[Rewmer]

I am trying to tune up my LPG system on my Thor engined 4.6.I have been having trouble matching the injecter timings when running on gas and then petrol due to the fact that my petrol timings seem to be excessive. Research has led me to believe that the petrol pressure could be down. Now I have the aforementioned Faultmate MSV2 and on the air and fueling page I have a section that says "Tank pressure" my question is this the actual pressure of the fuel rail? If so I should be seeing 50 (psi) should I not ? at the moment it is reading 30.99. Now I know Colin would say look in the help page, but due to what appears to be a clerical error the information for tank pressure relates to something totally unrelated.

Can anyone shed any light?

 

[allyv8]

I think you may be looking at this the wrong way,there is no point in trying to get pulse times the same on petrol as LPG.What you really need to do is to get someone to drive for you on a deserted road so you can note fuel trims on petrol,under certain loads /speeds.(I presume you use the "Modify Carb" page of the lpg software.)then switch to LPG and adjust the settings to match.This means the long term trims stay where they should be and there will be little difference between fuels - so the petrol ecu will stay running closed loop when it wants to and the petrol ecu wont be clogged with faults.

 

[Rewmer]

I here what your saying, but at the moment I think I have an underlying problem with petrol side. Sitting at hot idle on petrol, my injection pulses are in the range of 4.6/4.8 ms which I am told is way out. So my first thoughts are that the petrol pump is on its way out which is giving me poor pressure leading to longer pulses to compensate. I have good MAF readings (compared to figures that yourself supplied Ally a while back - thanks again). No faults are present, and I had a recent TPS and plugs.

I dont want to start fiddling to much with the LPG untill such time I am happy the petrol side is running as it should.

 

[allyv8]

They do sound like a long time for idle pulses,is my memory right in thinking that you have/use a scope ? You could confirm the pulse width with that - might give a better clue as to whats going on.What do the short term trims sit at when its idling on petrol ?

 

[Rewmer]

What do the short term trims sit at when its idling on petrol ?

Short term idle trim is 1.8.

Both my Faultmate and LPG software are reporting the same figures for the pulses, but I will put the scope on to check.

 

[allyv8]

Your Bosch system expresses the trim as a ratio to one - so 1.8 to 1 is quite high.Being as the LPG software and the Faultmate say the same I think thats good enough.I'd look at the rail pressure next - good luck,its a pig to get at the valve.I think its quite a high constant pressure from memory,but I cant remember the figure.Have you got a way of checking the pressure ?

 

[Rewmer]

I remember finding the valve when I fitted the LPG and also remember thinking "what a stupid place to put it, I hope I dont need to get to that in the future". I will beg borrow or make a gauge over the next few days and see what she says. This brings us back nicely to my original question......

Faultmate MSV2 and on the air and fueling page I have a section that says "Tank pressure" my question is this the actual pressure of the fuel rail?

I will still stick my scope on the injectors - just cause I can, and its nice to get a feel for how things operate.

 

[allyv8]

Sorry I didnt answer that before,no is the answer - the pressure reg is with the pump/contents sender in the tank.I the petrol ecu just assumes a constant pressure in the rail and trims the injector pulse width to suit.
If the pump is not delivering the full pressure,I guess the fuel trims further up the rev/load range should be towards the high end of the scale - plus if the oxy sensors stay down at 0v under full throttle conditions you would have more evidence of low fuel pressure.

 

[paul.adshead]

This brings us back nicely to my original question......

Faultmate MSV2 and on the air and fueling page I have a section that says "Tank pressure" my question is this the actual pressure of the fuel rail?

I would suspect it is 'Petrol Tank Pressure' and related to the EVAPS/emissions stuff, so that petrol vapour is not vented straight into the atmosphere.
Maybe.