looking at?
    • SS Inductions Growler CIA - $599.00 - too expensive
    • K&N drop in panel filter - doesn't solve my backfire resistance issue.

Note: I am also hearing a whine in the lower throttle ranges coming from my engine. I believe i have a vacuum leak or a hose has come off.. I will investigate this coming weekend and report back. Also there are sometimes where I get a strong whiff of unburnt LPG filter through into the cabin or when I finish a drive and shut off the engine and step out of the car.

I will continue updating this Original Post as I get swayed/convinced one way or another and get closer to what I want/should need to do. Is there anything I'm missing that would be beneficial? Please keep in mind I am trying to save for buying a house so expensive mods will unfortunately be off the table.

Should I consider replacing:

• MAF sensor
• O2 sensor
• Crank Angle?

Any encouragement, guidance, advice and criticism would be greatly appreciated. Sorry in advance if some/much of this is covered on previous thread, if so just link. Many thanks in advance.

 

[strgas]

NGK BP6EFS gapped to 1.0mm good set of sprial core leads , bosch sports , IC&E , top gun anything with a sprial core is great for LPG , check over all vacum lines and injector seals , the whine noise maybe the vacum hose off the bottom of the throttle body runs to the rear of the engine to the evap soleniod , replace this hose with a single peice of rubber hose , factory hose was a 3 peice hose with glued on elbows .
poor fuel ecomony on both fuels is a good sign of bad O2 sensors .
K&N panel filters and MAFs dont work well together as the oil coats the sensors , seen some hot wire sensor catch fire due to oiled up filters ,
Drilling a hole in the top of the airbox and fitting a bath plug attached to a wire is a simple backfire valve .

 

[_R_J_K_]

K&N filter really isn't worth the money, and if your airbox shatters again it will be toast. It won't give you any extra airflow/power as the stocker won't be a restriction on your setup.

Only replace the MAF and CAS if you're actually having associated problems with running the car (I.E. car turns off/stalls, slow etc...). Putting new ones in blindly won't really make a difference.

 

[Arthur De Vroome]

Had the same problem with my VX Series 1 running LPG. Solved by drilling an 2" hole in the bottom of my Airbox with an hole cutter to allow more air in, as the standard cold air intake is too small when running LPG. This immediately stopped the back firing and blowing up of my airbox. The hole is hidden from prying eyes unless they remove the air filter. Had already replaced plugs with Irridium, 4 core NGK plugs. Good quality 8mm HT leads but was still backfiring at times. Simple solution I thought.

Art