VN backfire on gas....help!

[ryan21]

hey guys,

i reset my ecu about a week ago and just run the car on petrol, i wanted to make it run a bit better on petrol and it did.

Switched it over to gas today and drove to work ran fairly crap and idle wasnt great.

After work i stoped at a set of lights when the light went green went to take off and bang! afterwards it was stuttering a bit so i flicked it to petrol and drove home and everything was fine.

Thought i would do the same thing reset the ecu and start on gas, when i popped the bonnet to remove the engine fuse i glansed over at the air box and it had a massive hole in the side.

the engine was running while i was checking this all out and a heard a tic from a relay (usualy happens just before thermo fan comes on) but this time no thermo fan.. and it continued to not turn on even a little past halfway on the temp guage still nothing.

car is still running ok on petrol and gas.

my question is this: what should i check after the backfire and make sure is ok? and what could be wrong with the thermo fan situation? since the relay is ticking could it just be the wiring from relay > fan or the fan its self or are there more possibilities.

also gas has been tuned not to long ago sparkplugs leads etc changed less than 20,000 ks ago

any help would be much appreciated.

Thanks.

[shnap2nd]

hey bud is it man or auto?

[scvs6]

Old or faulty spark plugs make cars backfire on gas. Once mine backfires, I change the spark plugs and that lasts about 30,000-40,000kms, then it will backfire again. I have gone through a couple of air boxes as well haha.

[ryan21]

hey thanks for the replys its auto and the spark plugs are 20,000 ks old this is the first time its done an airbox and ive had it for 70,000ks its only ever back fired twice this being the second time, any ideas on the thermo fan?

[1_johnboy]

also make sure that the pluggs are also gapped correctly. LPG need a different gap that petrol, 1mm from memory....as the other guys have said, 20,000kms can be also on plugs in a duel fuel car...also look at stainless steel leads

[ryan21]

hey started it this morning checked the thermo fan manually and it worked started it up and the thermo fan was working again guess it was just being temperamental, so all good guys thanks for the suggestions i might change the plugs anyway it cant hurt before i put in the pregapped ngk plugs, does anybody know if the ngk irridium plugs are good for gas?

[Cheap6]

The recommended service interval for 'plugs on a Commodore V6 running on LPG is 20000 okm so if they're that old that's a no brainer.

I've had no issues with genuine 'plugs and leads, standard gap, 'plugs replaced every 20000km as per GM's recommendation.

There may be a tune issue with the gas, the recent retune may be correct and OK, if the plugs and leads are OK but lean enough to misfire if they are not.

Most often a backfire won't hurt anything more than the airbox but potentially can bend the throttle plate or even damage the IAC valve. If with new plugs the car runs fine I wouldn't be concerned about it.