Thread: Fuel starvation on LPG

It would really help if you told us what kind of LPG system you have. Gas can run lean for a huge number of reasons. Blocked filters generally don't cause lean running at low power, they do limit fuel flow and therefore can lean out at maximum power though. In any case there are usually a number of filters that can be checked although I've seen systems with original filters that have done 200 000km without loss of performance. It depends on the quality of LPG you buy. Some retail chains are much worse than others. If you are running injected gas one of the most common problems is that the main regulator pressure drops a bit as it settles in and the system needs recalibrating at around 5000km from a new installation.

Where are these filters - I have not spotted any on my system - old style - remote converter and vapourizer (lpg carby) between the airfilter and petrol carbies.

Thanks

Garry

Hi

Apologies for the lack of technical info

MY99 Thor with Omegas sequential injection by Landi-Renzo.

The filter is in the gas feed line just before the evaporator.

I always try to buy gas at the same place.

It mainly happens when it is under load, eg going up the Mooney Mooney Bridge on the M1 at 110K


Steve

All LPG systems should have at least two liquid line filters, one before the gas lock at the tank and one before (usually integrated with) the main gas lock under the bonnet. The tank one is little more than a fine gauze, the main one is usually a pleated paper type. Neither should be expected to need replacement unless you are very unlucky and get a load of particulate rubbish with your gas. I don't service these filters unless there's a problem. APA brand tanks have a big filter sock like on an EFI fuel pump and last virtually forever. The best way to determine if a filter has a problem is to drive the vehicle hard, stop quickly and feel both valve bodies. A major pressure drop across a blocked filter will cause the valve to ice up as the liquid turns into vapour. I'd expect to change a main filter at around 200,000km or even longer. Usually when I reinstall a used system all filters are checked or replaced.

Now there's your injection system, most have a vapour filter in the hose from the converter to the injectors. The recommended interval is around 40 000km for service, although I've seen them go much longer without much issue. The local glazier put 80,000km on his V6 Triton before I got to do the filters but it was running perfectly. The filter was faintly grubby.

The other thing about a blocked filter causing lean out is that it would result in a pressure drop and trip the automatic changeover back to petrol. If that doesn't happen under hard acceleration I'd expect it needs a retune.

Hi,

Thanks for all the info, I am pretty much a novice at the injection stuff, especially LPG.

Give me a pair of SU's or Webers and I am right at home

I can now visit my LPG guy armed with more info.

Thanks
Steve

Hi

Well i took it to the service center and all looks OK. The pressure is a steady 2bar and there are no other fault codes.

I haven't hammered it up a steep hill for a while, so I don't know if it is still happening.

He did say that if I can give him the revs at which it starts to misfire, then he can make it a bit richer above those revs

He also reset the fuel trims by disconnecting the battery and shorting the leads together so it relearns.

So i will see what happens next, but it's weird it never did it for months and then started.

Steve

HI

I still have this problem and it seems to be getting worse

The service guy said it all looked good.

He reset the fuel trims by removing the battery clamps and holding them together for about a minute, I assume this does work.

He also said that if i told him what revs the problem starts around, he could adjust the gas and give it a bit more at higher revs.

Still getting left and right bank to lean messages as well.

I am beginning to wonder if I have a MAF or Lambda (O2) sensor issue. I cleaned the MAF a while ago and it's readings look OK.

I have no idea when the O2 sensors were last replaced and my software only seems to show one sensor reading.

It feels to me like the engine is misfiring, but I don't see any misfire codes.

Time to replace the Lambda sensors maybe?

Steve

Just for the hell of it I'd try some different spark plugs. I've had a couple of cases recently where misfiring happened regardless of mixtures, and only a different set of plugs fixed it. Remember also to keep the gaps down to 0.7mm for any LPG vehicle, this reduces the load on the ignition coils. Just because petrol runs fine doesn't mean the plugs aren't inadequate. Electrical load on LPG is considerably higher, all other things being equal. Suitable LPG plugs will be also at least 1 heat range colder than stock, or 2 if you work it hard.