Bad vibrations and loss of power on ML in LPG mode

[GseRacing]

Evening all, hope the world is treating you well.

I have just had a day of travelling back and forth from basinstoke a couple of times today and i have had some issues with my ML.

As the bottom of this thread will show its an 02 plate ML 55 AMG with an LPG conversion. Its not full time LPG, i can manually switch between the two fuels whenever i want.

I was going up a hill on the way there and hit the loud pedal and pulled into the lorry overtake lane. the car made it about 100 metres before it lost power, flicked off the LPG and i had to move back in. No matter how many times i pressed the button it would not re-engage the LPG. When i came to a rest the engine was unbelievably lumpy and when moving it would not go above 2000rpm. If i managed to get it above 2000rpm by manual shifting it would suddenly surge in speed and then change itself and go straight back into lumpy no power mode.

I pulled up in basinstoke, turned the engine off for ten minutes. started again and it was as sweet as anything, even on LPG. no issues for the rest of the day. Then when i went back to basinstoke later to drop my friend off it did exactly the same thing.

Two things come to mind. It only does it under hard acceleration. And this again only occurs if the LPG is on.

On my return from basinstoke on the last dual carriage way out i was being crept up on by an SLK, thinking this would be the best opportunity to test the acceleration issue i flicked over to petrol and gave it full tilt. it accelerated beautifully (much to the slk's apparent disgust) and i had no issues at all. Now i would have driven home on petrol but i never fill this up as i run it full time on LPG so i had the fuel light on. I flicked it back to LPG and it ran smoothly all the way home.

The obvious answer i know is, if im going to give it some, do so on petrol but this doesnt solve the issue. it just drives around.

Im going to contact the LPG specialist in yorkshire that fitted it a year ago and also my local one in oxford for their thoughts but does anybody here think they might be able to shed some light?

I was wondering about the lumpiness. kinda felt like a miss fire.

Anywho, many thanks if you can help at all.

 

[215m3]

I have just sold my Legacy GTB that ran on LPG. It had a small mis fire when i got it, but was unaware of it, as it came and went, but did not effect the running. The LPG fitter told me about the misfire too.

Cut a long story to what it ended up being, the plug on the end of the injector. It was spotted just before i sold it. The mechanic accidently nudged it will looking for a stalling fault and it changed the engine tone. He changed the wiring not the plug, but it came back later that day. I went to a scrappy, got 2 injector plugs, soldered the wires back on and it worked a treat. It was in fact the plug and not the wiring.

 

[Seamaster15]

LPG runs hotter, I got this on my ML320 with LPG, had to check the plugs. Problems fixed. Check your plugs, if not go to your local LPG Service centre, they can adjust the running via a laptop.

 

[TheScrapman]

It sounds like the car is going into limp mode for some reason, especially as it restores to normal after switching the engine off. Might be worth getting someone to look at the fault codes?

My LPG'd S320 doesn't like being revved hard on LPG (i.e full throttle over 5k), but it only misfires until you take your foot off a bit. I just press the button over to petrol when overtaking.

 

[GseRacing]

215m3 and Seamaster15, can you just clarify what you mean by plug?

Sorry for the silly question.

I have a blue inch cube on each cylinder which is part of the LPG system. should i be looking here for something?

 

[Frub]

Two things come to mind. It only does it under hard acceleration. And this again only occurs if the LPG is on.

I assume that it's a newish system and multi point - given the age of your car I guess thats a stupid question!

I have a 3ltr Volvo which runs like you know what off a teflon shovel on LPG. I think it's all about making sure that your ignition system is spot on all of the time and you have your LPG system serviced, filter change etc, on a regular basis.

Frub

 

[GseRacing]

I have just spoken to a guy at Oxford Autogas and his suggestion is that the engine is being starved of gas. It is almost exactly one year old. His first port of call is a system service, needs to be done once a year like a regular car service. Only £50-70.

So failing that he might plug his laptop in to the LPG ECU and see whats a doing. But, he says, its isnt going to be a really big issue and cost lots.

We are smiling again.

I will of course update once the car has gone in. just for future reference for those of you also running on LPG.

 

[GseRacing]

New twist, it did it last night while running on petrol.

Beginning to get slightly concerned and frustrated. I dont want to be using it as a racing car but i cant seem to accelerate anymore than if im just bimbling around otherwise the engine goes really horrible.

Am i going to have to admit defeat and take it to the local MB?

 

[GseRacing]

Well i have had a verbal with a guy at MB and he suggested a change of plugs at £620! I'm beggining to feel like i have bitten off more than i can chew with this car. Running it in the literal sense i can afford but maintenance is becoming an issue. Even if i could afford it MB wont do the work as it has an LPG kit on it, neither will my local garage who our family has taken our cars to for years and the LPG garage wont touch anything other than the LPG!

I love my car but i think i might have to bite the bullet and see about moving it on.

 

[BlackC55]

have you had it plugged into a Star yet?

It might be somthing simple as a dodgy plug or coil pack.

 

[GseRacing]

I dont have a star, the only place that i think will is MB and they dont want my car in their garages unless i have the LPG removed which will cost £2k and then another to have it put back on!