Problems with 740 LPG Installation

[volvovic]

I am up to my second 740 installation after an unsatisfactory initial installation. The problem with the first was the position of the reducer due to lack of space.
With the help of the forum modifications were made which allowed for what I thought would be a better outcome. My installer chose to use an IMPCO system. I attach pictures.
The problem is difficulty starting. As it goes from petrol to gas, the car stops abruptly as if the gas supply is cut off. Further attempts result in the same cut out. Solution to the problem has been to open the butterfly which has increased the revs. This is OK when it is on gas, but on petrol it idles at about 1000-1100.
Otherwise, it drives well.
I have changed: oxygen sensor, plugs, mass air meter dizzy cap and rotor, IAC valve, cleaned throttle body
My thought is that the idle should not be affected by the gas system at idle and that there is a flaw with the system. Any comments would be appreciated. Would it be better to use my old system was a generic mixer with OMVL reducer. Would an AEB Leonardo (marketed as a 295 in Australia) added to this system solve my problems?

[classicswede]

I'm pretty sure I can see the issue here.

You have solved one problem with threducer position but by changing to impco have now introduced another by positioning the mixer to far away from teh manifold.

It should still run but is more likely to backfire and have switch over issues (lag when changing from petrol to gas).

Now that the impco is on you do need to check for air leaks between teh manifold nad mixer. Also with it ticking over on gas read the labda probe for a short time. It should be switching from between 0.2 volt to 0.8 volt ish

If the labda is sitting close to 0 all the time then the mixture is lean
If sitting close to 1 all the time it is to rich

Incorrect fuel mixture will stop it from idling correctly.

Also it is a good idea to regularly clean the idle control valve as tehy have a habbit of sticking. You do need a touch more air for tick over with LPG

[volvovic]

You are not the classsic swede you are the SUPERSWEDE! Thank you for your input.
What sealant would you recommend to seal between the plastic that is bridging the manifold and throttlebody to minimize air leaks?
It sounds like the other configuration that I had would have been better suited on this installation as you described on a previous post. Thanks.

[classicswede]

Any kind of universal flexible sealant will do. In teh Uk we have blue heritite that works quite well. If builders silcone mastc will do the job.

[Clifford Pope]

It's not clear from the picture how the pipe from the Idle Air Valve connects to the air intake. Is it at a dual-elbow mixer? It draws pure air when running on petrol, but air/gas mix when on gas.

[volvovic]

Clifford, I think you are correct. Since last post,I have since taken throttle body off, opened the butterfly 1/4 turn more than it should be, and made sure that the new TPS is engaged to switch on without fail when there is any movement in the butterfly. The car is now idling well in both lpg and petrol. Starting is still a little unpredictable when the car has been switched off, then a while latter on when it has been active for a while. When it switches from petrol to gas, the revs can drop close to zero when the gas is activated. If I am lucky, revs will then jump to 1000 and then stabilise to 750.
If unlucky, then I have to turn the key a second or third time. I guess with the system as it is I will live with it. If the postion of the breather is changed to beforethe mixer, will it make a difference or won't the system work like that?
Thank you all again for your time and knowledge!

[classicswede]

Idle pipe need to be between the mixer and thrttle housing. Breather needs to be on the air filter side of the mixer or it will suck oil out of teh engine.

[volvovic]

thanks again

[volvovic]

Best wishes to all forum members.
Thank you for your help and advice. Hope you all have a safe Holiday season and the best of luck in 2010.