530iA recently LPG converted with misfire issue. HELP!

530iA recently LPG converted with misfire issue. HELP!

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matt21

Original Poster:

3,690 posts

159 months

Thursday 17th June 2010
quotequote all
I have posted similar before, but a lot has progressed since last time so thought I would start a new thread....

Bit of background....I bought a 2000 142k 530iA 12mths ago. In April at 161k I LPG'd it....BRC, 80 litre tank. A good system.

Fairly soon it began to develop a misfire on gas. When misfiring it would not switch to petrol and wound shake violently and be down on power.

It was diagnosed as ignition coils. I replaced all 6, together with 6 new spark plugs but the problem remains.

It occurs every day or so. Turning it off and restarting and keeping it on petrol its fine and I can switch back to gas after 10mls or so for another day or so.

It is random when it happens. Sometimes at idle then cures itself, it normally appears to occur when coasting (in drive of course) to a junction.

On petrol it appears fine all the time - however does not seem quite so lively as it did before gas conversion on petrol but maybe thats me.

The LPG guy has remapped it and all his believes it could be is the ignition coils which we know it is not. He is at a dead loss and believes it is ignition related, something magnified on gas.

Does anyone have any thoughts? It has new microfilters, recent oil change, new oil and air filter too. It should be sweet as a nut. He does not believe it is MAF or o2 sensor.....I can't think what else. And it runs ok on petrol and only iffy on gas every 100 miles.

The car is still with him and he is working on it as we speak but I think we are both starting to run out of ideas.

Thanks.

8400rpm

1,777 posts

122 months

Thursday 17th June 2010
quotequote all
What heat range and gap are the plugs? I'm guessing they're fine for petrol usage, but not for gas. Is it getting detonation from pre-ignition, or is it not sparking adequately enough?

matt21

Original Poster:

3,690 posts

159 months

Thursday 17th June 2010
quotequote all
8400rpm said:
What heat range and gap are the plugs? I'm guessing they're fine for petrol usage, but not for gas. Is it getting detonation from pre-ignition, or is it not sparking adequately enough?
Not sure, would assume the "expert" has checked that but will ask.

He told me to fit Champion plugs, to which I assumed he meant something decent. I fitted NGK to which he suggested I ripped out and put in Champion as they are far better suited for gas. Whilst I cannot see why thats what I did.

Not sure on your second question, sorry! :S

8400rpm

1,777 posts

122 months

Thursday 17th June 2010
quotequote all
NGK plugs are brilliant, but the manufacturer means little, the heat range and plug gap are what matter.

My Type-R for example, needs a heat range 7 and plug gap 1.1mm, if after a while those plugs wear down and the gap gets to 1.4mm, it starts running funny and can develop misfires at high rpms.

1.4mm gap in other vehicles however, may well be fine.

Similarly, for high pressure, high temperature turbo application, a heat range 7 may be inappropriate, so a colder plug like a 5 or 6 would be called for.

Detonation is when the fuel ignites before the spark, and would point towards the gas map being too lean. If it's just not firing properly and running off, then it would point towards incorrect plugs.

It's difficult to diagnose and explain stuff over the internet, I'm sure an expert in LPG will be along in a minute. I only know about basics with petrol motors, but I would figure the same principles apply.

Fire99

9,710 posts

184 months

Thursday 17th June 2010
quotequote all
My Jeep runs on LPG. When on 'Gas' it is more sensitive to good ignition components.
Firstly, I would check the plugs and ensure they are all a nice tan colour and gapped correctly.

Things like the MAF and O2 are a red herring in my opinion. The O2 sensor wouldnt cause a violent misfire situation and the MAF would show itself whilst on petrol.

Have you had your fault codes read? They should show any failing components on the OEM setup of the car.

But with such a violent running situaiton I would be looking at the Gas delivery. Maybe a 2nd opinion from another LPG company would be a good route.

Vasilisbrcgreece

2 posts

109 months

Friday 24th June 2011
quotequote all
8400rpm said:
What heat range and gap are the plugs? I'm guessing they're fine for petrol usage, but not for gas. Is it getting detonation from pre-ignition, or is it not sparking adequately enough?
Tell the technician to connect the gray rpm wire to the crankshaft or to a camshaft. Not to a coil on a BMW do this and ur problem will be solved. A p& d system needs gor rpm signal

Regards
Vasilis

Vasilisbrcgreece

2 posts

109 months

Friday 1st July 2011
quotequote all
Vasilisbrcgreece said:
Tell the technician to connect the gray rpm wire to the crankshaft or to a camshaft. Not to a coil on a BMW do this and ur problem will be solved. A p& d system needs good rpm signal


If the problem persits then look at you're coil wires, they are attached with the coil. The may be shooting the electricity on the motor.

We currently had the same problem with a x5 and this was the problem. The problems where exactly the same
Regards
Vasilis

BadgerBill

274 posts

194 months

Friday 1st July 2011
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Sounds like a solution has been found. OP have you any feedback to give, is it solved?

BB