Help needed.

[Carolyn]

I am having constant problems with my W registered 320 converted to LPG in June last year and I am not sure if it is a petrol or LPG problem. My car began to misfire only on LPG so my garage told me it was not a petrol problem. Gastech, Huntingdon told me it was not an LPG problem. They told me it was proably my HT leads so back I went to the garage. I ended up with new plugs 30,000 miles earlier than usual all set to .9mm, new coil packs and HT leads. None of this made any difference other than to my bank account! True to form, whenever I took the car to Gastech, it was out of misfiring mode. I left the car with them for nine days and they eventually made it misfire to order but could find no LPG faults, however they said that they checked and tightened every nut, bolt, screw and wire. I am still left with a car that has now been misfiring for 1,000 miles and is unpleasant to drive. My car never misfires on petrol.

Another LPG convertor I contacted told me it is a petrol problem manifested by the LPG, a more sensitive fuel. My garage just shrug their shoulders and Gastech are not responding. I am at a loss as to where to turn. Has anyone else had this experience and can enlighten me?

 

[Martyndogs]

Lpg Missfiring

Hi I suggest you go on the LPG 2000 web site(find it with Google). The thread there under 'discussions' is very imformative. I have had lots of LPG cars but NOT as yet a Merc, (my SL does not do enough miles to warrent the conversion cost). There are a lot of people in the LPG trade who comment on this site so may be able to point you in the right direction.
Regards Martyn.

1978 SL450
'03 Subaru Forrester (LPG)
'03 Spacewagon (LPG)

 

[Hurm]

Worth a look

I used to run a Nissan Patrol (damn fine car) on LPG and when I bought that it had a horrific misfire only when on LPG. LPG requires more energy than petrol to ignite it in the cylinders under compression therefore a minimum of 8mm plug leads are required and slightly larger plug gaps. Careful with these leads as if you want the car to still appear relatively standard you will have to buy the clips that go with the leads to clip them down to the engine, they will not fit into the standard clips. The other thing LPG is very, very sensitive to is air leaks at the inlet manifild or its associated vacuum piping. Whilst it will run like a dream with a very slight manifold leak on petrol, on LPG it will missfire like crazy. Took me ages to track it down as I couldnt believe it was an air leak. Changed the inlet manifold gasket - perfect.
Track down exactly which cylinder is missfiring on LPG then with the engine running squirt WD40 sparingly around the affected cylinders inlet manifoild position. Dont spray it all over the plug leads (if your leads generate a stray spark it will catch fire. When you find the leak the engine will rev up slightly. I had to soak the manifold on the Nissan and the revs went up by about only 100rpm but that was the fault and once the gasket was changed it was prefect. Sorry this is longwinded but I like to explain any pitfalls!!

 

[jibcl500]

Can you tell me what system is fitted, is it a single point or multi point LPG system, I take in a lot of Range Rovers with LPG systems and its the oposite with them, they run great on LPG and run like pigs on petrol.

Do you or did you get any backfire through the inlet, or have you had any back fires, if so that could have caused the problem, for example on a classic range rover if it should backfire up through the induction system it can in most cases destroy the MAF, this is common, on modern cars the backfire can crack or break inlet pipes, blow holes in rubber air intakes etc.
LPG needs more spark to ignite it, LPG burns slower than liquid fuels which can cause a misfire.

Pesonally I wouldnt recommend LPG systems to anyone, I wouldnt buy a car for myself with LPG fitted, but thats just my point of veiw.

jib

 

[Hurm]

Blowback through the induction

jib,
The most common reason for LPG enabled cars to spit back through the induction is the default setup on some gas systems is for the petrol to LPG changeover to occur on acceleration.....big problems if its left like that. It should be set for about 1200rpm on deceleration that way you wont get the spitting back