Problem at 3/4 of deposit
 

Good afternoon,
I am Julio B. Leis from Bilbao in northern Spain.
I have a small collection of Volvos including the classic coupes models. P1800, AMAZON, 262C, 780.
Every day I drive a V70 bifuel from 2005, which I bought second-hand with 340,000km in Germany.
The car was very well maintained but I had problems in the gas system (green necam) I have been solving them thanks to its magnificent teachings related in this forum. I have changed the regulator that had leaks in the membranes, I have changed spark plugs and coils, I have cleaned the throttle butterfly and the car is going really well. But a few weeks ago a problem appeared.
When the gas tank reaches the area between 3/4 and 1/2 the car cuts off the ignition and stops without automatically switching to petrol. When I start it, the starter turns a lot because there is gas in the combustion chambers. The car starts in petrol mode and stops again when the gas is connected. I have tried several times, accelerating the engine or switching to driving gas mode over 100Km / h and it stops. The next day when the engine is started, the gas is switched on automatically and no longer gives any problem until all the gas in the tank is spent. This situation has been repeated in the last three gas refueling. Always between 3/4 and 1/2 deposit.
I think it is a problem related to the tank opening valve that sends some signal that causes the ignition to be cut.
Thanking your interest I ask for advice on this problem.
Kind Regards
Julio

YOu don't say what car you own. Not seen this one, but I have heard of the solenoids going faulty on one CNG tank. This will cause this. You can usually find any solenoid of same internal diameter to fit.

In Finland they have solenoid kit, http://www.cnghouse.fi/tuote/55015_volvo-pullohana/ if its really the case. This is for the biggest tank, you might need other 2 for smaller ones, or no.
Now just brainstorming here, but idea that you have 3 tanks, 1 big, and 2 smalls. Not exactly sure how they works, but if its the case that one opens only after other one is completely empty, then my guess is that the problem with opening valves of 2 tanks :?