Trouble cold starting ...

[Probs]

Hi folks,

Bit of an odd one. So when I run the car on LPG the following day the car fails to start on petrol. Symptoms are one of two things:

1) Starts briefly and cuts out. Crank a few times and eventually it starts
2) Doesn't start, need to crank a few tines, eventually starts.

If the car is ran on petrol all day this doesn't happen, ever. Car has happily ran on petrol-only for months and this was never an issue.

I initially thought it might be a bit of a slow leak from an injector leaking into one of the cylinders and flooding it over night but now I'm not so sure.

Any thoughts? Only happens overnight, all other cold(ish) starts throughout the day are fine.

[Brian_H]

Slow leak from an injector is one possibility, also a leaking diapgram in the vapouriser filling the manifold up with gas could be the cause, much the same result in either case (manifold full of gas so no air in there for the petrol to burn in or not enough at least)

Its a case of pulling the hoses off to see if you can locate the leaky part, I'd try the vapouriser first personally.

If you try either killing the gas supply and letting the engine switch back before switching it off (to remove the residual front end pressure) I'd suspect it would start ok, if you want a further way to confirm (disconnect either of the solenoids or shut the rear manual valve if you have one).

[Probs]

So I thought I'd start by swapping each injector one by one with a known 'good' injector and just seeing what happened each morning as to whether it failed to start again.

I've done all four injectors now and it still has the same issue. Which leads me to think maybe I have more than one leaky injector, or another issue?

Brian, I have a H4 so obviously two intake manifolds, could the vapouriser diaphram leaking still cause the scenario you are talking about?

[Brian_H]

Yes - I'd locate it and pull it off when running on gas see if you can detect leaking gas coming down it (put end of hose into water with other end onto vapouriser)

Don't know what system you have - most have the vacuum line though not all do.

[Probs]

Hey Bryan, It's a BRC Genius Max vapouriser. It goes from the vapouriser to a t-piece which goes to two manifolds.

Sorry for my ignorance, are you suggesting to pull the main feed from the vapouriser to the manifolds after the engine is switched off ?

[Brian_H]

No, you want the small pipe from the vapouriser labelled as feedback, find the other end of that, pull it from the t piece and put the open end from the vapouriser side into a pot of water. (this should only have air/vacuum in it if its working as it should be!)

Bubbles out of the pipe, would be leaking gas (you may get a little air at first, but anything more than that would indicate a problem).

Not on that particular vapouriser, but on others I've had it fail badly enough that the gas can be seen to leak, and pressure detectable if you put your finger on the end of the hose

Best do it with engine running - just plug the open end to the manifold to keep it running if needed.

Picture is taken from this link if you want the whole installation manual which might explain how it works (of course just because the vapouriser is BRC doesn't mean the rest of the install is though!)

https://www.remixbg.com/Documentation/D ... 1_3_en.pdf

[Pinger]

A problem I had that messed up running on petrol (including starting) was due to the fuel (petrol) pressure regulator sticking open. My theory is that with the petrol pump running at full tilt when running on LPG the FPR is wide open for long periods of time and eventually sticks in that position.
If your set-up leaves the petrol pump running during LPG operation, check fuel pressure on start up (doesn't have to be with a gauge, you are looking for the difference between a trickle and a spurt).

How old is the fuel in the tank? Stale fuel manifests itself during cold starts.

[Brian_H]

It may also be worth posting your vehicle details - some require a fuel return fitting and if this isn't there that can cause issues, additionally if one is fitted but not working as required, that may cause issues when trying to run on petrol? Though the description suggests petrol only running is ok so think its more likely a gas filled manifold - effectively too much fuel and not enough air until its flushed enough out of the manifold to correct it.