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  #11  
Old 17th October 2016, 04:27 PM
ulfilias ulfilias is offline
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Hi There,

Got a new longer LPG cable come through today which meant I could sit in the car and have a look at what was going on etc.

Inbetween playing with VAGCOM and the LPG software i found some interesting and confusing stuff.

I could monitor the engine missfire counters. You get loads on Cylinder 8, but only if below 1500-2000 RPM. Over that and nothing and the count resets. Over 100+ and you get the car disabling the cylinder and it gets lumpy

This only happens LPG, all on petrol and it's fine. Switching one cylinder at a time to Petrol and the same thing. I tried all but running 8 in petrol mode with the rest on LPG and the same missfires when the revs are below 2000rpm!

The intake switchover is ~5500 so the 2000rpm mark isn't to do with that.

I had another go at tuning the the LPG system. It still seems to be burning rich as after heavy revs I get an exhaust pop, which is usually indicative of overfueling!

It's a real head scratcher!

Lee
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  #12  
Old 17th October 2016, 11:30 PM
Mechcanico Lee Mechcanico Lee is offline
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Couple of thoughts ...on some engine missfire detection only works up to about 1000 /1200 rpm when stationary any higher than this it switches off

It may detect missfire whilst driving as road speed re establishes the function .

The switching injectors over to petrol one of a time is a strange one , does the gas system have a single map sensor or twin ?

Try in plugging both lamda sensors whilst on gas to see if trim adaptations is affecting time open duration on that number 8 .

Does the gas have one feed to the gas rail or twin , is gas pressure ok , are gas filter units ok .

If it has twin gas regulators you could try swapping supply pipes over on gas rail to see if it transfers to other bank , obviously if it's only one supply and regulator type forget all this .

Whose system is the gas .......Romano ....Bi gas ??
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  #13  
Old 26th October 2016, 02:01 PM
ulfilias ulfilias is offline
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Hi There,

Haven't had a chance to play as went up to Scotland for a wedding. ~750miles on petrol and she did fine. I did notice a couple of times when the girlfriend booted it there was a flashing check engine light (though not set on)

Just checked and both Cat errors, a missfire on Cylinder 2 (not 8 as on LPG) and a Bank 1 secondary air system too low (intermitent)

Got about 25mpg off the 4.2 and moving swiftly which wasn't bad. I get 18-20 on my 10 mile daily commute, so not bad.

Lee
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  #14  
Old 17th April 2018, 03:42 PM
ulfilias ulfilias is offline
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Back to trying to solve this.... from http://forum.a8parts.co.uk/showthread.php?t=14011

As i can get it to MOT on gas and pass

Swapped the MAF yesterday....it was a straw i was grasping at, but has done little to change anything. ~90 off Amazon for a Bosch one as I recall the A8s being picky!

Just had a play with my software and it's still a misfire on 8....There was a new release of the LPG software and i updated the system, but that made little difference too!

It's ran a couple of years now on Petrol with barely an issue. I've still got Cat errors and that's it and I can't see a Cat fault throwing the LPG into a misfire situation within two minute on gas ???
__________________
Current :
2005 A8 Sport 4.2 V8 D3 - LPG not working still....

Previous :
1998 S8 PF 4.2 V8 D2 - Gearbox died ~120k
2002 S8 FL 4.2 40v V8 D2 Prins LPG - Engine valves met pistons ~230K

Also :
1996 Jeep Grand Cherokee 4.0l (not worth selling!)
2003 Brabus Smart FourTwo (for sale)
2003 Mazda Rx8 2.3 (should sell)
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  #15  
Old 9th October 2018, 11:02 AM
ulfilias ulfilias is offline
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Been playing with this AGAIN

So a friend of mine has done some LPG installations and I've ran it past him a few times. Also a qualified electrician so we've checked quite a bit of stuff. There was voltage difference that we've evened up, though it made little difference and a few pipes we've straightened and then on a run out with the car he noticed it was over fueling that side of the engine on LPG and there were other misfires and stuff happening.

It led us to manifold pressure and the vaporiser. I had a "spare" from my old S8 and a Prins kit that i removed various bits off the old car before it getting passed on.

It looks like to get a manifold pressure feed for the vaporiser they put a port in the opposite side of the manifold to cylinder 8. We suspected a diaphragm leak on the kit, which then feeds excess LPG into the manifold and causes problems. It would certainly explain the over fueling and why No.8
The hot water hose had a kink in it meaning it probably didn't get hot enough and damaged the vaporiser!


With a bit of a fiddle we swapped them and now back to trying to tune things, but we don't seem to be getting No.8 cutting out
__________________
Current :
2005 A8 Sport 4.2 V8 D3 - LPG not working still....

Previous :
1998 S8 PF 4.2 V8 D2 - Gearbox died ~120k
2002 S8 FL 4.2 40v V8 D2 Prins LPG - Engine valves met pistons ~230K

Also :
1996 Jeep Grand Cherokee 4.0l (not worth selling!)
2003 Brabus Smart FourTwo (for sale)
2003 Mazda Rx8 2.3 (should sell)
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  #16  
Old 18th October 2018, 11:00 AM
ulfilias ulfilias is offline
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Following up......The "new" vaporiser wasn't getting particularly warm. We investigated, tried bleeding as we may have got an airlock. NOPE, no coolant at all. We tried a rod down the hose, but didn't get anywhere so we started tracking back.

It seems when they cut the audi water hoses at the back of the engine, they did a crap job. One of the T-pieces was solid, had various glues and sealants and was pretty broken up from over clamping. Swapped it out, recut the pipe and got a good seal (Air pump test first) and then refilled and bled the coolant and it heats up nicely.

It explains why last year I was struggling with cabin heat and when draining, cleaning and filling the coolant i got so much grit out. Think they must have used some form of rad-weld in the system *Shudder*.

And this place that did the conversion in Romania seems to be highly rated!!!

Still, the LPG is now working and doing what it should. It need tuning up, but preliminary tests show it to be a good and capable it. I could floor it and she goes like she does on petrol!

Cleaner emissions and half price 4.2l power awaits
__________________
Current :
2005 A8 Sport 4.2 V8 D3 - LPG not working still....

Previous :
1998 S8 PF 4.2 V8 D2 - Gearbox died ~120k
2002 S8 FL 4.2 40v V8 D2 Prins LPG - Engine valves met pistons ~230K

Also :
1996 Jeep Grand Cherokee 4.0l (not worth selling!)
2003 Brabus Smart FourTwo (for sale)
2003 Mazda Rx8 2.3 (should sell)
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  #17  
Old 18th October 2018, 06:27 PM
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Norretal Norretal is offline
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Well done Lee, over two years of perseverance and investigation finally paid off

I do love a happy ending
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Jobs done so far - Inlet manifold overhauled , new ATE discs and pads all round, new front grille, new foglight units and foglight grilles, new Longlife tailpipes fitted and centre silencers removed, wheels refurbished, detailed twice and several coats of wax applied

Jobs to do - drive it more

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  #18  
Old 18th October 2018, 11:26 PM
Mechcanico Lee Mechcanico Lee is offline
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Mmmmm interesting ....does the system have 1 vaporiser per bank , if it does have 2 ...one per bank ,I wonder why there was not an issue with a full bank of cylinders with a cold vaporiser .
Well done sticking at it Lee
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  #19  
Old 22nd October 2018, 11:32 AM
ulfilias ulfilias is offline
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It's a single vapouriser. They usually are because cost and I don't exactly feel this was a "premium" installation anyway!

I've slowly kept chiseling away at things, but finding time, inclination and the help to get a spark of "I wonder" is not always the easiest. It also had the problem of it works on petrol and is usable so I didn't need to dedicate time to it (i also have this with my home cinema set-up, I can watch films in it and they're good, but i still have jobs to do).

A *lot* of LPG theory says that it highlights faults in the cars system being fussier than petrol, which *IS* true, but in this case also proved a red herring. I was expecting a minor petrol fault to get worse and it never did. The age of the LPG installation being under a year before i got the car also pointed that way. However, despite them being quite well known, there was obviously someone doing less than perfect installs.
__________________
Current :
2005 A8 Sport 4.2 V8 D3 - LPG not working still....

Previous :
1998 S8 PF 4.2 V8 D2 - Gearbox died ~120k
2002 S8 FL 4.2 40v V8 D2 Prins LPG - Engine valves met pistons ~230K

Also :
1996 Jeep Grand Cherokee 4.0l (not worth selling!)
2003 Brabus Smart FourTwo (for sale)
2003 Mazda Rx8 2.3 (should sell)
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  #20  
Old 24th October 2018, 12:25 PM
ulfilias ulfilias is offline
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Posts: 794
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Did a reasonable trip at the weekend (Watford, Harry Potter!) and running around to and from work and then topped up this morning. About 200 miles for 42l, which is 20ish a gallon.

Petrol is 1.35 for non supermarket round here for unleaded. 0.72 for LPG, so that's about half, so ~38-40 MPG price equivalent!!!

However, I've a Flogas outlet on the industrial centre in Peteborough who have an LPG pump and it's 0.52 a litre!!!

That makes it over 50MPG equivalent

It also produces less emissions, burning cleaner and hotter.

Driving generally isn't effected, normal stuff you wouldn't know. Starts up for a mile or so on Petrol to warm up the engine but then the change over is hardly noticeable. Normal cruising is the same, decent acceleration is nice and vroomy.

*REALLY* booting it and it beeps and drops back to petrol but there doesn't seem to be a noticeable lag like my old Prins system. We're talking major kick down here and once at rocket speeds a press of the button and you are back on LPG anyway!

It is a bit of messing around, particularly with a european adapter type filler which is frowned upon, but I do like a big 4.2 V8 mega spec comfy sporty car that is also cheap to run (260 tax too, being an '05)

Lee
__________________
Current :
2005 A8 Sport 4.2 V8 D3 - LPG not working still....

Previous :
1998 S8 PF 4.2 V8 D2 - Gearbox died ~120k
2002 S8 FL 4.2 40v V8 D2 Prins LPG - Engine valves met pistons ~230K

Also :
1996 Jeep Grand Cherokee 4.0l (not worth selling!)
2003 Brabus Smart FourTwo (for sale)
2003 Mazda Rx8 2.3 (should sell)
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