Fuel vapour & LPG??? (problem solved)

6

68PBBurntGrey

New Member
Hello Gents (@ Stina),

Since the implementation of a LPG installation in the car, I had a strange problem.
When running on LPG the engine wouldn't idle en even sometimes stutters under 1/3-1/2 throttle. Specially after stong acceleration and more than normal breaking, the engine stalled and wouldn't start easily. Engine runs fine on petrol and most of the times on LPG and problems only occur when engine is warm.

Although the engine runs fine when cold and always is good on petrol, I suspected an electrical problem because the rev-counter moved vigouresly when the problem occurred. Also because the wiring from rev-counter to coil was somewhat dodgy. But with bypassing the rev-counter the engine still had the same problem.
After this testrun and with engine idling, I noticed bubbles in the petrol-filter when running on LPG. Strange......
Another testrun with the petrol-line physically blocked (M8 bolt in it) the problem never occured again!?!

Conclusion: vapourlock pushes petrol into the engine while running on LPG!!
My setup is an electrical petrolpump (Hardi, low pressure) under the bonnet and an LPG-system that switches off power to the petrolpump when running on LPG. In theory it should work fine. But when running on LPG, the petrol in the fuelline will vapourate when engine gets hot, specially because the petrol is not moving. This will pressurize the petrolline and 'pumps' some petrol in to the carbs. Under acceleration and specially under breaking the air/petrol collum will shift and the 'vapour-pump' starts again. The Hardi petrolpump is off, but won't block the slightly pressurized petrol, so the engine runs on LPG & petrol. In idle that definately causes stalling of the engine.

So an extra petrol-valve will be added under the bonnet. And I repaired the dodgy wiring of the rev-counted when I was at it.

Thought you might have some interest in this problem if you're running on LPG too.....

Best regards,

Rene
 
Re: Fuel vapour & LPG??? (problem solved0

Interesting to know! How does it run generally? What's 'mpg' like compared to petrol?

Rich
 
Re: Fuel vapour & LPG??? (problem solved0

Hi Rich,

Car runs great in generally. Engine runs even smoother on LPG that on petrol. And no pinking (V8, 10,5 cr)!
Performance is somewhat less on LPG and the exhaust-note is less powerfull (but I removed the 1st silencer, so still have a nice sound).

Mpg is approx 1:6 (fast-mode) to 1:7 (cruising) km/ltr LPG (mpg 16,6-19,7), motorway and 60% city. On petrol this was 19,0-25,4 mpg.

Greetings,

Rene
 
Your best bet would be to fit a solenoid in the fuel line up near the carb so that you physically turn the petrol off when the pump is turned off.

http://www.ebay.co.uk/itm/Petrol-soleno ... em2567e7c8

Also, LPG needs a better spark than petrol so think about upgrading your ignition system (OMG I sound like RPI now :shock:)

I might convert Sparky some time

Richard
 
Thinking about this (I know I shouldn't...), when you switch the pump off, and go over to LPG, I presume it uses the remaining fuel in the float chambers for the first few seconds, and I guess the same thing in reverse when you switch back to petrol (i.e. there is no fuel in the floats until the pump fills them), does this cause any problems ?

I guess part of the vapourisation problem is that there is no flow of fuel through the lines with the LPG on, so it just sits there and heats up until it vapourises.

I like Richard's idea of the solenoid valve to prevent the vapours getting to the carbs, I suppose the only other idea would be a two way valve that allows the fuel to bypass the carbs and flow back to the tank (to avoid vapourisation), but it seems a bit daft to run the fuel pump while you're running on LPG.
 
Hi, or have the two way valve and switch pump off. Any pressure from vaporisation can
then vent back to the tank.

Colin
 
Hi Richard, Colin & others,

Yes, I will need a selenoid (thanks 4 the link) in the petrol line before the carbs. Only a one-way will do.
The stationary petrol in the fuel line obviously aggrevates the vapourizing and pressurizing effect.

And, Richard, switshinh fro LPG to petrol is straight forward. Swith set from LPG to petrol and go; a 2-3 sec hesitation during driving while the petrolpump is filling carbs and.... go!
From petrol to LPG you switch to a 'neutral' setting first to allow the carbs to empty. When the engine has no petrol left, set switch on 'LPG' en inmediately the engine starts to run again. So the LPG installation has 3 settings: petrol, neutral (no petrol, no LPG) and LPG.

The ignition is already upgraded electronic (123-ignition), good coil (red bosch), new leads and new sparkplugs. Ignition is set at 5deg. bdp, with is perfect for LPG, the petrol is RON 98 with octanebooster.

Kind regards,

Rene
 
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