LPG just died on 940

I drive 1991 Volvo 940 with LPG (existing in the car since new). It reads on the "pump" (is it called the LPG pump?) "specially made for Volvo by Vialle". The system has been modified as I think there are remnants (electronics with some relays) that did not have any use now, cut wires in the engine compartment, then some very strange system for providing good idling rpm on LPG, etc. But the car run PeRfEcT on LPG - literally perfect, making it 8-9 EUR / 100 km in town, for years.Then today, at a traffic light, the rpm stayed high - 1.200 rpm, and did not want to go down. I hate to be in a car with higher rpm, and my first thought was that there was either a mechanical issue with the accelerator cable, although it never happens on 940s and should not happen on this one as it is in good order, or something in connection with that strange idling control system on the main LPG pipe (there is a valve linked to a vacuum controller, but that controller is disconnected from any vacuum system, no pipes present or other parts to which it could be connected, and its lever was fixed in one position with a piece of wire; if it would be moved tiny amount from its good position, idling will become very bad, but it was well fixed and working like that for years). another option was some problem with any of the working vacuum / air pipes - but that would then affect both fuels somehow, I think. Because it was a very busy street, of a highway profile, without possibility to stop immediately and have a look under the hood, I continued to drive (it is few km of such road, and disconnection would mean loss of too much time and I was in a hurry, so I continued). At the next traffic light it was the same higher rpm. In normal driving, everything was fine. I was thinking whether it would be wise to change to petrol or not, but I did change the fuel while standing still on that traffic light (it is a computer controlled LPG, not G3, and the car has electronic petrol injection, so change of fuel is possible at any moment by touching a sensor button). The fuel change went well, I reversed it back to LPG, initially it was ok, normal rpm, but after pressing accelerator pedal, the rpm stayed high again[/b], I did another change, moved forward and made another 2 - 3 changes of fuel while driving, when on the last change from petrol to LPG, motor died, I immediately changed to petrol, everything works, LPG change again, doesn't work. I decided to go immediately to a place where they work with LPG, because it was in a vicinity of where I was, thinking maybe when it is this fresh, they could detect something. (LPG tank is full, filled 30 km before this happened with 67 lit of LPG fuel. I have to say that I was surprised that it took 67 lit, when earlier it would usually accept around 10 lit less when all the LPG will be used, and I was always filling it up in that way, enabling the car to drive on petrol a bit). When I filled it that last time, it started with more than one familiar sound from the back, when after turning the engine on, LPG engages automatically, this time it was 2 times the noise, but the car went on smoothly and I made those 30km after that filling. The problems, in fact started on that day before the filling, when I was expecting the LPG to be fully spent - I was going uphill (20m short steep uphill ramp), the engine went off while the car was not horizontal, which was strange and not expected - so I thought could it be that the engine went off because of very low LPG level - but then - isn't it different than with petrol - I don't know - but I did not bother myself about that, as it started normally after that ''incident'' (and with Volvos 700 and 900 (and 200) series any shaking let alone dying while driving is a big incident as they are extraordinarily reliable); now I think was it an announcement of this problem? Later on, the car behaved like usual when LPG really went out soon that day - it looses power, but still possible to drive it low speed on LPG, this is when I always put it on petrol until filling LPG. The point of this part of the story was that I had a thought - could it be that those 2 times LPG engagement sound immediately after filling the LPG was because it somehow was overfilled (as I know it reads on the pump that it must be filled with 80% of the tank volume, and I always thought my tank is 60 lit - but maybe it is 80); then putting it in context of today, yesterday it was much colder when that filling was made, much below 20 degrees, and today it was extremely hot outside, and inside the car and on that street definitely more than 30 degrees when it died. So question here is: what determines when the lpg tank is full and can the overfill happen and what happens if it is overfilled? Or, can such problems be put in connection with the fact that the tank is simply full, and something not good in the back of the car? That "back sound" when LPG starts does not seem to be that strong as usual, but maybe this is my paranoia. There is that sound now after changing to LPG, and the car dies immediately. Anyway, I stopped by the mechanic, not knowing that the real "LPG professor" is on holidays, and person who offered to help me immediately with some diagnostics, in fact knows about LPG not more than myself. But it was good to try something, and he did some very unskilled checkups of the 2 valves i.e. solenoids in the engine compartment, and also the one in the back, on the tank. he concluded that the one in the tank is working, but for the 2 in the motor compartment he was not sure if they worked or not i.e. he replaced both (there are 2 solenoids, different in size, one before the "LPG pump" and another on the pump) with at least 10 other similar valves, leaving it always as a possibility that none of them was good, as all of them were found among some used parts. So he concluded that he cannot help me. He said he never saw such a system with so many wires and unknown elements (it is not exactly that complicated or messy, and wires are clean and good looking, connectors also. So I went home, and encouraged with such poor performance of a professional, and all that in a workshop which is specialised for LPG cars, I checked both front valves at home in 5 min by connecting the solenoids directly to 12v, and both valves are working well, the noise of moving of the valves is very clear, and I can felt it on my finger if I hold the solenoids. I even unscrewed the one valve on the pump to see how it all looks inside, and was happy to see everything clean and good looking. When I started the engine on petrol, and had my neighbor touch the LPG button to change to LPG, I did not hear or felt anything on either of the valves, so I concluded that both valves do not get 12V to open when the conversion of fuel is made from petrol to LPG, and the engine dies because there is no LPG coming to the pump.I removed the inside panel to see what was once shown to me to be the LPG computer, to check if the connectors are fine. There are 6 connectors; "engine'', ''general", "diagnosis", "switch'', "actuator 2" and ''actuator 1". When ignition is on and sensor (connected to the "switch" connector point on the computer) touched, I can hear the moving of the relay switch inside the computer box, the light on the sensor changes accordingly, so everything looks like working fine. Computer memorises which fuel was on when engine was last time used. The two connectors that read ''engine" and ''general'' - if any of them is removed, motor cannot be started, there is no light on the sensor, "diagnosis" and "actuator 2" are free connectors, and connection or disconnection of the cable on "actuator 1" has no effect on the present situation - the engine now starts immediately on petrol, doesn't work on LPG, with that "actuator 1" connector or without it. What is that "actuator" wire for?There are also 3 separate "hand made'' and added later, not by Volvo factory, fused wires in the engine compartment, I checked all the 3 fuses, they are fine, one of them when removed, will not let the light on the sensor to be lit, computer forgets if the last time it was on LPG if that one is removed (but the engine will start and run on petrol, without the red petrol led if that fuse is disconnected), so all that behaves like it should (I had once the problem of LPG intermittently working, and not working, when at that time, the LPG light would be off - this reminds me of few visits to LPG "specialists" at that time, who could not even detect the existence of that fuse, because it was taped with some other wires... and at the end I found it, cleaned the contacts, and the car made another almost 100.000 km without a single problem, until today. So, I like the car and don't want to discard it (in spite of 400 EUR tax every 3 months...), and I would like to determine where the problem is: but where to go (and not spend hundreds of EUR for "specialist" or specialist work[/b]), is there a place that can utilize that "diagnosis" connector as I assume it is there to be connected to some diagnostics equipment, or use common sense and real knowledge of automotive technics to find out the cause for this? I think that maybe with those changes of fuel while I was driving I might have damaged the computer if the switching was attempted very fast, without letting the car's electronics in that computer to really adjust on the change, on the other hand, I tried afterwards to switch it manually with a bit higher rpm when running on petrol (car standing still), when after changing to LPG engine goes off, immediate touching of the sensor to convert to petrol will make it alive, and so on few times, with no problems, it will always react as ususal, immediate change of light from red to green and vice versa etc etc.I live in Den Haag - can somebody advise what would be the best approach to resolving this malfunction of the LPG? Thanks to those who had nerves to read all this...

Quite a long story! I just skim-read it, and maybe I overlooked, but did you mention anywhere what type of LPG installation you have? Is it the liquid LPG injection system of Vialle (LPi)?
Anyhow, there is no such thing as an overfilled LPG tank. There should be a valve in the filling line which closes once the tank is filled for about 80%. The 20% left is intended for expansion of LPG. If this valve is stuck, you can fill it up further, but this has no adverse affect on any part of the LPG system. The only risc is the overpressure safety valve blowing off when the LPG in the tank expands when it heats up in the sun.
Did the high idling also occur during running on petrol? If so, it is probably not LPG related, but due to a malfunction in the CIS valve (Constant Idling Speed) or the  (setting of the) switch located on the throttle shaft. Cleaning of the CIS valve and throttle housing might also help.
You're in luck; there is plenty of knowledge about LPG systems in the Netherlands available!

Hi Dusan, thats al long time ago! sorry i cant help you with the LPG. My LPG died on me today as wel. Once i switchted  form petrol to LPG it went dead. Finnaly, when i switched when driving 80 km/hour it was ok and i had no more problems. I got a OMVL with a millenium computer..
 
Well, succes and i hope someone here can give you a good tip!
 
Greetings, Rudiger

 
From the description i think it is likely to be a Vialle AMS system, as Volvo used this system as the " Volvo" LPG system off the factory (or dealer). Later did Volvo use Vialle LPi but i think that was from '95 or so. LPi uses 4 additional in the engine bay, you have 3 which supports the guess that it would be AMS. AMS has no pump in the tank. AMS has an evaporator in the engine bay, I'm not so familiar with AMS but i understood that there is an idle speed controller in or near this evaporater with a stepper motor. Maybe cleaning/testing that might be a solution. Another thing to check is the relay that stops the petrol injectors to inject fuel when the engine is running on LPG. Too much fuel, both LPG and petrol, will stop the engine from running. This can happen smoothly, it can feel if you released the gas pedal and the car keeps rolling from its previous speed and weight but no reaction when you press on the pedal. Maybe someone can suggest more good LPG specialists near The Hague? I'm not familiar there.

I drive a 940 from '91 with a Vialle AMS system. Mine gave troubles last year with LPG. The vacum operated valve in the LPG hose (between the evaporator and airinlet) did not work proper anymore. After removal the issue was gone.

pvrakking schreef : I drive a 940 from '91 with a Vialle AMS system. Mine gave troubles last year with LPG. The vacum operated valve in the LPG hose (between the evaporator and airinlet) did not work proper anymore. After removal the issue was gone.

 
Thanks. I learn more about the system now, and also how is it called.
I really do not understand how the system works on my car. That vacuum operated valve in the lpg hose is disabled - disconnected and fixed in one position with a piece of wire, yet the car run perfectly: starting at any outside temperature or motor temperature, changing to LPG automatically and running well, with normal low idling rpm... maybe first minute after cold start was not really nice when it is cold outside, but after that I cannot imagine that a car could work better... until yesterday - and after I posted an advertisement for sale, Murphy's law in its best appearance
With me it is definitely that the evaporator does not get LPG, both valves in the engine compartment are not operated.
There is an excellent Volvo forum in Croatia www.vkh.hr where they advised me to check a relay that is hung on the inner side of the right wing of the car - for which the specialist told me yesterday when I pointed on that, that it has nothing to do with LPG, so I am going to check that further today

henk 940LPT schreef :  
From the description i think it is likely to be a Vialle AMS system, as Volvo used this system as the " Volvo" LPG system off the factory (or dealer). Later did Volvo use Vialle LPi but i think that was from '95 or so. LPi uses 4 additional in the engine bay, you have 3 which supports the guess that it would be AMS. AMS has no pump in the tank. AMS has an evaporator in the engine bay, I'm not so familiar with AMS but i understood that there is an idle speed controller in or near this evaporater with a stepper motor. Maybe cleaning/testing that might be a solution. Another thing to check is the relay that stops the petrol injectors to inject fuel when the engine is running on LPG. Too much fuel, both LPG and petrol, will stop the engine from running. This can happen smoothly, it can feel if you released the gas pedal and the car keeps rolling from its previous speed and weight but no reaction when you press on the pedal. Maybe someone can suggest more good LPG specialists near The Hague? I'm not familiar there.

Thanks I understand better how that system works now, that stepper motor is probably the thing on the evaporator with 4 wires, but the problem with me is that there is no LPG coming inside the evaporator.

rudiger schreef : Hi Dusan, thats al long time ago! sorry i cant help you with the LPG. My LPG died on me today as wel. Once i switchted  form petrol to LPG it went dead. Finnaly, when i switched when driving 80 km/hour it was ok and i had no more problems. I got a OMVL with a millenium computer..
 
Well, succes and i hope someone here can give you a good tip!
 
Greetings, Rudiger

 
Thanks Rudiger. And still shame I cannot write in Dutch after so many years...
Indeed, with help from here and also from Croatian Volvo club, maybe I save it, as going to the workshop(s) seems to be not that successful. Have to find really a good place if I want to have LPG...
what's OMVL and millenium computer?? ... you see how much I know about LPG

pvrakking schreef : I drive a 940 from '91 with a Vialle AMS system. Mine gave troubles last year with LPG. The vacum operated valve in the LPG hose (between the evaporator and airinlet) did not work proper anymore. After removal the issue was gone.

 
It works fine again, but I installed separate switch for the 2 LPG electromagnetic valves as I could not detect a problem with the electrical installation in terms of bad fuse or no ground somewhere.
Another LPG "specialist" did not want to take the car for work as they do not have experience with this system, let alone parts, so it was either driving it to the junkyard, or trying this, which I did out of curiosity.
There is a metal box attached to the car below the evaporator, and there was a sticker next to it, unfortunately, everything except the letters LPG is washed out from the sticker. Inside that box there are 2 relays and some electronics. I assume this was responsible to switch the LPG valves on. It has no effect on running the engine - if the ground wire is removed (and it is soldered to the circuit board inside that box, the box itself has no contact with its parts), nothing changes. I am tempted to cut it completely (it has 5-6 wires entering inside).
I'd really like to learn what exactly happens when the system was complete and fuel changed, but there is no detailed scheme on the Internet.
The best I found was this: <a href=" www.expert-gas.ru/index.php?page=61 "> www.expert-gas.ru/index.php?page=61
The vacuum operated valve was already disabled and fixed in one position. There is still occasional high rpm after decceleration: changing to petrol puts the rpm down (and it is never high rpm on petrol), but then again after accelerating engine, it stays high, sometimes going down after 2-3 sec. I cleaned the Idle Control Valve i.e. sprayed WD40 inside, it is not stuck but whether it really works I don't know. Connecting it and disconnecting shows no or very little change to the speed of the engine...maybe idling a bit better on petrol.
Sometimes I have lambda sond light on, then sometimes off after few minutes - should it not stay on once it is lit until disconnecting the battery, regardless of the signals given by the lambda sond? I still think it is something wrong with the computer or its connector. But the car runs perfect on LPG, and starts perfect.
There is also no audible effect if I disconnect the Throttle Position Sensor. But I did not drive without it. It is fairly clean iside the throttle body, I sprayed it also with WD, and the main hose into the intake manifold is not damaged... One original pipe connection, just next to the throttle body, on that main plastic intake pipe is closed. The fuel pressure regulator is also connected to something below the LPG evaporator, into which I think originally  a vacuum pipe led out towards an electromagnetic vacuum valve, which was then originally connected to that vacuum operated valve on the LPG hose. But that was already all out of function.... I sprayed all the connections of pipes and hoses and around injectors while engine is running, expecing that if there is a problem, it will affect the work of the engine, or I possibly see an air or vacuum leakage, but nothing could be seen.

Hi,

I more or less have the same issues, high idle and a lambda lamp that goes on and off.
One of the thing I noticed it that the high idle speed only occurs on LPG, not on petrol. This leaves me to believe the idle valve is not dirty, but it gets a wrong signal.
Strange thing is also when the car is rolling the idle speed is around 2000 rpm. It dropt to 600 rpm when the car completly to a halt (eg infront of a traffic light), so I have the feeling there is a connection between the speed and controlbox towards the idle valve. Btw this issue is only on LPG, not on petrol.
Since I could not find the issue, I went to a friend with lots of knowledge and parts and we decided to block out possible issues. Together we have made the LPG inlet "original" since I have just a LPG mixing ring somewhere in the middle of the inlet hose. Now I have a mixing ring attachted to the airinlet on the engine and a new hose, so I do not have the issue of air leakage.

Next step was the exchange of the air mass meter and the issue was gone. A funny extra was that the electronically controller valve on the vapourator (Actuator) now also suddenly worked and my CO went from 6% to 0.5%.
Hope this helps.

Btw the lambda light still goes on and off, with code 2-1-2. It seems the light is also controlled by speedbumps, so I guess a wire is broken or makes a unplanned connection somewhere. Anyway the car does not run worse if the light goes on.