LPG 1 - Conversion
Using this example of a sequential gas fuel injection system, we'll be looking at the difficulties that can be encountered during the change-over. In this case, sequential means that with each injector-valve, the
beginning and duration are determined by a separate control device. Through a BUS-connection to the original engine management, it's advantages are maintained, and it can be used for the gas injection. Of course
the diagnosis through the fault recorder and the reference- and actual value comparison of the measurement values also takes place here.
The fact is, that with gas injection, the starting is still done with petrol, indeed, in less than one minute and above a certain engine temperature, even automatically. With new vehicles, the converters even stipulate a
running-in phase using petrol. However, don't even think about using the petrol, which you filled up in summer, in the following winter.
Let's turn to the installation. On the dash board, a selector switch for activation/display of the gas equipment must be present. The remaining fuel-amount shown on the display is less reliable than the standard fuel
gauge. At least however, the equipment does switch over automatically if the gas tank is empty, and of course, also informs the driver. There is also the opposite case: Switching over to petrol, e.g., when a defect in the
gas section is detected. By the way, the installation of this type of display, cannot as a rule, be reversed, the result would be a hole in the dash board.
The control device needs it's own protected niche, best of all in the car interior. The gas equipment has an evaporator, which is rather large and has special requirements: a vertical installation and a lower location
than certain cooling system components. This is an important reason, why the equipment can not be cold-started. By the way, the connection with our modern cooling systems might pose an increasing problem,
because the gas equipment needs a coolant that warms up as quickly as possible. What can be done, if there is no thermostat, and thus, no small cooling-circulation system exists?
One doesn't think of it straight away, but subsequently installed parts can also cause noises. This should be considered during the installation. When choosing the components, the performance efficiency of the
engine also plays a part. The gas-volume distributor is something like the distributor pipe, or the rail, with it's accompanying electrical system. The additional gas-temperature sensor distinguishes it from the injector-
valve or injector. Then, near the engine intake valves, only small injectors are necessary, however, a certain amount of technical talent (drilling, thread cutting) and some assembly work is necessary when
dismounting/mounting the metal inlet-manifold.
As simply built up as some modern, system pressure regulators for petrol injection are, this is not valid for LPG. In this case, it is measured by a suitable MAP-sensor and then evaluated electronically. Bit by bit, a
second wiring harness is developed. Sometimes it still does access one of the available lambda sensors. In this case, the pin assignment from the respective manufacturer must be exactly followed. The electric
control to the petrol injectors is cut-off and connected with the gas equipment. This actually sounds quite simple because, almost everything is mass-clocked. Therefore, it is a matter of searching, in each case for the
negative pole. It is astonishing that here, the allocation to the individual gas valves is important. Can the equipment also be run half on gas?
The installation of the gas tank probably causes rather a mechanical problem and perhaps, some discussion with the user, whereby, the laying of the piping can provide even more brainwork. By the way, the LPG also
needs a filter, in fact, one with even substantially shorter change intervals. Apart from that, you should, perhaps, also not change it yourself. Electrically seen, it is once again interesting, to calibrate the various tank
transducers in such a way, that a fairly exact prediction of how much gas is still in the tank, can be made. However, this is only a small part of the extensive work which, in the end, is to be done on the PC. Experienced
equipment builders are able to dig into the depths of the mixture ad measurement for individual areas, but please, only those should also do this. 10/09