LPG backfire issue

[EYY]

Forget about the petrol injectors. Gas needs a healthy spark so will highlight any shortcomings in your ignition system by backfiring.

 

[pete d]

hi guys my friend has a vr commodore with gas he had the same problem backfiring blowing air boxes to pieces changed every thing in the ignition system it would be ok for a while and then start backfiring again found out it was the fuel injectors leaking when they were supposed to be switched off when running on gas this caused the mixture to be rich running on two fuels and causing backfires new injectors fitted and no more backfires . he only found out the injectors were leaking because he took manifold off to fix a leak and some injectors were wet. so if you have tried everything to stop backfiring maybe its your injectors hope this helps someone

pete d

 

[Vince89]

Back fire with gas



My VR would back fire at random times and only stop after running on petrol for a couple days then back fire again.

first I adjusted the gas- maybe too lean - no not that

changed spark plugs and leads - after 3 months back fired again etc - changed spark plugs again - after 2 months back fired again- no not that then.

adjusted the gas to be a little richer- only a touch - OK for a while, back fired again- no not that

heard a noise one day coming from the back of the car- a friend told me it was the petrol pump.
So I added a treatment for the petrol pump and that also cleaned the injectors
after a couple of weeks the noise stopped.

NOTICED THAT CAR WASN'T BACK FIRING!!!???

conclusion the injectors needed cleaning!!!

it has now been 8 months on the same spark plugs and leads --trying to get to one year maybe I will change the spark plugs then but manual says 2 years.
I will wait and see
so far so good no back fires. LOL

UP DATE ------ its been over a year and the car would stall when driving so I changed the spark plugs.
Conclusion THE PETROL TREATMENT DID IT cleaning the injectors- PS my car doesn't have a carburettor- if you do you need the lead replacement oil that drips into the fuel/air flow- ask the guy that fitted the LPG.

UP DATE ---- - my car started to BACK-FIRE ETC AGAIN. PUT SOME MORE petrol treatment- stopped for about 3weeks.

One day it didn't have the same pick up etc. It stalled and no start on gas or petrol.

RAA man said it was the CRANKSHAFT POSITION SENSOR. Have a look in the manual, the sensor is just behind the crankshaft balancer

HE said the sensor can become faulty and hot. He poured water over it to cool it and the car started again and ran normally.

A mechanic replaced the sensor for $160 and now the car hasn't MISSED ON GAS SINCE. It has been well over a year!
Perhaps one only needs to pour water onto this sensor to see if the BACK-FIRES, stalls, rough idle etc stops for a couple of kms etc

The crankshaft position sensor may need replacing?!

good luck

UP DATE UP DATE UP DATE UP DATE
16/01/17 NOT BACK FIRING AT ALL USES VERY LITTLE GAS, POWER LIKE A NEW ENGINE.
Have not replaced the spark plugs or treated the fuel or anything but changed oil and filters, water etc.
Having the Crankshaft Position Sensor replaced did it for my engine.
Good luck.

 

[jeepster]

Most LPG backfires are due to faulty leads. You'll find 9/10 times replacing the leads will eliminate the problem.

I had an Ecotec LPG going bang. Changed spark plugs, DFI coils, CAS, exhaust sensors and so on. Eventually dealer workshop found that problem was the LPG controller took an RPM signal from the DFI module and crappy soldering was intermittent, so cause misfire (often when accelerating hard or
hitting a bump). After fixing dodgy wiring, it never missed a beat. So the LPG conversion was of itself to blame.

 

[strgas]

common causes for backfiring on LPG , poor spark plug choice and gap , faulty leads and coils , air leaks in the intake from split hose or gaskets leaking injector orings , poor mixture control , poor installation of LPG system , dirty/poor electrical connections , worn engine components , poor tunning maintance of LPG system .
Some of these issue may affect running on both fuels or more so on LPG , always starting with base engine tune plugs and leads coils then looking at hoses and gaskets that maybe split or dislodged.

 

[CCCMikey]

I think by design the fuel pump still runs even when using LPG - perhaps so changeover to petrol is smooth.

I wonder if disabling the fuel pump would also help diagnose this cause - provided you have a means to start on LPG.