Idling and LPG

[Oxmerc]

Can anyone help? About six months ago I had my 1995 E220 coupe converted to run on LPG by a reputable installer in Wycombe.

I have been getting really good fuel economy up to now, about the equivalent of 50 mpg, but there is a problem with the engine tickover on both petrol and LPG, which has been there since the installation, but has been getting worse.

The tickover is lumpy, and the engine stalls completely sometimes, especially when I stop at traffic lights after driving for a mile or so. The tickover seems OK when the engine is really warm after a longish drive.

I took the car back to the LPG guy after 1000 miles for its scheduled first checkup, and reported the tickover problem, which at that time was not quite so severe. He used his laptop to do some adjustments, which improved things only for a while. In all I have done about 5000 miles now. In all other respects, the car runs well.

Has anyone had similar problems with LPG? I have read as many of the LPG posts on the forum as I can, but this problem doesn't seem to be mentioned.

Grateful for any ideas.

 

[Mark-R]

Sounds like a vacuum pipe broken ar come adrift. I had the same problem, got gradually worse until the engine cut out last week. The RAC towed me home. I then had to have the car picked up and taken to a garage where the fault was diagnosed.

LPG apparently breaks down the rubber causing this kind of hose problem to be quite common. Fortunately the hose was only £3 from my MB dealer. Pity it took 2 days to get it.

 

[jules335500]

had the same problem but the lpg garage said it was the computer management system............some mercs ok and others have a slight problem.
mine just splutters wen cold but fine once warm.no leaks on pipes as there have been checked

 

[jako999]

On a v8 land rover the same thing happened then it started to backfire it turned out to be the leads and a spidder? It may be the same, try and find out or see if you can borrow a set of leads befor you spend lots of cash.
Jako

 

[Oxmerc]

update

Thanks for your replies.

I have had the LPG installer take a look at it, and the fault seems to be either the air flow sensor of the MAF sensor, or perhaps a vacuum pipe.

He showed me how the laptop showed the engine response exactly the same under petrol and LPG. So it does not seem to be related to the LPG, but a more general idling problem.

I've done more research on this site, and have come across some advice concerning idling problems, which means I can go to the Mercedes specialist armed with some useful information. I'm going to John Griffiths in Caversham, near Reading.

I'll keep you posted, and thanks again for your help.

 

[Oxmerc]

another update

Well, John Griffiths refused to touch the car because it had been converted to LPG. Their diagnostic system said the problem was the Lambda proble, so the obvious answer was to replace that, but they refused to do it.

So, I'm taking it next week to Star Motors in Caversham, who said they service and repair a number of LPG cars, so are prepared to look at mine.

More soon.

 

[grober]

to convert or not convert

Interested to hear of your experience. What make of system did your installer use? Did you opt for a spare wheel type tank or a cylinder? And present problems aside was the conversion worth it in economic terms? Thinking about a conversion myself.

 

[Oxmerc]

my conversion

It's difficult to give clear advice on this.

The system is a BRC multivalve, with a Bigas vaporiser, done by Chiltern Gas Cars Converstion. I was offered a toroidal (doughnut shaped) tank to fit in the spare wheel well, but I didn't fancy using one of those kits you have to use when there's no spare wheel. So I had 70 litre cylindrical tank mounted front-to-back in the boot. Takes up about a third of the boot.

As far as economy goes, it's very good. I'm getting the equivalent of 50 mpg, and am saving £50-60 per month. I really don't notice any difference in performance between LPG and petrol, but as this is an E220, performance is sedate anyway.

Would I do it again? Having had these problems, at this precise moment, I think no. But the problem may soon be rectified, and seems not have anything to do with the LPG. So I'm reserving judgement for now.

I'll let you know more once Star Motors have had a look at it this Thursday.

There's a feature on LPG conversion in "Jobs and Money" in today's Guardian. Check it out!

 

[996jimbo]

Hopefully you've solved your problem but just for info: I had a Range Rover converted to LPG which quickly developed a lumpy tickover. After a couple of re-calibrations (unnecessary in fact thanks to the CPU) it was put down to ageing HT leads. The lumpiness was not really apparent on petrol; it seems that LPG being lower calorific value (?) doesn't like a weak spark. New HT leads certainly cured it completely.

I did go for the doughnut tank as every puncture I've ever had has gone down so slowly there's been plenty of time to get to any tyre dealer you fancy.

 

[Oxmerc]

resolution?

Well, Star Motors in Caversham, Reading, serviced the car today, and replaced the Lambda probe. They said that the earth strap from the engine had been broken, so they replaced that too. It ticks over better, but still not perfect. Star suggested it might be a problem with the gas, but right from the start it's behaved identically on gas and petrol.

Thanks for the advice on HT leads. I'll bear it in mind.

Now all I have to do is find three cheap low-profile tyres in or around Oxford, because I was advised I would need them soon, as well as the tracking checked. Not to mention a new rear screen due to delamination, as well as rust developing on the offside front wheel arch...

 

[Oxmerc]

more

Well, one week on from the service by Star Motors, and the idle is lumpy as ever.

On either gas or petrol, when the engine is hot, the idle speed surges to about 1500 revs every 20 or thirty seconds when in park or neutral.

I would try the new HT leads, but am so useless probably couldn't do it myself, and it's such a hassle taking it to a garage.

 

[996jimbo]

Easy check for the HT leads is to park in a darkened place with the bonnet up and engine running and see if you can see any sign of shorting between the (insulated) HT leads and any metal bodywork or engine casing they're against / close to.

Surging sounds like a completely different problem though so I'll bow out!

 

[telletubby]

Tyres near Oxford

There used to be a good cheap tyres place in Yarnton near Oxford. it's been a while since I lived there but perhaps worth checking out. Sorry I can't remember the name. But i remember they did me a good deal a few years back for my 560SEC.

 

[Copiertech]

is it a mixer system or a sequential multipoint system? if it is a mixer system you might just have to live with the fault as they are not ideally suited to these kind of engines, if it is a sequential multipoint setup check the injector nozzles are as close to the inlet valve as possible, check the length of every injector hose is exactly the same, check that all the injectors are the same flow rate (IIRC i think bigas use a letter stamped on the injector valve body somewhere) and that none of the hoses are kinked, and that the vacuum line to the pressure sensor (if fitted) and the vacuum line to the vaporiser is ok and not collapsing from heat under vacuum its important the vacuum line to the vaporiser is getting a strong vacuum signal as it affects the pressure of the lpg supplied to the injectors and otherwise it runs VERY rich at idle. the ideal place to take those vacuum lines from is a t piece from the petrol pressure regulator. I would replace the plugs and leads as a matter of course if they are not new already as an lpg/air mixture has 25% higher electrical resistance than a petrol/air mixture. have they connected the purple/violet wire from the LPG ecu to the lambda probes signal wire? if they have get them to plug in the laptop and monitor the lambda output while the engine is idling on petrol then on gas and compare the readings and tweak the mixture at idle/low load. i`m not sure if your cars own ecu has serial diagnostics capability but if it does plug in a code reader and watch the Lambda integrator fuel trim value while the vehicle is idling/running on low load and comparing it to the readings while on lpg, you want to have them pretty close to each other, by adjusting the lpg ecus settings.
If you dont have any joy drop me an email at SMDevelopments@hotmail.com and i`ll give you my mobby number as its quite hard to run through the possibilities typing back and forward

 

[Copiertech]

also, have you tried cleaning out the idle control valve and throttle butterfly area with carb cleaner?

 

[Oxmerc]

thanks...

for all this advice. I appreciate you going to so much trouble. However, I am absolutely hopeless at all technical stuff, so I wouldn't be able to find most of the parts you mention, let alone fiddle with them. Do you know of any specialist in such problems I could go to? I live in Oxford, work in Reading.

 

[Copiertech]

Sorry, cant help you there, i stay in livingston, near edinburgh. dont know anybody down your way. I think autogas worldwide are the bigas importers but i`m not 100% sure about that. find out who the importers are, call their tech. support and tell them you are having bother and your installer has tried to fix it but cant and they should recommend someone else to go to. they wont want faulty installs damaging their reputation. you might have to pay the other installer to fix it then claim against the garage that done your install if they cant fix your problems.

 

[jules335500]

Had the same but fine now as they replaced the air mass metre sensor £349

 

[Oxmerc]

Back again

Well, time has moved on but my problems remain.

Today my car stalled as I was waiting at traffic lights, and I held up a long queue of traffic that wanted to get through them, as I tried to restart the car. An oik in a Peugeot leaned out and yelled obscenities as he went round me, asking why I had stopped there. Obviously, hazard warning lights are not known yet in oikland.

I emailed my LPG installer about my problems, citing this thread, but he seems to have lost interest and I have had no reply. I emailed Andy Gayle of Smethwick, but no reply there either.

What I need is an independent Mercedes specialist not too far from Oxford (where I live) or Reading (where I work), who is not frightened by an LPG car, to diagnose this problem once and for all.

As it is, my car may well not get through its MOT next month, and then it will be undrivable and unsellable.

I don't know whether the LPG conversion is responsible for these problems, but they began immediately after the installation. So draw your own conclusions...

 

[fwb44]

LPG troubles

In the last 12 months we've had two vehicles LPG-converted by Gastech of Huntingdon, who use the latest injection technology and are right up to date on all matters LPG. Nothing has ever been too much trouble for them - not that there's been much trouble with the cars they've done for us - but we did have to replace HT leads on both a Volvo V70 and a VW Caravelle after conversion. If you contacted them they might be able to refer you to a reputable LPG technician in your area: 08707 357777, ask for Stuart Eckersley. You could mention my name as someone who recommended them, if it would help: PM me & I'll give details.