I have a 1991 300GE, which was converted to LPG last year, as the local petrol price in Latvia does not quite add up to the local salaries.
The LPG conversion kit used was an atmospheric one with a regulator, i.e., it is connected to the oxygen sensor and throttle position sensor of the KE-Jetronics and is capable of opening the LPG flow a bit wider when you step on the accelerator. A nice thing.
Nevertheless, several things were noticed:
1) the oxygen sensor, while working perfectly on petrol, is veeeery slow to respond on LPG, and actually stalls after a short while. This, beyond doubt, causes the engine to run either rich or clean (depending on which position the LPG controller stalls). Could that be a dying oxygen sensor or what? Why is it good running on petrol and very slow on LPG? I am going to change the oxygen sensor anyway, but want to be sure this could be the problem.
2) While the emissions are perfect on petrol, CO readings on LPG are 2 times the norm (1.2 percent CO is allowed, about 3 is read). If the engine is accelerated, CO goes back to norm. The problem is just when idling.
3) When running on LPG (on petrol everything's fine, though), in idle, there's some blue smoke coming out the exhaust pipe (I suppose this can be correlated with (2)). If I step on the accelerator, the blue smoke is blown out with a puff and the exhaust seems to be fine further on - until the engine is run in idle again for some time. I understand that LPG can show up problems in a more accute way than petrol, so I suspected valve seals. Changing them made basically no difference.
I think these can't be the rings, as the blue smoke comes out just on LPG, and just when running idle.
So, there are 3 problems:
1) the oxygen sensor on LPG is very slow and eventually stalls
2) CO emissions are way too high (on LPG, idle)
3) there's some blue smoke in exhaust (on LPG, idle)
If the engine is accelerated, problems (2) and (3) seem to go away. Unfortunately, CO metering is done on idle.
Has anyone seen such a problem before on the M103 engine?