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PostPosted: Sat Oct 15, 2016 7:46 pm 
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Joined: Sun Nov 13, 2011 2:35 pm
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I wonder if anyone can suggest a solution for me, I have a Saab 9-5 Aero which has been converted for around 7 years and runs sweetly on LPG or petrol. However, recently it will not change over to gas, and acts as if the gas has run out i.e. alarm beep then flashing green light. If i press the switch to petrol, then back to gas again it usually won't kick back into gas again, but if i leave it a while then repeat the process it sometimes goes back on to gas after several attempts, but sometimes not. The problem seems to be random, though at various times i have convinced myself it has something to do with holding the engine under load while i switch it over, which then proves completely ineffective the next time! It has been doing this for a couple of months now, and once it is fully warmed up on a long journey, it can sometimes run on gas for many miles without a problem, sometimes it has done 90-100 miles, then just as i convince myself it has righted itself, off it goes again and won't change over!
I have had a mobile LPG specialist look at it, and he was very helpful, giving the system a service while trying a few things, we changed the front solenoid because my old one was cracked, then after driving it whilst connected to the diagnostics, it appeared the pressure was dropping and rising, so i ordered a MAP sensor (ESGI) from Germany but when i tried it, it is exactly the same! So, if the pressure really is fluctuating, what might cause this? I know the rear solenoid is operating OK, I have occasionally caught a whiff of LPG smell, but no different from normal, the injectors are relatively new, i think the vaporiser is the original, the switch sometimes won't respond to the press of the button i.e won't come off gas setting (even though it isn't actually working, the green lights stay on and can't be cancelled, but leave it a few minutes and try again and it works again! I do know that each time the gas tries to cut in, the solenoid is operating OK, but the pressure seems to be inadequate, or the MAP sensor thinks it is, and that is why it seems to kick the system out like it has just run out of gas!
Sorry if this seems long-winded, i just wanted to mention some of the things i've tried in order to give an idea what i'm up against, it is one of those annoying problems that will probably right itself if i take it to be looked at!
Thanks for reading and hope someone can suggest something i can try?


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PostPosted: Sat Oct 15, 2016 7:53 pm 
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Joined: Mon Jan 23, 2012 12:21 pm
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Location: Milton Keynes
You mention that you've swapped the solenoid coil - have you checked the plunger is working (they sometimes gum up and get stuck - the front one should be fairly straightforward to remove and check/clean up, the tank one will depend on the tank - if you have a shutoff for it then it should be ok, usually the case with a single hole tank, a 4 hole usually not - in which case you want to empty it first if at all possible (run on it till you think its as empty as your going to get first). When you say the rear solenoid is ok do you hear it click/clunk when the switch is pressed - if so then what happens on the front one - if theres no click (you may be able to use a piece of small pipe to listen to it - put one end on the solenoid other at your ear) then its some sort of issue with it - either the coil doesn't work (unlikely since its been swapped) its gummed up or the wiring to it isn't providing enough current.


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PostPosted: Sat Oct 15, 2016 8:46 pm 
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Joined: Sun Nov 13, 2011 2:35 pm
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Hi, thanks of the reply, i definitely hear the rear solenoid kick in every time, and the LPG expert was aware of the gumming up issue, i think he eliminated that, I has a similar problem to this a few years back and it was the MAP sensor, which was thought to be the most likely this time, but after having to send off for it i have since changed it and it made no difference! Is this indicative that the dropping of pressure is really happening, or is it possible it is receiving false readings from something other than the MAP sensor, and if so, any ideas?


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PostPosted: Sun Oct 16, 2016 3:00 pm 
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Joined: Mon Jan 23, 2012 12:21 pm
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Location: Milton Keynes
If the pressure is erattic it could well be that the vapouriser is having problems - I see your original post also says you sometimes smell lpg - this might be part of your problem. It wouldn't be a bad idea to start trying to locate where the lpg is coming from if possible - I'd guess you've already had a try at doing so and not managed to do so. A minor leak is unlikely to cause the failure to switch in itself, but could be indicating the vapouriser isn't performing as it should, so start with either soapy water over it or leak detector spray and see if its leaking (you should see bubbles if so). If nothing visible check the pipes (output from the vapouriser to injectors) are all done up correctly.

I don't know what vapouriser you've got fitted (it could be pretty much anything, you will need to look) but if it has a vacuum line it can be worth pulling that off and checking if there is any gas leaking from there - this is a sure sign the vapouriser needs attention, though they can fail in other ways. This could account for both the smell and erratic pressure though.
Do you know which pressure he was looking at (manifold or gas? - some systems have both sensors combined into the same unit, don't know on ESGI if this is the case, but someone will be able to confirm). Or if you have the diagnostic lead yourself what pressure it shows? (if your not sure then some screenshots may help).


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PostPosted: Mon Oct 17, 2016 1:54 pm 
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Joined: Wed Sep 29, 2010 5:01 pm
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Location: Yorkshire
Agreed with all Brian's points.

1. Dodgy reducer or injectors could sometimes leak gas (in case of reducer often out of the vacuum port) into the engine, could account for whiff of gas especially if this occurs with engine off after attempting to run on gas. ESGI software allows changing setting for length of time between solenoids opening and switching of cylinders to LPG - issue could drain all gas pressure to injectors, then without enough time between solenoids opening and cylinders switching to LPG pressure may not build enough for when it switches cylinders to LPG. Unlikely though, unless the problem was very severe (big leak, usually consistent) would expect pressure to be there for repeat attempts.

2. ESGI ECU's have a weak relay that sends power to solenoids, more prone to failure than similar in most ECUs, but this won't be the problem if you're sure the tank solenoid always works. If tank solenoid always works, as Brian said have another look at the reducer solenoid. An intermittent near short circuit on one solenoid coil could prevent both solenoids from working, or only one, or lead to other problems as in below (4).

3. Few different types of ESGi pressure sensors, presuming the ECU is metal bodied (other type was plastic known as ESGI Black, they are different systems and use different software and sometimes different sensor on later Blacks) all use 4 pin Supaseal plugs and measure both gas pressure and vacuum, none include a gas temp sensor. They are inter-compatible but depending on type use either male or female Supaseal connections, male and female types have opposite pinouts... So if changing the pressure sensor type involves changing the type of connector then the opposite pinout must of course be accounted for. Unlikely this is wrong or might never switch to LPG but unusual results are possible including changing to LPG with no gas pressure but high manifold pressure and including maybe the interior switch issue.

4. If you can switch from one fuel to the other (including standby / waiting to change to LPG mode) but not back again this might point to something at the ECU end rather than a fault with the switch itself. ECU problem could be brought on due to excess electrical load on the ECU pulling the ECU's voltage down (maybe failing coil) or poor main battery earth/live connections.. In petrol mode the ECU won't need much power but even in standby mode it may open solenoids. Have known quite a few bad ESGI ECUs, they can fail with all sorts of problems including disregarding switch presses.

5. ESGI will report errors such as bad / disconnected pressure sensor, temp sensor(s) or bad supply voltage and refuse to run on gas similarly to when you've run out of LPG / pressure too low. Errors are recorded and can be read in software, most handy for intermittent problems, not necessary for consistent problems where incorrect readings would be immediately apparent elsewhere in software - in either case just need the software and cable, both easily got hold of.

Software would make for easiest diagnosis. Without software could run tests like: Solenoid test - Unplug LPG ECU, disconnect injector feed pipe, disconnect wires to solenoids, use multimeter to check resistance between each solenoid wire and earth, reconnect solenoid wires, connect 12v to solenoid wire that wasn't earthed, since solenoids are wired in parallel on this system they should both open so gas should flow out of the pipe (if no wire was connected to earth you'd have to connect an earth wire too. Bare in mind solenoid coils can be polarised in which case polarity will be marked on the coil). Even if gas came out check the resistance across the coils, since they're wired in parallel resistance should be around 7 ohms / Leak test - same as above but with pipe connected, pipe should remain pressurised or where is the leak? / Temp sensors test - multimeter across the reducer temp sensor, across the gas vapour temp sensor, if either is below a few hundred ohms or above 10Kohms there's a problem.

Simon

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