Why is Single Point Vapour LPG on D2 a bad idea???

[GunMetalRover]

Ok I have googled the **** out of this and the consensus is....don`t do it because it will backfire and blah blah blah. Most of the comments refer to the motronic engine management which causes the problems.
Bee utey, maybe you can shed some light.

Can the old vapour style single point injection work properly on a D2?

I am a proud owner of a `99 model D2 with the old style lpg. I have a very small backfire during overrun mostly and light throttle. Just changing gaskets in the exhaust and checking for leaks atm.

There is no check engine light on so where do I go from here?

Just answer my questions please without making wise cracks about how much better sequential injection gas systems are.

Thanks very much

[Mick_Marsh]

I knew a fellow who had that setup on a Ford EFI motor. It backfired one too many times often which assisted his mechanic in putting the mechanics kids through private school.
It blew all the plastic bits on the air intake apart, often.

[bee utey]

Can the old vapour style single point injection work properly on a D2?

Yes. keep the plug gaps at 0.6mm/0.024". Don't bundle the ignition leads, use separators. Don't leap on the loud pedal, use moderation. Fit a metal air cleaner housing. If the ignition coils die, find good original ones, not chinese cheapies.



I am a proud owner of a `99 model D2 with the old style lpg. I have a very small backfire during overrun mostly and light throttle. Just changing gaskets in the exhaust and checking for leaks atm.

Dunno, it's unlikely to damage anything IMHO. Get under the vehicle with the engine running, when its still cold, look for leaks with a strip of paper held in long nose pliers. Wave the strip past all joints, welds etc.



There is no check engine light on so where do I go from here?

It takes a lot to get a check light up on an early D2. I've not managed with major injector or mixture faults. The engine has to be falling out, I believe.



Just answer my questions please without making wise cracks about how much better sequential injection gas systems are.

Why not? They are.



Thanks very much

You're welcome.

[ozscott]

Following plug gaps as recommended by beeuty my land Reno that is now 5 years old works well. Lambda controlled main valve and idle. Cheers

[TDman]

There are things that you can do for back-firing that the automotive types don't generally bother with:

Flash back arrestor, All commercial gas-trains on burners have them (just a fine steel or S/S gauze)
Explosion cover, (I have herd of people using bath plugs on a string as they pop out and then can just be put back in:p) You could make a section with a spring loaded flap that seals when closed but can vent excess pressure and then spring closed to seal the air intake again.
This assumes that you will at some point have a back-fire but will prevent it being the end of the air intake!
Food for thought anyway.

TD

[bee utey]

There are things that you can do for back-firing that the automotive types don't generally bother with:

Flash back arrestor, All commercial gas-trains on burners have them (just a fine steel or S/S gauze)
Explosion cover, (I have herd of people using bath plugs on a string as they pop out and then can just be put back in:p) You could make a section with a spring loaded flap that seals when closed but can vent excess pressure and then spring closed to seal the air intake again.
This assumes that you will at some point have a back-fire but will prevent it being the end of the air intake!
Food for thought anyway.

TD

All of that, but I tend to use these:

http://www.aulro.com/afvb/attachment.php?attachmentid=40722&stc=1&d=1320910381

Inline backfire flaps, used downstream of the mixer, but have an effect on maximum gas flow. They are relatively reliable at sealing dust. Spring loaded flaps and plugs are a good recipie for dust ingestion, they are rarely made with any degree of skill (or they fall out, or the rubber goes hard and doesn't seal!).

Fine stainless steel mesh (like fitted to MAF's) tends to end up torn out and spat into the air cleaner housing.

[PhilipA]

I do not know anything about gas , but just observe that the inlet manifold to vapour injector volume of a Thor manifold is much larger than a 14CUX inlet manifold volume, and the distance is much greater from the cylinder to throttle body.( over 1 metre)

IMHO this would tend to make any bang originating at a cylinder much bigger and potentially more damaging than with a smaller volume explosion as in a D1.
It would be pretty spectacular.
Regards Philip A

[Blknight.aus]

yes, it can be done but as with all things its a compromise.

any backfiring is bad as the pressure spikes will make short work of all the one way valves and sensors on the manifold as well as all of the gaskets, joints and the ABS plastic bits.


take it to a gas workshop whose work is generally reputed as being "fornicationing Great, Pricey but worth it" where the guy doing the work looks like hes been in the business since before Watts re-invented the steam engine and can quote optimal stoic ratios for varying pressure densities in the same way (and rate) that a politician can break promises. (which is intended to mean: easily, often and at the drop of a hat.)

[bee utey]

I do not know anything about gas , but just observe that the inlet manifold to vapour injector volume of a Thor manifold is much larger than a 14CUX inlet manifold volume, and the distance is much greater from the cylinder to throttle body.( over 1 metre)

IMHO this would tend to make any bang originating at a cylinder much bigger and potentially more damaging than with a smaller volume explosion as in a D1.
It would be pretty spectacular.
Regards Philip A

This is quite correct, the Thor's explode much louder when they do. However they seem to be able to cope so long as the intake hose and air cleaner can are of stronger materials.


yes, it can be done but as with all things its a compromise.

any backfiring is bad as the pressure spikes will make short work of all the one way valves and sensors on the manifold as well as all of the gaskets, joints and the ABS plastic bits.


I saw one that had failed coils and would backfire each and every time you applied any amount of throttle, so it had taken dozens of hits. Apart from the air cleaner and hose, everything still worked as it should, and it ran perfectly on both fuels after the coils and air cleaner were replaced.

Not everybody can afford to use gas injection so proper care in use and tuning is essential with single point systems.

It is possible to have backfires even with injection but because of the small volumes of combustible gas/air mixture right in the port the potential for damage is slight.

[Blknight.aus]

I saw one that had failed coils and would backfire each and every time you applied any amount of throttle, so it had taken dozens of hits. Apart from the air cleaner and hose, everything still worked as it should, and it ran perfectly on both fuels after the coils and air cleaner were replaced.

Not everybody can afford to use gas injection so proper care in use and tuning is essential with single point systems.



yep, sometimes they go forever without damaging anything, others backfire once and then you have to rework half the intake, fortunately it generally tends to not take out too much other than the hoseclamps and push on fittings.


and..

hence taking it to the guy with all the good experience.

[TDman]

My understanding is that sequential injection is that best way, but, you can make the other systems work and they are a lot cheaper.
The installer I dealt with said that to get rid of the back firing issue you need to have good plugs, leads and dizzy (if you have one) . In short, if it's all ok it won't jump and cause a backfire.
He seems to know his stuff and has a RR sport on a Prins system for what it's worth.

TD