Submitted: Monday, Aug 18, 2003 at 15:41
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hi all i have a 1991gq which runs on gas and petrol the problem is when it runs on gas it makes a backfire type of noise in the engine area like a pop sound does anybody no what would cause this any help would be much appreciatrd robert
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Reply By: Member - Paul H - Monday, Aug 18, 2003 at 16:06

Monday, Aug 18, 2003 at 16:06
Try checking your ignition electrics. if theres a misfire under load this will cause a backfire. I had a similar problem on my nk Pajero. Better still get rid of the gas & put in a reserve petrol tank, I did & have never looked back. off to googs track & gawler ranges................Sept hol's.
AnswerID: 28305

Reply By: Hero - Monday, Aug 18, 2003 at 16:48

Monday, Aug 18, 2003 at 16:48
I have had similar on a Land Rover Discovery (quite common), go back and bug the installer, my problem was mixture settings. The backfiring is obviously not good for your intake system so, the sooner the better, I was lucky to find in time my airflow sensor gauze dislodged and on the brink of going down into the butterflys.
AnswerID: 28309

Reply By: ThePublican - Monday, Aug 18, 2003 at 17:24

Monday, Aug 18, 2003 at 17:24
Robert, if your in the greater Brisbane area ,sugest you take her in for a tune at Hycraft automotive at Clontarf/Redcliffe,, they are the ducks guts on petrol/gas.
AnswerID: 28314

Reply By: bozo - Monday, Aug 18, 2003 at 19:04

Monday, Aug 18, 2003 at 19:04
I have the same problem with my GQ from time to time Robert, gas service ($110-$120) fixes it. I suspect that it is electrical-probably spark plugs but a full service is still a good idea once a year.
AnswerID: 28339

Reply By: howesy - Monday, Aug 18, 2003 at 20:06

Monday, Aug 18, 2003 at 20:06
Had gas on a 351 cleveland for years. he problem you describe can have a couple of causes all tune related both timing and mixture. the other less likely prospect is the diaphram in the converter. Most have a drain screw and over time condensation
builds up in the converter. If you have never done it before it wont hurt to drain the converter of any water present as this causes improper diaphram operation. Put em all together and you might solve it.
AnswerID: 28346

Reply By: Voxson (Adelaide) - Monday, Aug 18, 2003 at 22:02

Monday, Aug 18, 2003 at 22:02
My GQ has done it twice for no apparent reason because it is always in a good state of tune....... Like the other reply said,,, dice the lpg and go a larger petrol tank...
Gas is a an engine killer anyway........_____________________________________________

AnswerID: 28370

Reply By: Janset - Tuesday, Aug 19, 2003 at 17:19

Tuesday, Aug 19, 2003 at 17:19
Hi Robert.

I do not know about GQ's but here is my 5 cents worth relating my experiences on previous FJ45 Troopie.

My gas system was an Impco, which uses a early model Holden paper air cleaner element, with an metal cover over the top and an aluminium underside and part of the Gas installation was inside the element.

Anyway, I stated to get these back firings through the carby after I had the installation on for about 12 months.

I ran it on gas all the time. The only time I would switch over to petrol was overnight and when I knew I was not going to use the vehicle for a time, this was to stop the gaskets in the carby from drying out.

Back firing though the carby on the Impco system is murder. It causes the metal plate in the centre of the diaphragm over the Carby, (or was it a metal extension to the carby, can't remember) to violently open and then slam shut causing the plate to buckle and thus letting un-metered air into the air intake casing/carby causing the engine to run leaner with each back fire.

The mere fact that a petrol engine runs too lean it another reason to backfire through the carby.The problem became so compounded that the last time I did the Nullabor I had to switch to petrol whenever I slowed down in country towns otherwise my engine would stop if I slowed to less that 50Km.

I drove the rig like this until I reached Pt Augusta where I bought another diaphragm for about $70 (about 15 years ago) from a gas conversion place.

It was only then that I was told that the reason for the backfire after telling him on my woes.

In those days, an oil injection system for a gas conversion was unheard of.

He told me that on a trip I should run petrol one tank to 3 tanks of gas and in the metro area, a couple of times a week.

The reason he said was that the gas fuel dried out the valve guides in the head causing sticking valves, hence upon ignition whenever an inlet valve was sticking, the back fire occurred.

I though to myself "Oh Yeah!" But what had to loose.

I took his suggestion switched to petrol, started the engine and squirted oil into the carby until it was evident in the exhaust and (this I was told would overcome the immediate dryness problem).

The next tank full, I ran on petrol and then continued his suggestion.

I kept that Troopie for the next 3 years and not one back fire did I get after that.

Rather long winded but I hope someone may benefit from my mistake.


AnswerID: 28452

Reply By: Ferret - Sunday, Aug 24, 2003 at 14:12

Sunday, Aug 24, 2003 at 14:12
Get your valve/tappet clearances checked. If they are too tight you can get gas back through the inlet valves and bang! I was told by my gas guy that GQ's on gas need tappets checked every 20,000k's. Just had mine done and it made the world of difference.
AnswerID: 28904

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