2002 S60 Won't switch to LPG

[nige0568]

The light is constantly flashing, it goes to permanently on when I press the switch to indicate petrol, when I disconnected battery before and reconnected I started the engine with light flashing, should I start with light on then press the button for lpg, I just guessed the ecu was on bulkhead I haven't actually looked

[nige0568]

I've just tried "Reggit's" method of disconnecting the battery then when reconnected, start the car with the light on the switch permanently on then once the engine is started press the button for gas, it now switches and runs on gas faultlessly. Could it really be just the method of re starting the gas system that was my problem?

[Lpgc]

Common fault: When you first switch to gas the LPG system works, then stops working and the light starts flashing. Sometimes after that's happened the system won't switch to LPG at all, but disconnect the battery for a while and the LPG system works again at least for a while...

Your petrol injection system has a factory programmed 'map' that tells it how much fuel to inject at a wide range of rpm's and loads... Imagine a spreadsheet with rpm going across and load going down, all the numbers in the boxes tell the system how much fuel to inject at that particular rpm/load point. The petrol system also stores 'fuel trim' information in a separate spreadsheet style grid, each fuel box grid covers a grouped range of boxes on the map grid. Fuel trims are not factory programmed, they are stored as your injection system learns to fuel your engine. Fuel trims add or subtract a % from the numbers they relate to in the map. If any fuel trim goes outside a certain range (maybe down to -25% and up to +25%) then the engine warning light will come on but the vehicle will still drive on petrol in 'limp home mode'.

Most LPG systems work as a slave to the petrol system, they don't have their own map or fuel trims, due to the slave nature they don't need them, they rely on the petrol fuel system fuel trims.

The factory fitted systems do not work as a slave to the petrol system, they work as a standalone fuel system (but use the petrol system's ignition system) so they have their own pre-programmed map and store their own fuel trims. Just like the petrol system, if a factory LPG system fuel trim goes outside a certain range it will switch the LPG system to 'limp home mode'. Limp home mode for a factory LPG system is to disable the LPG system (you've noted the switch flashing and inability to run on LPG - this is the LPG system's way of saying it has detected a fault), and means the vehicle will only run on petrol (to prevent an incorrect mixture running on LPG damaging the engine)! Disconnecting the battery clears a factory LPG system's fuel trims and clears the limp home mode...

So far the fuel trims that I have mentioned have been the 'slow fuel trims', these are stored in the ECU memory and are learned slowly over time. But there is a 'Fast fuel trim' that is not stored but works on a moment to moment basis. The Fast fuel trim will again only go within a range of about -25% to +25% before an error is stored (and the vehicle won't run on LPG)... The system cuts back to petrol with the light flashing... Factory systems allow about 5 seconds for the fast fuel trims to adjust to allow the fuel mixture to become correct (according to the lambda probe in the exhaust) before going into error mode.

The actual fuelling the engine gets is based on the factory programmed map, plus the (stored) slow fuel trim, plus the fast fuel trim. The memorised slow fuel trims are slowly adjusted according to the fast fuel trim, so if you have a slow fuel trim of +10% and the fast fuel stays at -5%, then the slow fuel trim will slowly be steered towards +5%.

Sometimes, simply disconnecting the battery on a vehicle with a perfectly working factory fit LPG system can cause the LPG system to go into error mode when the vehicle is next run on LPG. This is because all the LPG system long term trims are forgotten and the short term trims have to move much further to get the mixture to be correct.. because the short term trim has to move further it can take longer than 5 seconds and go into error mode.

When a factory system goes into error mode due to fuel trim issues (which as said can happen after the battery has been disconnected) there are two ways to approach a fix. Either drive the vehicle in a way that allows the short term trims to steer the long term trims, but avoid staying in the range of one long term trim (at least while the mixture is incorrect) for more than 5 seconds... Or, adjust the pressure on the reducer to allow the short term trims to adjust the mixture to correct within 5 seconds. The second method is preferable, but usually a fix will involve a bit of both methods... Because the system has more than one trim, it is possible to set a pressure that allows idling or driving at some rpm/load combinations but not others. A pressure gauge is good for setting the pressure within a ball park range, this method would probably work every time with a new engine and new factory LPG system, but as parts wear etc any method (even using a gauge) will probably still involve some setting up while driving. I have a gauge but never use it for setting systems up!

All the above assumes the Vovo factory fit system is the usual Nikon Koltec system. I believe some Volvo's have other types of factory fit system such as Landirenzo IG or Tartarini Etagas. At least with the Koltec system you get a warning that all is not well with the mixture. The other factory systems will continue to run on LPG even with a very incorrect mixture and this can damage the engine valves or catalytic converter!

All the above also assumes the LPG system is in good working order and simply requires adjustment. Factory systems are not very good, parts are expensive and faults are common. Mechanics that are not knowledgeable on how factory fitted LPG systems work (and this includes most LPG installers) often assume they can diagnose faults and check fuel mixture over the vehicle OBD port - This is incorrect, most factory systems send emulated (fake) mixture readings etc to the petrol ECU to prevent the petrol system picking fault with the fuel mixture while the vehicle is running on LPG. LPG system problems are seldom diagnosable using the petrol systems OBD port (the OBD port is for the petrol ECU not the LPG ECU).

Faults that can affect fueling with a system that apparently work OK at times, without causing misfires, but sometimes cut back to petrol and refuse to switch back to LPG can include a range of internal reducer parts, worn injectors, worn fuel distribution unit (that includes the stepper motor part). Reducer rebuild kits are relatively cheap but they only include the rubber parts that go in the reducer. Reducers also contain jets, etc, which can become worn and, where this is the case, a rebuild kit will not fix a worn reducer.. A rebuilt reducer is not a new reducer! Koltec reducers are not the easiest to rebuild either... Since factory LPG system components are so expensive it can often be a much better idea to replace a factory fitted system with an aftermarket system. A factory reducer might be £400, a set of factory injectors might be £350 (and you might be sent the wrong spec injectors), a factory fuel distribution unit might cost £200 (and again you might be sent the wrong spec unit - there are many different models!). You might fix the factory system one day and the next day another component might break, need diagnosing and need replacing. When you can buy a new aftermarket kit for a 5 cylinder engine for £500 with warranty on all the components, or have one supplied and professionally fitted for not much more, with a warranty on the whole LPG system, it is doubtful whether it is worth fixing a factory fit system if it needs any parts at all....

Simon
www.Lpgc.co.uk

[nige0568]

Hi Simon, thank you for your very in depth reply, you are clearly a very knowledgeable guy when it comes to lpg, ecu, fuel trims etc, I'll keep my fingers crossed now hoping that the system continues to work, if it fails then I will probably look at getting the front end of the lpg system replaced with a more modern user friendly aftermarket system

[nige0568]

It's just done it again, Saturday it was completely fine switching and running on LPG no problem, Sunday morning it refused to switch to LPG again, I haven't had chance to look at it yet as I've just come out of hospital today after having surgery on my back. A few weeks ago I had the engine light on, ran an OBD2 diagnostic and it highlighted a failed heating system on the post cat Lambda sensor so I changed it for a known working second hand one but not specifically for an LPG vehicle only a 2.4 non turbo, now the EML light is off but could it be this sensor that is sending signals to the ECU that is affecting the LPG system?

[nige0568]

Right, I've now pin pointed the problem to be the tank solenoid valve sticking, the coil energizes but sometimes the plunger inside the valve sticks, I think the ecu recognises reduced pressure because the gas isn't flowing from the tank and puts it into limp mode I.e off, I put a 12v supply across the solenoid initially nothing then after a short time I hear the solenoid clicking, I reset the ecu by disconnecting battery and it switches and runs on gas again, question is can the valve be stripped and cleaned?