LPG haters - please advise (post 62 & 80)

2773 Views 83 Replies 23 Participants Last post by Dave2302, 2 mo ago

Bohemian TopDown

Discussion Starter · 3 mo ago

So, I took a day off today and went to the best Mercedes mechanic in Prague (judging by the reviews) because of that horrible rattling metallic noise that I have every time the tachometer needle touches the 2500rpm, every gear, both accelerating or slowing down, with or without gear, even revving with the car stopped.

As soon as his dog stopped chewing my leg, he took a look at the engine, saw the lpg system, and said: I'm not touching this car until the LPG is removed. You're destroying the car this way, Mercedes are not intended to be converted. When you install an lgp system in a Mercedes the engine head must be replaced with something compatible with this gas, and here it has not be done.

Now, I bought this car already converted, and given the price of the gas here, I don't mind paying a third. I wouldn't have done it myself, but it was there already, and I must admit it works pretty well.

He didn't say anything about the noise, didn't even want to listen to it, he went on for 20 minutes just cursing the LPG (I left, probably he's still going on).

My concern now is that I'll never be able to have a mechanic, because my car is converted... And yes, I tried the LPG shop, they said no, we only deal with lpg related problems, this noise is not related, go find a mechanic.

Do you really think I should have the system removed? Am I destroying the engine? Is it that bad? I just wanted to get rid of that rattling noise (not the engine supports, got them checked), I'm quite happy with having the option to save some money when I don't need to score the best lap time on qualifying session... But if it's really that bad, I can live without.

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Turbo

· #21 · 3 mo ago

It's not at all unheard of that "something" rattle only at a very specific RPM. Have to do with resonance frequency etc. Something I don't fully understand, but I've seen it proven.

Destroying vine glasses with the voice is probably the most famous example of that..

Reactions: 4

i860

· #22 · 3 mo ago

Turbo said:
Which is technically correct, the best KIND of correct .

That's why they, MB, created the M113k engine. Stronger parts, to take into account the added compression rate..

But just because something isn't designed for it, doesn't mean it's not a good idea.. Which have been proven .

On the lpg the problem could be the valve material ( but as we know MB made only good quality components see balance shaft, as intended of cours..) You burn the valves if you run lean, i you run lean lpg or petrol you have lambda probe to tell you that.
I will not go in any polemics but we are on a reputable forum and people are coming here for advices, poor or ritch ( as i was told long time by some one).
So your problem is not lpg related, slk 200, slk 280/350 all have faults, only bulletproof car is 55 less than transmision.

Reactions: 5

Bohemian TopDown

Discussion Starter · #23 · 3 mo ago

Turbo said:
It's not at all unheard of that "something" rattle only at a very specific RPM. Have to do with resonance frequency etc. Something I don't fully understand, but I've seen it proven.

Destroying vine glasses with the voice is probably the most famous example of that..

Also true...
My wife broke some glasses yelling at me when I spilled a drop of oil in the garden, next time will measure the frequency.

Reactions: 5

BaD_81

· #24 · 3 mo ago

Saying metallic noise, is it from the engine bay or under the car?
Gear Selector has a rubber, that I recently changed disgusting sound, that made me disassemble the cockpit more than once. If you are not sure what is checked, just raise the car on a platform/lift reach for the linkage between gearbox and shifter and make sure you shake it well. That bushing is 2GBP-2.5EUR let's say but the pleasure to replace it....

There is an example for the test, take the FUSE(s) of the lpg out - still the same - no LPG issue.
However inadequate LPG settings will lead to what i860 has covered.
SO, as a different approach, speak with a dyno test garage to check the car underneath (if possible of course) in 2500 rpms.
If they see a drop at 2500 rpms - that is serious.
If not, that would be every spinning component betweeen engine and exhaust - prop_shaft - has bearing, pulleys in the engine bay - bearings... they usually are audible in range, like 2000-2500 not only 2500, but who knows something very small could've keep exactly that frequency.
Can you make a video, like open your glove-box let the phone face up or down and start driving so the video gets that sound.
Someone can recognize it...

See less See more

Reactions: 5

efair

· #25 · 3 mo ago

@Bohemian TopDown I am just curious: is it easy to find LPG filling stations in your home town? I live in a fairly populous suburban area but the closest LPG filling station is a half-hour drive away.

Reactions: 3

i860

· #26 · 3 mo ago

In Eu they have lots of lpg station, in my case i have one in my village, if that goes busted the next one is 25miles. So for 50mile go and back there is no point having lpg.

Reactions: 5

Bohemian TopDown

Discussion Starter · #27 · 3 mo ago

efair said:
@Bohemian TopDown I am just curious: is it easy to find LPG filling stations in your home town? I live in a fairly populous suburban area but the closest LPG filling station is a half-hour drive away.

1 out of 3 gas station has lpg here, very easy to find

Reactions: 5

Sneaky Pete

· #28 · 3 mo ago

As @i860 said lots of stations. In my small town in a 25km radius 63 stations.

Reactions: 5

Bohemian TopDown

Discussion Starter · #29 · 3 mo ago

BaD_81 said:
Saying metallic noise, is it from the engine bay or under the car?
Gear Selector has a rubber, that I recently changed disgusting sound, that made me disassemble the cockpit more than once. If you are not sure what is checked, just raise the car on a platform/lift reach for the linkage between gearbox and shifter and make sure you shake it well. That bushing is 2GBP-2.5EUR let's say but the pleasure to replace it....

There is an example for the test, take the FUSE(s) of the lpg out - still the same - no LPG issue.
However inadequate LPG settings will lead to what i860 has covered.
SO, as a different approach, speak with a dyno test garage to check the car underneath (if possible of course) in 2500 rpms.
If they see a drop at 2500 rpms - that is serious.
If not, that would be every spinning component betweeen engine and exhaust - prop_shaft - has bearing, pulleys in the engine bay - bearings... they usually are audible in range, like 2000-2500 not only 2500, but who knows something very small could've keep exactly that frequency.
Can you make a video, like open your glove-box let the phone face up or down and start driving so the video gets that sound.
Someone can recognize it...

Thanks mate, tomorrow I'll make the video and post. Hard to say where it comes from, seems like somewhere between the engine and the cockpit, more to the right side.
When I test it in neutral, it still does the noise, but much less, so it's difficult to find the source.
And of course, when I am with the mechanic it's the quietest car in the world, a Tesla basically. Left the car repair shop, a tractor again.
In the next days I will also go and ask how much it would be to remove the lpg system, just out of curiosity. Again, I am happy with it, but every time you visit a mechanic they treat you like you have the plague. Liquid PlaGue.

Reactions: 5

Bohemian TopDown

Discussion Starter · #30 · 3 mo ago

Sneaky Pete said:
As @i860 said lots of stations. In my small town in a 25km radius 63 stations.

Like, for real? Here in CZ I would say one every 10/15km.

Reactions: 3

Sneaky Pete

· #31 · 3 mo ago

Bohemian TopDown said:
Like, for real? Here in CZ I would say one every 10/15km.

Yes for real.

Reactions: 4

efair

· #32 · 3 mo ago

If the noise subsides when in neutral then I would suspect the motor/transmission mounts.

Reactions: 4

BaD_81

· #33 · 3 mo ago

Bohemian TopDown said:
Thanks mate, tomorrow I'll make the video and post. Hard to say where it comes from, seems like somewhere between the engine and the cockpit, more to the right side.
When I test it in neutral, it still does the noise, but much less, so it's difficult to find the source.
And of course, when I am with the mechanic it's the quietest car in the world, a Tesla basically. Left the car repair shop, a tractor again.
In the next days I will also go and ask how much it would be to remove the lpg system, just out of curiosity. Again, I am happy with it, but every time you visit a mechanic they treat you like you have the plague. Liquid PlaGue.

I wouldn't be bothered to remove the Liquid PlaGue (some sense of you humor you have) just to prove it ain't it.
But it will not hurt to check the fittings/holders/clamps....etc.

Reactions: 3

Bohemian TopDown

Discussion Starter · #34 · 3 mo ago

Trying to upload the audio file...

Reactions: 2

Turbo

· #35 · 3 mo ago

Upload it to YouTube and then post the link here..

Reactions: 4

Bohemian TopDown

Discussion Starter · #36 · 3 mo ago

20230314_134822.m4a

drive.google.com

drive.google.com

Reactions: 1

Turbo

· #37 · 3 mo ago

Yeah, it just asked me for access.. You need to make the link public..

Reactions: 2

Bohemian TopDown

Discussion Starter · #38 · 3 mo ago

Should work now...

Reactions: 3

Turbo

· #39 · 3 mo ago

Doesn't sound like a bracket or flap or anything, sounds more like a metal shielding being loose somewhere..

There's one, at least on my 55, between the engine and the firewall, but also a few underneath between the exhaust and the chassis.. I'd check those first.

Reactions: 5

efair

· #40 · 3 mo ago

Nobody is gonna listen if you post a link that asks for a password...

Reactions: 2

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