Having Troubles Restarting On Petrol - Edit: Won't Start Now!

[cybernck 402 1 Cars]

The car has been fitted with a crude LPG system - mostly being started on petrol and then running on LPG.

Trying to run it on petrol non-stop (as it is supposed to ) has made a restarting problem obvious.

 

Basically, if it's run on LPG, it will restart fine on petrol (and on LPG too, providing there's enough gas left in

the manifold). However, if it's run on petrol, then it takes a lot of cranking to eventually get it started up again.

 

The behavior described is related to trying to start it when it's hot. Haven't tried it when cold.

 

The only thing I can think of is that the LPG system's controller leaves the injectors open when the engine is run on petrol

and then shut off therefore flooding it, as a duff ignition amp or something like that wouldn't care for type of fuel used.

 

By the way, it's a late 1.9 GTI, but the engine seems to have been swapped for a BX DFZ Motronic engine in the past.

 

Thanks.

[dobbo26 2]

Hi does it run ok on petrol after you have got it to start? eg power wise running on all four etc. done a few cars that run lpg and the fuel lines get blocked up because they are only ever started on petrol the put straight to gas.

[cybernck 402 1 Cars]

Alright, I tried starting it up when cold today and yesterday. It took a little bit of cranking

but started up. Much better than the situation after being driven. It seems to be chucking

some blue smoke on start up (probably stem seals or might be something valves-related).

 

What got me a little bit worried is that it stinks of unburnt fuel, so it must be overfueling,

which would explain the problem with starting. I didn't drive it as the registration run out

a couple of days ago, but it didn't seem to jerk or bog down when I had driven it on Saturday

(on petrol, easy city driving).

 

I am planning on taking off the LPG system soon and then troubleshooting it more closely.

 

P.S. How much does a litre of LPG cost in the UK and is it easily obtainable on petrol stations?

 

Thanks, Nikica.

[dobbo26 2]

would be worth checking fuel pressure etc. has it done alot of miles on gas? the few i have seen seem to burn the valves after about 50k

[Anthony 1,003]

P.S. How much does a litre of LPG cost in the UK and is it easily obtainable on petrol stations?

Generally around 70-80p a litre at the moment from what I've seen, although I no longer have an LPG car so I don't pay as close attention as I used to. It's fairly easy to get, but petrol stations that sell it are in the minority still, especially away from the motorway / trunk road services.

[cybernck 402 1 Cars]

The engine's top end sounds pretty loud but I think a part of the noise is coming from the exhaust manifold.

 

There's definitely some valve clapping going on and I think it's been running on LPG for several years, so we might be on the right track.

 

Would that cause the issue that seems like overfueling though? And would it show up on compression testing?

 

I've an idea to fit 1.6 injectors - that would effectively downsize the injection map, wouldn't it?

[dobbo26 2]

you will probably find its running lean. would be worth doing a cylinder leakage test first and check the valve clearances. hope this helps.

[cybernck 402 1 Cars]

An update.

 

We've taken the LPG system off today and the engine won't start up anymore.

 

Basically, there was a fused positive lead going from the coil to the LPG controller and an additional relay that

used to power up the injectors and switch them off when LPG was switched on. The trouble is, this was hacked

into the wiring and, with the relay thrown out, has left a mess, see below:

 

 

 

 

It was getting dark and I need to refresh my memory of wiring anyway, so I'll look into it tomorrow,

but that section should just have wires passing though, without any interconnections, if I'm not mistaken?

 

Any ideas welcome!

 

 

P.S. Nuts on the exhaust manifold seem to be improperly tightened and/or damaged, so it's possible that

the exhaust manifold gasket has gone, contributing towards the noise.

[cybernck 402 1 Cars]

I've found all the injector wires now, but having trouble determining what are the two whites for

(one is thicker and one is normal, no numbers printed), as well as the green one, that actually

splits to two orange wires than end up in an unused (?) plug near the AFM.

[cybernck 402 1 Cars]

OK, got it all sorted out and running. Still don't know what the plug near the AFM for though.

 

Now I have to see what it will run like without LPG on.