Vialle LPi issue
 

Please are there anyone with experience with LPi? I have this system in my 940, LPE 4
Problem is occasional (~once per 400miles) hesitation on LPG, I think engine is not running on all cylinders when this is happening and wideband shows me lean mixture, so I think it is probably problem with lpg injection,
when I switch on petrol, it drives normal and when I switch back on lpg after a mile or so, it is running normal again for a while...
What can be bad? The in-tank pump was rebuild about year ago

Very rare system


Have you replaced all the ignition components?

Yes new NGK bpr7es spark plugs (gapped to 0,6mm) and cables, the rest of ignition system are wasted spark components, no problem when driving on petrol...
Oh and I forgot, interesting is it´s worse in winter time when temps are below 10°C

LPi
 

LPi is a Dutch system and very commonly used in Dutch 940s, so much more experience with LPi here in Holland. You could post your question on volvo700vereniging.nl for more reactions.
Overall it is a good system injecting liquid LPG into the inlet manifold. The results is no power loss compared to petrol or even a slight increase as the cold, vapourising LPG has an intercooling effect on the combustion air. The system always starts on petrol and switches over automatically after some time.
In case of any problems with the LPi system, taking out all four fuses will completely shutdown and isolate the LPG system.

Typical problems with LPi are:
1. Petrol injection inhibit relay block
2. In tank fuel pump
3. Leaking LPG injectors
4. Corroded fuse block

1. The system simply uses the signal for the petrol injectors to power the LPG injectors, while inhibiting petrol injection. Petrol injection is inhibited by a relay block, putting a pair of two petrol injectors in series with a 100 Ohm resistor. This relay is known to fail regularly and intermittently, especially the older versions, resulting in a simultanuous injection of LPG and petrol on two of four cylinders. Easy check: if the running problems occur while the engine is running on LPG, disconnect one of the petrol injector connectors. This should not affect the idle speed. If the speed drops and stabilizes again, petrol is injected together with LPG and the relay block is defective.
2. The intank LPG pump boost the LPG pressure to approx. 5 bar. If the pumps starts to get bad, the pressure will be lower at higher flow demands, so the engine will hesitate when accellerating at higher loads. Do you hear the pump running and switch to high speed when the engine (under some load) speed reaches approx. 2000 rpm?
3. A leaking LPG injector will fill slowly fill the inlet manifold with LPG when the engine is not running, causing an increased cranking time before the engine picks up, typically after longer periods of not running (overnight).
4. Originally the four fuses used for the LPi system are rather exposed to the elements, causing the fuses to corrode after a few years, causing different problems. Worth a check as well.

i have exact this problem
"simultanuous injection of LPG and petrol"

but i cant find this relay block on my Volvo 940