LPG problem - wont start and backfiring - help needed

[VRcommondoor]

Here I go again... Maybe some day I will stumble upon a thread in which I might be able to give some help, but anyway, here goes...

I have a dual fuel VR V6 and I don't know what kind of system it is. Has 2 adjustable parts on the converter and 1 screw labeled "idle" on the mixer thing just before the throttle body. Fuel pump is cactus and so can't start using petrol.

Driving last night all was fine. Went to start it early this morning and it wouldn't start, just a small backfire. Tried again, sort of started with a put put put and a rough shake then a loud backfire and stopped again. Popped the bonnet and the air filter box is broken and displaced. There was also a funny burning smell that lingered for about 15 secs. Smelt a bit like gunpowder or something, like what you smell from a cap gun. I fiddled with all the leads to the spark plugs, checked there was gas etc. and tried once more. Still the same.

Any ideas what might be causing this? How to fix it maybe?

I last week replaced the water pump, heater tap, bypass bung etc. and all has been running really well.... now this... never ends! Ready to toss in a match.

Any help appreciated guys and thanks in advance.

PS. not sure if this is relevant or related but on about 6 occasions in the past 18 months when I have started the engine it has been really rough with a really violent shake. Sometime it settles in about 5 seconds other times its really rough and I turn it off and start it again and it settles in 2-3 secs.

[Ron41]

Gas needs more spark than petrol so the first things I would check is plugs, then check resistance on leads, test coils and DFI.
I had the same problem, all of a sudden she ran like a dog, but only on gas, checked all of the above, the plugs looked ok but I changed them to the bosche platinum tipped and the gap was smaller at 1.1 mm instead of 1.3mm, no problems since.
I should add through a previous experience, bench testing the coils doesn't prove their spot on, so if you can borrow some off a mate to swap, it might help.

good luck.

[sleepa]

Gas needs more spark than petrol so the first things I would check is plugs, then check resistance on leads, test coils and DFI.
I had the same problem, all of a sudden she ran like a dog, but only on gas, checked all of the above, the plugs looked ok but I changed them to the bosche platinum tipped and the gap was smaller at 1.1 mm instead of 1.3mm, no problems since.

I agree with the plugs and leads on an LPG vehicle. My old car was driving crap till I replaced the leads, then she was all sweet.
The converter usually needs to heat up a bit which is another reason cars start on petrol then switch to gas, always harder to start on gas. and make sure your maf sensor isn't screwed from the backfire.

[Brett_jjj]

Id also replace the fuel pump and start running it on petrol once a week for a few minutes.

[kennym08]

i would check the coils there are post on the forum which will help i saved these and they are spot on my coils sparked all over the place changed them and no more back fire, i also changed plugs and leads most backfire is due in my opinion to either or to plugs leads and coils


Try this mate,
With the engine off, remove the first 2 leads of the first coil pack and then start the car, a spark should be jumping from metal tip 2 tip on your coils, if the spark jumps anywhere else (like downwards or onto any other part of the coil) then that coil is fualty and needs replacing! Either way mate hope ya get it sorted & best of luck
Edit: obviously if the first coil pack is fine and works well then turn the engine off, replace the leads and move onto your 2nd then 3rd coils
__________________
Theres a similar trick to the one above to check if one of your leads is rooted, take a spray bottle at night and spray mist around the heads of your leads to see for any spark jumps.


Ok fellas, to test your coil packs,
With the engine off, take the first 2 leads of the first coil pack and then start the engine, now have a look @ the metal tips on the coil pack, the spark should be jumping from tip to tip, if the spark jumps anywhere else then the coil is stuff/on its way out! If the coil is ok then turn engine off, replace leads and move onto coil pack num2 and so forth on number 3!

[ChrisR91]

I was told and it happened to me, when gas backfires its 9/10 it will be the leads cross-firing, so make sure your leads and plugs are good. also with gas i was told not to use cheap lead. i use Bosch High Performance Motorsport Ignition Lead Kit and i have not had one issue with my gas.

It could also be the gas is not been covered when its cold so it could be the thermostat but that would not make it backfire, i do not think.

[VRcommondoor]

Try this mate,
With the engine off, remove the first 2 leads of the first coil pack and then start the car, a spark should be jumping from metal tip 2 tip on your coils, if the spark jumps anywhere else (like downwards or onto any other part of the coil) then that coil is fualty and needs replacing! Either way mate hope ya get it sorted & best of luck
Edit: obviously if the first coil pack is fine and works well then turn the engine off, replace the leads and move onto your 2nd then 3rd coils
__________________
Theres a similar trick to the one above to check if one of your leads is rooted, take a spray bottle at night and spray mist around the heads of your leads to see for any spark jumps.

I am really hesitant about trying to crank the engine again as I dont want to do any more damage with it backfiring... Will it not be guaruteed to backfire if i disconnect ignition leads? I dunno, starting to get lost with it, lol. Should i undo all the clips on the filter box to stop the replacement one blowing to bits? Or maybe tape up the old one so it blows the tape if anything?

I will replace all ignition leads and spark plugs anyway as I would say they are due and it can't do any harm (been about 60,000kms and 22mths i think since last done :S) and try it again. Failing that I will have to check these coils. What are coils worth roughly?

[Brett_jjj]

It wont hurt it to just get it going with no air box connected.You dont want to ruin another one if it backfires again.Just leave it off until you get it running fine.Then replace it before driving it.Just make sure nothing gets sucked up inside the open pipe.Maybe tie some cloth over the end of the pipe.

[sleepa]

My parents had an old fairlane on gas which would occasionally backfire and stall, but what would happen is the intake pipe would blow off, you'd plug it back on and away you went. Cheaper than an air filter box. I think one of the clamps were loose (or missing) so it just blew the hose off.

[kennym08]

Yes the first thing is replace plugs and leads, making sure leads are in correct position, undo the clips on the air cleaner box so if it does backfire it will lift up and not explode u can tie it down with a ocky strap (not to tightly)which will absorb the shock of a backfire, I am more inclined to think it is coils though as it is such a dramatic decline as per your description, - a back fire is caused by a build up of gas being ignited so there is gas there just not the spark to ignite it at the correct time - when i checked my coils as per the method described it did not backfire but did run terrible as you would expect on 4 cylinders but i could sure see that 2 of my 3 coils were intermittently misbehaving with spark shooting in all directions. I was lucky and a neighbor lent well actually gave me a new coil pack, (thanks Ben) put it on no backfire and runs to reline easy

[VRcommondoor]

OK... Thanks for all the suggestions guys. Problem found... I think... Blown head gasket... upon removing the spark plugs one of them was moist and had small amounts of corrosion. Does this mean it has been like this for a while to have built corrosion? My suspicion is that once I repaired the whole cooling system, the pressure built up enough to blow the already fatigued gasket. Is this likely? Any reason it ran well for a few days then just overnight decided to stop? Any ideas?

[Brett_jjj]

It might be just the inlet manifold gasket leaking or blown,a very common problem on these engines,fairly easy and cheap to fix though.Get a workshop manual and do it yourself and save a heap of money.Cheers

[VRcommondoor]

It might be just the inlet manifold gasket leaking or blown,a very common problem on these engines,fairly easy and cheap to fix though.Get a workshop manual and do it yourself and save a heap of money.Cheers

Yeah, got a gregorys to help me along. I was scouting around and found your other posts regarding oil in coolant and coolant in oil etc. I can see no trace at all of either.

I got a Lube Mobile mech to come give me a diagnosis. I thought he was going to do like a pressure test or something. He just removed the spark plug that I pointed out to be suspect and said "Yep thats wet. There is also a bit of corrosion around the porcelain part inside the plug." He then stuck his hand down there and got me to turn the key. Didnt start but didn't backfire either. When he pulled his hand back out of wherever he had it (near the spark plug hole somewhere) he said yeah yeah, coolant in there.

He told me that the car was virtually no good and not worth it and that he new a guy who could come and take it away as scrap if I wanted. This I might add is after he has tried convincing me to let him have it taken back to the workshop where he could pull it apart and quote me accurately. Anything between $500 & $1000 he said. He also tried talking me in to buying a pulsar he had at the workshop instead of fixing my car... For this I payed the man his $70 call out fee and he went on his merry way.

Having only just repaired almost the entire cooling system joins, hoses, pump, thermostat, gaskets etc. and then the car just stops 3 days later, would the return of pressure in the cooling system have just found a weak spot somewhere else? Any tell tale signs for coolant in the cylinder but none in the oil and no oil in the coolant... ?


Thanks again

[Brett_jjj]

Id say the engine has blown a head or inlet manifold gasket.That guy should have done a compression test and a cooling system pressure test to verify exactly what is wrong.That way you would know if it was a head gasket or just the inlet manifold gasket.Also you can have a blown gasket where theres no water in the oil or vice versa,it just dependes exactly where the gasket is blown out or leaking.You really need to get the engine compression tested and the cooling system pressure tested to find out for sure exactly what gasket needs replacing.If the compression is good,but the cooling system is loosing pressure,it will most likely be a leaking/blown inlet manifold gasket,If there is pressure leaking from the cooling system and the compression is down on a cylinder or two,then its mosty likely going to be a blown head gasket.Either way, they are not that hard to replace.Just follow the manual,especially take note of the recommended bolt tension (torque) settings for the inlet manifold and head bolts,and also the tightening sequence for both.Cheers.

[scv6]

on lpg commodores theres really only 2 things that will cause a backfire.
1 electrical misfire
2 lean mixtures
ive seen coolant in the chambers from inlet gaskets failing.
It is entirely possible that the backfire blew out your inlet gasket which could explain coolant in the pot.
I think the most likley reasons it back fired where convertor not primed in morning = lean or electrical misfire ie bad plug, lead, coil
I would be comp testing and pressure testing cooling system like brett said. ( Id also leak down test the engine). I wouldnt be pulling it apart until I was sure wot da problem is, due to the Big cost difference between valley gasket and head gasket replace.

[YILDI2]

i used to have gas running through my system before i got my engine rebuilt
the only time mine would backfire is when the pipe connected to the pod filter came loose
id just push it back in then no worries
and yes i do agree its harder to start the car on gas especially on a cold morning make sure you start it on petrol first then switch to gas way more easier
and i also recommend a pod filter since i have heard that backfires can stuff your stock cai box, sorry for going over what everyone else said
but pod filter might help in the future