Trying to trace a leak

[mondeoman]

I'm getting a gas smell on cold startup, I'm hoping someone might have come across this before, as I am struggling to find out where it is coming from. It's most apparent in the cabin, and only lasts for a few seconds, and only on the first cold start of the day. It doesn't recur if I restart thhe car later, even if it's been left standing for a few hours.

It occurs as soon as the gas switches over. If anyone has any ideas it would be appreciated. Otherwise is there a colour changing leak detector? I cannot find bubbles using standard leak detector?

[LPGC]

Hi Paul,

A gas leak at the rear of a vehicle can easily have gas make it's way to inside of a vehicle via eddy currents bringing gas forward into the heater air intake - If you can't find any leaks at the front, check the rear too. Where I've found leaks at the rear of vehicles, owners have often said they wouldn't have thought gas would make it's way from the rear to the front and into heater air intakes.

When checking the front end for leaks, check under the same conditions as when you smell the gas (cold engine, just switched to gas) - pipe joints can be gas tight at one temperature and leak at another temperature, as can reducer diaphragms and other seals. Maybe apply bubble liquid before starting the engine and watch as it switches to gas.

Check the reducer diaphragm by disconnecting the vac pipe from reducer and checking for gas exiting that port.
If you have the software for the system, check what pressure is in the system when gas solenoids first open.. Reducers can develop a fault where system pressure continues to rise (albeit slowly) when there is no gas bleed/drain (i.e. if gas solenoids are open but engine isn't using gas yet because it is still running on petrol waiting for, say, rpm to rise above a certain level before it switches to gas).

Your problem may be due to unburned gas exiting the exhaust, which can occur if a vehicle with slave type LPG system switches to gas too soon when petrol ECU is running in cold start/choke mode, can also occur if LPG system is generally calibrated too rich or correction for cold temps isn't properly calibrated. Could sniff the exhaust to check!

Would guess you'll find a rubber pipe joint that leaks only when cold, or the exhaust smells of gas as described. If rubber pipes are long enough, maybe cutting an inch from each end and doing up with a new clip would sort a problem you wouldn't get chance to detect with bubbles.

Never used the colour changing stuff, always thought it might be of limited use in an engine bay environment with wide ranging temps and HC's floating about.

Simon

[Tubbs]

I had a few instances of this over the years. One that springs to mind was a customer who drove all the way from Northampton. 'It only smells first thing in the morning' leak checked it. Found nothing. Was using those click clips at the time. So I replaced them all with jubilee clips and nipped them up tight. He phoned me the next day to say it was fine. No longer smelt of gas. Stopped using click clips after that. Shame. The click clips look neater than jubilees.

[LPGC]

Know what you mean about quick clips, I liked them when I used to fit mostly OMVL stuff years ago, stopped using them after that... Bought from OMVL supplier, kits came with OMVL spec pipes (which are generally a bit thicker than other pipes of same internal diameter) and OMVL spec clips which suited perfectly... Difficult to ascertain correct clips for varying brand pipes which all have slightly different OD's for same spec ID, anything but exactly the correct clip is likely to leak, or blow off at some point. I miss them because they were neater and were quicker to fit, except in awkward locations.. Jclips are easer in awkward locations especially with flexible coupling tools. Like you say though, neater than JClips. Got to be careful choosing which Jclip to use too though, too wide and will clamp pipe mostly over ridges when clips should really be just after ridges on fittings, some type Jclips can't be torqued nearly enough, Jclips all have mechanism section that has preset curve that needs to be right. .

Pet hate regards piping connections is seeing silicon hose unsecured for gas pressure sensor fittings, great stuff for vac fittings though.

Simon

[mondeoman]

Thanks for all your suggestions. I have a day off tomorrow, so will have a serious look then. My thought was to coat everything with the standard leak spray, I have an almost full can, get the good lady wife to start it up and see if I can spot anything obvious. If not I'll start working through your suggestions and report back.

As always, your input is very much appreciated.

[mondeoman]

OK, problem solved. Sorry it has taken a while to post back but the best laid plans oft go awry, and my day off disappeared.

I did get chance yesterday to act out the plan, so everything got a good soak in leak detector, the current Lady Mondeoman cranked her up and then when it switched over the gas smell appeared. No doubt it was under the bonnet. Another quick spray of everything showed a leak from the outlet joint of the vapour filter, but after about ten seconds running it stopped, and didn't reoccur.

I tightened the jub clip, only about a sixteenth of a turn and it seems to have solved the problem.

Given the nature of the leak, occurring only briefly as it did I would not have expected the filter.

[LPGC]

Rubber pipe leaking on filter when cold then, not the filter itself..?

May be an idea, as said, to cut that end bit of pipe off and do up with a new clip.

Glad you're sorted mate.

Simon