backfiring on lpg

Rosscco · 04-09-2011, 09:58 PM

When I bought my car - Fairmont AUII Tickford dual fuel - about 6 months ago it backfired a few times and burst the concertina pipe. I replaced the pipe and sparkplugs and it hasn't done it for a few months, but has recently started doing it again. Any ideas of anything else to check?
Why would it backfire in the intake manifold? Intake valves?

bryanj · 04-09-2011, 10:32 PM

Quote:

Originally Posted by Rosscco

When I bought my car - Fairmont AUII Tickford dual fuel - about 6 months ago it backfired a few times and burst the concertina pipe. I replaced the pipe and sparkplugs and it hasn't done it for a few months, but has recently started doing it again. Any ideas of anything else to check?
Why would it backfire in the intake manifold? Intake valves?

Hi, You mentioned that you replaced the sparkplugs, but did you replace the leads? If not get some good quality ones that are wire wound.
There are a few good brands and the price usually determines the ones you will choose. I have Bosch leads on mine and they are ok.
I put another brand on an EL on gas as the price was bettter on that brand for an EL. Up to $15.00 depending on brand and application/model. I went to Sprint and then to Autopro.

As you didn't mention whether it backfired on start-up or normal driving this is a good startng point.
Also make sure you inlet manifold studs are tight. Most are not and if your real keen put some meduim loctite on them and they will hold forever. You can blow the inlet manifold gasket if its very loose and backfires and the car will regularly miss. Leads and manifold studs are a must. There are some other things but hopefully this will fix it.

I'm sure there will be others with extra ideas as this is a great help forum for Ford owners.

Regards Bryan

FGII-XR6 · 05-09-2011, 09:57 AM

I have tried a lot of leads and plugs and eventually found the stock factory LPG leads and plugs to be the best for gas . go all out replace plugs ( standard ford LPG not irridium) leads and coil pack and it will feel like a new car.
Get a set of LPG airbox clips ( they have springs in them) and if you have a backfire there will be no damage done. you can normally find them cheap on ebay

Veefore · 05-09-2011, 12:42 PM

If it is backfiring it is probably because it is running lean. I have to adjust the idle mixture on mine twice a year. Once in spring, once in autumn as the ambient temperature changes. If I forget to do it in spring, I get backfiring when I press the throttle open quickly due to the inlet charge suddenly leaning out.

I also notice that I get 310km from a tank full of LPG in summer and 360km from a tank full in winter.

FGII-XR6 · 05-09-2011, 12:49 PM

most LPG systems don't need this as the computer takes care of it, with some old school systems this might be the case but modern LPG uses the stepper motor to control idle mixture. The majority of backfire issues are caused by spark problems,

Quote:

Originally Posted by Veefore

If it is backfiring it is probably because it is running lean. I have to adjust the idle mixture on mine twice a year. Once in spring, once in autumn as the ambient temperature changes. If I forget to do it in spring, I get backfiring when I press the throttle open quickly due to the inlet charge suddenly leaning out.

I also notice that I get 310km from a tank full of LPG in summer and 360km from a tank full in winter.

PoweredByCNG · 05-09-2011, 02:28 PM

^ Provided that the gas system has a working fedback system, and that the engine's oxygen sensor is in good condition, of course.

But yeah, new spark plugs (0.7-0.9mm gap, one heat range colder than petrol), new heavy duty leads and new coil pack will generally stop backfires.

Rosscco · 05-09-2011, 08:27 PM

I guess it's a pretty common fault then? Mine's done it about 6 times since I've had it, usually after idling a bit at a stoplight or something.
The other day, I was just rolling slowly down a 50km/h street, just touched the accelerator lightly and boom ... stall. Had to switch to petrol to get it started again. I also noticed it seems to idle smoother on petrol than lpg (but only slightly noticeable.)

PoweredByCNG · 05-09-2011, 11:35 PM

Common problem and as I said above, easy to fix.

FGII-XR6 · 06-09-2011, 10:28 AM

it's so common ford made special airbox clips, thay are worth fitting as the springstretch to let out the pressure in a backfire

Rosscco · 06-09-2011, 09:38 PM

OK, I got a new set of leads (not fitted yet), I guess I better get a new coil too. I got a new set of airbox clips too.
Thanks for everyone's help.

LANKY 1 · 08-09-2011, 01:56 PM

I had similar backfiring problem. It went away when i put on extractors and exhaust

Veefore · 08-09-2011, 02:31 PM

Quote:

Originally Posted by au3xr6

most LPG systems don't need this as the computer takes care of it, with some old school systems this might be the case but modern LPG uses the stepper motor to control idle mixture. The majority of backfire issues are caused by spark problems,

In the case of my gas powered Falcon, it was set to open loop instead of closed loop at idle by the installer so that it could be set a little richer (only at idle), reducing the chances of backfire on quick throttle openings. It was a huge improvement not only in reducing the backfires but also in the transition from idle to off-idle.

The reason being that the sudden intake of air on a quick throttle opening won't register on the EGO sensor until AFTER it has passed through the engine. This can cause a lean-out until that air passes the EGO sensor and registers on the computer. By then it has already backfired and blown the fire out.

Just running the idle a little richer can stop those lean-outs and backfires. It has also made an improvement to the idle-off idle transition as well compared to others I have had/driven.