Misfire ???

ulfilias · #1 26th October 2016, 01:01 PM

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

ulfilias · #2 17th April 2018, 02:42 PM

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 ???

ulfilias · #3 9th October 2018, 10:02 AM

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

ulfilias · #4 18th October 2018, 10:00 AM

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

Norretal · #5 18th October 2018, 05:27 PM

Well done Lee, over two years of perseverance and investigation finally paid off

I do love a happy ending

Mechcanico Lee · #6 18th October 2018, 10:26 PM

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

ulfilias · #7 22nd October 2018, 10:32 AM

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.