LPG issues

[85_Calais]

Hi everyone,

I took my car (1985 VK Calais 3.3L EFI) in to have its LPG system looked at yesterday as it has been running rough for the last one or two weeks (This roughly corresponds with when I changed the rotor button as I have been trying to overcome a "backfiring" problem. The distributor cap was also changed not long before that).

My injectors had been blocked for quite a while and it has been something that I have been meaning to get fixed. I finally bit the bullet and got them cleaned out today because the gas mechanic told me that my LPG system is fine, but my ignition system had problems and it would be best if the EFI mechanic looked at it when I get my injectors cleaned out.

My car now runs perfect on petrol, but still runs rough (and frequently stalls) on LPG. The EFI mechanic says that my ignition system is fine, but that the car was running "a little lean" on gas.

So now I'm really not sure whether there is a problem with my ignition system or my gas mixture, and I really don't want to go back to a mechanic a third time. To test this out, (and I know I really need specialist equipment), but can anyone tell me how to make my car run "richer" on gas, just so I can get an idea of what the actual problem is?

[VN_Luke]

do you have any more info on what kind of gas system it is? or pictures of the setup? - there's a few various kinds of setups that are all tuned a bit differently.

LPG is generally a LOT more straining on the ignition system. - where a problem like a slightly dodgy coil might go un-noticed on petrol, LPG will find it promptly. (BANG )

Perfect plugs, dizzy contacts, cap, coil, leads go a long way.

What spark plug gap are you running?

[db_notso]

if car runs great on petrol and crap on lpg then fault is in your lpg system for sure not ignition (by great i mean no misfire under load etc)
this is where it gets tricky, to check for gas leaks on an lpg is dangerous but IF U HAVE TO DO IT a small amount of washing up detergent and water in a spray bottle and start squirting with car running (on gas) im guessing around where you worked on the car just before it started playing up... when you spray it on a leak it will blow bubbles and theres your leak (my educated guess fyi)

a leaking or pinholed lpg pipe will cause car to run "a little lean" and stall at idle especially an auto in drive

if you find a leak you should turen off your gas at the tank and take it to a professional to repair and show him where its leaking (you think)

oh and vn_luke you are correct lpg is actually a higher octane fuel and burns/combusts differentlyso very worn plugs could cause a fault but genereally if not missing under load on petorl should idle on gas.

[85_Calais]

do you have any more info on what kind of gas system it is? or pictures of the setup? - there's a few various kinds of setups that are all tuned a bit differently.

LPG is generally a LOT more straining on the ignition system. - where a problem like a slightly dodgy coil might go un-noticed on petrol, LPG will find it promptly. (BANG )

Perfect plugs, dizzy contacts, cap, coil, leads go a long way.

What spark plug gap are you running?

It's a sprint gas system (ring / mixer type). The spark plugs are NGK 15s but adjusted to a 14 gap.

[db_notso]

fixed it? or you still having dramas?

[85_Calais]

Nah still not fixed yet. I replaced the coil but experienced only a marginal improvement.

It's going back to the gas mechanic for another look tomorrow.

[db_notso]

okay just explain to him NICELY so he gives a rats ass that it only happens on lpg then hopefully he will get more in depth with it
good luck matie!~

[85_Calais]

Sorted - cracked ignition lead. Replaced it and it ran fine. He showed me how to check for this in the future and didn't charge me anything. Awesome

[db_notso]

wow nice guy to have!~ dont suppose you could elaborate?
cracked lead? as in the sheath over the wire or broken core of wire?

[85_Calais]

It was just a crack in the sheath of the lead. The crack was really tiny. But when he did what you said with the water and detergent, the effect it was having became really obvious.