C200K Air Buffetting / Noise after LPG Conversion

[swimbrazil]

I am new to the forum and am proud owner of my first Merc a C200K 2002, with only 30K on clock.

I got an Autogas conversion done when I bought the car. No doubt I will get stick for that, but I went for top quality system and good installer, I thought. Had a few problems in that installer forgot to connect Kompressor initially but after that engine went well. I lost 21% economy compared to petrol though, am getting 26 all round average on lpg and 34 on petrol. Slightly disappointing and with price of petrol now am regretting doing it. So what is my problem ?

Ever since conversion I am getting excess cabin noise and feel slight vibration. It is a sort of wind buffeting/pressure rythmic sound and it is ruining experience of owning the Merc. Seems to vary a little with road conditions and speed. Bit like when you've got a rear window a tad open. Symptoms present either driving on LPG or petrol. LPG installer has been over it twice comprehensively checking LPG tank installation, venting and the cabin vents (whatever they are). Can find no fault. I think it must be something aerodynamic or to do with exhaust/cat or road wheels. On perfect road surface symptoms are less. Have had all wheels balanced and new tyres - no change.

Very grateful if anyone could help please.

 

[TheScrapman]

A "good" installer that forgets to reconeect a major engine component. Hmm. :-?

I have LPG on my '98 S320. It is a good system, closed loop piggy-back ecu and injectors on each cylinder. It does around 27mpg on petrol, 24mpg on LPG - about 6% less as would be expected. Basically means I can afford to drive an S-class for Mondeo money!

I have fitted lpg to a number of vehicles, and even on cars with carbs with crude open-loop systems, I am only seeing a 10-12% drop in economy. 21% is hugely excessive. Have you lost much power?

At first reading, a vibration would point toward something mechanical touching the chassis - exhaust maybe, or something around the engine touching the body? Has the airbox/intake or any other engine component been moved at all? On a w126, you have to raise the air box up about an inch to locate the lpg mixer. This is fine on a saloon, but the coupe bonnet slopes lower, causing interference and vibrations between engine and body.

I would be very suprised if the extra gubbins under the bonnet are causing aerodynamic resonances. Where is the regulator located? where does the fuel pipe and solenoids run and sit?

Oh, welcome to the forum!

 

[codes]

I also have a C200K with LPG fitted. None of the symtems you describe have surfaced. Runs well on LPG, the throttle response is a little slower but other than that it's ok.

 

[jberks]

I'd have another installer take a look.